A solid-phase radioimmunoassay for detection of IgM antibodies to hepatitis A virus

The conditions for a sensitive and specific solid-phase radioimmunoassay (RIA) for the detection of IgM antibodies to hepatitis A virus (HAV) were optimized, and the RIA was used to assay sera from patients with hepatitis. IgM antibodies to HAV reached highest concentrations between one and three weeks after onset of icterus and were measurable in follow-up sera for at least 12 months after infection. To prove the specificity, the IgG antibodies were separated from patient sera by sucrose density-gradient centrifugation. The remaining IgM antibodies, after treatment with beta-mercaptoethanol, did not bind in the RIA, and, when the anti-IgM antibody bound to the solid phase was replaced with anti-IgG, a negative result was obtained with incubation of IgM antibody to HAV. Also, the presence of IgG was shown not to interfere with measurement of IgM antibody to HAV. Finally, as a further specificity control, 50 sera positive for rheumatoid factor or from patients infected with hepatitis B virus, cytomegalic inclusion disease, infectious mononucleosis, influenza A virus, rubella, or measles were tested, and all of these sera were negative for IgM antibody to HAV.