Detection of two associated precipitating autoantibodies (DA1 and DA2) in sera from patients with systemic lupus erythematosus.

In a clinical and serological study performed on a large series of patients with different connective tissue disorders, only sera from patients with systemic lupus erythematosus (SLE) contained two precipitin systems (DA1 and DA2) directed against nuclear proteins present in a total extract of human spleen. DA1 antibody appeared in 5% of SLE patients and was always associated with DA2 antibody which was found in about 22% of SLE patients. Sera monospecific for DA1 and DA2 antibodies gave a speckled staining pattern on both rat kidney and HEp2 cells. DA1-positive patients showed a higher incidence of photosensitivity (p less than 0.001), hepatosplenomegaly (p less than 0.001), hemolytic anemia (p less than 0.05), CNS involvement, vasculitis, and diffuse proliferative glomerulonephritis than DA1-negative ones. DA2-positive patients showed an increased incidence of leukopenia (p less than 0.05) and thrombocytopenia (p less than 0.01) than controls. While several indirect evidences suggest that DA1 precipitin might be identical to the previously described MA antibody, DA2 precipitin appears as a new system in SLE. The serological association between DA1 and DA2 antibodies might be analogous to the well known ones between antibodies to Sm and nRNP and to SSA/Ro and SSB/La.