Effects of transforming growth factor β₁ on rainbow trout Oncorhynchus mykiss macrophage respiratory burst activity

Natural bovine transforming growth factor β₁ (TGF-β₁) was found to have both enhancing and suppressing effects on the respiratory burst activity of rainbow trout, Oncorhynchus mykiss, head kidney macrophages. Incubation with TGF-β₁ alone increased respiratory burst activity using doses from 0.05 to 0.2 ng/mL. However, incubation of activated macrophages with TGF-β₁ decreased their respiratory burst activity in a dose-dependent manner. Coincubation of macrophages with activating signals (macrophage activating factor containing supernatants and tumor necrosis factor α) and TGF-β₁ inhibited the ability of such signals to increase respiratory burst activity. Similarly, pretreatment of macrophages with TGF-β₁ prior to treatment with activating signals resulted in a time and dose-dependent decrease in activity relative to cells not treated with TGF-β₁. These suppressive effects were largest using higher doses of TGF-β₁ (1 ng/mL). The conservation of TGF-βs and their possible mode of action are discussed.