Demonstration of EBNA (Epstein-Barr virus nuclear antigen) antibodies of different immunoglobulin classes.

Anit-EBNA IgM, a previously unknown antibody, was detected by the antihuman globulin anticomplement immunofluorescence (ACIF) method in serum samples from acute infectious mononucleosis (IM) of Epstein-Barr virus (EBV) origin. The antibody disappears from the serum in some weeks during convalescence. It was absent in anti-EBV=positive sera of healthy donors and in serum samples taken from patients with IM caused by cytomegalo-virus. The antibody appears simultaneously with anti-EBV IgmM and, reaching a lower titre than the latter, its titre curve runs parallel with the anti-EBV IgM curve. Since in acute EBV infections, anti-EBNA IgM always appeared, its presence may serve as an additional evidence of the acuteness of EBV infection. In EBV-seropositive healthy subjects, the bulk of antibodies belongs to the IgG class, non-complement-fixing IgA antibodies occur only sporadically.