Alterations in antibody-dependent cellular cytotoxicity during the course of HIV-1 infection. Humoral and cellular defects

HIV-1-specific cell-mediated cytotoxicity (CMC) is a form of antibody-dependent cellular cytotoxicity (ADCC) in which HIV-1-specific antibodies arm NK cells directly to become cytotoxic for targets bearing HIV-1 antigenic determinants. This non-MHC-restricted cytotoxic activity is present in early stages of disease and declines markedly with disease progression. To understand the cellular and humoral factors contributing to the reduction in this activity, the conditions under which maximal arming of cells occurs was examined in vitro. With the use of a large patient cohort, a strong positive correlation was found between the capacity of a serum to direct lysis in standard ADCC assays and its ability to arm NK cells. Patients with minimal HIV-1-specific ADCC-directing antibodies exhibited low levels of CMC and were unable to arm normal effector cells in vitro. The lack of sufficient ADCC-directing antibodies was found to be one cause of defective CMC in some patients. Unlike asymptomatics, only a weak positive correlation was found between arming and ADCC with sera from AIDS patients, indicating that a factor other than absolute HIV-1 specific antibody titer was responsible for decreased CMC in this patient population. Another group of patients was found to have diminished CMC despite the presence of antibodies in the serum that were fully capable of arming normal effector cells to become cytotoxic for gp120-expressing targets. When compared with those of normal individuals, lymphocytes from seropositive patients mediated significantly reduced levels of cytotoxicity in ADCC and arming assays with the use of a high titered HIV-1-specific serum. In both assay systems, the magnitude and frequency of dysfunction in antibody-dependent cytolysis was found to be greater among AIDS patients than among asymptomatic individuals. The demonstration of both cellular and humoral defects in the ability of seropositive individuals to manifest ADCC reactivities strongly suggests that HIV-1 infection may significantly compromise the effectiveness of this potentially important cytolytic reactivity in vivo.     

Attrition of TCR Vα7.2+ CD161++ MAIT Cells in HIV-Tuberculosis Co-Infection Is Associated with Elevated Levels of PD-1 Expression

Mucosal-associated invariant T (MAIT) cells are evolutionarily conserved antimicrobial MR1-restricted CD8⁺ T cells co-expressing the semi-invariant TCR Vα7.2, and are numerous in the blood and mucosal tissues of humans. MAIT cells appear to undergo exhaustion in chronic viral infections. However, their role in human immunodeficiency virus type 1 (HIV-1) mono-infection and HIV/tuberculosis (TB) co-infection have seldom been elaborately investigated. We conducted a cross-sectional study to investigate the frequencies and phenotypes of CD161⁺⁺CD8⁺ T cells among anti-retroviral therapy (ART)/anti-TB therapy (ATT) treatment-naïve HIV/TB co-infected, ART/TB treated HIV/TB co-infected, ART naïve HIV-infected, ART-treated HIV-infected patients, and HIV negative healthy controls (HCs) by flow cytometry. Our data revealed that the frequency of MAIT cells was severely depleted in HIV mono- and HIV/TB co-infections. Further, PD-1 expression on MAIT cells was significantly increased in HIV mono- and HIV-TB co-infected patients. The frequency of MAIT cells did not show any significant increase despite the initiation of ART and/or ATT. Majority of the MAIT cells in HCs showed a significant increase in CCR6 expression as compared to HIV/TB co-infections. No marked difference was seen with expressions of chemokine co-receptor CCR5 and CD103 among the study groups. Decrease of CCR6 expression appears to explain why HIV-infected patients display weakened mucosal immune responses.     

