microRNA-99b regulates Bacillus Calmette-Guerin-infected immature dendritic cell-induced CD4 T cell differentiation by targeting mTOR signaling

Objective: This study aimed to elucidate the mechanisms by which microRNA-99b (miR-99b) regulates CD4 T cell differentiation induced by Bacillus Calmette-Guerin (BCG)-infected immature dendritic cells (imDCs). Methods: BCG-infected imDCs were employed to induce CD4 T cell differentiation. Levels of miR-99b, interferon-gamma (IFN-γ), Foxp3, interleukin (IL)-10, IL-17, IL-23, and ROR-γt were assessed. Effects of miR-99b inhibition and mechanistic target of rapamycin (mTOR) agonist on Th17/Treg cell ratio and cytokine levels (IL-6, IL-17, IL-23) were studied. Expression of mTOR, S6K1, and 4E-BP1 related to miR-99b was analyzed. Results: BCG-infected imDCs led to CD4 T cell differentiation and altered levels of IFN-γ, Foxp3, IL-10, miR-99b, IL-17, IL-23, and ROR-γt. Inhibition of miR-99b increased the Th17/Treg cell ratio in CD4 T cells co-cultured with BCG-infected imDCs, and this effect was further enhanced by the mTOR agonist. Additionally, the miR-99b inhibitor elevated the levels of IL-6, IL-17, and IL-23 when CD4 T cells were co-cultured with BCG-infected imDCs, and the mTOR agonist further amplified this increase. Notably, miR-99b negatively regulated mTOR signaling, as the miR-99b inhibitor upregulated the expression levels of mTOR, S6K1, and 4E-BP1 while decreasing miR-99b. Conclusion: miR-99b modulates CD4 T cell differentiation via mTOR pathway in response to BCG-infected imDCs. Inhibiting miR-99b affects Th17/Treg ratio and pro-inflammatory cytokines, potentially impacting tuberculosis immunotherapies.