Michael Palm Basic Science, Vaccines & Prevention Project Weblog

Bridging the Neurology-Immunology Barrier

The Cell Press journals Neuron and Immunity have collaborated to produce a timely free-access special issue focusing on the interrelatedness of neural and immune systems. The editors of Neuron write:

"The brain was once thought to be a largely 'immune-privileged' system. Traditionally, research has reflected this segregation, with neuroscientists focusing on the nervous system and immunologists focusing on the immune system. Yet as science in both realms has moved forward, it has become clear that the nervous and immune systems interact on many levels, in both disease states and under healthy conditions. It is also clear that molecules traditionally viewed as neural- or immune-specific play important and often distinct roles in the other system. Experimental evidence of interactions between the neural and immune systems continues to accumulate, and the two research communities are beginning to communicate more as well. In this same spirit, Neuron and Immunity have coordinated to bring together a compilation of articles on selected topics related to the interface between the nervous and immune systems."

The issue includes articles addressing "Immune Activation in Brain Aging and Neurodegeneration" and "Neuroimmune Crosstalk in HIV Infection."

SIV Pathogenesis: An Immune Response, Unresolved

SIV infection of two natural host species, sooty mangabeys and African green monkeys (AGMs), is rarely pathogenic. A trio of newly published studies evaluate the changes in gene expression that result from SIV infection in these animals compared to rhesus macaques, in which SIV typically causes T cell loss and simian AIDS. A novel feature of the research is that gene expression is analyzed from very early time points (~3 days onwards) in order to capture any transient changes during acute infection. All three studies report the same key finding: sooty mangabeys and AGMs initially mount an immune response to SIV that is accompanied by massive changes in gene expression, but these changes largely resolve after acute infection. In contrast, altered gene expression – particularly involving genes related to immune activation - persists in pathogenic SIV infection of rhesus macaques. These new papers refute a prior theory that SIV is generally non-pathogenic in sooty mangabeys and AGMs because their immune systems essentially ignore the virus.

The studies place a particular focus on genes related to the production of type 1 interferons and interferon-stimulated genes (ISGs) due to a previous report suggesting that sooty mangabey dendritic cells fail to produce interferon after exposure to SIV. The gene expression data clearly show that interferons and ISGs are massively but transiently upregulated during acute SIV infection in both sooty mangabeys and AGMs. In rhesus macaques, there is also a massive increase in expression of interferon genes and ISGs during acute SIV infection and these genes remain persistently upregulated into the chronic phase.

The research team led by Steven Bosinger also analyzes differences between sooty mangabeys and rhesus macaques by grouping genes together into seven broad categories: cell-mediated immune response, humoral immune response, inflammatory response, immune cell trafficking, cell death, cell cycle and hematopoiesis (click on the image to the left to see detail). The striking contrast that emerges from this analysis is that genes involved in cell mediated, humoral and inflammatory immune responses are more strongly upregulated at day 10 after infection in sooty mangabeys compared to rhesus macaques, but by day 180 this difference is reversed. Cell cycle gene upregulation also disappears by day 180 in sooty mangabeys but remains significantly upregulated in rhesus macques, consistent with pathogenic SIV infection causing increased T cell turnover. In both sooty mangabeys and AGMs, the rapid curtailment of immune activation after acute infection is associated with the upregulation of genes known to be involved in downmodulating immune responses.

The overall picture conveyed by the data is that sooty mangabeys and AGMs make a potent innate and adaptive immune response against SIV immediately after infection, but this immune response resolves (despite the fact that relatively high levels of SIV replication persist in the chronic phase). In contrast, rhesus macaques make a weaker initial response and continue to mount responses throughout the course of infection. A systems biology analysis by Bosinger and colleagues identifies the T cell exhaustion marker LAG3 as being a strong correlate of persistent immune activation in macaques, perhaps suggesting that T cell dysfunction plays an important role in the unresolved immune response against SIV in these animals.

J. Clin. Invest.  doi:10.1172/JCI40115.

Global genomic analysis reveals rapid control of a robust innate response in SIV-infected sooty mangabeys (free access to full text)

Steven E. Bosinger1,2, Qingsheng Li3, Shari N. Gordon1, Nichole R. Klatt1, Lijie Duan3, Luoling Xu2, Nicholas Francella1, Abubaker Sidahmed2, Anthony J. Smith3, Elizabeth M. Cramer1, Ming Zeng3, David Masopust3, John V. Carlis4, Longsi Ran2, Thomas H. Vanderford1, Mirko Paiardini1, R. Benjamin Isett5, Don A. Baldwin1,5, James G. Else6, Silvija I. Staprans7, Guido Silvestri1,6, Ashley T. Haase3 and David J. Kelvin2,8

1 Department of Pathology and Laboratory Medicine, and Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA. 2 Division of Experimental Therapeutics, University Health Network, Toronto, Ontario, Canada. 3 Department of Microbiology, Medical School, University of Minnesota, Minneapolis, Minnesota, USA. 4 Department of Computer Science and Engineering, Institute of Technology, University of Minnesota, Minneapolis, Minnesota, USA. 5 Penn Microarray Facility, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA. 6 Yerkes National Primate Research Center, Emory University, Atlanta, Georgia, USA. 7 Merck Vaccines and Infectious Diseases, Merck and Co., West Point, Pennsylvania, USA. 8 Division of Immunology, International Institute of Infection and Immunity, Shantou University Medical College, Shantou, Guangdong, People’s Republic of China.

Authorship note: Steven E. Bosinger and Qingsheng Li, as well as Guido Silvestri, Ashley T. Haase, and David J. Kelvin, contributed equally to this work.

Natural SIV infection of sooty mangabeys (SMs) is nonprogressive despite chronic virus replication. Strikingly, it is characterized by low levels of immune activation, while pathogenic SIV infection of rhesus macaques (RMs) is associated with chronic immune activation. To elucidate the mechanisms underlying this intriguing phenotype, we used high-density oligonucleotide microarrays to longitudinally assess host gene expression in SIV-infected SMs and RMs. We found that acute SIV infection of SMs was consistently associated with a robust innate immune response, including widespread upregulation of IFN-stimulated genes (ISGs) in blood and lymph nodes. While SMs exhibited a rapid resolution of ISG expression and immune activation, both responses were observed chronically in RMs. Systems biology analysis indicated that expression of the lymphocyte inhibitory receptor LAG3, a marker of T cell exhaustion, correlated with immune activation in SIV-infected RMs but not SMs. Our findings suggest that active immune regulatory mechanisms, rather than intrinsically attenuated innate immune responses, underlie the low levels of immune activation characteristic of SMs chronically infected with SIV.

