Increased Oxidative Stress Contributes to Impaired CD56dimCD57+ NK Cells in Patients With Systemic Lupus Erythematosus

Abstract Background: Systemic lupus erythematosus(SLE) is characterized by loss of immune tolerance and imbalance of immune cell subsets. NK cells contribute to regulate both the innate and adaptive immune response. In this study, we aimed to detect peripheral NK cell subsets in SLE patients, investigate their cytotoxic effect on activated CD4+ T cells, and explore intrinsic mechanisms contributing to NK cell abnormality.Methods: Blood samples from healthy controls(HCs) and patients with SLE and rheumatoid arthritis(RA) were collected. The NK count, NK subsets(CD56bright , CD56dimCD57- , and CD56dimCD57+), phenotypes, along with apoptosis were analysed by flow cytometry. The t-stochastic neighbor embedding (tSNE) analysis of lymphocytes based on immune cells flow cytometry markers was performed. Mitochondrial reactive oxygen species(mtROS) and total ROS levels in NK cells were detected by MitoSOX Red and DCFH-DA staining respectively. Published data(GSE63829 and GSE23695) from Gene Expression Omnibus(GEO) was analyzed by Gene Set Enrichment Analysis(GSEA).Results: NK count was down-regulated in untreated SLE patients in comparison to untreated RA patients or HCs and the count was negatively correlated with disease activity. SLE patients exhibited a selective reduction in CD56dimCD57+ NK cell proportion, which was negatively correlated with Systemic Lupus Erythematosus Disease Activity Index(SLEDAI) and positively correlated with complement C3 and C4. CD56dimCD57+NK cells exhibited increased cytotoxic effect on activated CD4+ T cells relative to CD56dimCD57- NK cells. Compared with HCs, CD56dimCD57+ NK cells in SLE patients exhibited impaired cytotoxic function, increased apoptosis and higher levels of both mtROS and ROS. GSEA analysis indicated that ROS pathway was significantly enriched in NK cells from lupus. Compared with CD56dimCD57- NK cells in SLE patients, CD56dimCD57+ NK cells showed higher levels of oxidative stress and apoptosis. Furthermore, oxidative stress levels were negatively correlated with perforin expression and positively correlated with apoptosis. CD56dimCD57+ NK cells were more prone to undergo apoptosis when exposed to ROS in vitro. Conclusion: Beyond the reduced NK cell number, our study demonstrated a selective loss of mature CD56dimCD57+ NK cell subset, which was conversely correlated with disease activity. This subset showed attenuated cytotoxic function, up-regulated endogenous apoptosis and increased oxidative stress, which might contribute to NK cell abnormality.