Sex Bias in IL-10 Production by Type I Regulatory T Cells Regulated by PI3K/mTOR Signaling

Multiple sclerosis (MS) is more prevalent in women, with a female-to-male ratio of 3:1. The molecular mechanisms driving this sex difference are still mostly unknown. MS results from immune dysfunction, with an imbalance in effector and regulatory T cells. Among the latter, Type I regulatory T cells (Tr1) are dysfunctional in people with MS (pwMS), secreting less IL-10, a potent anti-inflammatory cytokine, than in healthy donors. Our objectives were to explore the effect of biological sex on Tr1 cell differentiation in healthy donors and pwMS.

CD4⁺ T cells were isolated from peripheral blood mononuclear cells, and Tr1 differentiation was induced by costimulation with the complement regulator CD46 or IL-27. The frequency of Tr1 cells and their production of IL-10 and IFN-γ were examined. The impact of the PI3K/mTOR pathway on male and female Tr1 cells was also studied.

We found that healthy female Tr1 cells produce less IL-10 than male cells (16 women and 16 men, 18-45 years old, p = 0.0053). This sex difference was only observed when Tr1 cells were differentiated by CD46 costimulation. Mechanistically, this sex difference in IL-10 expression by Tr1 cells was due to the differential activity of a negative feedback loop targeting PI3K signaling in male vs female Tr1 cells. In contrast to findings in healthy donors, no sex difference in IL-10 production was observed when CD4⁺ T cells from pwMS (12 women and 12 men, 18-48 years old) were differentiated to Tr1 cells via the CD46 pathway, further emphasizing the dysregulation of Tr1 generation in MS. However, PI3Kδ inhibition in MS cells also revealed a sex bias, as it reduced IL-10 production by IL-27-induced Tr1 cells only in men (7 men and 5 women, p = 0.0043), while increasing IL-10 levels in the CD46 pathway in both sexes (8 men and 11 women).

We demonstrate that sex influences IL-10 production by Tr1 cells via the PI3K pathway, potentially contributing to the greater susceptibility of women to MS. Furthermore, our data suggest that targeting PI3Kδ may represent a novel therapeutic strategy to boost IL-10 production in female pwMS.