Epstein-Barr virus-specific serum immunoglobulin A as an acute-phase antibody in infectious mononucleosis.

Immunoglobulin A (IgA) antibodies to Epstein-Barr virus viral capsid antigen were assayed serially in 19 patients with infectious mononucleosis and in 38 controls. Seventy-four percent of infectious mononucleosis patients demonstrated IgA antibody, whereas this was found in 13% of controls. This antibody appeared early in infectious mononucleosis and was virtually gone 10 weeks after onset. Comparison of IgA antibody kinetics was made with IgG and IgM antibodies to viral capsid antigen, heterophile antibody, and antibody to Epstein-Barr virus early antigen and nuclear antigen. Failure to demonstrate IgA antibody was associated with severe illness, prolonged illness, delay in IgG and anti-Epstein-Barr virus nuclear antigen antibody, and low or absent heterophile and anti-early antigen antibody. Assay of IgA antibody to viral capsid antigen is a potentially useful adjunct in the serodiagnosis of infectious mononucleosis or recent Epstein-Barr virus infection, as are the other antibodies tested, but in this study IgM viral capsid antigen antibody was the only acute-phase antibody present in all patients.