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Mycobacterium tuberculosis (Mtb) and Human Immunodeficiency virus (HIV) are important causes of death in infected patients worldwide, and act synergistically to worsen disease in those with co-infection. C-type lectin receptors (CLRs) are an important component of innate immunity that can recognize and respond to pathogen-associated signals. The macrophage galactose-type lectin (MGL, CLEC10) has been described as an immunomodulatory CLR associated with M2 macrophages and regulation of inflammation following infection. Our lab previously identified an important antibacterial role of murine MGL-1 in host immunity to Mtb. More recently we observed that human peripheral blood mononuclear cell-derived macrophages, and THP-1 cells, upregulated MGL following in vitro exposure to Mtb, Mycobacterium bovis BCG, and TLR2 agonists. Silencing of MGL in primary human macrophages permitted greater intracellular Mtb replication. Interestingly, we observed that MGL is suppressed by HIV in differential transcriptome analysis of lung from HIV-infected humanized mice, in lung and spleen of autopsy specimens from HIV-infected decedents, and upon in vitro infection of human macrophages. Using a recombinant human MGL/Fc chimeric molecule we observed that Mtb, and not HIV, directly bound MGL. MGL surface expression was reduced in lung of mice with chronic HIV infection compared to those with Mtb, and variable in co-infected animals. These results indicate that human MGL is an important CLR for pathogen recognition and initiation of protective immunity by host macrophages to Mtb. The suppression of MGL due to HIV may increase susceptibility to Mtb in people with HIV or exacerbate disease progression in those with co-infection. Supported by grants from NIH (R33 AI138328, R61 AI138328, U24 MH100930)

The study of HIV infection and pathogenicity in physical reservoirs requires a biologically relevant model which resembles the human immune system and physiology. The human immune system (HIS) mouse is well established as a model of HIV, but defects in immune tissue reconstitution remain a challenge for examining pathology in tissues. Herein we show that exogenous injection of the human cytokine FLT-3L into the HSC cord blood HIS mouse model significantly expanded the total area of axial lymph nodes and the circulating percentage of human T cells, thus enabling us to visualize and quantify HIV infectivity in the secondary lymphoid tissues of the spleen and axial node. Further, we detected cell death and T cell depletion in tissues, consistent with HIV pathogenesis. Treatment with the caspase-1 inhibitor VX-765 significantly decreased viral load as measured by gag qPCR, and apoptosis as measured by TUNEL assay, in the spleen. A significant restoration of CD4+ T cells in the spleen due to VX-765 treatment was observed via flow cytometry. In situ hybridization further demonstrated a significant decrease in viral RNA in both the spleen and axial lymph nodes. Transcriptomic analysis further revealed an upregulation in host HIV restriction factors such as APOBR, SAMHD1 and APOBEC3A as a result of VX-765 administration. These findings demonstrate FLT-3L as a mechanism whereby the human immune environment in HIS mice can be enhanced to support investigations of HIV pathogenesis and immune outcomes in tissue compartments. Preliminary results indicate that targeting inflammasome pathways with VX-765 in HIS mice treated with FLT-3L, and infected with HIV, preserved T cell populations and decreased viral load. Supported by R01 A1HL129881, NIH/NHLBI

In the era of highly active antiretroviral therapy, HIV infection still produces 800,000 deaths and 1.2 million new infections per year. People living with HIV (PLWH) are vulnerable to several co-morbidities and co-infections, due to depletion of CD4+T cells and other incompletely characterized immune disturbances. To address the mechanisms involved, lung mRNAs from humanized mice co-infected with HIV and Mycobacterium tuberculosis (Mtb) were screened. Macrophage Galactose-type Lectin (MGL) was differentially regulated in co-infected animals. When MGL protein was quantified in biobanked frozen human lung specimens from 47 HIV-infected decedents, it was lower in the lung specimens with actively replicating HIV-1, as compared to those lacking detectable viral load. Lung MGL levels were negatively correlated with HIV RNA copies in the lung, and in the spleen, which is a key lymphoid organ that influences systemic immunity. Peripheral blood leukocytes from HIV infected patients showed that MGL activation was abnormal in those cells; comparable results were obtained in cultured HIV-infected macrophages. Molecular silencing of MGL in human monocyte-derived macrophages in vitro produced increased growth of Mtb, suggesting that lower MGL expression in PLWH could compromise their innate immunity to opportunistic pathogens such as Mtb. Macrophage MGL is a novel target to elucidate how HIV infection disrupts innate immunity and increases vulnerability to tuberculosis.

HIV infection causes dysfunction and progressive depletion of human CD4 T cells, leading to enhanced host susceptibility to opportunistic infections (OIs). However, loss of immune control over different OIs occurs at different stages of HIV disease in patients; while CMV infection usually causes active disease at late stage with low CD4 counts, mucosal candidiasis caused by fungal pathogen C. albicans can become evident earlier at fairly high CD4 counts. The underlying mechanism is not well defined. We have established an in vitro system to model the interactions between HIV and pathogen-specific CD4 T-cell populations, and have shown that C. albicans-specific CD4 T cells are more permissive to HIV than CMV-specific cells in vitro. We further examined the in vivo impact of HIV on these two groups of pathogen-specific CD4 T cells in HIV-infected patients and the functional parameters involved. We found that compared to CMV-specific CD4 T cells, which manifest a polarized Th1 phenotype, C. albicans-specific CD4 T cells demonstrate mixed Th17-Th1 phenotype, producing high levels of IL-22, IL-17 and IL-2, in addition to IFN-γ and MIP-1β. The Th17 functional subsets (IL-22, IL-17 and IL-2) of C. albicans-specific CD4 T cells are more permissive to HIV in vitro and manifest an earlier impairment in vivo in HIV-infected individuals. Longitudinal analysis of infected subjects with ongoing CD4 depletion showed that C. albicans-specific CD4 response was preferentially and progressively depleted. These data altogether provide compelling evidence for differential susceptibility of pathogen-specific CD4 T cells to HIV infection and dysfunction, suggesting a mechanisms for pathogen-specific immune failure in AIDS.