J. Clin. Invest.  doi:10.1172/JCI40093.

Nonpathogenic SIV infection of African green monkeys induces a strong but rapidly controlled type I IFN response (free access to full text)

Béatrice Jacquelin1, Véronique Mayau1, Brice Targat2, Anne-Sophie Liovat1, Désirée Kunkel1, Gaël Petitjean1, Marie-Agnès Dillies3, Pierre Roques4, Cécile Butor5, Guido Silvestri6, Luis D. Giavedoni7, Pierre Lebon8, Françoise Barré-Sinoussi1, Arndt Benecke2,9 and Michaela C. Müller-Trutwin1

1 Institut Pasteur, Unité de Régulation des Infections Rétrovirales, Paris, France. 2 Institut des Hautes ωtudes Scientifiques, Bures-sur-Yvette, France. 3 Institut Pasteur, Plateforme 2, Paris, France. 4 CEA, Division of Immuno-Virology, DSV/iMETI, Fontenay-aux-Roses, and Université Paris-Sud 11, UMR E01, Orsay, France. 5 Laboratoire d’Immunologie Humaine, INSERM U743, and Université Paris Diderot, Paris, France. 6 Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA. 7 Southwest National Primate Research Center, Southwest Foundation for Biomedical Research, San Antonio, Texas, USA. 8 Hôpital Saint-Vincent de Paul and Université Paris Descartes, Laboratoire de Virologie, Paris, France. 9 Institut de Recherche Interdisciplinaire, CNRS USR3078, Lille, France.

African green monkeys (AGMs) infected with the AGM type of SIV (SIVagm) do not develop chronic immune activation and AIDS, despite viral loads similar to those detected in humans infected with HIV-1 and rhesus macaques (RMs) infected with the RM type of SIV (SIVmac). Because chronic immune activation drives progressive CD4+ T cell depletion and immune cell dysfunctions, factors that characterize disease progression, we sought to understand the molecular basis of this AGM phenotype. To this end, we longitudinally assessed the gene expression profiles of blood- and lymph node–derived CD4+ cells from AGMs and RMs in response to SIVagm and SIVmac infection, respectively, using a genomic microarray platform. The molecular signature of acute infection was characterized, in both species, by strong upregulation of type I IFN–stimulated genes (ISGs). ISG expression returned to basal levels after postinfection day 28 in AGMs but was sustained in RMs, especially in the lymph node–derived cells. We also found that SIVagm induced IFN-α production by AGM cells in vitro and that low IFN-α levels were sufficient to induce strong ISG responses. In conclusion, SIV infection triggered a rapid and strong IFN-α response in vivo in both AGMs and RMs, with this response being efficiently controlled only in AGMs, possibly as a result of active regulatory mechanisms.

J. Clin. Invest.  doi:10.1172/JCI41509.

Commentary

Resolution of immune activation defines nonpathogenic SIV infection

Olivier Manches, Nina Bhardwaj

Natural nonhuman primate hosts of SIV do not succumb to AIDS despite significant viral replication, a phenomenon attributed to reduced levels of chronic and deleterious “immune activation.” Two studies in this issue of the JCI, by Bosinger et al. and Jacquelin et al., now show that SIV induces vigorous immune activation and upregulation of IFN-stimulated genes in both natural and susceptible hosts, but strikingly, the responses resolve only in the former (see the related articles, doi:10.1172/JCI40115 and 10.1172/JCI40093, respectively). Thus, natural hosts for SIV actively engage mechanisms to abort sustained immune activation and its associated harmful effects.

JVI Accepts, published online ahead of print on 25 November 2009

J. Virol. doi:10.1128/JVI.01496-09

Non pathogenesis of SIV infection is associated with reduced inflammation and recruitment of plasmacytoid dendritic cells to lymph nodes, not to lack of an interferon type I response, during the acute phase.

Laure Campillo-Gimenez, Mireille Laforge, Michèle Fay, Audrey Brussel, Marie-Christine Cumont, Valérie Monceaux, Ousmane Diop, Yves Lévy, Bruno Hurtrel, John Zaunders, Jacques Corbeil, Carole Elbim, and Jérôme Estaquier

INSERM U955, Faculté Créteil Henri Mondor, Créteil, F-94000, France; Université Paris 7 Denis Diderot, Faculté de Médecine, site Bichat, Paris, F-75018, France; Unité de Physiopathologie des Infections Lentivirales, Institut Pasteur, 28 rue du Docteur Roux, Paris, F-75015, France; Institut Pasteur, Dakar, Sénégal; Centre for Applied Medical Research, St Vincent's Hospital, Darlinghurst, NSW, Australia; Université Laval, Centre de Recherche en Infectiologie, G1V 4G2 Québec, Canada; Centre de Recherche des Cordeliers, Université Pierre et Marie Curie – Paris 6, UMR S 872, Paris, F-75006 France; Université Paris Descartes, UMR S 872, Paris, F-75006 France; INSERM, U872, Paris, F-75006,France; Assistance Publique-Hôpitaux de Paris, Hôpital Henri Mondor, Créteil, France

Abstract

Divergent Toll-like receptor (TLR)-7 and TLR-9 signaling has been proposed to distinguish pathogenic from non pathogenic SIV infection in primate models. Herein, we demonstrate that increased expression of type I IFN in pathogenic rhesus macaques as compared to non pathogenic African green monkeys was associated with the recruitment of plasmacytoid dendritic cells (pDCs) in the lymph nodes and the presence of an inflammatory environment early after infection, instead of a difference in TLR-7/9 response.

Aging, HIV Infection & the Immune System

In the November 9^th issue of New York Magazine, David France reports on the emerging issue of accelerated aging in people with HIV infection. The article offers a series of disturbing vignettes about the complications some individuals are facing as they age, such as bone problems and impaired cognitive function, and raises important questions about how much attention is being paid to the issue by current research, particularly in terms of pursuing new therapeutic options. However, beyond mentioning inflammation, the piece does not really delve into the underlying immunological parallels between HIV infection and aging and consider how they might fit into the picture. This is a potentially important omission, as there is accumulating evidence that the accelerated aging of the immune system that has been documented in people with HIV is likely to be related to many of the clinical phenomena described in France’s article.

