Fig. 2

The main functions of transitional B cells. 1) TrB cells suppress the proliferation of autoreactive CD4⁺ T cells. 2) TrB cells prevent the differentiation of CD4⁺ T cells into Th1 and Th17 cells, thus limiting the production of excessive pro-inflammatory cytokines (TNF-α, IFN-γ, and IL-17). 3) TrB cells promote the conversion of effector CD4⁺ T cells into CD4⁺FoxP3⁺ Tregs. 4) TrB cells inhibit CD8⁺ T cell responses. The suppressive functions of TrB cells are partially dependent on the secretion of IL-10, which can down-regulate CD86 expression in an autocrine manner. TrB cells can also secrete pro-inflammatory cytokines, such as IL-6 and TNF-α. The imbalance between pro- and anti-inflammatory cytokine productions in TrB cells may affect their functional stability and thus participate in the development of immune diseases