Separation and characterization of immune complexes containing 19S IgM rheumatoid factor-IgG in juvenile arthritis

Sera from 10 patients with juvenile arthritis (JA), 2 seropositive and 8 with hidden rheumatoid factor (RF), were subjected to affinity chromatography on a rabbit anti-human IgM column. Material retained by the column was eluted sequentially by 1M NH3 and 0.1M glycine-HCl buffer, pH 3.0. The affinity fractions contained both 19S IgM RF and IgG, while corresponding fractions from healthy controls contained neither. Sera from 15 patients with JA, 1 seropositive and 11 with hidden RF, were subjected to 4% polyethylene glycol precipitation followed by acid dissociation of the precipitate. Ten of 15 resultant fractions contained both IgM RF and IgG, while corresponding fractions from healthy controls contained only traces of IgG. Sera from 7 of these JA patients were subjected to sucrose density gradient centrifugation and the resultant fractions analyzed for the presence of immune complexes by the C1q solid-phase assay. Immune complexes were detected at and ahead of the IgM marker, as expected for IgM RF-IgG complexes. These combined data show that the majority of JA patients with classic or hidden 19S IgM RF have immune complexes containing IgM RF and IgG in their sera.