No abstract

Asbestos produced a cytotoxic effect on transformed cells of rat pleural mesothelium and on IAR2 epithelial cells and Rat1 fibroblasts transformed by ras oncogene, but not on normal cells of these strains under conditions of coculturing with peritoneal macrophages. Contact of mesothelioma cells, but not macrophages with asbestos was necessary and sufficient for attaining the cytotoxic effect. Macrophage-conditioned medium potentiated asbestos cytotoxicity for transformed mesothelial cells, but not for IARS-ras and Rat1-ras.

Rat peritoneal macrophages and human peripheral blood monocytes secrete a protein with a molecular weight of 450 kDa, which specifically inhibits proliferation of cultured rat pleural mesothelial cells, but not fibroblasts and epitheliocytes. Protein secretion does not depend on the activation of macrophages. This cytokine is not a cobalamin-binding protein and has no arginase activity.

We studied the effect of myofibrils on proliferation and differentiation of myoblasts cocultured with macrophages as well as the effect of incubation of macrophages with myofibrils on the expression by macrophages of the compounds that are cytokines for muscle cells. In the cocultures, macrophages stimulated the proliferation of myoblasts. Myofibrils greatly enhanced the stimulating effect of macrophages, whereas lipopolysaccharide (LPS) completely abolished it. The culture medium conditioned by macrophages activated the proliferation of myoblasts that were incubated with myofibrils but inhibited it when myoblasts were incubated with LPS. Possibly, myofibrils and their constituent proteins activate macrophages in an alternative pathway, enriching the population with M2-type macrophages.Z.