Aberrant Inflammasome Activation Characterizes Tuberculosis-Associated Immune Reconstitution Inflammatory Syndrome.

Tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) complicates combination antiretroviral therapy (cART) in up to 25% of patients with HIV/TB coinfection. Monocytes and IL-18, a signature cytokine of inflammasome activation, are implicated in TB-IRIS pathogenesis. In this study, we investigated inflammasome activation both pre- and post-cART in TB-IRIS patients. HIV/TB patients exhibited higher proportions of monocytes expressing activated caspase-1 (casp1) pre-cART, compared with HIV patients without TB, and patients who developed TB-IRIS exhibited the greatest increase in casp1 expression. CD64(+) monocytes were a marker of increased casp1 expression. Furthermore, IL-1ß, another marker of inflammasome activation, was also elevated during TB-IRIS. TB-IRIS patients also exhibited greater upregulation of NLRP3 and AIM2 inflammasome mRNA, compared with controls. Analysis of plasma mitochondrial DNA levels showed that TB-IRIS patients experienced greater cell death, especially pre-cART. Plasma NO levels were lower both pre- and post-cART in TB-IRIS patients, providing evidence of inadequate inflammasome regulation. Plasma IL-18 levels pre-cART correlated inversely with NO levels but positively with monocyte casp1 expression and mitochondrial DNA levels, and expression of IL-18Rα on CD4(+) T cells and NK cells was higher in TB-IRIS patients, providing evidence that IL-18 is a marker of inflammasome activation. We propose that inflammasome activation in monocytes/macrophages of HIV/TB patients increases with ineffective T cell-dependent activation of monocytes/macrophages, priming them for an excessive inflammatory response after cART is commenced, which is greatest in patients with TB-IRIS.

Intracellular dynamics of HIV infection.

Early studies of HIV infection dynamics suggested that virus-producing HIV-infected cells had an average half-life of approximately 1 day. However, whether this average behavior is reflective of the dynamics of individual infected cells is unclear. Here, we use HIV-enhanced green fluorescent protein (EGFP) constructs and flow cytometry sorting to explore the dynamics of cell infection, viral protein production, and cell death in vitro. By following the numbers of productively infected cells expressing EGFP over time, we show that infected cell death slows down over time. Although infected cell death in vivo could be very different, our results suggest that the constant decay of cell numbers observed in vivo during antiretroviral treatment could reflect a balance of cell death and delayed viral protein production. We observe no correlation between viral protein production and death rate of productively infected cells, showing that viral protein production is not likely to be the sole determinant of the death of HIV-infected cells. Finally, we show that all observed features can be reproduced by a simple model in which infected cells have broad distributions of productive life spans, times to start viral protein production, and viral protein production rates. This broad spectrum of the level and timing of viral protein production provides new insights into the behavior and characteristics of HIV-infected cells.

Differences in coreceptor specificity contribute to alternative tropism of HIV-1 subtype C for CD4(+) T-cell subsets, including stem cell memory T-cells.

BACKGROUND: CD4(+) memory T-cells are a major target for infection by HIV-1, whereby latent provirus can establish and endure suppressive antiretroviral therapies. Although HIV-1 subtype C strains (C-HIV) account for the majority of HIV-1 infections worldwide, the susceptibility of CD4(+) memory T-cells to infection by CCR5- (R5) and CXCR4-using (X4) C-HIV is unknown. Here, we quantified the susceptibility of naïve and memory CD4(+) T-cell subsets, including stem cell memory T-cells (TSCM), to infection by HIV-1 subtype C (C-HIV) strains from treatment-naïve subjects who progressed from chronic to advanced stages of disease whilst either maintaining CCR5-using (R5) viruses (subjects 1503 and 1854), or who experienced emergence of dominant CXCR4-using (X4) strains (subject 1109). FINDINGS: We show that R5 and X4 C-HIV viruses preferentially target memory and naïve CD4(+) T-cell subsets, respectively. While TSCM were susceptible to infection by both R5 and X4 C-HIV viruses, the proportion of infected CD4(+) T-cells that were TSCM was higher for R5 strains. Mutagenesis studies of subject 1109 viruses established the V3 region of env as the determinant underlying the preferential targeting of naïve CD4(+) T-cells by emergent X4 C-HIV variants in this subject. In contrast, the tropism of R5 C-HIV viruses for CD4(+) T-cell subsets was maintained from chronic to advanced stages of disease in subjects 1503 and 1854. CONCLUSIONS: This study provides new insights into the natural history of tropism alterations for CD4(+) T-cell subsets by C-HIV strains during progression from chronic to advanced stages of infection. Although not preferentially targeted, our data suggest that TSCM and other memory CD4(+) T-cells are likely to be viral reservoirs in subjects with X4 C-HIV infection.

