TGF-β affects multiple components of the immune system. TGF-β inhibits the function of natural killer (NK) and CD8+ CTL (cytotoxic T lymphocytes), blocking the ‘cytotoxic program’ key proteins such as perforin, granzymes and cytotoxins. TGF-β induces Treg and Th17 cell differentiation and inhibits B-cell proliferation and IgA secretion. In addition, TGF-β inhibits dendritic function, block type I macrophage and neutrophil development but promotes type II macrophages and neutrophils, and mediates the immune suppression function of MISCs.