Objective: To compare frequencies of natural killer (NK) cell subsets and their surface expression of the NKG2D receptor in patients with primary biliary cirrhosis (PBC), and to determine the correlation between expression of MICA on monocytes and function-associated receptors on the NK cells of PBC patients.
Methods: Twenty patients with PBC and 18 healthy donors were included in the study. Peripheral blood samples anticoagulated with heparin were labeled with the following antibody combinations: anti-CD45/anti-CD14/anti-MICA, antiCD3/anti-CD56/anti-CD16/anti-NKG2D. Frequencies of MICA-positive monocytes, NK cell subsets, and NK cells with surface expression of NKG2D were measured with flow cytometry. Correlation of MICA expression on monocytes with NKG2D expreesion on NK cells was assessed through linear correlation and regression analysis.
Results: The PBC patients had significantly lower percentages of NK cells than the healthy donors (6.8%+/-2.9% vs.16.4%+/-3.4%, P =0.000<0.05). In the PBC patients, the percentage of CD56-positive NK ceils was significantly higher than that of CD16-positive NK cells (4.2%+/-2.8% vs.1.4%+/-0.7%, P=0.003<0.05). The PBC patients also had significantly higher percentage of NKG2D surface expressing CD56-positive NK cells than the healthy donors (79.4%+/-10.2% vs.64.8%+/-10.7%, P=0.000<0.05). The PBC patients and healthy donors showed no statistically significant differences in percentages of NKG2D surface expressing CDl6-positive NK (70.1%+/-12.9% vs.61.1%+/-5.9%, P=0.078>0.05). MICA was seldom detected on normal monocytes (2.6%+/-1.9%), but present for 51.6%+/-16.2% of monoeytes from the PBC patients (P =0.000<0.05). There was a significant difference in frequency of CD14/MICA double-positive monocytes between the healthy donors and PBC patients. No correlation of MICA expression on monocytes with NKG2D expression on NK cells was found.
Conclusion: PBC patients have lower levels of NK cells in peripheral blood than their healthy counterparts. PBC patients also have higher levels of the CD56+ NK cell subset and cells with surface expression of the activated NKG2D receptor. It appears that PBC patients have a greater level of CD14+MICA+ peripheral blood mononuclear cells. NK cells may be affected by the PBC-related monocytes and participate in disease pathogenesis through immune regulation.