CD1d-restricted human natural killer T cells are highly susceptible to human immunodeficiency virus 1 infection

CD4+ NK cells can be productively infected with HIV, leading to downregulation of CD4 expression and changes in function

NK cells mediate the innate immune response, and HIV-infected individuals demonstrate altered NK cell phenotype and function. We find that CD4+ NK cells are susceptible to HIV infection; this could account for the NK cell dysfunction seen in HIV-infected individuals. CD4+ NK cells express CXCR4 and can be infected with X4-tropic viruses and some primary R5-utilizing viral isolates. Treatment with the CXCR4 ligands AMD3100 and SDF-1alpha partially blocks infection with X4-tropic virus, treatment with anti-CCL Igs upregulates CCR5 surface expression and enables infection with HIV-Bal. HIV infection of NK cells results in CD4 downregulation and the production of infectious virus. HIV-infected CD4+ NK cells mediate NK cell cytotoxicity, however, HIV infection is associated with decreased chemotaxis towards IL-16. Thus, HIV infection of CD4+ NK cells could account for the NK cell dysfunction observed in HIV-infected individuals. Furthermore infected NK cells could serve as a viral reservoir of HIV in vivo.

Characterization of quantitative and functional innate immune parameters in HIV-1-infected Colombian children receiving stable highly active antiretroviral therapy

BACKGROUND

The immunological benefits of highly active antiretroviral therapy (HAART) in HIV-1-infected children include reconstitution of CD4+ T-cell count and functional activity. The effect of HAART on innate immune cells has not been well established.

AIM

To characterize innate immune responses in HAART-treated HIV-1-infected children.

PATIENTS AND METHODS

23 HIV-1-infected children on stable HAART and 23 uninfected children were evaluated. The frequency of innate immune cells in peripheral blood was determined by flow cytometry and functional activity was evaluated using Toll-like receptor agonists.

RESULTS

Compared with uninfected children, HAART-treated HIV-1-infected children exhibited a significant decrease in the frequency of plasmacytoid dendritic cells and natural killer and T-cell receptor (TCR)-invariant CD1d-restricted T cells. This deficiency of innate immune cells was observed mainly in children with detectable viral load. We also compared the magnitude of the quantitative restoration of those cells comparing HIV-1-infected children with HIV-1-infected adults and found a partial effect of HAART on immune restoration that was independent of age. In both pediatric and adult subjects Toll-like receptor agonists induced expression of costimulatory molecules and production of proinflammatory cytokines by dendritic cells. Peripheral blood mononuclear cells of HIV-1-infected children produced significantly reduced amounts of interferon-alpha compared with uninfected children.

CONCLUSIONS

HAART administration to HIV-1-infected children does not lead to a complete increase of circulating innate immune cells, particularly in patients with incomplete suppression of HIV.

Glycolipid ligands of invariant natural killer T cells as vaccine adjuvants

Invariant natural killer T (iNKT) cells are a unique subset of T lymphocytes that recognize glycolipid antigens in the context of the antigen-presenting molecule CD1d. Upon glycolipid antigen stimulation, iNKT cells rapidly produce copious amounts of immunomodulatory cytokines, leading to potent activation of a variety of innate and adaptive immune cells. These immune-potentiating properties of iNKT cells hold great promise for the development of vaccine adjuvants. This review aims to summarize the immunomodulatory activities of iNKT cell ligands and to discuss prospects for developing iNKT cell-based vaccine adjuvants.

Peripheral NKT cells in simian immunodeficiency virus-infected macaques

NKT cells are a specialized population of T lymphocytes that have an increasingly recognized role in immunoregulation, including controlling the response to viral infections. The characteristics of NKT cells in the peripheral blood of macaques during simian immunodeficiency virus (SIV) or chimeric simian/human immunodeficiency virus (HIV) (SHIV) infection were assessed. NKT cells comprised a mean of 0.19% of peripheral blood lymphocytes across the 64 uninfected macaques studied. Although the range in the percentages of NKT cells was large (0 to 2.2%), levels were stable over time within individual macaques without SIV/SHIV infection. The majority of NKT cells in macaques were CD4(+) (on average 67%) with smaller populations being CD8(+) (21%) and CD4/CD8 double positive (13%). A precipitous decline in CD4(+) NKT cells occurred in all six macaques infected with CXCR4-tropic SHIV(mn229) early after infection, with a concomitant rise in CD8(+) NKT cells in some animals. The depletion of CD4(+) NKT cells was tightly correlated with the depletion of total CD4(+) T cells. R5-tropic SIV(mac251) infection of macaques resulted in a slower and more variable decline in CD4(+) NKT cells, with animals that were able to control SIV virus levels maintaining higher levels of CD4(+) NKT cells. An inverse correlation between the depletion of total and CD4(+) NKT cells and SIV viral load during chronic infection was observed. Our results demonstrate the infection-driven depletion of peripheral CD4(+) NKT cells during both SHIV and SIV infection of macaques. Further studies of the implications of the loss of NKT cell subsets in the pathogenesis of HIV disease are needed.

Augumentation of natural killer activity with exogenous interleukins in patients with HIV and pulmonary tuberculosis coinfection

A depressed level of natural killer (NK) activity is one of the various immunological abnormalities in HIV infection. Defective NK cell functions can be partially restored in vitro by interleukin (IL)-2 and IL-12. IL-15 shares receptor and several biological properties with IL-2. The effect of IL-15 on NK cells in patients with HIV and tuberculosis coinfection (HIV-TB) is unclear. This study examined the cytotoxic activity and cytokine response of NK cells in HIV-TB after stimulation with IL-15 and IL-12/IL-2. The study includes 16 normal healthy subjects (NHS), 15 patients with pulmonary tuberculosis (TB), 15 HIV-infected subjects (HIV), and 15 HIV-TB patients. The cytotoxic activity of NK cells was assessed by dioctadecyloxacarbocyanine dye-based flow cytometry. Interferon-gamma present in the culture supernatants was measured by enzyme-linked immunosorbent assay. Basal NK cytotoxicity was found to be lower in HIV-TB (p < 0.05) and HIV when compared to NHS or TB. Maximal NK cytotoxicity (p < 0.05) was observed with an IL-15 and IL-12 combination in all the groups. At a 50:1 effector/target ratio, the mean fold increase in NK cytotoxicity upon stimulation was 2.11 for HIV and 1.84 for HIV-TB. Interferon-gamma levels from the stimulated cultures were elevated (p < 0.05) in the HIV and HIV-TB groups. We found no correlation between NK cytotoxicity and CD4 counts in HIV-TB. There is a positive correlation between NK cytotoxicity and interferon-gamma secretion for HIV-TB. The combination of IL-15 and IL-12 may have potential to improve the NK activity of HIV and HIV-TB.

