Complement (C3)‐Receptor‐Mediated Phagocytosis of Agarose Beads by Mouse Macrophages

Abstract

The phagocytosis by macrophages of C3bi[inactive complement component 3b]-coated agarose beads reached a plateau after 15 min, compared with 30 min for C3b-coated beads. By using 125I-labeled C3bi or C3b coupled to the agarose beads, 70 and 95% of total radioactivtiy were removed from the beads after 12 h and 36 h of intracellular digestion, respectively. Intracellular degradation of C3bi linked to agarose beads was also demonstrated by testing binding of monoclonal antibodies against human C3c, C3g and C3d to beads extracted from the cells after phagocytosis. Such extracted beads also showed reduced attachment to new macrophages compared with non-ingested beads. Treatment of the cells with leupeptin, an inhibitor of the lysosomal enzyme cathepsin B, or with dextran sulfate to inhibit phagosome-lysosome fusion greatly reduced the release of labeled protein from the agarose during the 1st 12 h. C3bi and C3b on agarose is destroyed intracellularly by lysosomal enzymes.