Role of macrophages in mesothelial healing

The role of macrophages in rat mesothelial healing was evaluated in vivo and in vitro. In animals whose circulating monocytes were severely depressed, the healing rate was retarded; however, this effect was partly reversed by the introduction of macrophages into the injured site, suggesting that macrophages are of fundamental importance in the healing of mesothelial wounds. Furthermore, it was found that wound exudates stimulated DNA synthesis in normal quiescent mesothelial cells and the component principally responsible for this activity was the macrophage. Cultured macrophage-conditioned media also induced an increase in mesothelial replication. Moreover, the mitogenic activity present in both wound exudates and macrophage-conditioned media was increased by dialysis and diminished by heating at 80 degrees C for 1 h. The putative mesothelial mitogenic factor in the supernatant of wound exudates and macrophage cell cultures has a molecular size greater than 7000 dalton and is stable after mild heating (60 degrees C, 1 h). It is postulated that exudate macrophages secrete mitogenic factor(s) which stimulate mesothelial proliferation, and initiate healing.