Distinct signatures of B-cell homeostatic and activation-dependent chemokine receptors in the development and progression of extragastric MALT lymphomas

Chemokine receptors mediate migration and activation of lymphocytes through binding of their ligands. Recent studies have revealed important contributions of chemokine receptors to the development, progression, and dissemination of haematopoietic neoplasms. Because the chemokine receptor expression profile in extragastric MALT lymphoma is unknown, we performed a comprehensive study on tissue samples of parotid glands, parotid glands affected by Sjögren syndrome, extragastric MALT lymphoma, and extranodal diffuse large B-cell lymphoma (eDLBCL) originating from MALT lymphoma (transformed MALT lymphoma). By investigating the expression of 19 chemokine receptors by real-time PCR using a semi-quantitative approach and of four chemokine receptors (CCR1, CCR5, CXCR6, and XCR1) by immunohistochemistry, we show that the chemokine receptor expression profiles of extragastric MALT lymphomas differ substantially from those of extranodal DBLCL, with lower expression of CCR1, CCR8, and CXCR3, and the absence of expression of CX3CR1 and XCR1 in eDLBCL. Expression of CCR6, CCR7, CXCR3, CXCR4, and CXCR5, responsible for B-cell homing to secondary lymphoid tissue, was detected in both B-cell malignancies. Expression of CCR4 was just detected in trisomy 3-positive MALT lymphoma cases. Comparing gastric with extragastric MALT lymphomas, up-regulation of CXCR1 and CXCR2 accompanied by down-regulation of CCR8 and CX3CR1 and loss of XCR1 expression in extragastric MALT lymphomas appear to be key determinants for the site of origin of MALT lymphomagenesis. Our results support a model of stepwise progression of extragastric MALT lymphoma from a non-neoplastic event to Sjögren syndrome, to MALT lymphoma, and finally to overt eDLBCL, guided by differentially expressed B-cell homeostatic and activation-dependent chemokine receptors and their ligands.

Activation of invariant NKT cells enhances the innate immune response and improves the disease course in influenza A virus infection

Invariant NKT (iNKT) cells have an indubitable role in antiviral immunity, although the mechanisms by which these cells exert their functions are not fully elucidated. With the emerging importance of high-pathogenicity influenza A virus infections in humans, we questioned whether iNKT cells contribute to immune defence against influenza A virus and whether activation of these cells influences outcome. We show that activation of iNKT cells with alpha-galactosylceramide (alpha-GC) during influenza virus infection transiently enhanced early innate immune response without affecting T cell immunity, and reduced early viral titres in lungs of C57BL/6 mice. This is accompanied by a better disease course with improved weight loss profile. Temporal changes in iNKT cells in the liver, blood and lungs suggest activation and migration of iNKT cells from the liver to the lungs in mice that were administered alpha-GC. Improvement in viral titres appears dependent on activation of iNKT cells via the intraperitoneal route since intranasal administration of alpha-GC did not have the same effect. We conclude that activation of iNKT cells enhances early innate immune response in the lungs and contribute to antiviral immunity and improved disease course in influenza A virus infection.

Suppression of HIV-specific and allogeneic T cell activation by human regulatory T cells is dependent on the strength of signals

Regulatory T cells (Tregs) suppress immune responses against both self and non-self antigens. Tregs require activation through the T cell receptor (TCR) and IL-2 to exert their suppressive functions. However, how strength of TCR signals modulate the potency of Treg-mediated suppression of antigen-specific T cell activation remain unclear. We found that both strength of TCR signals and ratios of Tregs to target cells, either through superantigen, allogeneic antigens or HIV-specific peptides, modified the suppressive ability of Tregs. While human Tregs were able to mediate suppression in the presence of only autologous antigen-presenting cells, this was much less efficient as compared to when Tregs were activated by allogeneic dendritic cells. In another physiologically relevant system, we show that the strength of peptide stimulation, high frequency of responder CD8+ T cells or presence of high IL-2 can override the suppression of HIV-specific CD8+ T cells by Tregs. These findings suggest that ratios and TCR activation of human Tregs, are important parameters to overcome robust immune responses to pathogens or allogeneic antigens. Modulating the strength of T cell signals and selective enhancement or depletion of antigen-specific Tregs thus may have implications for designing potent vaccines and regulating immune responses during allogeneic transplantation and chronic infections.

Impact of bacteria on the phenotype, functions, and therapeutic activities of invariant NKT cells in mice

Invariant NKT (iNKT) cells are innate-like lymphocytes that recognize glycolipid antigens in the context of the MHC class I-like antigen-presenting molecule CD1d. In vivo activation of mouse iNKT cells with the glycolipid alpha-galactosylceramide (alpha-GalCer) results in the acquisition of a hyporesponsive (anergic) phenotype by these cells. Because iNKT cells can become activated in the context of infectious agents, here we evaluated whether iNKT cell activation by microorganisms can influence subsequent responses of these cells to glycolipid antigen stimulation. We found that mouse iNKT cells activated in vivo by multiple bacterial microorganisms, or by bacterial LPS or flagellin, became unresponsive to subsequent activation with alpha-GalCer. This hyporesponsive phenotype of iNKT cells required IL-12 expression and was associated with changes in the surface phenotype of these cells, reduced severity of concanavalin A-induced hepatitis, and alterations in the therapeutic activities of alpha-GalCer. These findings may have important implications for the development of iNKT cell-based therapies.

CD1d-restricted glycolipid antigens: presentation principles, recognition logic and functional consequences

Invariant natural killer T (iNKT) cells are innate lymphocytes whose functions are regulated by self and foreign glycolipid antigens presented by the antigen-presenting molecule CD1d. Activation of iNKT cells in vivo results in rapid release of copious amounts of effector cytokines and chemokines with which they regulate innate and adaptive immune responses to pathogens, certain types of cancers and self-antigens. The nature of CD1d-restricted antigens, the manner in which they are recognised and the unique effector functions of iNKT cells suggest an innate immunoregulatory role for this subset of T cells. Their ability to respond fast and our ability to steer iNKT cell cytokine response to altered lipid antigens make them an important target for vaccine design and immunotherapies against autoimmune diseases. This review summarises our current understanding of CD1d-restricted antigen presentation, the recognition of such antigens by an invariant T-cell receptor on iNKT cells, and the functional consequences of these interactions.

