Abnormal interferon modulation of natural cytotoxicity in systemic lupus erythematosus. Relation to suppressive serum factors.

In the present study we examined one aspect of the derangement in natural cytotoxicity (natural killer, NK) activity observed in some patients with systemic lupus erythematosus (SLE), i.e., the lack of enhancement of NK activity usually seen with interferon (IFN). NK activity of SLE patients as a group was 23.0 +/- 3.9 lytic units (LU)/10(7) cells (mean +/- SE). This contrasted with the NK activity found in normal controls (45.0 +/- 3.8 LU/10(7) cells) (P less than 0.05). The enhancement seen with IFN was an increase of 15.4 +/- 4.0 LU/10(7) cells in SLE patients compared with 104.6 +/- 192 LU/10(7) cells in control subjects (P less than 0.05). SLE sera and aggregated IgG (Agg-IgG) also inhibited the increase in NK activity of normal peripheral blood mononuclear cells after IFN priming. The results reported here support the hypothesis that the impaired baseline NK activity and poor response to IFN noted in SLE are secondary, in part, to the presence of inhibitory serum factors and preactivation by IFN.