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.