Invariant NKT cells from HIV-1 or Mycobacterium tuberculosis-infected patients express an activated phenotype

The frequency, subsets and activation status of peripheral blood invariant NKT (iNKT) cells were evaluated in pulmonary tuberculosis (TB) patients and in chronically HIV-1-infected subjects. The absolute numbers of iNKT cells were significantly decreased in TB patients and in HIV-1+ individuals who were antiretroviral therapy naive or had detectable viremia despite receiving HAART. iNKT cell subset analysis demonstrated a decreased percentage of CD4(+) iNKT cells in HIV-1+ subjects, and a decreased percentage of double negative iNKT cells in TB patients. Peripheral blood iNKT cells from HIV-1+ and TB patients had significantly increased expression of CD69, CD38, HLA-DR, CD16, CD56, and CD62L. The expression of CD25 was significantly increased only on iNKT cells from TB patients. These findings indicate that peripheral blood iNKT cells in these two chronic infections show an up-regulated expression of activation markers, suggesting their role in the immune response to infection.

CXCL16/SR-PSOX--a friend or a foe in atherosclerosis?

Chemokines, scavenger receptors and adhesion molecules have long been known as important players in the pathogenesis of atherosclerosis. A series of studies conducted in the past few years described CXCL16/SR-PSOX--a new molecule combining those three functions, and suggested that CXCL16/SR-PSOX can be a potential player in atherogenesis. Initial ex vivo studies showed that CXCL16/SR-PSOX is abundant in human and murine atherosclerotic lesions. Following in vitro studies suggested that as an adhesion molecule CXCL16/SR-PSOX might mediate T-cell adhesion to the endothelium, as a chemokine - drive T-cell migration, stimulate cell proliferation and elicit inflammatory phenotype in smooth muscle cells (SMC) and, finally, as a scavenger receptor - mediate uptake of atherogenic lipoproteins by macrophages and SMC. All these effects are known to be pro-atherogenic. Surprisingly, in vivo studies performed in murine models of atherosclerosis suggested that CXCL16/SR-PSOX is atheroprotective, while its receptor CXCR6 is harmful. In addition, studies investigating the association of circulating CXCL16/SR-PSOX plasma concentrations with the presence and extent of coronary artery disease (CAD) in humans are controversial suggesting both positive, negative and no association. To finally answer the question whether CXCL16/SR-PSOX can serve as a causative factor, biomarker or even a therapeutic target in atherosclerosis, we are currently in need of carefully designed animal and human studies investigating the effects of CXCL16/SR-PSOX and CXCR6 deficiency, inhibition and over-expression on the progression of atherosclerosis. Such complex approach will help us unravel the mystery of CXCL16/SR-PSOX in atherosclerosis and hopefully develop better ways of treating atherosclerosis by targeting this interesting molecule.

Human natural killer T cells infiltrate into the skin at elicitation sites of allergic contact dermatitis

The purpose of this study is to identify invariant natural killer T cells (NKT cells) in cellular infiltrate of human allergic contact dermatitis (ACD) skin challenge sites. Skin biopsy specimens were taken from positive patch test reactions from 10 different patients (9 different allergens) and studied by immunochemistry, real-time PCR, nested PCR, and in situ hybridization to identify NKT cells and the cytokines associated with this cell type. Invariant NKT cells were identified in all the 10 skin biopsy specimens studied, ranging from 1.72 to 33% of the cellular infiltrate. These NKT cells were activated in all cases, as they expressed cytokine transcripts for IFN-gamma and IL-4. Invariant NKT cells are present in ACD, regardless of the allergen that triggers the reaction, and are in an activated state. We conclude that innate immunity plays a role in late phases of type IV hypersensitivity reactions and may be responding to self-lipids released during allergic inflammation. These data complement the previous work by other investigators that suggest that NKT cells are important in the early cellular response during primary immune responses to allergens. Herein, it is demonstrated that NKT cells are constantly present during the late elicitation phase of human type IV hypersensitivity reactions.

Virally induced CD4+ T cell depletion is not sufficient to induce AIDS in a natural host

Peripheral blood CD4+ T cell counts are a key measure for assessing disease progression and need for antiretroviral therapy in HIV-infected patients. More recently, studies have demonstrated a dramatic depletion of mucosal CD4+ T cells during acute infection that is maintained during chronic pathogenic HIV as well as SIV infection. A different clinical disease course is observed during the infection of natural hosts of SIV infection, such as sooty mangabeys (Cercocebus atys), which typically do not progress to AIDS. Previous studies have determined that SIV+ mangabeys generally maintain healthy levels of CD4+ T cells despite having viral replication comparable to HIV-infected patients. In this study, we identify the emergence of a multitropic (R5/X4/R8-using) SIV infection after 43 or 71 wk postinfection in two mangabeys that is associated with an extreme, persistent (>5.5 years), and generalized loss of CD4+ T cells (5-80 cells/microl of blood) in the absence of clinical signs of AIDS. This study demonstrates that generalized CD4+ T cell depletion from the blood and mucosal tissues is not sufficient to induce AIDS in this natural host species. Rather, AIDS pathogenesis appears to be the cumulative result of multiple aberrant immunologic parameters that include CD4+ T cell depletion, generalized immune activation, and depletion/dysfunction of non-CD4+ T cells. Therefore, these data provide a rationale for investigating multifaceted therapeutic strategies to prevent progression to AIDS, even following dramatic CD4 depletion, such that HIV+ humans can survive normal life spans analogous to what occurs naturally in SIV+ mangabeys.

Proliferative activation up-regulates expression of CD4 and HIV-1 co-receptors on NK cells and induces their infection with HIV-1

NK cells play important roles in immune surveillance against malignancy and virus-infected cells. NK cell functions are affected in patients infected with HIV-1; however, whether there is direct interaction between NK cells and HIV-1 remains controversial. In this study the expression of CD4, an important receptor for HIV-1, was up-regulated on NK cells co-cultured with an NK cell-selective stimulating cell line, HFWT, and rIL-2. Although the level of CD4 was lower on NK cells than on CD4+ T cells, expression of the HIV-1 co-receptor CCR5 was clearly up-regulated on CD4+ NK cells. CD4+ NK cells expressed higher levels of HLA-DR and CD25 than CD4- NK cells, suggesting that they were highly activated. Cell-free HIV-1 could not infect the NK cells, but NK cells were infected when co-cultured with HIV-1-infected T cells. Using this co-culture system, we can better understand how HIV-1 infects NK cells and how NK cell functions are affected in AIDS.