Dendritic cells in innate immune responses against HIV

Dendritic cells (DCs) were recently found to be innate immunity effectors against tumoral cells and viruses. (i) In response to most viruses, including HIV, plasmacytoid DCs are responsible for most of the type I IFN secretion, which is strongly anti-viral and induces TH1 type responses. Myeloid DCs secrete IL-12, which is also important for TH1-type and cytotoxic responses. In HIV patient blood, both DC population numbers decrease as early as the primary stage. Plasmacytoid DC numbers correlate with type I IFN secretion, which is a prognosis predictor, particularly under treatment. IL-12 secretion is also defective. Immunotherapies to replace the defective cytokines or to restore a potentially defective DC-T lymphocyte feed-back might help patients restore their immune responses under antiviral therapy. (ii) After measles and other viral infections, or incubation with dsRNA, DCs become cytotoxic and consequently exhibit natural killer function, through upregulation of type I IFN secretion which enhances TRAIL expression. In HIV infection, this mechanism was not demonstrated yet, but it might a) be responsible for the massive apoptosis of uninfected lymphocytes, and b) increase specific immunity through cross-presentation of antigens from infected cells killed by DCs. (iii) DCs direct expansion and effector functions of NK cells in the absence of adaptive-type cytokines and modulate NKT cell IFN-gamma production. Reciprocally, NK activation triggers DC maturation. HIV-1 Tat inhibits NK cell cytotoxicity directly and probably through inhibition of IL-12 secretion by DC. Therefore, understanding the functions of DCs in innate immune responses and in pathogenesis will help obtain better HIV replication control.     

IL-21 promotes differentiation of naive CD8 T cells to a unique effector phenotype

IL-21, the most recently described member of the common gamma-chain cytokine family, is produced by activated CD4 T cells, whereas CD8 T cells express the IL-21 receptor. To investigate a possible role for IL-21 in the priming of naive CD8 T cells, we examined responses of highly purified naive OT-I CD8 T cells to artificial APCs displaying Ag and B7-1 on their surface. We found that IL-21 enhanced OT-I clonal expansion and supported development of cytotoxic effector function. High levels of IL-2 did not support development of effector functions, but IL-2 was required for optimal responses in the presence of IL-21. IL-12 and IFN-alpha have previously been shown to support naive CD8 T cell differentiation and acquisition of effector functions through a STAT4-dependent mechanism. Here, we show that IL-21 does not require STAT4 to stimulate development of cytolytic activity. Furthermore, IL-21 fails to induce IFN-gamma or IL-4 production and can partially block IL-12 induction of IFN-gamma production. CD8 T cells that differentiate in response to IL-21 have a distinct surface marker expression pattern and are characterized as CD44(high), PD-1(low), CD25(low), CD134(low), and CD137(low). Thus, IL-21 can provide a signal required by naive CD8 T cells to differentiate in response to Ag and costimulation, and the resulting effector cells represent a unique effector phenotype with highly effective cytolytic activity, but deficient capacity to secrete IFN-gamma.     

MAIT Cells Detect and Efficiently Lyse Bacterially-Infected Epithelial Cells

Mucosal associated invariant T cells (MAIT) are innate T lymphocytes that detect a large variety of bacteria and yeasts. This recognition depends on the detection of microbial compounds presented by the evolutionarily conserved major-histocompatibility-complex (MHC) class I molecule, MR1. Here we show that MAIT cells display cytotoxic activity towards MR1 overexpressing non-hematopoietic cells cocultured with bacteria. The NK receptor, CD161, highly expressed by MAIT cells, modulated the cytokine but not the cytotoxic response triggered by bacteria infected cells. MAIT cells are also activated by and kill epithelial cells expressing endogenous levels of MRI after infection with the invasive bacteria Shigella flexneri. In contrast, MAIT cells were not activated by epithelial cells infected by Salmonella enterica Typhimurium. Finally, MAIT cells are activated in human volunteers receiving an attenuated strain of Shigella dysenteriae-1 tested as a potential vaccine. Thus, in humans, MAIT cells are the most abundant T cell subset able to detect and kill bacteria infected cells.     

Elevated ATP via enhanced miRNA-30b, 30c,and 30e downregulates the expression of CD73 in CD8+ T cells of HIV-infected individuals

