Variations in binding characteristics of glycosylated human C-reactive proteins in different pathological conditions.

C-reactive protein (CRP) is a clinically important classic acute phase pentameric protein. It is thought to play an important role in immunomodulation. Earlier reports convincingly demonstrated that human CRP is differentially glycosylated in different pathological conditions. Although CRP is considered to be a clinically important molecule, changes in binding characteristics with appropriate ligands with respect to glycosylation remain unexplored. In an effort to demonstrate that these glycosylated molecular variants are capable of modulating their binding activity with different ligands, CRPs were affinity purified from six different clinical samples. Variable amounts of linkage-specific sialic acid derivatives were found in these CRPs with varying tryptophan contents. Differential binding patterns with antibodies against human CRP, human IgG, and other ligands like fibronectin, fetuin, and asialofetuin indicated that the purified CRPs differed significantly in their lectin-like interactions. Thus, we have convincingly demonstrated that differentially induced CRPs exhibited variable binding characteristics. These results may have far reaching practical applications for understanding acute phase responses.