Specific inhibition of macrophage antibody-dependent endocytosis by p-chloromercuribenzenesulphonic acid: identification of sensitive membrane proteins.

Murine macrophage Fc receptor function has been studied with the membrane-impermeable sulphydryl-blocking reagent p-chloromercuribenzenesulphonic acid (PCMBSA). Antibody-dependent endocytosis of fluorescein-labelled immune complexes was studied with video intensification microscopy. PCMBSA was found to inhibit the endocytosis of immune complexes at 10 nM. Control experiments indicate that the inhibition is due to an effect upon the cell, not the immune complex. Furthermore, specificity is suggested by the fact that complement-mediated and latex bead phagocytosis were not affected. 203Hg-PCMBSA labelled three macrophage proteins of molecular weight (MW) 25,000, 35,000 and 50,000. A 25,000 MW PCMBSA-binding protein has been found that is specifically immunoprecipitated by an anti-Fc receptor antibody. These studies suggest that perturbation of a cell surface sulphydryl group(s) of one of the three major PCMBSA binding membrane proteins, possibly an Fc receptor-associated protein, blocks a molecular signal required for antibody-dependent endocytosis.