Function of NKT cells, potential anti-HIV effector cells, are improved by beginning HAART during acute HIV-1 infection

NKT cells are a subset of lymphocytes that share features of T cells and NK cells and bridge the innate and adaptive immune responses. They are able to be infected by HIV, but their function in HIV-infected individuals is not known. NKT cell percentage and function was measured in individuals with acute HIV infection before and 1 year into highly active anti-retroviral therapy (HAART). This study demonstrates that percentages of both CD161+ NKT cells and CD161+, CD4+ NKT cells decline within the first few months after HIV-1 infection, but initiating therapy during the acute infection period can prevent a further decline in these NKT cell subsets during the first year. NKT cell function is also impaired during early HIV infection, but significantly improved by effective treatment with HAART. Finally, preservation of NKT cell function may be important in HIV-infected individuals, as NKT cells display an anti-HIV-1 activity in vitro, mediated by IFN-gamma secretion.

Polymorphisms of Cx(3)CR1 and CXCR6 receptors in relation to HAART therapy of HIV type 1 patients

The chemokine polymorphisms CXCR6-3E/K, In1.1T/C, H7 haplotype, CX(3)CR1-V249I, and CX(3)CR1-T280M have been shown to affect the course of HIV infection. We studied their influence on immunologic and virologic response to HAART in a group of 143 HIV-1 patients. We performed Kaplan-Meier analysis using the following end-point criteria: (1) time from HAART initiation to undetectable viral load (VL < 50 copies/ml), (2) maximum duration of viral suppression, (3) time from HAART administration until CD4 elevation above 200 cells/microl for patients with baseline CD4 below 200 cells/microl and above 500 cells/microl for patients with baseline CD4 between 200 and 500 cells/microl, respectively, and (4) time from HAART initiation until CD4 reduction below baseline values. Our results revealed an improved immunologic response to HAART in patients with the CX(3)CR1-249I or CX(3)CR1-280M allele. On the contrary, patients with initial VL suppression due to HAART showed a faster virologic failure in the presence of the CXCR6-3K allele. The In1.1T/C polymorphism and H7 haplotype did not reveal any specific effect on HAART response.

Delayed reconstitution of CD4+ iNKT cells after effective HIV type 1 therapy

CD1d-restricted natural killer T (iNKT) cells are increasingly recognized as key immunoregulatory cells linking innate and adaptive immunity. These fall into functionally distinct CD4+ versus CD4- subsets that are believed to steer cellular immunity toward tolerigenic/atopic versus proinflammatory phenotypes, respectively. Preferential depletion of the CD4+ subset has been observed in HIV-1 infection, but the repletion of these cells after antiretroviral therapy has not been examined in detail. T lymphocytes, CD8+ lymphocyte activation, viremia, and iNKT cell subsets in peripheral blood were compared between 18 HIV-1-uninfected (Control) and 18 seropositive (SP) men initially not on suppressive antiretroviral therapy. Compared to the Control group, the SP group demonstrated reduction of CD4+ and lesser reduction of CD4- iNKT cells at baseline. After initiation of suppressive antiretroviral treatment, the SP CD4+ iNKT cell levels remained unchanged after a year and increased by 2 years, while CD4+ iNKT cells showed a gradual increase notable after the first year. Over the first year of treatment, there was a significant correlation between changes in total CD4+ T lymphocyte and changes in CD4+ iNKT cell levels, and a significant inverse correlation between changes in CD8+ T lymphocyte activation and changes in CD4- iNKT cell levels. These results confirm preferential depletion of tolerigenic/atopic CD4+ iNKT cells by HIV-1, and suggest that disproportionate persistence of proinflammatory CD4- iNKT cells could contribute to the inappropriate immune activation believed to cause immunodeficiency in HIV-1 infection.

Production of specific mRNA transcripts, usage of an alternate promoter, and octamer-binding transcription factors influence the surface expression levels of the HIV coreceptor CCR5 on primary T cells

Surface levels of CCR5 on memory CD4(+) T cells influence HIV-1/AIDS susceptibility. Alternative promoter usage results in the generation of CCR5 mRNA isoforms that differ based on whether they contain or lack the untranslated exon 1. The impact of exon 1-containing transcripts on CCR5 surface expression is unknown. In this study, we show that the increased cell surface expression of CCR5 on primary T cells is associated with selective enrichment of exon 1-containing transcripts. The promoter that drives exon 1-containing transcripts is highly active in primary human T cells but not in transformed T cell lines. The transcription factors Oct-1 and -2 inhibit and enhance, respectively, the expression of exon 1-containing transcripts and CCR5 surface levels. However, polymorphisms at homologous octamer-binding sites in the CCR5 promoter of nonhuman primates abrogate the binding of these transcription factors. These results identify exon 1-containing transcripts, and the cis-trans factors that regulate the expression levels of these mRNA isoforms as key parameters that affect CCR5 surface expression levels, and by extension, susceptibility to HIV/AIDS among humans, and possibly, the observed interspecies differences in susceptibility to lentiviral infection.

The in vivo response of invariant natural killer T cells to glycolipid antigens

Invariant natural killer T (iNKT) cells are a subset of T lymphocytes that recognizes glycolipid antigens presented by the major histocompatibility complex class I-related protein CD1d. Although iNKT cells have received a lot of attention as targets for the development of immunotherapies, few studies have investigated the in vivo response of iNKT cells to glycolipid antigen activation. Accumulating evidence indicates that iNKT cells generate a dynamic response to in vivo activation by glycolipid antigens that is characterized by surface receptor downmodulation, expansion, cytokine production, cross talk with other cells, homeostatic contraction, and acquisition of an anergic phenotype. These studies provide new insight into the biology of iNKT cells and have important implications for designing safe and effective iNKT cell-based vaccines and therapies.

Identification of a CCR5-expressing T cell subset that is resistant to R5-tropic HIV infection

Infection with HIV-1 perturbs homeostasis of human T cell subsets, leading to accelerated immunologic deterioration. While studying changes in CD4(+) memory and naïve T cells during HIV-1 infection, we found that a subset of CD4(+) effector memory T cells that are CCR7(-)CD45RO(-)CD45RA(+) (referred to as TEMRA cells), was significantly increased in some HIV-infected individuals. This T cell subset displayed a differentiated phenotype and skewed Th1-type cytokine production. Despite expressing high levels of CCR5, TEMRA cells were strikingly resistant to infection with CCR5 (R5)-tropic HIV-1, but remained highly susceptible to CXCR4 (X4)-tropic HIV-1. The resistance of TEMRA cells to R5-tropic viruses was determined to be post-entry of the virus and prior to early viral reverse transcription, suggesting a block at the uncoating stage. Remarkably, in a subset of the HIV-infected individuals, the relatively high proportion of TEMRA cells within effector T cells strongly correlated with higher CD4(+) T cell numbers. These data provide compelling evidence for selection of an HIV-1-resistant CD4(+) T cell population during the course of HIV-1 infection. Determining the host factors within TEMRA cells that restrict R5-tropic viruses and endow HIV-1-specific CD4(+) T cells with this ability may result in novel therapeutic strategies against HIV-1 infection.

