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Receptor II
Correspondence to: Terry W. Du Clos, VA Medical Center, Research Service 151, 1501 San Pedro S.E., Albuquerque, NM 87108. Tel:505-256-5717 Fax:505-256-2794 E-mail:tduclos{at}unm.edu.
C-reactive protein (CRP) is an acute phase serum protein that shares several functions with immunoglobulin (Ig)G including complement activation and binding to receptors on monocytes and neutrophils. The identity of the receptor for CRP has been the target of extensive research. We previously determined that CRP binds to the high affinity receptor for IgG, Fc
RI (CD64). However, this interaction could not account for the majority of binding of CRP to neutrophils or monocytic cells. We now determine that CRP also interacts with Fc
RIIa (CD32), the low affinity receptor for IgG on monocytes and neutrophils. COS-7 cells were transfected with a construct containing the human Fc
RIIA cDNA. CRP binding and the presence of CD32 were detected by mAb and analyzed by two-color flow cytometry. Cells expressing CD32 bound CRP in a dose-dependent and saturable manner consistent with receptor binding. CRP bound to transfectants and K-562 cells with similar kinetics, and in both cases binding was completely inhibited by aggregated IgG. On monocytic cell lines, treatment with Bt2cAMP increased Fc
RII expression and enhanced CRP binding. CRP also specifically precipitated Fc
RI and Fc
RII from the monocytic cell line, THP-1. It is suggested that the major receptor for CRP on phagocytic cells is Fc
RII.
Key Words:
C-reactive protein, Fc receptors, Fc
RII, receptors, immunoglobulin G
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