Characterization of a monoclonal antibody to guinea pig peritoneal macrophages that inhibits phagocytosis of unopsonized zymosan: Structural and functional similarities of the antigen to human and mouse CR3

Abstract A monoclonal antibody, anti-Z-1, was established by fusion of spleen cells from mice immunized with guinea pig thioglycollate-induced peritoneal macrophages (TGC-Mos) with mouse myeloma cells, P3-X63-Ag8-6.5.3. The Fab′ fragments of anti-Z-1 bound to almost all of the TGC-MoS with a high association constant (6.0 ± 0.8) × 10 8 m −1 , and effectively inhibited phagocytic activities of the cells for unopsonized zymosan and serum-treated zymosan. On the contrary, neither the phagocytic activity for rabbit IgG antibody-sensitized sheep erythrocytes nor that for periodate-treated sheep erythrocytes was inhibited by anti-Z-1. Immunoprecipitation analysis revealed that the antigen recognized by anti-Z-1, which was named Z-1 antigen, consists of a polypeptide chain with a molecular weight of 140,000 (α chain) noncovalently associated with a polypeptide chain of 95,000 (β chain). The epitope with which anti-Z-1 reacts was found to be on the α chain by Western blotting. Furthermore, it was found that Z-1 antigen solubilized from the cells with nonionic detergent was capable of binding to unopsonized zymosan, suggesting that Z-1 antigen may function as a receptor for zymosan. These findings show the structural and functional similarities of Z-1 molecules on guinea pig peritoneal macrophages to the third complement receptor on human and mouse leukocytes.