RAT IGG SUBCLASSES MEDIATING BINDING AND PHAGOCYTOSIS OF TARGET-CELLSBY HOMOLOGOUS MACROPHAGES

Attachment and ingestion of Cr-51-labelled TNP-SRBC sensitized by rat IgG1, IgG2a or IgG2b-type antibodies by homologous, elicited peritonea l macrophages were studied. IgG1 was found to be the most efficient is otype in mediating these functions. The antibody doses required for a significant attachment were found to differ with the isotype of Ab, wh ile doses needed for a significant phagocytosis and antibody-dependent cellular cytotoxicity (ADCC) varied between 400-700 Ab/SRBC with all the isotypes studied. Both binding and phagocytosis were also influenc ed by the degree of hapten conjugation when target cells were sensitiz ed by IgG1. Inhibition of these functions by soluble immune complexes and monomeric immunoglobulins suggests the involvement of two Fcgamma in binding of the three isotypes. Based on the present work and on pre vious results we conclude that IgG2a interacts with a receptor binding complexed IgG only (Fcgamma RII), IgG2b binds to a different receptor which appears to bind monomeric ligand as well (Fcgamma RI), while Ig G1 seems to interact with both types of receptor. We propose that phag ocytosis can be mediated by both FcgammaRI and FcgammaRII.