Role of interleukin 2 in inducing normalization of natural killer activity in systemic lupus erythematosus.

A low natural killer (NK) activity has been well documented for lymphocytes from systemic lupus erythematosus (SLE) patients. Given the defect in interferon-gamma (IFN-gamma) and interleukin 2 (IL-2) production also reported in SLE, it seemed possible that the absence of these molecules could account for some of the defective NK activity. We have tested the NK activity present in peripheral blood mononuclear cells (PBMC) from SLE patients and its in vitro modulation by different preparations of exogenous IL-2. We have found a low NK activity for PBMC from steroid-treated SLE patients, and we report an enhancement in lytic activity after incubation with mitogen-induced, IL-2-containing supernatants obtained from human tonsils. This increase did not seem to be due to recruitment of new effectors because the numbers of cells expressing NK phenotype (Leu 7+ or Leu 11b+) did not change after the incubation, nor did the target specificity of the lysis. However, a similar degree in the improvement in cytotoxicity was not obtained by incubation with a purified preparation of IFN gamma and/or recombinant IL-2 (rIL-2). A possible role for a molecule other than these lymphokines that might influence this effect is discussed.