Interpretation of the cross-reactivity of anti-DNA antibodies with cell surface proteins: the role of cell surface histones

The putative cross-reaction of anti-DNA antibodies with "lupus-associated membrane proteins (LAMP)" on the surface of intact Raji cells was examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analyses. Cell surface proteins of 14, 17, 18, 33 and 34 kDa were detected by monoclonal anti-double-stranded (ds) DNA antibodies and the sera of patients with systemic lupus erythematosus (SLE) in active states, but were not detected by the sera of SLE patients in inactive states, nor in healthy controls. However, pre-treatment of these anti-DNA antibodies with DNase I markedly reduced the reactivity to the cell surface proteins. Judging from the electrophoretic mobility, these proteins were identical with histones, and purified histones inhibited the reaction of anti-DNA antibodies with the cell surface proteins. Moreover, affinity-purified antihistone antibodies could demonstrate histones in the Raji cell surface proteins. Thus, we conclude that "cross-reaction" of anti-DNA antibodies with LAMP is due to DNA-anti-DNA immune complexes which could react with cell surface histones.