MACROPHAGE SCAVENGER RECEPTOR MARCO - IN-VITRO AND IN-VIVO REGULATIONAND INVOLVEMENT IN THE ANTIBACTERIAL HOST-DEFENSE

Recently, a novel murine member of the scavenger receptor class A fami ly, designated MARCO, has been cloned [4]. Scavenger receptors have a characteristic broad ligand specificity and are able to bind various s ubstances, including bacteria cell surface components. The receptor MA RCO is expressed by a distinct subset of macrophages in spleen and lym ph codes. Using a panel of monoclonal antibodies (mAbs) specifically d irected against MARCO, we investigated the regulation of this receptor in vitro and in vivo. Stimulation of the mouse macrophage cell line J 774.2 in vitro with bacterial lipopolysaccharides (LPS) induces upregu lation of MARCO surface expression. In accordance with this observatio n, in mice suffering from endotoxin shock caused by bacterial infectio n, expression of MARCO is induced on macrophages in the liver, lung an d spleen, which normally do not express this receptor. We found that t wo of the anti-MARCO mAbs, ED29 and ED31, were able to block ligand bi nding. They inhibited the uptake of heat-killed Escherichia coli by MA RCO expressing CHO cells. Further experiments will be needed to confir m the importance of MARCO in the anti-bacterial host defense. (C) 1997 Elsevier Science B.V.