Distribution of anti-F(ab')2 antibodies and the 16/6 idiotype in systemic lupus erythematosus (SLE) probands and kindreds.

Levels of serum anti-F(ab')2 antibodies and expression of the 16/6 anti-DNA idiotype were studied in 103 sera from first-degree relatives of 17 systemic lupus erythematosus (SLE) kindreds. Among healthy SLE relatives, 35.9% showed anti-F(ab')2 elevations and 24%, Id 16/6 expression. Forty-three and two-tenths percent of healthy SLE relatives with elevated anti-F(ab')2 also showed expression of 16/6; when Id 16/6 was positive, 16 of 25 relatives (64%) showed parallel elevations of anti-F(ab')2. However, within individual families, distribution patterns of elevated anti-F(ab')2 and Id 16/6 often did not coincide. Affinity-isolated anti-F(ab')2 from four members of a single SLE kindred showed relative enrichment for Id 16/6 in only two of the four individuals studied. Moreover, none of the isolated anti-F(ab')2 antibodies within this kindred or another kindred showing 16/6 Id expression reacted directly with 16/6 Id. Our studies suggest that whereas both anti-F(ab')2 and Id 16/6 are increased within SLE kindreds, expression of the two does not always coincide. Furthermore, anti-F(ab')2 antibodies do not show direct reactivity with Id 16/6. A number of anti-DNA idiotypic markers may play a role in idiotypic networks among such SLE kindreds.