CD8⁺ T cells play a crucial role against chronic viral infections, however, their effector functions are influenced by the expression of co-stimulatory/inhibitory receptors. For example, CD73 works with CD39 to convert highly inflammatory ATP to adenosine. However, its expression on T cells in the context of viral infections has not been well defined. Here, we analyzed the expression of CD73 on human T cells in a cohort of 102 HIV-infected individuals including those on antiretroviral therapy (ART), ART-naïve, and long-term non-progressors who were not on ART. We found that the frequency of CD73⁺ T cells was markedly lower among T cell subsets (e.g. naïve, effector or memory) in the peripheral blood of all HIV-infected individuals. Notably, CD73 was decreased at the cell surface, intracellular and gene levels. Functionally, CD8⁺CD73⁺ T cells exhibited decreased cytokine expression (TNF-α, IFN-γ and IL-2) upon global or antigen-specific stimulation and impaired expression of cytolytic molecules at the gene and protein levels. In contrast, CD8⁺CD73⁺ T cells expressed elevated levels of homing receptors such as CCR7, α4β7 integrin, which suggests a migratory advantage for these cells as observed in vitro. We also observed significant migration of CD73⁺CD8⁺ T cells into the cerebrospinal fluids of multiple sclerosis (MS) patients at the time of disease relapse. Moreover, we found that elevated levels of ATP in the plasma of HIV-infected individuals upregulates the expression of miRNA30b-e in T cells in vitro. In turn, inhibition of miRNAs (30b, 30c and 30e) resulted in significant upregulation of CD73 mRNA in CD8⁺ T cells. Therefore, we provide a novel mechanism for the downregulation of CD73 via ATP-induced upregulation of miRNA30b, 30c and 30e in HIV infection. Finally, these observations imply that ATP-mediated downregulation of CD73 mainly occurs via its receptor, P2X1/P2RX1. Our results may in part explain why HIV-infected individuals have reduced risk of developing MS considering the role of CD73 for efficient T cell entry into the central nervous system.     

Natural killer cells in HIV-1 infection: role of NK cell-mediated non-cytolytic mechanisms in pathogenesis of HIV-1 infection

Natural killer (NK) cells exhibit both cytolytic and non-cytolytic effector functions against HIV-infected targets. Their precise role in immunopathogenesis of HIV-1 infection is yet to be fully understood. This review addresses the non-cytolytic functions exhibited by NK cells, their potential role in pathogenesis of HIV-1 infection and the effect of HIV-1 viremia on NK cell functions. Activated NK cells are capable of secreting CC-chemokines and suppressing HIV-1 replication in a non-cytolytic fashion. However, HIV-1 viremia suppresses the ability of NK cells to secrete CC-chemokines. Suppression of HIV-1 viremia by highly active antiretroviral therapy (HAART) restores the ability of NK cells to secrete CC-chemokines and suppress endogenous HIV-1 replication by non-cytolytic mechanisms. Better understanding of the mechanisms involved in HIV-1-NK cell interactions would be helpful in delineating novel therapeutic strategics against HIV-1.     

MR1-restricted V alpha 19i mucosal-associated invariant T cells are innate T cells in the gut lamina propria that provide a rapid and diverse cytokine response

Mucosal-associated invariant T (MAIT) cells reside primarily in the gut lamina propria and require commensal flora for selection/expansion. They are restricted by the highly conserved MHC class I-related molecule MR1 and, like most NK T cells, express an invariant TCRalpha chain. Although they probably contribute to gut immunity, MAIT cells have not been functionally characterized because they are so rare. To create a model in which they are more abundant, we generated transgenic mice expressing only the TCRalpha chain (Valpha19i) that defines MAIT cells. By directly comparing Valpha19i transgenic mice on MR1+/+ and MR1-/- backgrounds, we were able to distinguish and characterize a population of Valpha19i T cells dependent on MR1 for development. MR1-restricted Valpha19i transgenic T cells recapitulate what is known about MAIT cell development. Furthermore, a relatively high proportion of transgenic MAIT cells express NK1.1, and most have a cell surface phenotype similar to that of Valpha14i NK T cells. Finally, MR1-restricted Valpha19i T cells secrete IFN-gamma, IL-4, IL-5, and IL-10 following TCR ligation, and we provide evidence for what may be two functionally distinct MAIT cell populations. These data strongly support the idea that MAIT cells contribute to the innate immune response in the gut mucosa.     

Rate of increase in circulating IL-7 and loss of IL-7Ralpha expression differ in HIV-1 and HIV-2 infections: two lymphopenic diseases with similar hyperimmune activation but distinct outcomes

IL-7 is a nonredundant cytokine for T cell homeostasis. Circulating IL-7 levels increase in lymphopenic clinical settings, including HIV-1 infection. HIV-2 infection is considered a "natural" model of attenuated HIV disease given its much slower rate of CD4 decline than HIV-1 and limited impact on the survival of the majority of infected adults. We compared untreated HIV-1- and HIV-2-infected patients and found that the HIV-2 cohort demonstrated a delayed increase in IL-7 levels during the progressive depletion of circulating CD4 T cells as well as a dissociation between the acquisition of markers of T cell effector differentiation and the loss of IL-7Ralpha expression. This comparison of two persistent infections associated with progressive CD4 depletion and immune activation demonstrates that a better prognosis is not necessarily associated with higher levels of IL-7. Moreover, the delayed increase in IL-7 coupled with sustained expression of IL-7Ralpha suggests a maximization of available resources in HIV-2. The observation that increased IL-7 levels early in HIV-1 infection were unable to reduce the rate of CD4 loss and the impaired expression of the IL-7Ralpha irrespective of the state of cell differentiation raises concerns regarding the use of IL-7 therapy in HIV-1 infection.     

