C3 polymorphism and circulating immune complexes in patients with multiple sclerosis.

The phenotypes of the complement factor C3 have been evaluated in 60 patients with multiple sclerosis (M.S.), and the results correlated to the occurrence of circulating immune complexes (CIC). A significantly increased frequency of the C3F-gene was found among the patients, and closely associated with the occurrence of CIC. A relative risk incidence of 4.1 was found for C3F-positive individuals among M.S. patients with detectable CIC. Low C3 levels in serum were found in 30% of the patients, almost all belonged to the group without CIC and showed a C3-type distribution similar to normal controls. A different immunological reaction pattern (type II reaction) in these patients seems possible, and a genetically determined immunological abnormality predisposing to M.S. is therefore suggested.