A role for natural killer T cells and CD1d molecules in counteracting suppression of hematopoiesis in mice induced by infection with murine cytomegalovirus

OBJECTIVE

Infection of immunocompromised patients with cytomegalovirus (CMV), such as that occurring in patients undergoing hematopoietic stem cell transplantation, is a serious clinical problem. CMV infection has been reported to suppress hematopoiesis. In immunocompetent hosts CMV is controlled initially by the innate immune system, with CD1d molecules and natural killer T (NKT) cells playing a role in the antiviral immune response in several model systems. We hypothesized that CD1d and NKT cells are involved in protection of the hematopoietic modulating effects of CMV, and that adoptive transfer of NKT cells would protect against these infection-induced effects.

METHODS

To address our hypothesis, we used a murine CMV (MCMV) infection model in CD1d(-/-), Jalpha18(-/-), and wild-type (WT) control mice of two different genetic strains each.

RESULTS

Infection with MCMV was associated with significant suppression of absolute numbers and cell cycling status of myeloid progenitor cells (CFU-GM, BFU-E, CFU-GEMM) in the marrow and spleen, especially in CD1d(-/-) (lack both CD1d and NKT cells), and Jalpha18(-/-) (express CD1d but lack NKT cells) mice. Adoptive transfer of NKT cells into WT and Jalpha18(-/-) mice shortly before infection with MCMV counteracted myelosuppression.

CONCLUSIONS

The results implicate NKT cells, and also likely CD1d, in protection of progenitor cells from MCMV-induced suppression and suggest that NKT cells may be of value in an adoptive transfer setting to treat CMV-induced perturbations of hematopoiesis in immunocompromised individuals. However, further studies are required to better understand the full consequences of adoptive transfer in these settings.

Chemokines and their receptors as potential targets for the treatment of asthma

Asthma is a chronic and sometimes fatal disease, which affects people of all ages throughout the world. Important hallmarks of asthma are airway inflammation and remodelling, with associated bronchial hyperresponsiveness and variable airflow obstruction. These features are orchestrated by cells of both the innate (eosinophils, neutrophils and mast cells) and the adaptive (T(H)2 T cells) immune system, in concert with structural airway cells. Chemokines are important for the recruitment of both immune and structural cells to the lung, and also for their microlocalisation within the lung tissue. Specific blockade of the responses elicited by chemokines and chemokine receptors responsible for the pathological migration of airway cells could therefore be of great therapeutic interest for the treatment of asthma.

CXC chemokine ligand 16 in periodontal diseases: expression in diseased tissues and production by cytokine-stimulated human gingival fibroblasts

Periodontal disease is an inflammatory disorder characterized by the involvement of chemokines that are important for the recruitment of leucocytes. Several cytokines are involved in regulating levels of chemokines in periodontal disease. CXCL16 is a chemokine related to the migration of T helper 1 (Th1) cells and natural killer (NK) cells. In this study, we examined its expression in periodontal tissues. Moreover, we investigated the effects of cytokines on the production of CXCL16 by human gingival fibroblast (HGF). Reverse transcription-polymerase chain reaction (RT-PCR) analysis and immunohistochemistry revealed that CXCL16 and its receptor, CXCR6, were expressed at the mRNA and protein levels in diseased tissues. Proinflammatory cytokines [interleukin (IL)-1beta, tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma] increased the mRNA expression and release of CXCL16 in a dose-dependent manner. Moreover, treatment of HGFs with IFN-gamma in combination with IL-1beta had a synergistic effect on the production of CXCL16. On the other hand, IL-4 and IL-13 inhibited the IL-1beta-induced CXCL16 production by HGFs. Inhibitors of A disintegrin and metalloprotease (ADAM)10 and ADAM17, a recently identified protease of CXCL16, reduced the amount of CXCL16 released from HGFs. These results suggest that the CXCL16 produced by HGFs may be involved in the migration of leucocytes into inflamed tissues, and provide evidence that CXCL16 production is controlled by cytokines in periodontal disease.

Innate immune defenses in HIV-1 infection: prospects for a novel immune therapy

HIV-1 infection leads to a severe decrease of CD4(+) T lymphocytes, dysregulation of several leukocyte subpopulations and generalized immune activation, with the subsequent development of opportunistic infections and malignancies. Administration of highly active antiretroviral therapy (HAART) has been successful in reducing HIV-1 plasma viremia; however, the ability of HAART to restore immunocompetence appears incomplete, particularly in patients with chronic and advanced disease. Several components of the innate immune system have direct anti-HIV-1 effects, and studies to analyze the benefits of enhancing the function of the innate response during HIV-1 infection are increasing. Development of any complementary therapeutic approaches to HIV-1 infection, particularly those able to compensate for the limitations of HAART, and enhance the anti-HIV-1 innate immune activity would be of interest. The stimulation of innate immune responses using Toll-like receptor agonists, such as monophosphoryl lipid A and oligodeoxynucleotides with CpG motifs, are currently being investigated and their benefit in HIV-1-infected patients are under evaluation.

Human natural killer T cells are heterogeneous in their capacity to reprogram their effector functions

Background

Natural killer T (NKT) cells are a subset of T cells that help potentiate and regulate immune responses. Although human NKT cell subsets with distinct effector functions have been identified, it is unclear whether the effector functions of these subsets are imprinted during development or can be selectively reprogrammed in the periphery.

Results

We found that neonatal NKT cells are predominantly CD4+ and express higher levels of CCR7 and CD62L and lower levels of CD94 and CD161 than adult CD4+ or CD4− NKT cell subsets. Accordingly, neonatal NKT cells were more flexible than adult CD4+ NKT cells in their capacity to acquire Th1- or Th2-like functions upon either cytokine-mediated polarization or ectopic expression of the Th1 or Th2 transcription factors T-bet and GATA-3, respectively. Consistent with their more differentiated phenotype, CD4- NKT cells were predominantly resistant to functional reprogramming and displayed higher cytotoxic function. In contrast to conventional T cells, neither the expression of CXCR3 nor the cytotoxic capacity of neonatal NKT cells could be reprogrammed.

