We have investigated the regulation of transforming growth factor beta 1 gene expression in a variety of porcine immune cell populations, including peripheral blood mononuclear cells (PBMC), peripheral blood monocytes, alveolar macrophages and lymphoid cells from various swine lymphoid tissues. Using porcine transforming growth factor beta 1 cDNA probes in Northern blot assays, messages of 2.5 and 3.5 kb TGF beta 1 mRNA were detected in the cells investigated. A variety of mitogenic and immunomodulatory substances were examined for their ability to induce TGF beta 1 mRNA expression. These include phorbol 12-myristate 13-acetate (PMA), phytohemagglutinin (PHA), concanavalin A (Con A), lipopolysaccharide (LPS), dexamethasone (Dex), tumor necrosis factor (TNF) and interleukin (IL)-1 alpha. While low level constitutive expression of TGF beta 1 mRNA was detected from all cells investigated, PMA treatment of PBMC and alveolar macrophages resulted in a more than 10-fold increase in the steady-state level of TGF beta 1 mRNA within 2 hr of PMA addition. Also, the effect of opiate drugs, methadone (Md) and morphine (Mor), on TGF beta 1 gene expression was determined. Cells treated with opiates expressed the same levels of TGF beta 1 mRNA as untreated cells. Since TGF beta 1 biological activity can be induced by opiates, the regulation of TGF beta 1 gene expression likely involves mechanisms that do not cause changes in mRNA levels.