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

Abstract

Phagocytosis of agarose beads by macrophages cultured under serum-free conditions was studied; 48 h was needed before a plateau in the uptake was reached. The ingested agarose beads were coated extracellularly with macrophage-derived protein before attachment and ingestion of the beads. Intracellularly, the agarose-linked protein was removed from the agarose. If the ingested agarose beads were extracted from the macrophages within 24 h after the plateau in the uptake was reached, a fraction of the beads could attach to new macrophages, demonstrating modification of the agarose beads by opsonin(s). Because of binding of anti-human C3c [complement component 3c] antibodies to beads extracted from the macrophages after 24 h of phagocytosis and the trypsin sensitivity of the protein on the agarose, it was concluded that the main opsonin on the agarose beads is C3bi [inactivated C3b]. Requirements for the stimulatory effect of agarose on macrophages are summarized.