Incidence of anti-intermediate filament antibody in serum samples of students with suspected glandular fever.

Serum samples from 40 students with suspected infectious mononucleosis were tested for the presence of antibodies to intermediate filaments (AIFA) of the cytoskeleton. Twenty had antibodies to the Epstein-Barr virus capsid antigen before their illness, and during it their sera remained negative by the Paul-Bunnell test. The other 20 patients did not have antibodies to the Epstein-Barr virus capsid antigen before their illness and seroconverted during the illness. These patients (true infectious mononucleosis group) developed positive Paul-Bunnell tests. Sera from normal subjects (blood donors) were also tested for AIFA. AIFA was present in titres greater than 1/10 in 80% of the infectious mononucleosis group (mean titre 1/40-1/80), 10% of the Paul-Bunnell negative glandular fever group, and 8.5% of the normal blood donors.