HIV-Specific Antibody-Dependent Cellular Cytotoxicity (ADCC) -Mediating Antibodies Decline while NK Cell Function Increases during Antiretroviral Therapy (ART)

Understanding alterations in HIV-specific immune responses during antiretroviral therapy (ART), such as antibody-dependent cellular cytotoxicity (ADCC), is important in the development of novel strategies to control HIV-1 infection. This study included 53 HIV-1 positive individuals. We evaluated the ability of effector cells and antibodies to mediate ADCC separately and in combination using the ADCC-PanToxiLux assay. The ability of the peripheral blood mononuclear cells (PBMCs) to mediate ADCC was significantly higher in individuals who had been treated with ART before seroconversion, compared to the individuals initiating ART at a low CD4⁺ T cell count (<350 cells/μl blood) and the ART-naïve individuals. The frequency of CD16 expressing natural killer (NK) cells correlated with both the duration of ART and Granzyme B (GzB) activity. In contrast, the plasma titer of antibodies mediating ADCC declined during ART. These findings suggest improved cytotoxic function of the NK cells if initiating ART early during infection, while the levels of ADCC mediating antibodies declined during ART.     

T cells expanded in presence of IL-15 exhibit increased antioxidant capacity and innate effector molecules

Persistence of effector cytotoxic T lymphocytes (CTLs) during an immunological response is critical for successfully controlling a viral infection or tumor growth. Various cytokines are known to play an important part in regulating the immune response. The IL-2 family of cytokines that includes IL-2 and IL-15 are known to function as growth and survival factors for antigen-experienced T cells. IL-2 and IL-15 possess similar properties, including the ability to induce T cell proliferation. Whereas long-term IL-2 exposure has been shown to promote apoptosis and limit CD8(+) memory T cell survival and proliferation, it is widely believed that IL-15 can inhibit apoptosis and helps maintain a memory CD8(+) T-cell population. However, mechanisms for superior outcomes for IL-15 as compared to IL-2 are still under investigation. Our data shows that human T cells cultured in the presence of IL-15 exhibit increased expression of anti-oxidant molecules glutathione reductase (GSR), thioredoxin reductase 1 (TXNDR1), peroxiredoxin (PRDX) and superoxide dismutase (SOD). An increased expression of cell-surface thiols, intracellular glutathione, and thioredoxins was also noted in IL-15 cultured T cells. Additionally, IL-15 cultured T cells showed an increase in cytolytic effector molecules. Apart from increased level of Granzyme A and Granzyme B, IL-15 cultured T cells exhibited increased accumulation of reactive oxygen (ROS) and reactive nitrogen species (RNS) as compared to IL-2 cultured T cells. Overall, this study suggests that T cells cultured in IL-15 show increased persistence not only due to levels of anti-apoptotic proteins, but also due to increased anti-oxidant levels, which is complimented by increased cytolytic effector functions.     

Late expression of granulysin by microbicidal CD4+ T cells requires PI3K- and STAT5-dependent expression of IL-2Rbeta that is defective in HIV-infected patients

