Microbicidal cationic proteins of rabbit alveolar macrophages: amino acid composition and functional attributes.

We purified two microbicidal cationic proteins, MCP-1 and MCP-2, from rabbit alveolar macrophages. MCP-1 was remarkably rich in arginine (25.5 mol%) and half cystine (18.7 mol%) residues and constituted approximately 1.5% of the total protein content of Freund adjuvant-elicited alveolar macrophages. MCP-2 was approximately half as abundant as MCP-1 and contained relatively less arginine (14.9 mol%) and half cystine (9.8 mol%). The amino acid compositions of MCP-1 and MCP-2 resembled those reported for the lysosomal cationic proteins of rabbit granulocytes, but were distinct from those of any known histone. MCP-1 (1 microgram/ml) killed 99.6% of Candida albicans in 20 min, whereas MCP-2 killed approximately 80% under similar conditions. Both proteins rapidly suppressed O2 consumption by C. albicans and induced a rapid loss of intracellular 86Rb+. Although more information is needed about the biological origin, distribution, and roles of macrophage microbicidal proteins, it seems likely that MCP-1 and MCP-2 contribute to the microbicidal efficacy of rabbit alveolar macrophages.