Conclusions and Significance

Together, these results suggest that neonatal CD4+, adult CD4+, and adult CD4− NKT may represent unique states of maturation and that some functions of human NKT cells may be developmentally imprinted, while others are acquired similar to conventional T cell subsets during peripheral maturation and differentiation. Given the potent immuno-regulatory functions of NKT cells, these findings have important implications for the development of novel NKT cell-based therapeutics and vaccines.

Helicobacter pylori VacA toxin inhibits human immunodeficiency virus infection of primary human T cells

Human CD4(+) T cells are major targets for human immunodeficiency virus (HIV) infection. Resting T cells are resistant to HIV infection unless activated through the T-cell receptor (TCR) or by cytokine signals. How T-cell signaling promotes susceptibility of T cells to HIV infection remains poorly understood. Here we demonstrate that the VacA toxin produced by Helicobacter pylori can inhibit HIV infection of primary T cells, stimulated through the TCR or by cytokines alone. This activity of VacA was dependent on its ability to form membrane channels. VacA suppressed HIV infection of T cells at a stage after viral entry, post-reverse transcription and pre-two-long-terminal-repeat circle formation, similar to the cytokine signaling inhibitor rapamycin. Mechanistically, neither VacA nor rapamycin inhibited the activation of cytokine signal transduction components (STAT5, p42/44 mitogen-activated protein kinase, or p38), but both blocked activation of key regulatory proteins required for G(1) cell cycle transition. In contrast to rapamycin, VacA did not suppress phosphorylation of p70 S6 kinase but caused mitochondrial depolarization and ATP depletion within primary T cells. These results suggest that VacA inhibits T-cell activation and HIV infection via a novel mechanism. Identifying the host cell targets of VacA could be useful for elucidating the HIV life cycle within primary T cells.

CD1 Antigen Presentation by Human Dendritic Cells as a Target for Herpes Simplex Virus Immune Evasion

In contrast to MHC molecules, which present peptides, the CD1 molecules have been discovered to present lipid Ags to T cells. CD1-restricted T lymphocytes have been recently associated with resistance to virus infection. The mechanisms underlying activation of CD1-restricted T cells in the course of virus infection are not defined. In this study, we wanted to investigate the interaction of HSV with the antiviral CD1 Ag presentation system in human dendritic cells (DC). In response to low titers of HSV, the surface expression of CD1b and CD1d on human DC was up-regulated. These phenotypic changes enhanced the capacity of infected DC to stimulate proliferation of CD1-restricted T lymphocytes. High titers of HSV, however, lead to strong down-regulation of all surface CD1 molecules. This modulation of surface expression was associated with intracellular accumulation, colocalization with viral proteins, and disruption of the CD1 recycling machinery. Finally, even at low titers HSV interfered with the capacity of infected DC to stimulate the release of important cytokines by CD1d-restricted NKT cells. Thus, we demonstrate both the existence of a CD1 pathway allowing human DC to react to viral infection, as well as its blockage by a human herpesvirus.

Cutting Edge: Rapid Recovery of NKT Cells upon Institution of Highly Active Antiretroviral Therapy for HIV-1 Infection

CD1d-restricted NKT cells play important regulatory roles in various immune responses and are rapidly and selectively depleted upon infection with HIV-1. The cause of this selective depletion is incompletely understood, although it is in part due to the high susceptibility of CD4+ NKT cells to direct infection and subsequent cell death by HIV-1. Here, we demonstrate that highly active antiretroviral therapy (HAART) results in the rapid recovery of predominantly CD4(-) NKT cells with kinetics that are strikingly similar to those of mainstream T cells. As it is well known that the early recovery of mainstream T cells in response to HAART is due to their redistribution from tissues to the circulation, our data suggest that the selective depletion of circulating NKT cells is likely due to a combination of cell death and tissue sequestration and indicates that HAART can improve immune functions by reconstituting both conventional T cells and immunoregulatory NKT cells.

CD1d mediates T-cell-dependent resistance to secondary infection with encephalomyocarditis virus (EMCV) in vitro and immune response to EMCV infection in vivo

The innate and adaptive immune responses have evolved distinct strategies for controlling different viral pathogens. Encephalomyocarditis virus (EMCV) is a picornavirus that can cause paralysis, diabetes, and myocarditis within days of infection. The optimal innate immune response against EMCV in vivo requires CD1d. Interaction of antigen-presenting cell CD1d with distinct natural killer T-cell ("NKT") populations can induce rapid gamma interferon (IFN-gamma) production and NK-cell activation. The T-cell response of CD1d-deficient mice (lacking all NKT cells) against acute EMCV infection was further studied in vitro and in vivo. EMCV persisted at higher levels in CD1d-knockout (KO) splenocyte cultures infected in vitro. Furthermore, optimal resistance to repeat cycles of EMCV infection in vitro was also shown to depend on CD1d. However, this was not reflected in the relative levels of NK-cell activation but rather by the responses of both CD4(+) and CD8(+) T-cell populations. Repeated EMCV infection in vitro induced less IFN-gamma and alpha interferon (IFN-alpha) from CD1d-deficient splenocytes than with the wild type. Furthermore, the level of EMCV replication in wild-type splenocytes was markedly and specifically increased by addition of blocking anti-CD1d antibody. Depletion experiments demonstrated that dendritic cells contributed less than the combination of NK and NKT cells to anti-EMCV responses and that none of these cell types was the main source of IFN-alpha. Finally, EMCV infection in vivo produced higher levels of viremia in CD1d-KO mice than in wild-type animals, coupled with significantly less lymphocyte activation and IFN-alpha production. These results point to the existence of a previously unrecognized mechanism of rapid CD1d-dependent stimulation of the antiviral adaptive cellular immune response.

Enhanced ability of peripheral invariant natural killer T cells to produce IL-13 in chronic hepatitis C virus infection

BACKGROUND/AIMS

Human invariant natural killer T (iNKT) cells express a TCR Valpha24-JalphaQ paired with Vbeta11 and are activated by a surrogate ligand, alpha-galactosylceramide (alphaGalCer). The iNKT cells are involved in the regulation of anti-viral immune responses; however, little is known about their roles in hepatitis C virus (HCV) infection.

