IgA related disorders in rheumatoid arthritis.

Serum monomeric and polymeric IgA, IgA rheumatoid factor (IgA-RF) and IgA containing circulating immune complexes (IgA-CIC) were studied in 192 patients with rheumatoid arthritis (RA) to explore the relationships among IgA related abnormalities and to investigate their potential associations with disease activity, immunoregulatory disorders and effect of treatments. Total serum IgA and polymeric IgA (p-IgA) levels were elevated in 23 and 11% of patients with RA, respectively. Their respective mean concentrations in serum were significantly elevated compared to normal values (p less than 0.001 and p less than 0.004). A preferential increase in polymeric rather than monomeric IgA was observed. IgA-RF, detected by a solid phase ELISA, was found in 71% and was associated with decreased grip strength (p less than 0.005), active disease (p less than 0.05), increased p-IgA level (p less than 0.001), elevated p-IgA:total IgA ratio (p less than 0.05), the presence of IgA-CIC (p less than 0.005) and IgM-RF (p less than 0.005). Complement fixing IgA-CIC were detected in 40% of patients by IgA specific conglutinin and anti-C3 binding solid phase ELISA. High molecular weight IgA species precipitated by 2.5% polyethylene glycol from RA sera positive for IgA-CIC were shown to be IgA-RF complexed to IgG. Taken together, our results suggest that IgA-RF are essentially polymeric in nature and circulate as IgA-RF-IgG immune complexes. Although the presence of IgA-CIC was not associated with disease activity, IgA-CIC activated C3 and thus are potentially pathogenic.(ABSTRACT TRUNCATED AT 250 WORDS)