Granulysin is a cytolytic effector molecule used by lymphocytes to kill tumor and microbial cells. Regulation of granulysin production is complex. A significant delay (5 days) following stimulation of CD4(+) T cells with IL-2 occurs before granulysin is produced. Unfortunately, the mechanisms responsible for this delay are unknown. We have recently demonstrated that granulysin-mediated killing of Cryptococcus neoformans by CD4(+) T cells is defective during HIV infection. This is because CD4(+) T cells from HIV-infected patients fail to produce granulysin in response to IL-2 activation. The present studies examined the mechanism of delayed production of granulysin and the mechanism of the defect in HIV patients. We demonstrate that IL-2 initially requires both STAT5 and PI3K activation to increase expression of IL-2Rbeta, produce granulysin, and kill C. neoformans. The increased expression of IL-2Rbeta precedes granulysin, and preventing the increased expression of IL-2Rbeta using small interfering RNA knockdown abrogates granulysin expression. Moreover, following the increased expression of IL-2Rbeta, blocking subsequent signaling by IL-2 using IL-2Rbeta-specific blocking Abs abrogates expression of granulysin. Finally, CD4(+) T cells from HIV-infected patients, who are defective in both STAT5 and PI3K signaling, fail to express IL-2Rbeta and fail to produce granulysin. These results suggest that IL-2 signals via PI3K and STAT5 to increase expression of IL-2Rbeta, which in turn is required for production of granulysin. These results provide a mechanism to explain the "late" production of granulysin during normal T cell responses, as well as for defective granulysin production by CD4(+) T cells in HIV-infected patients.     

HIV-1 down-modulates gamma signaling chain of Fc gamma R in human macrophages: a possible mechanism for inhibition of phagocytosis

HIV-1 infection impairs a number of macrophage effector functions, thereby contributing to development of opportunistic infections and the pathogenesis of AIDS. FcgammaR-mediated phagocytosis by human monocyte-derived macrophages (MDM) is inhibited by HIV-1 infection in vitro, and the underlying mechanism was investigated in this study. Inhibition of phagocytosis directly correlated with the multiplicity of HIV-1 infection. Expression of surface FcgammaRs was unaffected by HIV-1 infection, suggesting that inhibition of phagocytosis occurred during or after receptor binding. HIV-1 infection of MDM markedly inhibited tyrosine phosphorylation of the cellular proteins, which occurs following engagement of FcgammaRs, suggesting a defect downstream of initial receptor activation. FcgammaR-mediated phagocytosis in HIV-infected MDM was associated with inhibition of phosphorylation of tyrosine kinases from two different families, Hck and Syk, defective formation of Syk complexes with other tyrosine-phosphorylated proteins, and inhibition of paxillin activation. Down-modulation of protein expression but not mRNA of the gamma signaling subunit of FcgammaR (a docking site for Syk) was observed in HIV-infected MDM. Infection of MDM with a construct of HIV-1 in which nef was replaced with the gene for the gamma signaling subunit augmented FcgammaR-mediated phagocytosis, suggesting that down-modulation of gamma-chain protein expression in HIV-infected MDM caused the defective FcgammaR-mediated signaling and impairment of phagocytosis. This study is the first to demonstrate a specific alteration in phagocytosis signal transduction pathway, which provides a mechanism for the observed impaired FcgammaR-mediated phagocytosis in HIV-infected macrophages and contributes to the understanding of how HIV-1 impairs cell-mediated immunity leading to HIV-1 disease progression.     

IL-10: a novel cytotoxic T cell differentiation factor

A previous report concluded that a new cytokine, designated IL-10, is a growth cofactor for thymocytes, spleen, and lymph node cells. In this report, we have focused on the effects of IL-10 on CD8+ spleen T cells. We first observed that IL-10 enhances the growth of CD8+ T cells to IL-2. We then investigated the effect of murine rIL-10 on the induction of murine effector CTL from CTL precursors (CTL-p) using both bulk and filler cell-free limiting-dilution cultures. IL-10 alone could not induce Con A-activated FACS-sorted CD8+ T cells either to proliferate or to generate effector CTL. In combination with IL-2, however, IL-10 augmented the cytolytic activity of effector CTL generated from Con A-activated spleen CD8+ T cells in bulk cultures incubated for 5 days. In limiting-dilution cultures (using solid-phase anti-CD3 mAb as stimulus), IL-10, in combination with IL-2, substantially increased the CTL-p frequency and augmented the cytolytic activity per clone expanded from one CD8+ T cell when compared with cells cultured in IL-2 alone. Kinetic studies showed that IL-10 is required at both early and late culture stages for optimal generation of effector CTL. The potentiating effects of IL-10 on CTL function were neutralized by an anti-IL-10 mAb. These results indicate that IL-10 has direct effects on mature T cells, and suggest that IL-10 also functions as a cytotoxic T cell differentiation factor, which promotes a higher number of IL-2-activated CTL-p to proliferate and differentiate into effector CTL. In contrast, IL-10 did not enhance significantly the lymphokine-activated killer cell activity of IL-2-grown CD8+ cytotoxic T cells.     