METHODS

We compared the frequency of peripheral iNKT cells and their cytokine producing capacity reactive to alphaGalCer between chronically HCV-infected patients and healthy subjects. Cytokine production of freshly isolated iNKT cells were analyzed by ELISPOT. Activated iNKT cells were obtained by culture with alphaGalCer-loaded dendritic cells (DCs) and re-stimulated with them for the measurement of cytokine production.

RESULTS

The frequencies of iNKT cells were not different between HCV-infected patients and healthy subjects. The number of fresh IFN-gamma-producing iNKT cells reactive to alphaGalCer was not different between the patients and controls, whereas fresh iNKT cells produced negligible amounts of Th2 cytokines regardless of HCV infection. In response to alphaGalCer, expanded iNKT cells from the patients secreted IFN-gamma comparable in amount to controls, whereas they released significantly more IL-13 than cells from controls.

CONCLUSIONS

Activated iNKT cells from HCV-infected patients gain more ability to secrete IL-13 than those from healthy subjects.

Immune pathogenesis of pediatric HIV-1 infection

Vertical exposure to HIV occurs at a time when functional capacity of the infant's immune system is attenuated through immaturity. Immune response capability is rooted in host genetic makeup, and the broad and fine specificity of innate and adaptive immune responses, respectively, shape the outcomes of HIV encounter in some instances and imprint viral changes through selective immune pressure in others. Findings from recent studies have profound implications for understanding immune pathogenesis of pediatric HIV infection and, in particular, highlight the importance of host genetics of both mother and child in determining whether an exposed child acquires HIV infection or not and, if infected, the rate of disease progression. This review focuses on the key host molecules, the CC chemokine CCL3 and HLA, which have taken center stage in these new developments.

Expansion of CD1d-restricted NKT cells in patients with primary HIV-1 infection treated with interleukin-2

Innate CD1d-restricted natural killer T (NKT) cells are infected and lost in HIV-1-infected patients, and this could contribute to HIV-1 pathogenesis because NKT cells play an important role in directing both adaptive and innate immunity. Administration of interleukin-2 (IL-2) to HIV-1-infected patients leads to substantial and sustained CD4+ T-cell expansion, involving both naive and memory cells. We investigated whether IL-2 treatment could restore the NKT cell compartment in patients with primary HIV-1 infection. We show that IL-2 combined with effective antiretroviral therapy (ART) resulted in significant expansion of CD1d-restricted NKT cells. Expansion occurred in both the CD4- and CD4+ subsets of NKT cells, and expanded cells expressed the CD161 maturation marker while expression of the HIV coreceptor CCR5 was reduced. These data indicate that IL-2 treatment in combination with effective ART is beneficial for the restoration of innate NKT cell immunity in patients with primary HIV-1 infection.

Pathogenic role of the CXCL16-CXCR6 pathway in rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with massive T cell infiltration into the synovium. The accumulated T cells express type 1 cytokines, such as interferon-gamma (IFNgamma) and tumor necrosis factor alpha, and activated markers of inflammation, such as CD154 and inducible costimulator (ICOS). It is thought that chemokines contribute to T cell accumulation in the synovium. In this study, we examined the role of CXCL16 and CXCR6 in T cell migration and stimulation in RA synovium.

METHODS

Expression of CXCL16 and CXCR6 was analyzed by immunohistochemistry, reverse transcription-polymerase chain reaction, Western blotting, and/or flow cytometry. Migration activity was assessed using a chemotaxis chamber. IFNgamma production was analyzed by enzyme-linked immunosorbent assay. The effect of anti-CXCL16 monoclonal antibody on murine collagen-induced arthritis (CIA) was evaluated.

RESULTS

CXCL16 was expressed in RA synovium. CXCR6 was expressed more frequently on synovial T cells than in peripheral blood. Moreover, CXCR6-positive synovial T cells more frequently expressed CD154 and ICOS than did CXCR6-negative T cells. Stimulation with interleukin-15 (IL-15) up-regulated the expression of CXCR6 on peripheral blood T cells, and then stimulation with CXCL16 induced migration of IL-15-stimulated T cells and enhanced IFNgamma production. Furthermore, anti-CXCL16 monoclonal antibody significantly reduced the clinical arthritis score and reduced infiltration of inflammatory cells and bone destruction in the synovium of mice with CIA.

CONCLUSION

Our results indicate that CXCL16 plays an important role in T cell accumulation and stimulation in RA synovium and suggest that CXCL16 could be a target molecule in new therapies for RA.

Impaired cell surface expression of human CD1d by the formation of an HIV-1 Nef/CD1d complex

The HIV-1 Nef protein causes a decrease in major histocompatibility complex (MHC) class I and CD4 molecule expression on the cell surface. To determine if Nef can affect components of the innate immune response, we assessed the ability of Nef to alter the cell surface expression of human CD1d. In cells co-expressing CD1d and Nef, a substantial reduction in the cell surface level of CD1d was observed, with a concomitant reduction in the activation of CD1d-restricted NKT cells. Nef had a minimal effect on the cell surface expression of a mutant CD1d molecule in which the last 6 or 10 amino acids of the cytoplasmic tail were deleted. Additionally, it was found that Nef physically interacted with wild-type (but not tail-deleted) CD1d. Therefore, one means by which HIV-1 may be able to establish a foothold in an infected individual is by directly interfering with the functional cell surface expression of CD1d.

Transcription factor GATA-1 potently represses the expression of the HIV-1 coreceptor CCR5 in human T cells and dendritic cells

CC chemokine receptor 5 (CCR5) is the major HIV-1 coreceptor and its expression levels are a critical determinant of HIV-1 infection. However, the molecular mechanisms of CCR5 regulation in primary targets of HIV-1 remain unknown. Despite binding to conserved DNA elements, we show that the transcription factors GATA binding protein 1 (GATA-1) and GATA-3 differentially suppress the expression of CCR5 in stem-cell-derived dendritic cells and primary human T-cell subsets. In addition, GATA-1 expression was also more potent than GATA-3 in suppressing T helper 1 (Th1)-associated genes, interferon-gamma (IFNgamma), and CXC chemokine receptor-3 (CXCR3). GATA-1, but not GATA-3, potently suppressed CCR5 transcription, thereby rendering human T cells resistant to CCR5-tropic HIV-1 infection. However, GATA-1 could also serve as a surrogate for GATA-3 in its canonic role of programming Th2 gene expression. These findings provide insight into GATA-3-mediated gene regulation during T-cell differentiation. Importantly, decoding the mechanisms of GATA-1-mediated repression of CCR5 may offer an opportunity to develop novel approaches to inhibit CCR5 expression in T cells.

