The mean fluorescence intensity (MFI) was used to quantify NK cells stained positive for perforin or granzyme B. The MFI of perforin was lower in NK cells from active SLE NK cells compared to that in controls (9052 ± 1696 vs. 15640 ± 2645, p = 0.031). This evidence concerns the gene GZMB and systemic lupus erythematosus.