Fate and Immunogenicity of Antigens Endocytosed by Macrophages: A Study Using Foreign Red Cells and Immunoglobulin G

Abstract

Abstract Peritoneal macrophages which had ingested 51Cr SRBC were transferred into syngeneic mice. The recipient mice made anti-SRBC antibodies indicating that immunogen of SRBC had become available for immunologic recognition. The immune response was directed both to antigen(s) bound to macrophages and to antigen released into the extracellular fluid. The antigen bound to macrophages induced a much stronger immune response. Treatment of the macrophages with antibody or trypsin prior to transfer abrogated to a great extent the immune response to macrophage-bound SRBC. Tissue culture studies with SRBC labeled with 125I indicated that subsequent to their ingestion by macrophages there was extensive release of non-protein bound I, a likely indication of catabolism in intracellular vesicles. However, small amounts of protein-bound I were found on the plasma membrane of macrophages (i.e., removed by trypsin) and in culture supernatants. Further experiments with macrophages that had ingested SRBC opsonized with 125I rabbit anti-SRBC IgG showed the release of a few IgG molecules, some of which were smaller in size than monomer IgG. It was apparent that some molecules of antigen ingested by macrophages could escape extensive catabolism and could become available for immunologic recognition either at the surface of the macrophage or at a distant site.