Secretion of two different monokines. Effect of TPA and silica

IL 1 can be released from P388D1 cells; addition of TPA increases the level of mitogenic activity but an analysis of the phenomenon shows that this increase is not due to a higher level of IL1 secretion but rather to a comitogenic activity that develops upon incubation of TPA in foetal Calf serum containing media. In contrast, addition of silica enhances the release of IL1. Murine peritoneal macrophages produce a monokine (FRM) with macrophage replacing activity for the in vitro antibody production against SRBC. The presence of silica induces supernatants which in addition increase the proliferation of thymocytes. Chromatography on ultrogel AcA54 shows that the activity obtained from resident cells is due to FRM (M.W. 35000) whereas IL1 (M.W. 15000) is released upon incubation with silica. The same effect has been observed with Rats: IL1 is released instead of FRM when silica is added to peritoneal macrophages.