Immune complex receptors on cell surfaces. III. Topography of macrophage receptors demonstrated by new scanning electron microscopic peroxidase marker.

Receptors for immune complexes have been localized on rabbit alveolar macrophages with scanning electron microscopy by exposing the cells first to a soluble immune complex composed of horseradish peroxidase and antibody to horseradish peroxidase, and then incubating with a benzidine-containing substrate that yields crystalline reaction product. Receptors were visualized by this means as sites of attachment of laminated slender crystals that were easily distinguished from macrophage surface structures. Receptors appeared most abundant on cytoplasmic veils and pseudopods and in the perinuclear region of macrophages minimally spread over the coverslip. Further macrophage spreading was associated with lighter receptor staining.