19S IgM Forssman-type heterophile antibodies in juvenile rheumatoid arthritis.

Fifty-four sera from children with juvenile rheumatoid arthritis (JRA) were separated by gel filtration at pH 4.05. The serum and IgM- and IgG-containing fractions were analyzed for heterophile antibodies by subjecting them to a hemolytic assay in tubes with the target cell a 1% washed sheep erythrocyte (SRBC) or beef erythrocyte (BRBC) in suspension. Thirty-three of 54 sera showed hemolytic antibody titers > 1:640 against SRBC alone and 4 of 54 had titers > 1:320 against SRBC and BRBC. All positive titers against SRBC and BRBC were associated with the IgM fraction. Differential absorption with SRBC, BRBC, and tissue sediment of homogenized guinea pig kidney revealed a Forssman specificity in 33 sera and Forssman and Hanganutziu-Deicher specificity in 4. The presence of heterophile antibodies in JRA correlated with the presence of hidden rheumatoid factor. There was also an increased incidence in patients with positive antinuclear antibodies and in teenaged females with polyarticular disease.