Although it’s not the sort of research that makes the front pages, the last decade or so has seen considerable progress in understanding the relationship between immune parameters and aging, and these studies provide a valuable frame of reference. Perhaps most importantly, an “immune risk phenotype” associated with mortality in the elderly has been described in some detail. The major features are an inverted CD4/CD8 T cell ratio, decreased proliferative responses and IL-2 production by T cells, increased levels of inflammatory cytokines (such as IL-6) and increased numbers of CD8 T cells lacking the CD28 co-stimulatory receptor (typically described as senescent cells). All of these immunological perturbations are also seen in HIV infection. Studies have also found that people with the chronic viral infections cytomegalovirus (CMV) and Epstein-Barr virus (EBV) face a greater likelihood of acquiring the immune risk phenotype in old age. The clinical manifestations associated with the phenotype include bone loss and increased fracture risk, cognitive impairment, increased susceptibility to infections and an increased incidence of cancers and cardiovascular, kidney and liver disease.

The overarching theme that is emerging from this research – although it is still in its infancy - is that a lifetime of antigenic challenges (in the form of all the pathogens an individual is exposed to) gradually erodes immune system resources, and this plays a major role in aging. This erosion of immune system resources has multiple facets:

• A steady decline in naive T cell production by the thymus from a torrent in childhood to a trickle in old age.
• Activation of antigen-specific naive T cells every time a new pathogen is encountered, which depletes the naive T cell pool and leads to a subset of these pathogen-specific cells maturing into memory cells (the impact of these episodes of naive T cell activation is minor when the thymus is vigorously producing new cells to replace those lost, but increases as thymic output declines).
• Repeated stimulation of memory T cells by pathogens, which can eventually lead to memory T cell senescence.

Chronic pathogens (that are controlled rather than cleared) play a particularly important role because they place a persistent drain on immune system resources, as indicated by the way that memory T cell responses to CMV accumulate over time, such that 25-30% of CD8 T cells can be CMV-specific in an infected elderly person. Untreated HIV infection has an even greater effect; a young individual with AIDS typically will have lost almost all their naive T cells and 20-50% of their memory CD8 T cells will be HIV-specific. As shown recently in a study of the MACS cohort, a fast accumulation of senescent CD8 T cells lacking the CD28 molecule is associated with rapid progression from HIV infection to AIDS.

Additional insight into how immunological aging relates to health may come from people who have had their thymus removed (a thymectomy) at birth. This procedure is sometimes performed to enable better access to the heart to correct congenital heart defects. A recent study published in the Journal of Clinical Investigation (abstract and accompanying commentary appended below) reported that thymectomized individuals show evidence of accelerated aging of the immune system similar to the immune risk phenotype, but it is not yet known whether this will lead to the same clinical manifestations seen in the elderly. Continued follow-up will be crucial to gaining a better understanding of the relationship between the immunological and clinical consequences of aging.

In terms of HIV infection, the issue of accelerated aging raises many new questions and considerations for future research:

• Is immunology research in HIV adequately prioritized? The main clinical research network in the US, the AIDS Clinical Trials Group (ACTG), once had a specific immunology research committee but it was dissolved a few years ago and squished into a broader committee designated “Translational Research and Drug Development” (TRADD). There may be a case for re-establishing a specific immunology committee within the network.
• Do current research funding mechanisms offer adequate support for multidisciplinary and translational research? The spectrum of clinical manifestations associated with accelerated aging calls for collaborative research between groups specializing in many different disciplines (e.g. immunology, virology, pharmacology, toxicology, musculoskeletal system, cardiovascular, renal, liver, etc.), and support for this type of complex collaboration may call for the design of a specific funding mechanism (RFA). Exploration of novel therapies also requires support for conducting translational clinical research, which can be difficult and complicated to obtain under current grant procedures.
• Will earlier initiation of antiretroviral therapy prevent accelerated aging? Long term follow-up from studies such as ACTG 384 clearly shows that earlier suppression of HIV is associated with an almost complete normalization of many potentially important immune parameters including the CD4/CD8 T cell ratio, the ratio of naive T cells to memory T cells and levels of immune activation. In contrast, among individuals initiating therapy at lower CD4 T cell counts, these parameters improve but do not come close to mirroring those of uninfected individuals even after seven or more years of continuous HIV suppression. This may suggest that people who start treatment earlier will be at less risk for accelerated aging, but this has not yet been established.
• To what extent do drug toxicities contribute to accelerated aging? The fact that there are many close parallels between the immunology of HIV infection and aging argues strongly against drug toxicity being the primary cause, but there are clearly specific toxicities that can contribute to problems such as bone loss and cardiovascular disease. Research needs to parse out the role of drug toxicities so that safer treatments can be developed.
• Can novel therapies be developed to delay or reverse accelerated aging? The current data suggest a number of key targets for therapeutic research, including: enhancing thymic function to boost naive T cell production, reducing immune activation/inflammation and reducing numbers of senescent immune cells. Research is ongoing in these and other areas but greater resources, coordination and prioritization is needed.

TAG’s Hepatitis Coinfection Project and Michael Palm Project are currently collaborating with several other community activists to produce a comprehensive report and advocacy recommendations on HIV and aging. The report will be released next year prior to the International AIDS Conference. 

J. Clin. Invest. doi:10.1172/JCI40855.

Commentary

Reduced thymus activity and infection prematurely age the immune system

http://www.jci.org/articles/view/40855

Ronald E. Gress, Steven G. Deeks

Published September 21, 2009

The aging process affects all aspects of the immune system, particularly the T cells. The immune system in older individuals is often characterized by lower T cell numbers, lower naive/memory T cell ratios, and lower T cell diversity. Most measures of inflammation increase with age. Why this happens, and why there is so much person-to-person variability in these changes, is not known. In this issue of the JCI, Sauce and colleagues show that removal of the thymus during infancy results in premature onset of many of these age-associated changes to the immune system (see the related article, doi:10.1172/JCI39269). The effect of thymectomy was particularly notable in those individuals who acquired CMV infection. Data from this study, as well as data from other observational settings, suggest that reduced thymic function and persistent viral infections combine to accelerate a decline in immunologic function.

J. Clin. Invest. doi:10.1172/JCI39269.

Research Article

Evidence of premature immune aging in patients thymectomized during early childhood (free access to full text)

Delphine Sauce1, Martin Larsen1, Solène Fastenackels1, Anne Duperrier2, Michael Keller3, Beatrix Grubeck-Loebenstein3, Christophe Ferrand2, Patrice Debré1, Daniel Sidi4 and Victor Appay1

1 Infections and Immunity, INSERM UMRS 945, Avenir Group, Hôpital Pitié-Salpêtrière, UPMC University of Paris 06, Paris, France.

