Th22 cells are a major contributor to the mycobacterial CD4+ T cell response and are depleted during HIV infection

Abstract

HIV-1 infection substantially increases the risk of developing tuberculosis (TB). Some mechanisms, such as defects in the Th1 response to Mycobacterium tuberculosis (M.tb) in HIV-infected individuals have been widely reported. However, Th1-independent mechanisms also contribute to protection against TB. To identify a broader spectrum of defects in TB immunity during HIV infection, we examined IL-17 and IL-22 production in response to mycobacterial antigens in individuals with latent TB infection (LTBI) and HIV co-infection. Upon stimulating with mycobacterial antigens, we observed a distinct CD4+ T helper lineage producing IL-22 in the absence of IL-17 and IFN-{gamma}. Th22 cells were present at high frequencies in response to mycobacterial antigens in blood and contributed up to 50% to the CD4+ T cell response to mycobacteria, comparable in magnitude to the IFN-{gamma} Th1 response (median 0.91% and 0.55%, respectively). Phenotypic characterization of Th22 cells revealed that their memory differentiation was similar to M.tb-specific Th1 cells (i.e. predominantly early-differentiated CD45RO+CD27+ phenotype). Moreover, CCR6 and CXCR3 expression profiles of Th22 cells were similar to Th17 cells, while their CCR4 and CCR10 expression patterns displayed an intermediate phenotype between Th1 and Th17 cells. Strikingly, mycobacterial IL-22 responses were three-fold lower in HIV-infected individuals compared to uninfected individuals, and the magnitude of responses correlated inversely with HIV viral load. These data provide important insights into mycobacteria-specific T helper subsets and suggest a potential role for IL-22 in protection against TB during HIV infection. Further studies are needed to fully elucidate the role of IL-22 in protective TB immunity.