IntroductionSystemic lupus erythematosus (SLE) patients have decreased natural killer (NK) cell counts. The decrease in the number of NK cells has implications for a decrease in the function of NK cells which can affect the progression of SLE disease. The study aim was to determine profiles of CD3–CD56bright and CD3–CD56dim NK cells in SLE patients and their relation to disease activity.Material and methodsThis study included 36 patients of SLE who fulfilled the ACR 1997/SLICC 2012 criteria, women aged 18–49 years. Disease activity was assessed by the Mex-SLEDAI. Peripheral blood samples from SLE patients were analyzed by flow cytometry to evaluate NK cell subsets, according to differential expression of the main subset of NK cells, which is CD3–CD56bright and CD3–CD56dim.ResultsThe mean percentage of regulatory NK cell count (CD3–CD56bright) in active SLE patients was significantly lower (p = 0.000) than in inactive SLE patients. The mean percentage of cytotoxic NK cell count (CD3–CD56dim) in active SLE patients was significantly (p = 0.000) higher than in inactive SLE patients. A correlation was observed between two subsets of NK cells with disease activity (p = 0.00). The percentage of CD3–CD56bright NK cells was negatively correlated with disease activity (r = –0.766), whereas the percentage of CD3–CD56dim NK cells positively correlated with disease activity (r = 0.761). ConclusionsThere is a difference in the mean percentage of the number of NK cells (CD3–CD56+) in both a subset of regulatory NK cells (CD3–CD56bright) and cytotoxic NK cells (CD3–CD56dim) in active and inactive SLE patients and it is closely related to SLE disease activity.