Foxp3+ regulatory T cells (Tregs) and natural killer group 2, member D (NKG2D)-positive natural killer (NK) cells are considered to be important in the immune escape of colorectal cancer (CRC). However, the association between these two variables remains obscure. Therefore, in the present study, the levels of peripheral Tregs and NKG2D expression in NK cells and the associations in CRC patients were investigated. A total of 35 CRC patients and 16 healthy controls were enrolled in this study. Flow cytometry was performed to assay Treg numbers and NKG2D expression levels in NK cells in peripheral blood samples. Serum carcino-embryonic antigen (CEA) protein was assayed by electrochemiluminescence. Peripheral Treg numbers were significantly increased (P<0.05), while NKG2D expression levels in NK cells were significantly reduced (P<0.01) in CRC patients compared with healthy controls. However, no significant differences were identified in Treg numbers between CRC patients with and without lymph node metastases and between CRC patients with different clinical stages of CRC. Similarly, no significant differences were detected in NKG2D expression levels in NK cells between the different patient groups. Statistical analysis revealed that increased Treg numbers were not correlated with reduced NKG2D expression levels in NK cells from CRC patients. In addition, no statistical correlation was observed between Treg numbers and serum CEA protein in CRC patients. In conclusion, the upregulation of Tregs was not significantly correlated with the downregulation of NKG2D expression in NK cells in peripheral blood from CRC patients.

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