PHA-induced cellular cytotoxicity. Inhibition by a nonimmunoglobulin factor present in sera from patients with active systemic lupus erythematosus.

Phytohemagglutinin-induced cellular cytotoxicity by normal mononuclear cells (MNC) is inhibited by serum of patients with active untreated systemic lupus erythematosus (SLE) but not by that of patients with untreated inactive SLE or rheumatoid arthritis. Three-hour preincubation of normal MNC with SLE sera suffices to inhibit throughout the assay. Preincubation with phytohemagglutinin (PHA) before addition of sera does not prevent the inhibition. DEAE-cellulose chromatography, Sephadex G-200 fractionation and immunoelectrophoretic analysis have shown the nonimmunoglobulin nature of this factor. It is thermostable and not affected by deoxyribonuclease or ribonuclease treatment. The mitogen-induced cellular cytotoxicity-inhibiting factor seems to be independent of other serum factors capable of blocking PHA-induced blastogenic transformation.