Superoxide generation by crosslinking of Fcγ receptors on the cell surface of macrophages

Abstract

Crosslinking of monomeric IgG 2 bound to specific receptor on the cell surface of guinea pig macrophages generated the triggering signal for superoxide generation system. Binding experiment of monomeric IgG 2 to macrophages indicated that macrophages had saturable binding sites for monomeric IgG 2. Scatchard analysis of binding experiment showed that macrophage had average of 3×105 binding sites per cell and the association constant of the binding was 8×106M-1. Binding of monomeric IgG 2 could be detected by the binding of 125I-labelled F (ab') 2 fragment of rabbit antibody specific for guinea pig Fab. Although binding of IgG 2 monomer to Fcγ receptor did not stimulate superoxide generation, further addition of F (ab') 2 fragment of anti-guinea pig Fab antibody did induce generation and release of superoxide which was dependent on the dose of cell-bound IgG 2. Addition of Fab monomer fragment of the same antibody did not induce superoxide release. These results show that crosslinking of Fcγ receptors results in generation of triggering signal for superoxide generation.