IgM autoantibody to intermediate filaments in infectious mononucleosis.

Sera from 17 patients with infectious mononucleosis reacted with fine cytoplasmic fibrils in monolayer cultures of fibroblasts. In cells pre-treated with vinblastine, the sera reacted with peri- or juxta-nuclear coils of filaments. These staining patterns were similar to those obtained by anti-intermediate filament autoantibody but different from the "actin-cables" stained by anti-actin autoantibody and from the "tubulin paracrystals" stained by anti-microtubule autoantibody. The autoantibodies belonged to the IgM class and ranged in titre from 1 : 16 to 1:512 (mean 1:64). A change in antibody titre was noted in sequential acute and convalescent sera. The results show that IgM autoantibodies to intermediate filaments occur frequently in sera from patients with infectious mononucleosis.