The Lupus Anticoagulant. A Disease Marker in Antinuclear Antibody Negative Lupus That is Cross-reactive with Autoantibodies to Double-stranded DNA

The lupus anticoagulant (LA) was demonstrated in 37% of 52 consecutive systemic lupus erythematosus (SLE) patients and patients with lupus-like syndromes, who were referred to our unit. The LA was found to be associated with a biologic false-positive VDRL (P less than 0.005), and the apparently paradoxical association of LA with vascular thromboses was confirmed (P less than 0.05). The presence of LA and a biologic false-positive VDRL defined a group of 7 antinuclear antibody negative patients with characteristic features of recurrent thromboses, spontaneous abortions, neurologic involvement, and renal disease. Further studies on 6 selected sera demonstrated LA in all 6 IgM fractions and in 3 of 6 IgG fractions. Inhibition of LA was shown in 6 of 9 Ig fractions after absorption with double-stranded DNA (dsDNA). Anticardiolipin antibody was shown by immunodiffusion in 3 LA positive IgG fractions from VDRL negative sera. Cardiolipin micelles partially inhibited anti-dsDNA binding of 4 IgG fractions, 3 of which were LA negative. In this report we discuss the overlapping specificities due to cross-reactivity between LA, anticardiolipin, and anti-dsDNA antibodies in human SLE, and we suggest that LA be considered equivalent to the biologic false-positive VDRL as a criterion for the diagnosis of SLE.