A new sensitive assay for the calcium-dependent binding of C-reactive protein to phosphorylcholine.

A new sensitive assay for the calcium-dependent binding of rabbit C-reactive protein to phosphorylcholine has been developed. The assay involves coating the wells of polyvinylchloride microtiter plates with a bovine serum albumin-phosphorylcholine conjugate followed by the addition of C-reactive protein. The quantity of C-reactive protein is determined by indirect enzyme-linked immunoadsorbent assay using first, affinity purified goat anti-C-reactive protein immunoglobulin followed by a commercial rabbit anti-goat immunoglobulin-alkaline phosphatase conjugate. The binding of rabbit C-reactive protein to the bovine serum albumin-phosphorylcholine conjugate is completely inhibited by free phosphorylcholine, by pneumococcal C-polysaccharide and by calcium chelators but not by high concentrations of neutral, cationic or zwitterionic detergents. The assay is sensitive to 2 ng C-reactive protein.