Antibodies to smooth muscle and other tissue components in infectious mononucleosis.

Antibodies to tissue components were studied by the indirect immunofluorescent method in 24 patients with infectious mononucleosis (IM). Smooth-muscle antibodies (SMA) were found in 70.8% of the patients, and in only one (3.8%) of 26 controls. SMA in patients were of the IgG (54.2%), the IgA (12.5%) and the IgM (41.6%) class. IgM-SMA occurred in the early phase of the disease, while IgG-SMA were found both early and late in its course. It was not possible to demonstrate that the development of SMA was due to liver involvement. Antinuclear antibodies, parietal-cell antibodies and antibodies to the cytoplasm of renal tubular cells were not detected significantly more often in patients than in controls. The serum concentrations of IgG, IgA and IgM were elevated in the acute phase of IM, and it was found that the Ig values were higher in patients with SMA than in those without.