2 INSERM U645, Etablissement Français du Sang Bourgogne/Franche-Comté, Besançon, France.

3 Institute for Biomedical Aging Research, Austrian Academy of Sciences, Innsbruck, Austria.

4 Service de Cardiologie Pédiatrique, Hôpital Necker Enfants Malades, Paris, France.

Address correspondence to: Victor Appay, Cellular Immunology Laboratory, INSERM U945, Hôpital Pitié-Salpêtrière, Paris, France. Phone: 33-1-40-77-81-83; Fax: 33-1-42-17-74-90

Published September 21, 2009

Received for publication March 20, 2009, and accepted in revised form July 16, 2009.

While the thymus is known to be essential for the initial production of T cells during early life, its contribution to immune development remains a matter of debate. In fact, during cardiac surgery in newborns, the thymus is completely resected to enable better access to the heart to correct congenital heart defects, suggesting that it may be dispensable during childhood and adulthood. Here, we show that young adults thymectomized during early childhood exhibit an altered T cell compartment. Specifically, absolute CD4+ and CD8+ T cell counts were decreased, and these T cell populations showed substantial loss of naive cells and accumulation of oligoclonal memory cells. A subgroup of these young patients (22 years old) exhibited a particularly altered T cell profile that is usually seen in elderly individuals (more than 75 years old). This condition was directly related to CMV infection and the induction of strong CMV-specific T cell responses, which may exhaust the naive T cell pool in the absence of adequate T cell renewal from the thymus. Together, these marked immunological alterations are reminiscent of the immune risk phenotype, which is defined by a cluster of immune markers predictive of increased mortality in the elderly. Overall, our data highlight the importance of the thymus in maintaining the integrity of T cell immunity during adult life.

Trends in Immunology: Free Access Issue on Immune Senescence

The journal Trends in Immunology has published a special issue on immune senescence, and access to all articles is being offered free of charge (thanks to the sponsorship of the National Institutes of Health). The parallels between immune senescence in uninfected elderly individuals and people with HIV are increasingly well-recognized and include:

• Depletion of naive CD4 and CD8 T cells
• Involution of the thymus and decreased thymic output
• Skewing of the CD4:CD8 T cell ratio
• Accumulation of dysfunctional CD8 T cells lacking the CD28 co-stimulatory molecule
• Decreased responses to new immunizations
• Decreased recall (memory) T responses to common antigens

Research into immune senescence and its association with illness and mortality has gained considerably more attention recently, and may have the potential to offer important insights into the pathogenesis of HIV infection. Additional background on the topic, along with a link to a webcast presentation by immune senescence expert Rita Effros, can be found in a post from January of this year, "Accelerated Aging of the Immune System in HIV Infection."

Immune Surveillance Below the Radar: Study Offers Explanation for Acyclovir’s Failure to Reduce HIV Risk

In a recent post on the Merck vaccine trial, I mentioned a new study from Larry Corey’s research group addressing the relationship between HSV-2 infection and enhanced susceptibility to HIV. The data were presented by Dr. Corey at the Keystone conference in March and were published online by Nature Medicine yesterday. The background to the work is that HSV-2 infection has been consistently associated with a 2 to 3-fold increased risk of acquiring HIV; a meta-analysis published in 2006 reported a relative risk of 3.1, 2.7 and 1.7 for women, heterosexual men and men who have sex with men, respectively. Recently analyzed data from the Merck vaccine trial are consistent with these findings in that HSV-2-infected participants were found to have approximately double the risk of acquiring HIV infection during the study. 

The mechanism by which HSV-2 infection increases HIV acquisition risk is not so clear, however, and has been the subject of debate. The general view is that local inflammation and damage to the integrity of the genital mucosa are plausible ways that HSV-2 infection may increase the chances of HIV transmission. This view led to the logical proposition that suppressing HSV-2 with chronic acyclovir treatment might be a means to also reduce the risk of HIV acquisition. Several large trials have now explored this hypothesis and, while acyclovir treatment was effective at reducing symptomatic HSV-2 reactivations, it did not reduce the incidence of HIV infection. 

The new study from Larry Corey’s laboratory set out to try and shed light on these trial results. The same group of researchers has previously shown that immune surveillance of HSV-2 is a far more active process than many had surmised. In a 2007 paper in the Journal of Experimental Medicine, they demonstrated that HSV-2-specific CD8+ T cells gather at sites of subclinical HSV-2 reactivation in the genital skin and persist for at least several months after HSV-2 DNA is no longer detectable. A year later in the Journal of Infectious Diseases, they published results of an intensive study in which participants took oral and anogenital swabs four times a day for 60 days. Analyzing the swabs for HSV-2 DNA, the researchers found that subclinical reactivations were frequent and typically lasted less than 12 hours, showing that there is an ongoing and dynamic effort on the part of the immune system to keep HSV-2 suppressed. 

These findings led the researchers to suspect that perhaps elevated levels of activated HSV-2-specific CD4 T cells would be present in the genital mucosa even during chronic acyclovir treatment, and this is exactly what they report in the Nature Medicine paper. The study initially took biopsies of genital skin during an acute, clinically symptomatic lesion and 2, 4 and 8 weeks after healing. Four participants subsequently initiated chronic suppressive acyclovir treatment at the start of their next symptomatic episode and had biopsies taken at 2, 4, 8, 16 & 20 weeks after healing. In all cases, control biopsies were obtained from an unaffected area of genital skin at each timepoint. 

During an acute HSV-2 lesion, the researchers found a “massive localized infiltration” of cells. Mean numbers of CD4 and CD8 T cells per mm² of skin were 655 and 618, respectively, compared to 68 and 55 per mm² of the unaffected skin sample. Although follow-up biopsies documented gradual clearance of HSV-2 and a decline in inflammation, elevated numbers of CD4 and CD8 T cells remained present locally for months. Eight weeks after healing, a median of 8-fold more CD4 T cells were present at the affected versus the unaffected site. Furthermore, even after 20 weeks of acyclovir treatment, the number of CD4 T cells remained significantly elevated. Additional analyses illustrated that the majority of these CD4 T cells expressed CCR5 and their presence was also associated with a significant increase in the numbers of DC-SIGN-expressing dendritic cells. The enrichment of CCR5-expressing CD4 T cells and DC-SIGN-expressing dendritic cells at the former lesion site was not significantly altered by chronic acyclovir treatment. 

The researchers acknowledge in the conclusion to the paper that the number of participants was small, but nevertheless state: “we feel that our central finding – that HSV reactivation leaves a residual inflammatory response not appreciated clinically – is typical of HSV-2 genital lesions.” They also note that “the wide anatomical distribution of HSV-2 in the male and female genital tract underscores the importance that these localized reservoirs of inflammatory cells are likely to have in HIV acquisition.” 

