C3bi/CR3 is a Main Ligand‐Receptor Interaction in Attachment and Phagocytosis of C3‐Coated Particles by Mouse Peritoneal Macrophages

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Abstract
We investigated the relative role of C3bi‐CR3 interaetion in the binding and phagocytosis of EAC43 by mouse peritoneal macrophages. Anti‐Mac‐1 F(ab′)2 markedly inhibited the binding and lymphokine‐induced phagocytosis of both EAC43b and EAC43bi, Fifty per cent inhibition of attachment and phagocytosis occurred at 1 μml of anti‐Mac‐1 F(ab′)2 in the incubation media. On the other hand, ElgG binding and phagocytosis were not inhibited at all even at a concentration of 10 μ/ml. Depletion of divalent ealions from the incubalion media abolished EAC43b and EAC43bi rosettes but not ElgG rosettes or phagocytosis. These data suggested that both EAC43b and EAC43bi binding to macrophages were mediated via CR3.Because a drastic decrease of FAC43bi rosettes was observed in the case of EAC43bi cells prepared with smaller amounts of C3, a small eontamination of C3bi molecules on EAC43b, itself, cannot explain the efficient attachment of EAC43b, We propose that EAC43b on the macrophage surface can be quickly converted to EAC43bi, forming EAC43bi rosettes, and that those erythrocytes are vigorously ingested by lymphokine‐activated macrophages. In accordance with this hypothesis, we demonstrated that EAC43b was converted to E AC43bi in the medium in whicb macrophages had been ineubated

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