CD27 defines phenotypically and functionally different human NK cell subsets

The absence of the TNF-receptor family member CD27 marks the stable acquisition of cytolytic effector functions by both CD4(+) and CD8(+) T cells. We found that the majority of circulating human NK cells was CD27(-). These cells were largely CD56(dim), contained high levels of perforin and granzyme B, and were able to exert strong cytotoxic activity. In contrast, circulating CD27(+) NK cells were mostly CD56(dim/bright), had significant lower levels of perforin and granzyme B, and had a low cytolytic potential. Primary and secondary lymphoid organs were markedly enriched for CD27(+) NK cells. When correlating the expression of CD27 to recently defined developmental stages of NK cells in tonsil, we observed that CD27 was exclusively found on mature CD94(+), stage 4 NK cells. On these cells, regulation of CD27 expression appeared to be controlled by the common gamma-chain cytokine IL-15, and down-regulation of CD27 was specifically induced by its ligand, CD70. Thus, the absence of CD27 expression allows the definition of cytotoxic effector cells within the known mature NK cell subsets in humans.     

Baseline viral load and immune activation determine the extent of reconstitution of innate immune effectors in HIV-1-infected subjects undergoing antiretroviral treatment

We analyzed dendritic cell (DC) and NK cell compartments in relation to CD4 recovery in 21 HIV-infected subjects followed to <50 copies/ml once starting antiretroviral therapy (ART) and observed for 52 wk of sustained suppression. Although CD4 counts increased in all subjects in response to ART, we observed a restoration of functional plasmacytoid DC (PDC) after 52 wk of sustained suppression under ART (from 1850 cells/ml to 4550 cells/ml) to levels comparable to controls (5120 cells/ml) only in subjects with a low baseline viral load, which also rapidly suppressed to <50 copies/ml upon 相似文献   

IL-7 induces immunological improvement in SIV-infected rhesus macaques under antiviral therapy

Despite efficient antiretroviral therapy (ART), CD4+ T cell counts often remain low in HIV-1-infected patients. This has led to IL-7, a crucial cytokine involved in both thymopoiesis and peripheral T cell homeostasis, being suggested as an additional therapeutic strategy. We investigated whether recombinant simian IL-7-treatment enhanced the T cell renewal initiated by ART in rhesus macaques chronically infected with SIVmac251. Six macaques in the early chronic phase of SIV infection received antiretroviral treatment. Four macaques also received a 3-wk course of IL-7 injections. Viral load was unaffected by IL-7 treatment. IL-7 treatment increased the number of circulating CD4+ and CD8+ memory T cells expressing activation (HLA-DR+, CD25+) and proliferation (Ki-67+) markers. It also increased naive (CD45RAbrightCD62L+) T cell counts by peripheral proliferation and enhanced de novo thymic production. The studied parameters returned to pretreatment values by day 29 after the initiation of treatment, concomitantly to the appearance of anti-IL-7 neutralizing Abs, supporting the need for a nonimmunogenic molecule for human treatment. Thus, IL-7, which increases T cell memory and de novo renewal of naive T cells may have additional benefits in HIV-infected patients receiving ART.     

Anti-CD3 antibody-induced activated killer cells: cytokines as the additional signals for activation of killer cells in effector phase to mediate slow lysis.

This study examines the role of cytokines in activating the effector cells to mediate slow lysis. After activation of splenocytes by alpha CD3, further culturing the cells in the absence of alpha CD3 resulted in the generation of activated killer cells (CD3-AK-) to mediate slow lysis. In contrast to fast lysis which was not affected by a PKC inhibitor H-7, slow lysis was inhibited. These findings suggested that a PKC-dependent activation phase preceded the lytic phase in slow lysis. To explore the mechanism for activating the lytic machinery in slow lysis, we examined the roles of cytokines in these reactions. First, it was found that alpha IL-2 or an alpha IL-2/alpha IL-4 combination inhibited slow lysis but had no effect on fast lysis. Secondly, IL-2, IL-4, or TNF alpha converted a noncytolytic CD3-AK- cells to mediate slow lysis, but they did not augment fast lysis. IL-2 and IL-4 had additive effect, and TNF alpha synergized with IL-2 to further augment the CD3-AK- cytolytic activity. Exogenous IL-6 and INF did not have any appreciable effect on the cytolytic activity of the killer cells. Besides TNF alpha, these cytokines were not directly cytotoxic to the target cells, indicating that they were not cytotoxic factors per se. Treatment with cycloheximide for 24 hr abrogated the cytolytic activities of CD3-AK cells, suggesting that a cytotoxic factor(s) was continuously synthesized to be stored in activated killer cells and was catabolized within 24 hr. Our results indicated that in the effector phase of slow lysis, after activating the CD3-AK- cells by the first signal (appropriate target cells), IL-2 and/or IL-4 appeared to be the second signal to initiate a cascade of events which triggered the release of other cytokines (e.g., TNF). This process resembles the secondary (memory) type of immune response. These events lead to full activation of the killer cells and converted the preformed cytotoxic factors into active form to initiate the lytic reaction and completed the lytic process.     

