Impaired natural killer cell function in systemic lupus erythematosus. Relationship to interleukin-2 production

Immune regulation requires clonal expansion of regulatory T cells which is dependent on the presence of interleukin-2 (IL-2). Previously, both natural killer (NK) cell function and IL-2 production were found to be depressed in systemic lupus erythematosus (SLE). This study was designed to determine the relationship between IL-2 production and NK cell activity in SLE. NK activity as determined by a standard 4-hour 51Cr-release assay was impaired in SLE (11.0 +/- 5.1 lytic units/10(7) cells) compared with controls (25.1 +/- 7.1 lytic units/10(7) cells) (P less than 0.05). IL-2 production was induced with concanavalin A and phorbol ester and quantitated using the IL-2 dependent cell line HT-2. IL-2 production was impaired in only 1 SLE patient, despite concomitant abnormalities in NK function in the SLE group as a whole. Moreover, in patients with impaired NK activity, incubation of lymphocytes with exogenous IL-2 did not restore NK activity to normal levels. These findings demonstrate that impaired NK activity in SLE is independent of IL-2 production and that defects in IL-2 production in SLE may not be as common as previously reported.