Nature Medicine

Published online: 2 August 2009 | doi:10.1038/nm.2006 

Persistence of HIV-1 receptor–positive cells after HSV-2 reactivation is a potential mechanism for increased HIV-1 acquisition 

Jia Zhu1,2, Florian Hladik1,3,4,6, Amanda Woodward1,3,6, Alexis Klock1,2, Tao Peng1,2, Christine Johnston1,3, Michael Remington2, Amalia Magaret1,2, David M Koelle1,2,3, Anna Wald1,2,3,5 & Lawrence Corey1,2,3,5 

Abstract 

To explore the mechanism by which herpes simplex virus (HSV)-2 infection is related to HIV-1 acquisition, we conducted in situ analysis of the cellular infiltrate from sequential biopsies of HSV-2 lesions from patients on and off antiviral therapy. CD4+ and CD8+ T cells and a mixed population of plasmacytoid and myeloid dendritic cells (DCs), including cells expressing the C-type lectin receptor DC-SIGN, persisted at sites of HSV-2 reactivation for months after healing, even with daily antiviral therapy. The CD4+ T cells that persisted reacted to HSV-2 antigen, were enriched for expression of the chemokine receptor CCR5, and were contiguous to DCs expressing the interleukin-3 receptor CD123 or DC-SIGN. Ex vivo infection with a CCR5-tropic strain of HIV-1 revealed greater concentrations of integrated HIV-1 DNA in cells derived from healed genital lesion biopsies than in cells from control skin biopsies. The persistence and enrichment of HIV receptor–positive inflammatory cells in the genitalia help explain the inability of anti–HSV-2 therapy to reduce HIV acquisition. 

1. Vaccine and Infectious Disease Institute, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA.

2. Department of Laboratory Medicine, University of Washington, Seattle, Washington, USA.

3. Department of Medicine, University of Washington, Seattle, Washington, USA.

4. Department of Obstetrics and Gynecology, University of Washington, Seattle, Washington, USA.

5. Department of Epidemiology, University of Washington, Seattle, Washington, USA. 

6. These authors contributed equally to this work.

Study Uncovers Sex Differences in Immune Activation

There is a large body of evidence showing that innate and adaptive immune responses can differ in women and men, but the reasons for these differences are only partly understood (as reviewed recently in Nature Reviews Immunology). In HIV infection, it has been reported that average viral loads in early infection are lower in women than men, but women face a 1.6-fold higher risk of developing AIDS compared to men with the same viral load. Marc Hellerstein’s group has also presented data demonstrating that women have significantly higher T cell turnover compared to men with similar CD4 T cell counts. The mechanistic basis for these differences has been unclear.

A paper in Nature Medicine now offers a possible explanation for the observed sex differences in HIV pathogenesis. Angela Meier and colleagues from Marcus Altfeld’s group at the Ragon Institute of Massachusetts General Hospital have previously shown that HIV stimulates an innate immune receptor called toll-like receptor-7 (TLR7). In the new study, they report that a key immune cell called a plasmacytoid dendritic cell (pDC) responds differently to TLR7 stimulation depending on the sex of the donor. Specifically, significantly more pDC from women produced interferon-alpha compared to pDC from men. The study authors note that this finding has also been reported with a different TLR7 stimulus, a drug called imiquimod.

The researchers went on to evaluate the role of sex hormones, finding that the percentage of pDC producing interferon-alpha after TLR7 stimulation was significantly correlated with plasma progesterone concentrations. There was also a trend toward lower percentages of pDC producing interferon-alpha in postmenopausal women compared to premenopausual women.

Because interferon-alpha induces the expression of the immune activation marker CD38 on CD8 T cells in vitro, the researchers decided to explore whether women might show higher levels of immune activation than men despite comparable viral loads. In a comparison of 109 women and 514 men participating in the ACTG 384 trial (all treatment naive), women were found to have significantly higher levels of CD8 T cell activation than men after adjustment for viral load. On average, women had 4.6% more activated CD8 T cells. As immune activation levels are the strongest predictor of disease progression in HIV infection, the study results offer a compelling explanation for why women have a higher risk of developing AIDS compared to men with the same viral load.

The authors conclude: “Modulation of the TLR7 pathways in pDCs could…represent a unique approach to reduce HIV-1–associated pathogenesis and might have implications that go beyond HIV-1 infection, as differential susceptibility to several RNA viruses have been described for men and women, and autoimmune diseases that show sex differences in their incidence, such as systemic lupus erythematosus, have also been shown to involve the TLR7 and TLR8 pathway.”

Nature Medicine

Published online: 13 July 2009 | doi:10.1038/nm.2004

Letter

Sex differences in the Toll-like receptor–mediated response of plasmacytoid dendritic cells to HIV-1

Angela Meier1,8, J Judy Chang1,8, Ellen S Chan2, Richard B Pollard3, Harlyn K Sidhu1, Smita Kulkarni4, Tom Fang Wen1, Robert J Lindsay1, Liliana Orellana2, Donna Mildvan5, Suzane Bazner1,6, Hendrik Streeck1, Galit Alter1, Jeffrey D Lifson7, Mary Carrington4, Ronald J Bosch2, Gregory K Robbins6 & Marcus Altfeld1,6

Manifestations of viral infections can differ between women and men1, and marked sex differences have been described in the course of HIV-1 disease. HIV-1–infected women tend to have lower viral loads early in HIV-1 infection but progress faster to AIDS for a given viral load than men2, 3, 4, 5, 6, 7. Here we show substantial sex differences in the response of plasmacytoid dendritic cells (pDCs) to HIV-1. pDCs derived from women produce markedly more interferon- (IFN-) in response to HIV-1–encoded Toll-like receptor 7 (TLR7) ligands than pDCs derived from men, resulting in stronger secondary activation of CD8+ T cells. In line with these in vitro studies, treatment-naive women chronically infected with HIV-1 had considerably higher levels of CD8+ T cell activation than men after adjusting for viral load. These data show that sex differences in TLR-mediated activation of pDCs may account for higher immune activation in women compared to men at a given HIV-1 viral load and provide a mechanism by which the same level of viral replication might result in faster HIV-1 disease progression in women compared to men. Modulation of the TLR7 pathway in pDCs may therefore represent a new approach to reduce HIV-1–associated pathology.

1. Ragon Institute of Massachusetts General Hospital, Massachusetts Institute of Technology and Harvard University, Boston, Massachusetts, USA.

