Elevated serum immune complex levels in Pogosta disease, an acute alphavirus infection with rash and arthritis.

Circulating immune complexes (CIC) were studied in Pogosta disease, an acute alphavirus infection with fever, rash and arthritis. The disease is caused by a virus antigenically closely related to Sindbis virus. 75 serum specimens from 25 patients with serologically verified infection were obtained from 1-87 days after the onset. Six different CIC detection methods were used and CICs were observed in all patients at least with one test. Tests based on CIC binding onto human platelets followed the natural course of the disease and maximal values were observed between 10-15 days after onset. Slightly elevated levels were observed 2-3 months after onset. The mean conglutinin binding test values were slightly elevated during the whole follow-up period. The severity of arthritis did not directly correlate to CIC levels. C3c and C1q-binding test were positive only in a few cases. Latex and enzyme immunoassay tests for rheumatoid factors gave low positive values in some of the sera. Agarose gel electrophoresis of serum proteins revealed non-specific changes in alpha 1-alpha 2 interzone characteristic of an acute infectious disease. The presence of CIC in the sera of patients with Pogosta disease may indicate body's natural clearange mechanisms of viral antigens. CIC may have a pathogenic role in the prolonged arthritis, even though no direct correlation with CIC levels and severity of arthritis was observed.