Systemic lupus erythematosus (SLE) is the prototype of human autoimmune diseases. Its genetic component has been suggested by familial aggregation (lambdas = 20) and twin studies. We have screened the human genome to localize genetic intervals that may contain lupus susceptibility loci in a sample of 188 lupus patients belonging to 80 lupus families with two or more affected relatives per family using the ABI Prism linkage mapping set which includes 350 polymorphic markers with an average spacing of 12 cM. Non-parametric multipoint linkage analysis suggests evidence for predisposing loci on chromosomes 1 and 18. However, no single locus with overwhelming evidence for linkage was found, suggesting that there are no 'major' susceptibility genes segregating in families with SLE, and that the genetic etiology is more likely to result from the action of several genes of moderate effect. Furthermore, the support for a gene in the 1q44 region as well as in the 1p36 region is clearly found only in the Mexican American families with SLE but not in families of Caucasian ethnicity, suggesting that consideration of each ethnic group separately is crucial.

Levels of interleukin-2 receptors (IL-2R), as measured by a double-antibody "sandwich" enzyme-linked immunosorbent assay technique, were markedly elevated in the serum of patients with systemic lupus erythematosus, rheumatoid arthritis, and bacterial endocarditis, but not in patients with acute gout. Serum levels of IL-2R correlated strongly with clinical and laboratory indicators of disease activity in patients with lupus and in those with rheumatoid arthritis. This relationship was confirmed by sequential determinations in individual patients. Serum IL-2R values correlated with disease activity better than did the Westergren erythrocyte sedimentation rate. Our findings indicate that serum levels of IL-2R may serve as a reliable serologic indicator of disease activity in inflammatory diseases characterized by immune system activation.

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