Precipitation of 19S IgM rheumatoid factor-IgG circulating immune complexes in patients with juvenile arthritis by polyethylene glycol and separation by immobilized protein A.

Immune complexes (IC) in sera and synovial fluid (SF) from patients with juvenile (rheumatoid) arthritis (JA) were isolated by making use of polyethylene glycol (PEG) to precipitate IC and then using staphylococcal protein A to separate the IC. The isolated IC were compared to IC in sera analysed by sucrose density gradients and measured by the C1q solid phase assay (ClqSPA). Isolated IC from sera of 10 of 16 JA patients demonstrated significant 19S IgM rheumatoid factor (RF) titres in their acid elutes utilizing the haemolytic assay. IgM and IgG were detected by low level radial immunodiffusion in the acid eluate of sera in all 10 patients who had significant RF titres. In isolated IC from SF, three of five JA patients had significant 19S IgM RF titres detected in their acid eluates. By sucrose density gradient analysis of these sera, elevated levels of IC detected by ClqSPA were found in the fractions of greater than or equal to 19S comparable to the previous isolated 19S IgM-IgG complexes. This detection of IC like material containing 19S IgM and IgG by the present method further supports the participation of classic and hidden 19S IgM RF in IC formation in JA patients.