Virologically suppressed HIV patients show activation of NK cells and persistent innate immune activation.

FcRγ is an ITAM-containing adaptor required for CD16 signaling and function in NK cells. We have previously shown that NK cells from HIV patients receiving combination antiretroviral therapy (cART) have decreased FcRγ expression, but the factors causing this are unknown. We conducted a cross-sectional study of cART-naive viremic patients (ART(-)), virologically suppressed patients receiving cART (ART(+)), and HIV-uninfected controls. CD8(+) T cells were activated, as assessed by CD38(+)HLA-DR(+) expression, in ART(-) patients (p < 0.0001), which was significantly reduced in ART(+) patients (p = 0.0005). In contrast, CD38(+)HLA-DR(+) NK cells were elevated in ART(-) patients (p = 0.0001) but did not decrease in ART(+) patients (p = 0.88). NK cells from both ART(-) and ART(+) patients showed high levels of spontaneous degranulation in ex vivo whole blood assays as well as decreased CD16 expression (p = 0.0001 and p = 0.0025, respectively), FcRγ mRNA (p < 0.0001 for both groups), FcRγ protein expression (p = 0.0016 and p < 0.0001, respectively), and CD16-dependent Syk phosphorylation (p = 0.0001 and p = 0.003, respectively). HIV-infected subjects showed alterations in NK activation, degranulation, CD16 expression and signaling, and elevated plasma markers of inflammation and macrophage activation, that is, neopterin and sCD14, which remained elevated in ART(+) patients. Alterations in NK cell measures did not correlate with viral load or CD4 counts. These data show that in HIV patients who achieve viral suppression following cART, NK cell activation persists. This suggests that NK cells respond to factors different from those driving T cell activation, but which are associated with inflammation in HIV patients.

The effector T cell response to ryegrass pollen is counterregulated by simultaneous induction of regulatory T cells.

Allergy is associated with pathological Th2 responses to otherwise harmless environmental Ags. In contrast, nonallergic individuals mount nonpathological immune responses to allergens, partly attributed to regulatory T cell (Treg) activity. Although thymus-derived natural Tregs have been shown to maintain tolerance to self-Ags and prevent autoimmunity, the generation of Tregs specific to non-self-Ags is less well understood. We investigated the potential for induction of Tregs from PBMCs of ryegrass pollen-allergic or healthy subjects by stimulation in vitro with ryegrass pollen extract in the absence of additional exogenous stimuli. We found that two subsets of proliferating CD4(+) T cells were induced, one expressing intermediate levels of Foxp3 (and IFN-gamma, IL-4, IL-17, or IL-2) and the other expressing high levels of Foxp3 (and no effector cytokines). After enrichment based on CD39 expression, the Foxp3(hi) subset suppressed CD4(+) T cell proliferation and IFN-gamma production. The Foxp3(hi) Treg originated from both conversion of dividing non-Tregs (CD4(+)CD25(-)CD127(hi)) and expansion of natural Tregs (CD4(+)CD25(+)CD127(lo)). Stable functional Tregs expressing high levels of Foxp3 were induced simultaneously with effector T cells by allergen stimulation. Induction of Foxp3(hi) Tregs was reduced in allergic subjects. These results indicate that the cogeneration of Foxp3(hi) Tregs in response to allergen may be a mechanism for controlling allergic reactions in healthy individuals, which is impaired in those with allergies.

Phagocytosis stimulates mobilization and shedding of intracellular CD16A in human monocytes and macrophages: inhibition by HIV-1 infection.

