CONTROL OF MAC-2 SURFACE EXPRESSION ON MARINE MACROPHAGE CELL-LINES

Mac-2 antigen, a 32-kDa murine macrophage cell-surface protein express ed on thioglycollate-elicited peritoneal exudate cells at higher level s than other macrophages, is a member of the S-(soluble) galactoside-b inding lectin family with homologies to carbohydrate-binding proteins of other cell types. Murine macrophage cell lines can be ordered in a linear differentiation sequence according to their expression of Mac-2 and other surface markers (Leenen et al., Differentiation 1986. 32: 1 57.) We show here that antigen expression in macrophage cell lines can be regulated at the level of protein secretion. WEHI-3 cells, classif ied as immature macrophages by virtue of their low level of surface Ma c-2 expression synthesize similar amounts of the antigen as more matur e J774.2 and P388.D1 cells that express high amounts of surface Mac-2, but unlike these latter cell lines WEHI-3 cells fail to secrete the p rotein. Exogenously added Mac-2 binds efficiently to WEHI-3 cells and putative Mac-2-binding carbohydrates are expressed equally on WEHI-3, J774.2 and P388.D1 cells as judged by binding of plant lectins of know n carbohydrate-binding specificities. Mac-2 secretion and surface expr ession in WEHI-3 cells is not significantly enhanced by calcium ionoph ore A23187, a powerful stimulator of Mac-2 secretion in other cells an d a moderate stimulator in J774.2 and P388.D1 cells. WEHI-3 cells prov ide a valuable system for studying the mechanism of intracellular tran sport and secretion of Mac-2, a protein that lacks a signal sequence a nd does not enter the classical secretory pathway.