HUMAN ANTIFIBRONECTIN ANTIBODIES IN SYSTEMIC LUPUS-ERYTHEMATOSUS - OCCURRENCE AND ANTIGENIC SPECIFICITY

Sera from patients with connective tissue diseases exhibit autoantibod ies to a spectrum of extracellular matrix proteins. Antibodies binding to solid phase bovine fibronectin (Fn) were investigated by ELISA in patients with systemic lupus erythematosus (SLE). Sera showing binding of 2 s.d. above the mean of the normal human control were considered positive and 43/150 SLE sera (28.7%) demonstrated such binding. These antibodies were mainly IgG and IgA as determined by isotype-specific E LISA. Specificity studies on selected positive sera revealed that bind ing was inhibited by preincubation with soluble Fn, but not with thyro globulin or type 1 collagen. The binding was demonstrated not to be re lated to interactions with rheumatoid factor, complement components or immune complexes. Additional studies to determine which Fn fragment i s bound by naturally occurring anti-Fn antibodies demonstrated that th e binding was predominantly to the 30-kD collagen binding domain (CBD) of Fn molecule. Inhibition studies using 120-kD, 40-kD and 30-kD Fn f ragments confirmed that this binding site was the 30-kD CBD.