2. Harvard School of Public Health, Boston, Massachusetts, USA.

3. University of California–Davis Medical Center, Sacramento, California, USA.

4. Cancer and Inflammation Program, Laboratory of Experimental Immunology and Science Applications International Corporation–Frederick, National Cancer Institute, Frederick, Maryland, USA.

5. Beth Israel Medical Center, New York, New York, USA.

6. Division of Infectious Diseases, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA.

7. AIDS and Cancer Virus Program, Science Applications International Corporation–Frederick, National Cancer Institute, Frederick, Maryland, USA.

8. These authors contributed equally to this work.

Lymphatic Tissue Gene Expression During HIV Infection

The new issue of the Journal of Immunology features a paper from Ashley Haase’s group looking at lymphoid tissue gene expression in HIV infection. The study, led by Qingsheng Li, uses microarray technology to investigate gene expression changes during the acute, asymptomatic and late (AIDS) stages of disease compared to healthy uninfected individuals. The analyses reveal that the expression of 46 genes is significantly altered (in most cases upregulated) at all stages of infection; half of these genes have known functions in immunity, particularly immune activation. Examples include CD38 (the well-known immune activation marker that predicts the pace of disease progression in HIV infection), CCR5, pro-apoptotic genes and nine different interferon-related genes.

Acute infection is associated with altered expression of another 358 unique genes, more than any other stage of infection. Again, in most cases (81%) these genes are upregulated and a large proportion are related to immune activation (e.g. proinflammatory cytokines, signal transduction molecules, activators of cell proliferation, mediators of cell cycle progression and the pro-apoptotic Fas-Fas pathway). However, there are also increases in the expression of genes associated with dampening the immune response such as IDO, an enzyme with powerful immune-suppressing properties. A suite of additional genes involved in innate immunity are also upregulated during acute infection, including the toll-like receptors TLR7 and TLR8 and numerous components of the interferon pathway.

The asymptomatic stage of infection is associated with a dramatic shift in gene expression, with levels returning to baseline in most cases. In addition to the 46 genes with altered expression at all stages of infection, only 18 genes are uniquely altered in asymptomatic individuals. The majority relate to immune activation and lymphoid tissue remodeling and repair.

In people with AIDS, 183 genes are uniquely altered and - in contrast to the other stages of infection - most of these genes (84%) are downregulated. Examples include genes involved in immune activation, apoptosis, and tissue remodeling and repair. A substantial proportion of the genes belong to the CD28 T cell co-stimulatory pathway, consistent with the accumulation of dysfunctional CD28-negative T cells that occurs over the course of HIV infection. The researchers also note that at this stage of disease “decreased expression could be due to loss of cells expressing these genes, decreased expression in a particular cell type, or both.”

In the discussion section of the paper, the authors conclude: “the major finding of this study is that there are stage-specific transcriptional signatures in lymphoid tissues during HIV-1 infection.” The results set the stage for additional investigations into the consequences of the documented changes in gene expression using a comprehensive systems biology approach. The ultimate aim is “not only to better understand viral pathogenesis during the various stages of HIV-1 disease but also to identify adjunctive approaches to improving treatment and immune reconstitution.”

FIGURE 2. In human LT of HIV-1-infected subjects, the general functional categories of genes with altered expression (1.7 times the level at baseline, p < 0.05). A, Common to all stages (C1); B, unique to the acute stage (S1); C, unique to the asymptomatic stage (S2); and D, unique to the AIDS stage (S3). Green and red letters indicate, respectively, decreased and increased expression. The size of each sector in a pie diagram is proportional to the number of genes in its category (in parentheses). All genes and their names derived from abbreviations can be found in supplemental Table I.

CREDIT: The Journal of Immunology, 2009, doi:10.4049/jimmunol.0803222

The Journal of Immunology, 2009, doi:10.4049/jimmunol.0803222

Published online July 13, 2009

Microarray Analysis of Lymphatic Tissue Reveals Stage-Specific, Gene Expression Signatures in HIV-1 Infection

Qingsheng Li2,*, Anthony J. Smith2,*, Timothy W. Schacker, John V. Carlis, Lijie Duan*, Cavan S. Reilly and Ashley T. Haase3,*

*Department of Microbiology  Division of Infectious Diseases, Department of Medicine, Medical School  Department of Computer Science and Engineering, Institute of Technology, and  Division of Biostatistics, School of Public Health, University of Minnesota, Minneapolis, MN 55455

Untreated HIV-1 infection progresses through acute and asymptomatic stages to AIDS. Although each of the three stages has well-known clinical, virologic, and immunologic characteristics, much less is known of the molecular mechanisms underlying each stage. In this study, we report lymphatic tissue microarray analyses, revealing for the first time stage-specific patterns of gene expression during HIV-1 infection. We show that although there is a common set of key genes with altered expression throughout all stages, each stage has a unique gene expression signature. The acute stage is most notably characterized by increased expression of hundreds of genes involved in immune activation, innate immune defenses (e.g., RIG-1, MDA-5, TLR7 and TLR8, PKR, APOBEC3B, 3F, 3G), adaptive immunity, and in the proapoptotic Fas-Fas ligand pathway. Yet, quite strikingly, the expression of nearly all acute stage genes return to baseline levels in the asymptomatic stage, accompanying partial control of infection. This transition from acute to asymptomatic stage is tied to increased expression of a diverse array of immunosuppressive genes (e.g., CLEC12B, ILT4, galectin-3, CD160, BCMA, FGL2, LAG3, GPNMB). In the AIDS stage, decreased expression of numerous genes involved in T cell signaling identifies genes contributing to T cell dysfunction. These common and stage-specific gene expression signatures identify potential molecular mechanisms underlying the host response and the slow, natural course of HIV-1 infection.

Human Herpesvirus Replication & Poor Immune Reconstitution on ART

Evidence from many studies indicates that persistent immune activation is associated with poor CD4 T cell recovery in individuals on antiretroviral therapy (ART), even when HIV viral load is suppressed to undetectable levels. One potential source of ongoing immune activation could be the replication of other co-infecting viruses, such as cytomegalovirus (CMV), Epstein-Barr virus (EBV) and Kaposi's sarcoma herpesvirus (KSHV).

To evaluate this possibility, a group of researchers at UCSF studied the levels of these viruses in both saliva and peripheral blood mononuclear cells (PBMC) of individuals with high CD8 T cell activation and poor CD4 T cell recovery on ART. These individuals were defined as “cases” and compared to controls with low CD8 T cell activation and good CD4 recovery. High CD8 T cell activation was defined as greater than 10% of CD8 T cells co-expressing the activation markers CD38 and HLA-DR, and poor CD4 recovery was defined as levels persistently below 500 cells/mL. Controls were selected based on the opposite criteria (<10% activated CD8 T cells and CD4 cells always >500 cells/mL). A total of 11 cases and five controls were evaluated.

