Opsonic Effect of CRP on the In Vivo Clearance of Sensitized, Autologous Erythrocytes

We investigated the opsonic capability and requirements of C-reactive protein (CRP) for clearance of autologous erythrocytes sensitized with pneumococcal C-polysaccharide (CPS) in mouse "in vivo" model. Mouse erythrocytes (E) were coated with CPS to provide a binding site for CRP. When E-CPS or E-CPS-CRP were injected into mice, E-CPS-CRP were preferentially sequested by spleen as compared to E-CPS. The increased splenic sequestration caused by CRP was abolished by pre-treating the mice with cobra venom factor. The removal of CRP from E-CPS-Complement with EDTA showed no increase in splenic sequestration It was also shown that E-CPS-CRP did consume significant amounts of both C4 and C3 in mouse serum. These results demonstrate that CRP mediates opsonic clearance of cells in vivo as well as anti-bodies, indicating that this opsonic effect requires both the complement activation and the continued presence of CRP.