ED2+ MACROPHAGES INCREASE SELECTIVELY MYOBLAST PROLIFERATION IN MUSCLE CULTURES

We have previously shown by coculturing myoblasts and macrophages that myotube formation is strongly increased in vitro by the presence of a n acid stable, heat-labile, soluble growth factor(s) secreted by macro phages, In this paper we obtained macrophages from peritoneal washing which also contained limited amounts of other cells such as lymphocyte s and mesothelial cells. We here demonstrate that an EDB-positive (ED2 +) macrophage subpopulation is responsible for myoblast, enhanced prol iferation, ED2+ macrophages were separated by a magnetic-activated cel l sorter (MACS) using a monoclonal antibody against ED2, a membrane an tigen peculiar to macrophages. Both ED2+ macrophages and their conditi oned medium increased myotube formation when added to primary muscle c ultures, Furthermore we demonstrate that muscle growth induced by macr ophages is mainly the consequence of an increased myoblast proliferati on by showing the presence of an increased number of MyoD-positive (My oD+) myonuclei. (C) 1997 Academic Press.