The results showed no differences between the groups, or any correlations between levels of any or all of the viruses and immune activation: “The proportions of all CMV, EBV or KSHV DNA positive specimens between the cases and controls were essentially the same, as were the proportions of subjects in each group that intermittently or continuously shed CMV, EBV or KSHV DNA in saliva. In addition, the median number of copies of CMV, EBV and KSHV DNA longitudinally in cases was virtually identical to that in controls.” The researchers offer the caveats that their study is very small, and sampling relatively infrequent. They are also exploring the same question in a different way, by investigating whether treatment with the anti-CMV drug valganciclovir can reduce immune activation and/or increase CD4 counts in individuals on ART. Results from this trial are expected later this year.

In discussing their findings, the authors write: “Given the strong association between inflammation/immune activation and disease outcomes in treated HIV disease, defining the mechanisms associated with HIV-associated inflammation is of high importance. Our preliminary data do not provide strong evidence for a role of persistent high level herpesvirus replication.”

PLoS ONE 4(4): e5277. doi:10.1371/journal.pone.0005277

Human Herpesvirus Replication and Abnormal CD8+ T Cell Activation and Low CD4+ T Cell Counts in Antiretroviral-Suppressed HIV-Infected Patients

Mark A. Jacobson, Dirk P. Ditmer, Elizabeth Sinclair, Jeffrey N. Martin, Steven G. Deeks, Peter Hunt, Edward S. Mocarski, Caroline Shiboski

Background

Most HIV-infected patients receiving virologically suppressive antiretroviral therapy continue to have abnormal, generalized T cell activation. We explored whether the degree of ongoing cytomegalovirus (CMV), Epstein-Barr virus (EBV) and Kaposi's sarcoma herpesvirus (KSHV) replication was associated with higher virus-specific T cell activation and the failure to achieve normal absolute CD4+ T cell counts in the face of long-term suppressive antiretroviral therapy.

Methodology

Longitudinally collected PBMC and saliva specimens obtained from HIV-infected patients on effective antiretroviral therapy for at least one year (plasma HIV RNA <75 copies/mL) were examined using a multiplex CMV, EBV and KSHV DNA PCR assay. Eleven cases were chosen who had CD8+ T cell CD38+HLA-DR+ expression >10% and plateau absolute CD4+ T cell counts <500 cells/µL. Five controls from the same study had CD8+ T cell CD38 expression <10% and plateau absolute CD4+ T cell counts >500 cells/µL.

Results and Conclusions

Among all subjects combined, 18% of PMBC samples were positive for CMV DNA, and 27%, 73% and 24% of saliva samples were positive for CMV, EBV and KSHV DNA, respectively. No significant differences or trends were observed between cases and controls in proportions of all CMV, EBV or KSHV DNA positive specimens, proportions of subjects in each group that intermittently or continuously shed CMV, EBV or KSHV DNA in saliva, or the median number of genome copies of CMV, EBV and KSHV DNA in saliva. Overall, number of genome copies in saliva were lower for KSHV than for CMV and lower for CMV than for EBV. Although replication of CMV, EBV and KSHV persists in many antiretroviral-suppressed, HIV-infected patients, we observed no evidence in this pilot case-control study that the magnitude of such human herpesvirus replication is associated with abnormally increased CD8+ T cell activation and sub-normal plateau absolute CD4+ T cell counts following virologically suppressive antiretroviral therapy.

IL-10 Upregulation in HIV Infection

The cytokine interleukin-10 (IL-10) is considered immunosuppressive because it is involved in shutting down immune responses. A number of studies have reported that IL-10 levels are increased in the setting of chronic progressive HIV infection. More recently, research has shown that blocking the receptor for IL-10 (IL-10R) can enhance virus-specific immune responses in mice chronically infected with lymphocytic choriomeningitis virus (LCMV).

In a new paper in the journal Blood, Mark Brockman and colleagues from the newly-inaugurated Ragon Institute at Massachussetts General Hospital offer a detailed analysis of IL-10 upregulation in HIV and explore the impact of blocking IL-10R in vitro on HIV-specific CD4 and CD8 T cell responses. The key findings include:

• In vitro blockade of IL-10R significantly increased HIV-specific CD4 and CD8 T cell proliferation, but only in the setting of uncontrolled viremia (there was a positive correlation between viral load and fold-increase in p24-specific proliferation). Blockade had no effect on T cell responses in elite controllers or individuals with undetectable viral loads on antiretroviral therapy (ART). CMV-specific T cell responses were not enhanced overall although blockade did increase these responses in a subset of study participants.
• Plasma levels of IL-10 protein correlated strongly with HIV viral load (R=0.6017; p=0.0001). The same held true for levels of IL-10 messenger RNA (mRNA) measured in peripheral blood mononuclear cells (PBMC). Both measures also correlated positively with the fold-increase in HIV-specific CD4 T cell proliferation obtained with IL-10R blockade in vitro.
• IL-10 mRNA levels were comparable between elite controllers and uninfected controls, but slightly higher among individuals with suppressed viral load on ART.
• Longitudinal analysis of several acutely infected study participants showed that IL-10 levels declined significantly after acute infection resolved; levels were significantly higher when measured within 30 days of infection compared to 6-12 months later.
• An investigation of IL-10 mRNA in different cell subsets revealed that, compared to uninfected controls, levels were significantly higher in CD14+ monocytes, CD4+ T cells, CD8+ T cells, CD19+ B cells, and CD56+ NK cells. There was no significant difference for plasmacytoid dendritic cells and levels were lower in monocyte-derived dendritic cells.

The researchers conclude that while IL-10 is clearly upregulated in HIV infection, its relationship with pathogenesis is likely complex. They cite a prior study suggesting that a genetic polymorphism associated with higher IL-10 production may slow disease progression, and note that this would be consistent with a possible beneficial effect of IL-10 in reducing immune activation (which correlates strongly with HIV disease progression). However, they also point out that a short placebo-controlled trial of IL-10 treatment found no benefit on surrogate markers of disease progression. In terms of the therapeutic potential of IL-10R blockade, the researchers argue that it will likely be limited as they observed no impact on HIV-specific immunity when viral load was controlled by ART. To gain a better understanding of the potential positive and negative effects of IL-10 in HIV, the researchers recommend developing strategies that allow specific targeting of the IL-10 production pathway in different cell subsets. 

