ACTIVE SYSTEMIC LUPUS-ERYTHEMATOSUS IS ASSOCIATED WITH DEPLETION OF THE NATURAL GENERIC ANTIIDIOTYPE (ANTI-F(AB')(2)) SYSTEM

Objective. To study the relationship of serum IgG anti-F(ab')(2) and c linical disease activity in 108 patients with systemic lupus erythemat osus (SLE) and to determine whether low serum antiF(ab')(2) with activ e renal disease is accompanied by deposition of anti-F(ab')2 in renal immune complex lesions. Methods. We studied 108 patients with definite SLE over a 5 yr period and assayed serum antiF(ab')(2) levels in rela tion to degree of clinical disease activity. Renal biopsy eluates of 2 6 patients with SLE were examined by enzyme linked immunosorbent assay (ELISA) for relative amounts of IgG, anti-DNA, and IgG anti-F(ab')(2) . Results. Active SLE was strongly associated with low serum anti-F(ab ')(2). SLE renal biopsy eluates frequently contained high levels of Ig e and IgG anti-DNA and lower, but definite, IgG antiF(ab')(2) activity . When specific activity of IgG anti-DNA and IgG anti-F(ab')2 was comp ared be tween kidney biopsy eluates and concomitant serum, marked rela tive renal concentration was found for both anti-DNA (19-fold) and ant i-F(ab')(2) (74-fold). Some biopsy eluates contained IgG antibodies be aring apparent double specificity for both DNA and F(ab')(2). Conclusi on. Active SLE is often associated with low serum anti-F(ab')(2). Rela tive enrichment over specific activity in serum of both IgG anti-F(ab' )(2) and anti-DNA in SLE kidney biopsy eluates may indicate participat ion of both reactants in the glomerular disease process. Low serum ant i-F(ab')(2) in active SLE may reflect downmodulation or failure of idi otypic control mechanisms associated with disease progression.