The effects of age and HIV infection on C-type lectin receptor function
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Aging is associated with an enhanced pro-inflammatory environment that may contribute to increased morbidity and mortality from infections along with decreased vaccine responses. Dysregulated inflammation arising from chronic infections such as HIV (even on antiretroviral therapy (ART)) is likely to potentiate this age-associated pro-inflammatory state and result in worsened impairments in immune responses. The interplay of inflammatory dysregulation, aging and HIV infection has consequences for the management of the rapidly expanding population of HIV-infected older adults. This inflammatory dysregulation reflects immune activation mediated by innate immune pattern recognition receptors (PRRs). Here we investigate the C-type lectin receptors (CLRs), Mincle and Dectin-1, which are critical for the innate immune recognition of mycobacteria and fungi. Mincle is the receptor for trehalose 6,6' di-mycolate (TDM) or “cord factor,” an abundant glycolipid in Mycobacterium tuberculosis, a leading cause of death worldwide, with increasing incidence of reactivation disease in both older adults and HIV infected individuals. Dectin-1 mediates the innate recognition of β-glucan components of cell walls from fungi. In addition, both Mincle and Dectin-1 also recognize endogenous ligands associated with cellular damage or necrosis, and may consequently contribute to the pro-inflammatory milieu beyond pathogen-associated responses. However, the effects of aging and HIV infection on Mincle and Dectin-1 function, remains unknown. The purpose of this proposal is to evaluate the effects of aging and HIV infection on Mincle and Dectin-1 function in an exploratory cohort of HIV-positive and HIV-negative young and older adults. We will carry out a comprehensive evaluation of human Mincle and Dectin-1 receptor function by stimulating with fungal/mycobacterial ligands and an endogenous damage- associated ligand to determine cytokine output and expression of costimulatory proteins in monocyte and dendritic cell populations. Our preliminary data already show dysregulation of cytokine production, including increases in the type and number of cytokines produced in the context of age and HIV infection. We will determine the signaling mechanisms underlying such changes in Mincle and Dectin-1 function by examining downstream signaling mediators, including the non-receptor tyrosine kinase Syk, CARD9 complex, and MAP Kinase and NF-κB-dependent pathways. Mincle and Dectin-1-dependent inflammasome activation will also be examined, including caspase-1 and 8 activation and ASC oligomerization. These studies will provide new insights into human CLR function; in addition, by interrogating innate immune receptor function instead of identifying elevations in plasma cytokines and other biomarkers, these studies should elucidate mechanisms underlying the pro-inflammatory state associated with age and/or HIV disease and identify pathways that could be targeted to enhance immune responses.
