Natural Killer Cells in Systemic Lupus Erythematosus

A monoclonal antibody, HNK‐1, that detects a differentiation antigen on human granular lymphocytes with natural killer (NK) activity was used to enumerate this subpopulation in the peripheral blood of 14 patients with systemic lupus erythematosus (SLE). Nine patients had severely decreased numbers of HNK‐1⁺ cells, 3 patients had elevated levels of HNK‐1⁺ cells, and 2 patients had appropriate numbers of HNK‐1⁺ cells compared with the levels in 112 normal controls. All SLE patients exhibited low NK killing ability against K562 target cells compared with controls. An increased proportion of the HNK‐1⁺ cells was categorized as immature granular lymphocytes in over 50% of the SLE patients because their HNK‐1⁺ cells coexpressed the OKT3 antigen and contained a paucity of cytoplasmic granules. The numbers of HNK‐1⁺ cells or the HNK‐1⁺ OKT3⁺ subgroup did not correlate with steroid therapy. This evidence suggests that levels of HNK‐1⁺ lymphoctyes are abnormal and functionally immature in most SLE patients. Longitudinal studies conducted over several months on a number of SLE patients demonstrated fluctuations in the ratio of mature and immature HNK‐1⁺ cells and total HNK‐1⁺ cells. Additional patients tested over longer periods of time will have to be studied to determine whether the proportion of mature NK cells (HNK‐1⁺ OKT3^‐) and immature NK cells (HNK‐1⁺ OKT3⁺) will be useful in predicting the clinical course of disease.