KLRK1 and esophageal squamous cell carcinoma: In comparison with matched ESCC patient blood samples, lower percentages of activator receptors, such as NKp30, CD16, NKp46, NKG2D, and CD226, and higher percentages of inhibitory receptors, such as NKG2A, were observed in adjacent tissues and tumour tissues (p < 0.05) (Fig. 2a and b).