A macrophage-dependent factor that stimulates the proliferation of fibroblasts in vitro.

Whole blood serum (HBS) stimulates the proliferation of fibroblasts in vitro, while platelet-poor plasma serum (PPPS) does not. Fibroblasts grown in the presence of PPPS are truly quiescent in that they are not deprived of nutrients in the culture medium and less than 3% of the cells synthesize DNA and divide. In vivo experiments have suggested that macrophages are necessary for stimulation of fibroplasia during wound repair. We have utilized the difference in growth-promoting activity between HBS and PPPS to study the ability of macrophages to produce growth-promoting activity in cell culture. Guinea pig peritoneal macrophages cultured in vitro in medium containing PPPS release into the medium, either directly or indirectly, a factor (or factors) that stimulates the proliferation of guinea pig wound fibroblasts. This macrophage-dependent, fibroblast-stimulating activity (MFSA) is nondialyzable, heat stable (56 C for 30 minutes), and requires culture in vitro for demonstration of activity. The relationship between MFSA and other growth factor(s) has not yet been determined. In contrast to the macrophage, lymphocytes prepared from mesenteric lymph nodes produced no figroblast-stimulating activity.