Radioimmunoassay detection of igm antibodies to the hbv‐associated delta (δ) antigen: Clinical significance in δ infection

A sensitive radioimmunoassay was developed for specific detection of IgM antibodies to the hepatitis B virus‐associated δ antigen. The test is based on the selective absorption of IgM by anti–IgM fixed on a solid phase. Transient primary IgM anti4 responses with no conversion to a secondary IgG response were observed in acute self–limited δ infection. IgM anti‐δ was invariably found in hepatitis B surface antigen (HBsAg) carriers with active δ infection and liver disease, while it was absent in HBsAg‐positive or negative individuals with anti‐δ of IgG class but without liver damage or intrahepatic δ antigen. IgM anti‐δ appears useful in defining the epidemiology of acute δ infection and in the serological diagnosis of active δ disease from nonpathogenic or past δ infection.