Surface and intracellular staining coupled with flow cytometric analysis was used to show for the first time that human macrophages and a minor subset of peripheral blood monocytes have an internal pool of CD16A, which is mobilized and shed during Fc receptor for immunoglobulin G-mediated phagocytosis. Human immunodeficiency virus type 1 (HIV-1) infection of monocyte-derived macrophages in vitro led to a reduction in the phagocytosis-induced up-regulation in CD16A shedding. These results suggest that monocytes and macrophages may be a source of soluble CD16A, which is elevated in the serum of patients in a variety of disease states and that the mobilization and shedding of CD16A in response to phagocytosis are disrupted by HIV-1 infection.

Interferon-gamma therapy activates human monocytes for enhanced phagocytosis of Mycobacterium avium complex in HIV-infected individuals.

Defective immunological function of cells of the macrophage lineage contributes to the pathogenesis of HIV-1 infection. Because monocyte/macrophage function is enhanced by cytokines such as interferon-gamma (IFN-gamma), the use of this immunomodulator is of potential clinical interest as adjunctive immunotherapy in immunosuppressed individuals. In this study, we show that adjunctive IFN-gamma treatment in an HIV-infected individual with Mycobacterium avium complex (MAC) infection increased phagocytosis of MAC by blood monocytes when compared to cells from an HIV-infected patient who was receiving standard chemotherapy alone. Enhanced phagocytic efficiency resulting from IFN-gamma therapy was associated with increased surface expression of MHC II (HLA-DR), a phagocytic receptor (CD16), and the activation marker (CD69), although the levels of activation markers were dissimilar at baseline in the two participants. These results imply that IFN-gamma may be useful in restoring antimycobacterial function in immunosuppressed patients.

Quantifying susceptibility of CD4+ stem memory T-cells to infection by laboratory adapted and clinical HIV-1 strains.

CD4+ T cells are principal targets for human immunodeficiency virus type 1 (HIV-1) infection. CD4+ T cell subsets are heterogeneous cell populations, divided by functional and phenotypic differences into naïve and memory T cells. The memory CD4+ T cells are further segregated into central, effector and transitional memory cell subsets by functional, phenotypic and homeostatic characteristics. Defining the distribution of HIV-1 infection in different T cell subsets is important, as this can play a role in determining the size and composition of the viral reservoir. Both central memory and transitional memory CD4+ T cells have been described as long-lived viral reservoirs for HIV. Recently, the newly described stem memory T cell subset has also been implicated as a long-lived HIV reservoir. Using green fluorescent protein (GFP) reporter strains of HIV-1 and multi parameter flow cytometry, we developed an assay to simultaneously quantify the susceptibility of stem memory (TSCM), central memory, effector memory, transitional memory and naïve CD4+ T cell subsets, to HIV-1 infection in vitro. We show that TSCM are susceptible to infection with laboratory adapted and clinical HIV-1 strains. Our system facilitates the quantitation of HIV-1 infection in alternative T cell subsets by CCR5- and CXCR4-using viruses across different HIV-1 subtypes, and will be useful for studies of HIV-1 pathogenesis and viral reservoirs.

Age-associated changes in monocyte and innate immune activation markers occur more rapidly in HIV infected women.

BACKGROUND: Aging is associated with immune dysfunction and the related development of conditions with an inflammatory pathogenesis. Some of these immune changes are also observed in HIV infection, but the interaction between immune changes with aging and HIV infection are unknown. Whilst sex differences in innate immunity are recognized, little research into innate immune aging has been performed on women. METHODS: This cross-sectional study of HIV positive and negative women used whole blood flow cytometric analysis to characterize monocyte and CD8(+) T cell subsets. Plasma markers of innate immune activation were measured using standard ELISA-based assays. RESULTS: HIV positive women exhibited elevated plasma levels of the innate immune activation markers CXCL10 (p<0.001), soluble CD163 (sCD163, p = 0.001), sCD14 (p = 0.022), neopterin (p = 0.029) and an increased proportion of CD16(+) monocytes (p = 0.009) compared to uninfected controls. Levels of the innate immune aging biomarkers sCD163 and the proportion of CD16(+) monocytes were equivalent to those observed in HIV negative women aged 14.5 and 10.6 years older, respectively. CXCL10 increased with age at an accelerated rate in HIV positive women (p = 0.002) suggesting a synergistic effect between HIV and aging on innate immune activation. Multivariable modeling indicated that age-related increases in innate immune biomarkers CXCL10 and sCD163 are independent of senescent changes in CD8(+) T lymphocytes. CONCLUSIONS: Quantifying the impact of HIV on immune aging reveals that HIV infection in women confers the equivalent of a 10-14 year increase in the levels of innate immune aging markers. These changes may contribute to the increased risk of inflammatory age-related diseases in HIV positive women.

