DNA-HYDROLYZING AUTOANTIBODIES

Catalysis by antibodies could be a frequent phenomenon if the immune s ystem generates a sufficiently diverse number of antibody-active sites , some of which may possess catalytic activity. A catalytic antibody c an be expected to do more damage than one that simply binds antigen. T he best biochemical marker of systemic lupus erythematosus (SLE) is pr esence of autoantibodies to DNA. In the present article, we describe t he DNA-hydrolyzing activity of DNA-binding autoantibodies purified fro m SLE patients. The substrates employed were supercoiled plasmid, radi olabeled plasmid fragments, and oligonucleotides. Hydrolysis of DNA by the antibodies was indicated by the appearance of fragments visualize d by ethidium bromide staining of agarose gels or autoradiography of p olyacrylamide gels. Changes in linear dichroism values were also indic ative of DNA hydrolysis. The antibody activity was purified by protein A-sepharose chromatography, high-performance liquid chromatography ge l filtration, and DNA-affinity chromatography. Scrupulous control stud ies were done to demonstrate that DNA-hydrolyzing activity really belo ngs to the antibodies. Purified Fab fragments showed hydrolyzing activ ity, whereas the Fc fragment was inactive. The specificity of DNA clea vage was investigated, and the rate parameters of hydrolysis by antibo dies and conventional nucleases were compared.