Purification of acute phase anti-hepatitis A virus (HAV) IgM and development of an IgM solid-phase radioimmunoassay for the detection of HAV.

A simple two-step procedure for the purification of IgM from acute phase hepatitis A infected chimpanzee serum has been developed. The procedure involves the precipitation of the euglobulin fraction with boric acid and the fractionation of the resuspended material on Sephacryl S-300 (Pharmacia Fine Chemicals, Piscataway, NJ). The purified IgM was used to develop a solid-phase radioimmunoassay (SPRIA) in which IgM was used as capture antibody and iodinated IgM was used as a probe. This assay was compared with a conventional IgG-based SPRIA. The IgM-based assay resulted in a superior response (P/N) for the detection of antigen in crude preparations; however, endpoint analyses demonstrated similar sensitivities.