Natural killer cells are decreased in systemic sclerosis and have diagnostic value for pulmonary arterial hypertension incorporation.

The aim of this study was to investigate lymphocyte subsets, especially natural killer (NK) cells, in patients with systemic sclerosis (SSc) and evaluate the diagnostic value of NK cells in secondary pulmonary arterial hypertension (PAH). A total of 115 SSc patients and 100 age- and sex-matched health controls (HCs) were enrolled in this study. Flow cytometry was employed to quantify NK cells, while the association between NK cells and disease activity as well as PAH was investigated to further elucidate its diagnostic potential. The absolute count of NK (CD3-CD56+) cells significantly decreased in SSc patients. There was a negative correlation between the mRSS score and the injury index. The levels of cytokine exhibited significant elevation among SSc patients. Conversely, SSc-PAH patients demonstrated significantly elevated levels of CRP, UA, and BNP. Additionally, there was a significant reduction in the absolute level of NK cells. ROC curve analysis revealed that the optimal cut-off point for NK cells was 185 cells/µL, while for BNP it was 70.50 pg/mL and for UA it was 323.00 µmol/L. Our study revealed a significant inverse correlation between peripheral blood NK cell levels and the incidence of complicated PAH in patients with SSc.