Lack of Chemokine Receptor CCR5 Promotes Murine Fulminant Liver Failure by Preventing the Apoptosis of Activated CD1d-Restricted NKT Cells

Fulminant liver failure (FLF) consists of a cascade of events beginning with a presumed uncontrolled systemic activation of the immune system. The etiology of FLF remains undefined. In this study, we demonstrate that CCR5 deficiency promotes the development of acute FLF in mice following Con A administration by preventing activated hepatic CD1d-restricted NKT cells (but not conventional T cells) from dying from activation-induced apoptosis. The resistance of CCR5-deficient NKT cells from activation-induced apoptosis following Con A administration is not due to a defective Fas-driven death pathway. Moreover, FLF in CCR5-deficient mice also correlated with hepatic CCR5-deficient NKT cells, producing more IL-4, but not IFN-gamma, relative to wild-type NKT cells. Furthermore, FLF in these mice was abolished by IL-4 mAb or NK1.1 mAb treatment. We propose that CCR5 deficiency may predispose individuals to the development of FLF by preventing hepatic NKT cell apoptosis and by regulating NKT cell function, establishing a novel role for CCR5 in the development of this catastrophic liver disease that is independent of leukocyte recruitment.

Mechanisms of nonrandom human immunodeficiency virus type 1 infection and double infection: preference in virus entry is important but is not the sole factor

We previously demonstrated that human immunodeficiency virus type 1 (HIV-1) infection is nonrandom and that double infection occurs more frequently than predicted from random events. To probe the possible mechanisms for nonrandom infection, we examined the role of HIV-1 entry pathways by using viruses pseudotyped with either CCR5-tropic HIV-1 Env or vesicular stomatitis virus G protein (VSV G). These two proteins use different receptors and entry pathways. We found that regardless of the protein used, double infection occurred more frequently than random events, indicating nonrandom HIV-1 infection in both entry pathways. However, the frequency of double infection differed significantly, depending on the envelope protein. In primary CD4(+) T cells, double infection occurred most frequently when both viruses had CCR5-tropic HIV-1 Env and least frequently when the two viruses had different envelopes. These results indicated that the preference in virus entry was a significant but not the only factor contributing to nonrandom double infection. Furthermore, we demonstrated that the CD4 expression level in primary T cells affects their susceptibility to CCR5-tropic HIV-1 infection but not VSV G-pseudotyped HIV-1 infection. We have also examined infection with two viruses pseudotyped with CCR5- or CXCR4-tropic HIV-1 Env and have found that double infection occurred more frequently than random events. These results indicate that coreceptor usage is not a barrier to recombination between the two virus populations. In our previous study, we also demonstrated nonrandom double infection via dendritic cell (DC)-mediated HIV-1 transmission. To test our hypothesis that multiple HIV-1 virions are transmitted during DC-T-cell contact, we used two populations of DCs, each capturing one vector virus, and added both DC populations to T cells. We observed a decreased frequency of double infection compared with experiments in which DCs captured both viruses simultaneously. Therefore, these results support our hypothesis that multiple virions are transmitted from DCs to T cells during cell-mediated HIV-1 transmission.

Long-term loss of canonical NKT cells following an acute virus infection

NKT cell activation plays an important role in regulating innate and adaptive immunity during infection. We have previously found that there is a dramatic reduction in the NKT cell population on day 3 after an acute lymphocytic choriomeningitis virus (LCMV) infection. In this study, we report that this loss continued for at least 3 months and was not simply due to internalization of the TCR. Concomitant with the decrease in NKT cells was an increase in the percentage of Annexin V(+) NKT cells that remained in vivo, suggesting that the reduction in NKT cells at these late stages post-infection occurred by activation-induced cell death. Interestingly, APC from LCMV-infected mice could activate NKT cells in vitro at higher levels than those from uninfected mice and was concomitant with an increase in apoptosis in NKT cells. However, this could not be blocked by mAb to murine CD1d, and APC from LCMV-infected (but not uninfected) CD1d1-deficient mice could also stimulate NKT cells. Collectively, our data suggest that the activation and subsequent long-term loss of NKT cells is a normal component of the host's antiviral immune response, and this occurs in a CD1d-independent manner.

Human immunodeficiency virus gp120 downregulates CD1d cell surface expression

CD1d is an MHC class I-like surface molecule that presents endogenous glycoplipid antigens. The effect of HIV infection on CD1d surface expression has not yet been reported. FACS analysis revealed significantly lower levels of CD1d on CD14(+) monocytes from HIV-infected subjects compared to HIV-infected subjects on HAART and healthy controls. CD1d expression correlated inversely with viral load in infected individuals. CD1d surface expression on human cell lines was downregulated after infection with M-tropic HIV, T-tropic HIV, or after exposure to HIV gp120 in vitro. These data suggest that CD1d-mediated responses are altered during HIV infection and may thus contribute to the global immunodeficiency seen in these patients.

Circulating Valpha24+Vbeta11+ NKT cell numbers and dendritic cell CD1d expression in hepatitis C virus infected patients

CD1d-restricted natural killer T (NKT) cells are involved in the regulation of various immune responses, and have been shown to inhibit viral replication in animal hepatitis models when activated by the glycolipid alpha-galactosylceramide (alpha-GalCer, KRN7000). Previous studies have indicated that alpha-GalCer-induced activation of the immune system requires both CD1d expression by antigen-presenting cells as well as (normal) numbers of NKT cells. Discrepancies exist over circulating numbers of human invariant Valpha24+Vbeta11+ NKT cells during hepatitis C virus (HCV) infection. Here, by cross-sectional analysis and longitudinal analysis of patients undergoing effective combination antiviral therapy, we demonstrate that circulating Valpha24+Vbeta11+ NKT cell numbers are not decreased during active HCV infection. Importantly, as we also show that CD1d is expressed at comparable levels by peripheral blood monocytes and CD1c+ myeloid dendritic cells (DC) of healthy individuals and HCV-infected patients, these data indicate that all ingredients for evaluating the antiviral effects of the Valpha24+Vbeta11+ NKT cell ligand alpha-GalCer in HCV-infected patients are present.

The innate immune system and HIV pathogenesis

Innate immunity represents the first line of defense against microbial infections. The innate immune system is activated by conserved structures present on most pathogens and profoundly regulates subsequent adaptive immune responses. HIV is notorious for evading and disrupting the immune system. Although HIV directly targets and gradually destroys the adaptive immunity, it has become clear that the virus also perturbs the components of the innate immune system. In this paper, we review the role of two innate lymphocyte subsets, natural killer and natural killer T cells, that are disrupted during HIV infection.