Natural killer cell activity in the systemic connective tissue diseases.

By doing 51Cr release assays with K562 cells and single natural killer (NK) cell assays with and without interleukin-2 (IL-2) containing supernatants, we were able to establish differences and similarities in NK cell function of patients with systemic connective tissue diseases. Decreased NK cell activity in systemic lupus erythematosus was found to be due to a paucity of active NK cells, with increased proportions of inactive and IL-2 unresponsive NK cells. The few active NK cells responded well to IL-2 by increasing their recycling capacity. Patients with mixed connective tissue disease had a normal baseline NK cell activity that responded poorly to IL-2 at the single cell level. This apparent normalcy was found to be maintained by few NK cells with high recycling activity that could not be increased further with IL-2. Patients with primary Sjögren's syndrome had very low NK activity carried out by few NK cells, with low recycling indices and poor response to IL-2. Patients with scleroderma had normal NK cell functions throughout, and patients with active dermatomyositis/polymyositis were found to have diminished NK cell function with low numbers of NK cells that reverted to normal upon disease inactivation.