Interferon and natural killer cells in systemic lupus erythematosus.

Natural killer (NK) cell activity against several types of target cells was found to be subnormal in patients with systemic lupus erythematosus (SLE). Interferon (IFN) boosted the NK activity of cells from SLE patients to a significantly lesser degree than cells from normal controls. The production of IFN after stimulation of blood cells with Sendai virus was significantly decreased in SLE patients with active disease, and in a substantial proportion of the patients the production of phytohaemagglutinin (PHA)-induced IFN was below normal limits. Although the production of virus-induced IFN was clearly inversely correlated to disease activity no such correlation was observed for PHA-induced IFN. Serum levels of both pH2 stable and pH2 labile IFN were significantly higher in SLE patients than in controls. The findings clearly show that SLE is associated with abnormalities in the NK cell-IFN system but it cannot be stated whether these abnormalities are causally related to the development of disease or are secondary to pathological changes in SLE.