Blood First Edition Paper, prepublished online April 13, 2009; DOI 10.1182/blood-2008-12-191296.

IL-10 is upregulated in multiple cell types during viremic HIV infection and reversibly inhibits virus-specific T cells

Mark A. Brockman, Douglas S. Kwon, Daniel P. Tighe, David F. Pavlik, Pamela C. Rosato, Jennifer Sela, Filippos Porichis, Sylvie Le Gall, Michael T. Waring, Kristin Moss, Heiko Jessen, Florencia Pereyra, Daniel G. Kavanagh, Bruce D. Walker, and Daniel E. Kaufmann

Ragon Institute of MGH, MIT and Harvard, Massachusetts General Hospital, Charlestown, MA, United States

Harvard Medical School, Boston, MA, United States

Howard Hughes Medical Institute, Chevy Chase, MD, United States

Jessen Praxis, Berlin, Germany

Brigham and Women's Hospital, Boston, MA, United States

Murine models indicate that IL-10 can suppress viral clearance, and interventional blockade of IL-10 activity has been proposed to enhance immunity in chronic viral infections. Increased IL-10 levels have been observed during HIV infection and IL-10 blockade has been shown to enhance T cell function in some HIV-infected subjects. However, the categories of individuals in whom the IL-10 pathway is upregulated are poorly defined, and the cellular sources of IL-10 in these subjects remain to be determined. Here we report that blockade of the IL-10 pathway augmented in vitro proliferative capacity of HIV-specific CD4 and CD8 T cells in individuals with ongoing viral replication. IL-10 blockade also increased cytokine secretion by HIV-specific CD4 T cells. Spontaneous IL-10 expression, measured as either plasma IL-10 protein or IL-10 mRNA in PBMC, correlated positively with viral load and diminished following successful antiretroviral therapy. IL-10 mRNA levels were upregulated in multiple PBMC subsets in HIV infected subjects compared to HIV-negative controls, particularly in T, B, and NK cells, whereas monocytes were a major source of IL-10 mRNA in HIV-infected and uninfected individuals. These data indicate that multiple cell types contribute to IL-10-mediated immune suppression in the presence of uncontrolled HIV viremia.

Regulation Gone Awry? Elevated Levels of Regulatory T Cells Linked To Disease Progression

Over the past decade it has become accepted that some T cells play a role in dampening down immune responses. These cells are dubbed regulatory T cells or Treg for short. In lab studies, Treg have been shown to suppress the activation of other T cells, and there is considerable evidence that this regulatory function is also performed in vivo. One problem, however, is that there are no definitive markers for Tregs. Initially, expression of a molecule called CD25 was used to define Treg, but CD25 can also be upregulated by other activated T cells. More recently, a transcription factor, Foxp3, has emerged as a more specific marker for Treg. Although several studies have explored the role of Treg in HIV infection, results have been inconsistent and hard to interpret because approaches to define the cells have varied. A new study in the journal AIDS Research & Human Retroviruses uses the combination of CD25 and Foxp3 to explore whether Treg levels differ in individuals with varying rates of disease progression.

Weiwei Cao and colleagues from UCLA employed a case-control approach to compare twenty fast progressors from the Multicenter AIDS Cohort Study (MACS) to forty matched slow progressors and nine uninfected individuals. Fast progression was defined as an AIDS diagnosis within 4 years after enrollment into MACS, whereas slow progressors were categorized based on the absence for an AIDS diagnosis for at least 8 years after entry into the cohort. Treg constituted 4.6% of CD4 T cells in uninfected study participants and this proportion was only slightly increased to 5.6% in slow progressors. Among fast progressors, however, the proportion of Treg was significantly higher at 11.3%.  Further analysis showed that Treg levels correlated with CD4 T cell activation; the proportion of CD4 T cells expressing the activation marker CD38 was 1.5% in uninfected individuals, 7.2% in slow progressors and 16.3% in fast progressors.

In the discussion section of the paper, Cao and colleagues suggest that these two phenomena may be linked, because other studies have shown that T cell activation can lead to the generation of Foxp3-expressing Treg from resting T cells that previously did not express the marker. Therefore it is possible that the persistently elevated levels of T cell activation in HIV infection leads to the observed accumulation of Tregs. Some researchers have suggested that immune activation in HIV infection is caused by a lack of Treg, but Cao and colleagues note that their data appears incompatible with this possibility. Rather, their data argues that Treg either have a negative effect – perhaps by interfering with HIV-specific immune responses, as some prior studies have posited – or alternatively the relative expansion of Tregs is just a by-product of immune activation which has no specific role in HIV disease progression.

AIDS Research and Human Retroviruses. February 2009, 25(2): 183-191. doi:10.1089/aid.2008.0140.

Regulatory T Cell Expansion and Immune Activation during Untreated HIV Type 1 Infection Are Associated with Disease Progression (free access to full text PDF)

Weiwei Cao,1 Beth D. Jamieson,2 Lance E. Hultin,1 Patricia M. Hultin,1 and Roger Detels1

1Department of Epidemiology, School of Public Health, University of California, Los Angeles, California 90095.

2Department of Medicine, Division of Hematology and Oncology, David Geffen School of Medicine, University of California, Los Angeles, California 90095.

Abstract

Regulatory T cells (Tregs) may play an important role in the immunopathology of chronic HIV-1 infection due to their potent suppressive activity of both T cell activation and effector function. To investigate the correlation between Tregs and immune activation during untreated chronic HIV-1 infection, we conducted a nested case–control study within the Multicenter AIDS Cohort Study (MACS). Twenty HIV-1-infected fast progressors (FP) and 40 slow progressors (SP) were included in our study using risk-set sampling. Nine age-matched HIV-1-uninfected men (UI) were also included. Cryopreserved peripheral blood mononuclear cells (PMBCs) were tested using flow cytometry analyses. We identified Tregs as Foxp3+CD25+CD4+ T cells and assessed the activation of CD4+ and CD8+ T cells by the expression of CD38, HLADR, or both markers simultaneously. There is a relative expansion of Tregs during HIV-1 infection, which is associated with disease progression. The increased CD38 expression on both CD4+ and CD8+ T cells expressed as either percentage or median fluorescence intensity (MFI) and the elevated proportion of CD8+ T cells that is HLADR+CD38+ were all associated with rapid HIV-1 progression. Counter to the assumed role of Tregs as the suppressors of activation, the expansion of Tregs was positively correlated with CD4+ T cell activation among HIV-1-infected fast progressors. The high level of Tregs associated with rapid HIV progression may suggest a detrimental role of these cells in the immune control of HIV-1 infection.