The magnitude of HIV-1 resistance to the CCR5 antagonist maraviroc may impart a differential alteration in HIV-1 tropism for macrophages and T-cell subsets.

Human immunodeficiency virus type 1 (HIV-1) resistance to CCR5 antagonists, including maraviroc (MVC), results from alterations in the HIV-1 envelope glycoproteins (Env) enabling recognition of antagonist-bound CCR5. Here, we characterized tropism alterations for CD4+ T-cell subsets and macrophages by Envs from two subjects who developed MVC resistance in vivo, which displayed either relatively efficient or inefficient recognition of MVC-bound CCR5. We show that MVC-resistant Env with efficient recognition of drug-bound CCR5 displays a tropism shift for CD4+ T-cell subsets associated with increased infection of central memory T-cells and reduced infection of effector memory and transitional memory T-cells, and no change in macrophage infectivity. In contrast, MVC-resistant Env with inefficient recognition of drug-bound CCR5 displays no change in tropism for CD4+ T-cell subsets, but exhibits a significant reduction in macrophage infectivity. The pattern of HIV-1 tropism alterations for susceptible cells may therefore be variable in subjects with MVC resistance.

Decreased NK Cell FcRgamma in HIV-1 infected individuals receiving combination antiretroviral therapy: a cross sectional study.

BACKGROUND: FcRgamma is an immunoreceptor tyrosine-based activation motif (ITAM)-signalling protein essential for immunoreceptor signaling and monocyte, macrophage and NK cell function. Previous study from our laboratory showed that FcRgamma is down-regulated in HIV-infected macrophages in vitro. FcRgamma expression in immune cells present in HIV-infected individuals is unknown. METHODOLOGY/PRINCIPAL FINDINGS: We compared FcRgamma expression in peripheral blood mononuclear cells isolated from HIV-1-infected individuals receiving combination antiretroviral therapy and healthy, HIV-1-uninfected individuals. FcRgamma mRNA and protein levels were measured using quantitative real-time PCR and immunoblotting, respectively. CD56(+) CD94(+) lymphocytes isolated from blood of HIV-1 infected individuals had reduced FcRgamma protein expression compared to HIV-uninfected individuals (decrease = 76.8%, n = 18 and n = 12 respectively, p = 0.0036). In a second group of patients, highly purified NK cells had reduced FcRgamma protein expression compared to uninfected controls (decrease = 50.2%, n = 9 and n = 8 respectively, p = 0.021). Decreased FcRgamma expression in CD56+CD94+ lymphocytes was associated with reduced mRNA (51.7%, p = 0.021) but this was not observed for the smaller group of patients analysed for NK cell expression (p = 0.36). CONCLUSION/SIGNIFICANCE: These data suggest biochemical defects in ITAM-dependent signalling within NK cells in HIV-infected individuals which is present in the context of treatment with combination antiretroviral therapy.

Defining target antigens for CD25+ FOXP3 + IFN-gamma- regulatory T cells in chronic hepatitis C virus infection.

The mechanism behind the apparent lack of effective antiviral immune responses in chronic hepatitis C virus (HCV) patients is poorly understood. It remains unclear if natural regulatory T cells (Treg) contribute to the induction and maintenance of HCV persistence. We herein report for the first time that CD25(high)IFN-gamma(-)FOXP3(high) Tregs can be rapidly induced by culturing peripheral blood mononuclear cells (PBMCs) of HCV-positive patients with HCV protein-derived peptides. The HCV-specific Tregs, generally CD4(+)CD45RO(+), did not proliferate in response to HCV peptide and failed to produce interferon (IFN)-gamma, in distinct contrast to antiviral effector cells. Stimulation of healthy donor PBMCs with HCV peptides did not result in CD25 and FOXP3 upregulation above non-antigen background. To further investigate the antigen specificity of these potentially disease-associated natural Tregs, CD25(+) cells were isolated from PBMCs, labeled with carboxyfluorescein diacetate succinimidylester and added back to CD25-depleted PBMCs, and the co-cultures were then stimulated with individual peptides derived from the HCV core protein. We found that the actual peptide that can stimulate Treg varied between patients, but within any given subject only a small number of the peptides were able to stimulate Treg, suggesting the existence of dominant Treg epitopes. Although functional experiments for these peptides are ongoing in our laboratory, data presented here suggests that HCV-specific natural Tregs are abundant in infected individuals, in contrast to the extremely low frequency of anti-HCV effector T cells, supporting the view that natural Treg may be implicated in host immune tolerance during HCV infection.

