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Transforming growth factor beta1 (TGF-beta1) is a member of a gene superfamily involved in the regulation of cell growth and differentiation, tissue repair, fibrosis, and inflammatory responses. Given the role of the mast cell (MC) in inflammation and fibrosis, the effect of TGF-beta1 on MC mediator release was studied. In vitro treatment of rat peritoneal MC (PMC) with TGF-beta1 (10(-10) M) for 20 h followed by washes inhibited (23%) antigen stimulated histamine release. Similar pretreatment of PMC with TGF-beta1 (10(-10) M) inhibited (27%) tumor necrosis factor-alpha (TNF-alpha) dependent cytotoxicity and reduced (31%) mRNA levels of TNF-alpha, but did not inhibit nitric oxide (NO) release. By contrast, the presence of TGF-beta1 throughout the cytotoxic assay, but without pretreatment of PMC did not modulate TNF-alpha release. At least 2 h pretreatment with TGF-beta1 was required to inhibit MC TNF-alpha-dependent cytotoxicity. This inhibitory effect of TGF-beta1 was abrogated by antibody to TGF-beta1. Interestingly, the treatment of PMC with anti-TGF-beta1 antibody alone significantly increased the release of histamine and TNF-alpha. Furthermore, freshly isolated rat PMC (10(7)) contained 35 +/- 7 pg latent TGF-beta1 and 51 +/- 9 pg was spontaneously released within 30 min of culture. However, stimulation of PMC with antigen inhibited the spontaneous release of TGF-beta1 by 43%. The duration of pretreatment with TGF-beta1 required to inhibit MC TNF-alpha release was similar to that required for downregulation of MC TNF-alpha-dependent cytotoxicity by IFN-gamma. TGF-beta1 and IFN-gamma had an additive inhibition on TNF-alpha release by PMC. This inhibitory effect was abrogated and TNF-alpha-dependent cytotoxicity was enhanced by the addition of anti-TGF-beta1 antibody, but not by anti-IFN-gamma. These results suggest MC mediator release is regulated by TGF-beta1 in an autocrine manner.