TH3 cells are involved in mucosal immunity and protecting mucosal surfaces in the gut from nonpathogenic non-self antigens. They mediate this non-inflammatory environment by secreting TGF-beta and IL-10. TGF-beta promotes the class switch to low concentrations of IgA which is noninflammatory. IgA does not usually activate the complement system and is not involved with phagocytosis. TH3 inhibits TH1 and TH2 cells. T helper 3 cell (Th3) have different cytokine requirements for their growth from CD25+ CD4+ Treg cells. The survival of CD25+ CD4+ Treg cells is dependent upon interleukin 2 (IL-2), while in vitro differentiation of Th3 cells is enhanced by transforming growth factor beta (TGF-), IL-4, and IL-10. Findings suggest that Th3 cells are a different linage from naturally arising CD25+ CD4+ Treg cells, but it is still unclear whether Th3 cells are the same as induced Treg cells because of the lack of a specific marker for Th3 cells.