Characterization of immune complexes in multiple sclerosis by an antigen-specific immune complex radioimmunoassay

Serum and cerebrospinal fluid samples from multiple sclerosis (MS) patients containing various levels of Clq-reactive immune complexes (IC) and samples from age- and sex-matched controls were tested by an antigen-specific IC radioimmunoassay which detects IC containing myelin membrane-related antigens. Positive reactivity in the assay was significantly associated with IC-containing MS sera (P less than 0.005) but such an association was not observed with MS cerebrospinal fluid. Analysis of longitudinal specimens revealed that the levels of the antigen-specific serum IC fluctuated with time. Significant correlation between serum levels of Clq-reactive IC and serum levels of IC containing myelin membrane-related antigens was observed (r = 0.62; P less than 0.001). Sucrose gradient centrifugation of sera from 1 patient showed that the IC had a peak density of 1.075 g/ml, indicating the presence of lipid material. The results suggest that serum IC of MS patients frequently contain myelin membrane-related antigens and that these antigens may be lipids or lipid-associated.