Aggregation in Dictyostelium discoideum

Cultured peritoneal macrophages have previously been shown to release a potent mitogen for mesenchymal cells. Peritoneal macrophages are derived from peripheral blood monocytes, one of the principal inflammatory cells associated with numerous tissue responses to injury. Cultured human monocytes can be activated by endotoxin or concanavalin A to secrete a potent growth factor(s) that is active on human smooth muscle cells, human fibroblasts and 3T3 cells. The optimal conditions for activation of monocyte release of this monocyte-derived growth factor(s) (MDGF) were to expose 5-day-old monocyte cultures (initially plated at 6.8 × 10⁵ cells/ml medium) to 10 μg/ml endotoxin or 6 μg/ml concanavalin A for approximately 20 hr. Monocytes can secrete MDGF into serum-free medium supplemented with 0.15% bovine serum albumin. MDGF stimulates both DNA synthesis and increase in cell number and is trypsin-sensitive, heat labile and nondialyzable. The relationship of MDGF to other monocyte products and its potential importance in wound repair and atherogenesis are discussed.