Endosomal MR1 Trafficking Plays a Key Role in Presentation of Mycobacterium tuberculosis Ligands to MAIT Cells

Mucosal-Associated Invariant T (MAIT) cells, present in high frequency in airway and other mucosal tissues, have Th1 effector capacity positioning them to play a critical role in the early immune response to intracellular pathogens, including Mycobacterium tuberculosis (Mtb). MR1 is a highly conserved Class I-like molecule that presents vitamin B metabolites to MAIT cells. The mechanisms for loading these ubiquitous small molecules are likely to be tightly regulated to prevent inappropriate MAIT cell activation. To define the intracellular localization of MR1, we analyzed the distribution of an MR1-GFP fusion protein in antigen presenting cells. We found that MR1 localized to endosomes and was translocated to the cell surface upon addition of 6-formyl pterin (6-FP). To understand the mechanisms by which MR1 antigens are presented, we used a lentiviral shRNA screen to identify trafficking molecules that are required for the presentation of Mtb antigen to HLA-diverse T cells. We identified Stx18, VAMP4, and Rab6 as trafficking molecules regulating MR1-dependent MAIT cell recognition of Mtb-infected cells. Stx18 but not VAMP4 or Rab6 knockdown also resulted in decreased 6-FP-dependent surface translocation of MR1 suggesting distinct pathways for loading of exogenous ligands and intracellular mycobacterially-derived ligands. We postulate that endosome-mediated trafficking of MR1 allows for selective sampling of the intracellular environment.     

Loss of Function of Intestinal IL-17 and IL-22 Producing Cells Contributes to Inflammation and Viral Persistence in SIV-Infected Rhesus Macaques

In HIV/SIV-infected humans and rhesus macaques (RMs), a severe depletion of intestinal CD4⁺ T-cells producing interleukin IL-17 and IL-22 associates with loss of mucosal integrity and chronic immune activation. However, little is known about the function of IL-17 and IL-22 producing cells during lentiviral infections. Here, we longitudinally determined the levels and functions of IL-17, IL-22 and IL-17/IL-22 producing CD4⁺ T-cells in blood, lymph node and colorectum of SIV-infected RMs, as well as how they recover during effective ART and are affected by ART interruption. Intestinal IL-17 and IL-22 producing CD4⁺ T-cells are polyfunctional in SIV-uninfected RMs, with the large majority of cells producing four or five cytokines. SIV infection induced a severe dysfunction of colorectal IL-17, IL-22 and IL-17/IL-22 producing CD4⁺ T-cells, the extent of which associated with the levels of immune activation (HLA-DR⁺CD38⁺), proliferation (Ki-67⁺) and CD4⁺ T-cell counts before and during ART. Additionally, Th17 cell function during ART negatively correlated with residual plasma viremia and levels of sCD163, a soluble marker of inflammation and disease progression. Furthermore, IL-17 and IL-22 producing cell frequency and function at various pre, on, and off-ART experimental points associated with and predicted total SIV-DNA content in the colorectum and blood. While ART restored Th22 cell function to levels similar to pre-infection, it did not fully restore Th17 cell function, and all cell types were rapidly and severely affected—both quantitatively and qualitatively—after ART interruption. In conclusion, intestinal IL-17 producing cell function is severely impaired by SIV infection, not fully normalized despite effective ART, and strongly associates with inflammation as well as SIV persistence off and on ART. As such, strategies able to preserve and/or regenerate the functions of these CD4⁺ T-cells central for mucosal immunity are critically needed in future HIV cure research.