Family study of natural killer cell activity in C1q-deficient patients with systemic lupus erythematosus-like syndrome: association between impaired natural killer cell function and C1q deficiency.

Impaired natural killer (NK) cell activity has been found in patients with systemic lupus erythematosus (SLE)-like syndrome. The mechanism by which NK cell function is impaired in SLE patients is not quite clear. We report here a family study of NK cell activity in C1q-deficient patients with SLE-like syndrome. In both SLE-active and SLE-inactive stages of the disease, NK cell function was significantly impaired when compared with the healthy controls (10.6 +/- 2.3% and 16.9 +/- 4.8% to 34.7 +/- 9.6%, p less than 0.025). On the other hand, differences in NK cell cytotoxicity between SLE-active and SLE-inactive members of the family were not statistically relevant (p less than 0.1). Further, we found no correlation between NK cell activity and clinical or laboratory values, except for a positive correlation between function of NK cells and C1q and CH50 values, respectively (rs = 0.93, 0.01 less than p less than 0.02). To our knowledge, this is the first report on a notable association between impaired NK cell activity and C1q deficiency. The type of inheritance of C1q deficiency in this family is also discussed.