Natural cytotoxicity in rheumatoid arthritis and systemic lupus erythematosus

Abstract

Natural killer (NK) activity was investigated in 23 patients with rheumatoid arthritis (RA) and 7 patients with systemic lupus erythematosus (SLE). Killing of K-562 target cells by the peripheral blood lymphocytes of 7 patients with inactive RA did not differ from that observed in 18 controls. However, 16 patients with active RA and all patients with SLE exhibited impaired natural cytotoxicity. A strong correlation existed between reduced NK activity and elevated erythrocyte sedimentation rate but no correlations were observed with total peripheral blood lymphocyte counts, or total T, or Fcγ-receptor-positive lymphoid subpopulations. Impaired NK activity also correlated with elevated concentrations of circulating immune complexes in SLE, but not in RA. The contribution of circulating humoral factors to the observed decreases in natural cytotoxicity was analyzed by the addition of sera from different sources to normal lymphocytes either throughout the NK cell assay or by preincubation with the lymphocytes prior to the actual test. Little or no effect was observed with normal serum, with serum from patients with acquired hypogammaglobulinemia, or with serum from patients with RA. In contrast, SLE serum strongly inhibited NK activity at 37°C even when lymphocytes were simply pretreated and then throughly washed before the assay. The consequences of defective NK activity are largely unknown but may be associated with, although not necessarily a cause of, the enhanced rate of malignancy noted in SLE and RA.