The CD16+ monocyte subset is more permissive to infection and preferentially harbors HIV-1 in vivo.

HIV-1 persists in peripheral blood monocytes in individuals receiving highly active antiretroviral therapy (HAART) with viral suppression, despite these cells being poorly susceptible to infection in vitro. Because very few monocytes harbor HIV-1 in vivo, we considered whether a subset of monocytes might be more permissive to infection. We show that a minor CD16+ monocyte subset preferentially harbors HIV-1 in infected individuals on HAART when compared with the majority of monocytes (CD14highCD16-). We confirmed this by in vitro experiments showing that CD16+ monocytes were more susceptible to CCR5-using strains of HIV-1, a finding that is associated with higher CCR5 expression on these cells. CD16+ monocytes were also more permissive to infection with a vesicular stomatitis virus G protein-pseudotyped reporter strain of HIV-1 than the majority of monocytes, suggesting that they are better able to support HIV-1 replication after entry. Consistent with this observation, high molecular mass complexes of apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G (APOBEC3G) were observed in CD16+ monocytes that were similar to those observed in highly permissive T cells. In contrast, CD14highCD16- monocytes contained low molecular mass active APOBEC3G, suggesting this is a mechanism of resistance to HIV-1 infection in these cells. Collectively, these data show that CD16+ monocytes are preferentially susceptible to HIV-1 entry, more permissive for replication, and constitute a continuing source of viral persistence during HAART.

Normal CD16 expression and phagocytosis of Mycobacterium avium complex by monocytes from a current cohort of HIV-1-infected patients.

Monocyte phenotype and function were measured in whole blood sampled from a current cohort of human immunodeficiency virus (HIV)-infected individuals attending a large, metropolitan, university-affiliated hospital. There was no significant difference in the prevalence of CD16+ monocytes or the capacity of monocytes to ingest heat-killed Mycobacterium avium complex between these individuals and HIV-uninfected control subjects, regardless of viral load, current CD4+ T cell count, nadir CD4+ T cell count, or time since diagnosis of HIV infection. CD16+ monocyte prevalence was, however, elevated in patients not currently receiving antiretroviral therapy. We conclude that HIV type 1 infection in the setting of highly active antiretroviral therapy is associated with normal monocyte function and phenotype.

Heterogeneity of freshly isolated human tonsil dendritic cells demonstrated by intracellular markers, phagocytosis, and membrane dye transfer.

BACKGROUND: Heterogeneity within human dendritic cells (DCs) has been described but its functional relationships to cells of macrophage lineage and its role in human immunodeficiency virus (HIV) infection in vivo remain unclear. METHODS: Tonsil macrophages and DCs were isolated from low-density cells by negative selection and DCs were sorted into myeloid and plasmacytoid populations using antibodies to CD11c or CD123. Phagocytosis of latex beads and uptake of dye-labeled target cells were compared by flow cytometry and CD68 and S-100 by immunofluorescence on cytospins of sorted cells. RESULTS: Bead uptake and membrane dye transfer were found in both blood and tonsil CD11c(+) DCs and in CD14(+) cells particularly from blood monocytes. CD11c(-) DCs were poorly phagocytic but took up fluorescent dye from intact, necrotic or apoptotic cells. Tonsil DCs and macrophages expressed both CD68 and S-100 but CD11c(-) DCs expressed CD68 only. CONCLUSIONS: Freshly isolated CD11c(+) tonsil DCs are similar to CD14(+) macrophages in phagocytic function but the poorly phagocytic CD11c(-) DCs can also take up membrane from target cells. The intracellular markers commonly used to identify DCs and macrophages in situ do not identify accurately the CD11c(-) DC subset nor do they distinguish tonsil macrophages from DCs.