Steroid hormones have long been known to modulate immune function, and recent studies indicate that one of the means by which they do so involves effects on the secretion of immunoregulatory cytokines. Our laboratory has found recently that estradiol (E2) selectively modifies cytokine secretion in proteolipid protein (PLP)-specific, CD4+ T cell clones isolated from patients with the demyelinating disease, multiple sclerosis, and from normal control subjects. The data suggest that E2 may play a role in regulating the balance between pro-and antiinflammatory conditions, especially at concentrations typical of pregnancy. To determine whether other pregnancy-associated steroid hormones are capable of similar activity, we expanded our testing to include estrone (E1), estriol (E3), progesterone, and dexamethasone. The results indicate that E1 and E3 enhance secretion of Ag-or anti-CD3-stimulated IL-10 and IFN-γ in dose-dependent fashion, almost identical to that of E2. The effect on IL-10 was more potent than occurred with IFN-γ. In addition, E1 and E3, like E2, had a biphasic effect on TNF-αβ secretion, with low concentrations stimulatory, and high doses inhibitory. None of the estrogens influenced IL-4 or TGF-β secretion. Progesterone enhanced secretion of IL-4, without affecting any other tested cytokine. Finally, dexamethasone induced TGF-β secretion, but inhibited IFN-γ and TNF-αβ. This differential effect of steroid hormones on the secretion of cytokines by CD4+ human T cell clones is consistent with the possibility that, collectively, they promote antiinflammatory conditions at high concentrations typical of pregnancy.