Defective natural killer (NK) and killer (K) cell function in systemic lupus erythematosus

Two aspects of lymphocyte function, natural killer (NK) and killer (K) cell activity have been studied in 21 normal subjects, 20 patients with systemic lupus erythematosus (SLE) and 6 patients with uraemia caused by non-immunological disorders. NK cell function was assessed by lymphocyte cytotoxicity of K 562 and Molt 4 target cells, and K cell function by killing of antibody coated Chang cells. Severely impaired NK and K cell activity was found in SLE (p = less than 0.001 for all target cells). In patients with uraemia (non SLE) NK cell cytotoxicity was normal, and K cell cytotoxicity was reduced but not as much as in the SLE group. Good correlation was found in normal subjects between NK and K cell activity. These results could not be directly related to disease activity, although NK and K cell function was lower in patients with active SLE than in patients with inactive disease, nor to treatment, for impaired killing was found in untreated patients in relapse and in patients in remission of all therapy. There was also no correlation between the level of circulating immune complexes and the defect in killing. These NK and K cell abnormalities could contribute to the pathogenesis of SLE by, for example, impairing mechanisms responsible for elimination of virus infected cells.