Lymphocytotoxic antibody activity in cryoprecipitates from serum of patients with SLE.

Complement-dependent cytotoxic activity against normal human peripheral blood lymphocytes was detected in 11 of 17 cryoprecipitates from the serum of patients with systemic lupus erythematosus (SLE). The lymphocytotoxicity was eliminated by treatment with 2-mercaptoethanol and iodoacetamide, and it was inhibited by antibody to human IgM but not anti-IgG. The titers of lymphocytotoxic activity in the cryoprecipitates were roughly proportional to the corresponding serum titers, but when they were normalized for IgM concentration it was apparent that selective concentration of lymphocytotoxic antibody occurred in the cryoglobulins. The relationship between cryoprecipitable lymphocytotoxicity and a number of laboratory and clinical parameters of SLE was studied. The amount of protein in the cryoprecipitates, which was greatest in patients with significant renal disease, correlated with a reduction of serum complement and the amount of antibody to DNA. However the lymphocytotoxic activity of the cryoglobulins did not correlate with the severity of SLE. The titer of lymphocytotoxic antibody was independent of a) the presence or absence of active lupus nephritis, b) the total protein or immunoglobulin content of the cryoprecipitates, c) serum complement levels, and d) the amount of circulating antibody to DNA. These findings cast doubt upon the pathogenetic significance of cryoprecipitable lymphocytotoxic antibody.