The production of antibody-dependent cellular cytotoxicity by immune complexes in systemic lupus erythematosus

Sera from 8 patients with systemic lupus erythematosus (SLE) which induced cytotoxicity of human target cells when co-cultured with normal human peripheral blood mononuclear cells were fractionated by Sepharose 6B chromatography and sucrose density-gradient ultracentrifugation in order to characterise the responsible serum factors. With Sepharose 6B chromatography, cytotoxicity was found in IgG containing fractions between 100,000-450,000 mol.wt. and occurred maximally in fractions containing dimer IgG. With sucrose density-gradient ultracentrifugation, cytotoxicity was found maximally in 7S fractions but also frequently extended into 10S and even 12S fractions. These findings suggest that immune complexes of small size in the sera of some patients with SLE may be an important factor in the production of antibody-dependent cellular cytotoxicity of human target cells.