CD4 + Foxp3 + T regs maintain immune homeostasis, but distinct mechanisms underlying their functional heterogeneity during infections are driven by specific cytokine milieu. Here we show that MyD88 deletion in Foxp3 + cells altered their function and resulted in increased fungal burden and immunopathology during oral Candida albicans (CA) challenge. Excessive inflammation due to the absence of MyD88 in T regs coincided with a reduction of the unique population of IL-17A expressing Foxp3 + cells (T reg 17) and an increase in dysfunctional IFN-g + /Foxp3 + cells (T reg IFN-g) in infected mice. Failure of MyD88-/-T regs to regulate effector CD4 + T cell functions correlated with heightened levels of IFN-g in CD4 + T cells, as well as increased infiltration of inflammatory monocytes and neutrophils in oral mucosa in vivo. Mechanistically, IL-1b/MyD88 signaling was required for the activation of IRAK-4, Akt, and mTOR, which led to the induction and proliferation of T reg 17 cells. In the absence of IL-1 receptor signaling, T reg 17 cells were reduced, but IL-6-driven expansion of T reg IFN-g cells was increased. This mechanism was physiologically relevant during Candida infection in aged mice, as they exhibited IL-1 receptor/MyD88 defect in Foxp3 + cells, loss of p-mTOR high T reg 17 cells and reduced levels of IL-1b in oral mucosa, which coincided with persistent tongue inflammation. Concurrent with T reg dysfunction, aging was associated with increased CD4 + T cell hyperactivation and heightened levels of IL-6 in mice and humans in oral mucosa in vivo. Taken together, our data identify IL-1b/MyD88/T reg axis as a new component that modulates inflammatory responses in oral mucosa. Also, dysregulation of this axis in an aging immune system may skew host defense towards an immunopathological response in mucosal compartments.

Metabolic changes of immune cells contribute to both physiological and pathophysiological outcomes of immune reactions. How viruses alter the metabolic states of mucosal T cells and the precise mechanisms underlying the persisting immune dysfunction during chronic viral infections are key questions that have not been fully addressed. Here, by comparing transcriptome and salivary metabolome profiles of the uninfected individuals and people living with HIV (PLWH) on treatment, we found a role of polyamine metabolism in immune perturbations of the oral mucosa of HIV+ patients. Flow cytometry analysis confirmed the higher expression of ornithine decarboxylase (ODC-1) and eukaryotic translation initiation factor 5A (EIF5A), the polyamine metabolism intermediates in CD4+ T cells in PLWH. Mechanistic studies using an in vitro human tonsil organoid infection model revealed that HIV infection of activated T cells also resulted in increased polyamine synthesis, which was dependent on the activities of caspase-1, IL-1β, and ODC-1. HIV-1 also led to elevated dysfunctional regulatory T cells (TregDys) /T helper 17 (Th17) cell ratios as well as heightened expression of ODC-1, EIF5A, and hypusinated EIF5A. Blockade of caspase-1, ODC-1, and EIF5A hypusination and not HIF-1α or NLRP3 reversed the frequency of TregDys showing the direct impact of polyamine pathway in Treg dysfunction during HIV-1 infection. The addition of exogenous polyamines increased TregDys percentages independent of HIV-1 infection in vitro. Finally, oral mucosal TregDys/Th17 ratios and CD4 hyperactivation positively correlated with the increases in salivary putrescine levels, which were found to be elevated in the saliva of PLWH. Thus by revealing the role of aberrantly increased polyamine synthesis during HIV infection, our study unveils a new mechanism by which chronic viral infections could drive distinct T cell effector programs and Treg dysfunction.