Effects of opioid therapy on human natural killer cells

Opioid compounds, such as morphine, induce powerful analgesic effects and are extensively used clinically to treat a wide variety of pain. The aim of our study was to evaluate the impact of opioid therapy on phenotype and function peripheral blood NK cells. The patients were referred to three Italian pain therapy centers (Milan, Pavia, Piacenza) for chronic pain in neuropathic or mixed somatic components. The patients were between 18 and 75years old and were of Caucasian ethnicity. We studied the expression of activating and inhibitory NK receptors to discriminate NK subsets with different CD56 surface expression intensities (CD56bright and CD56dull NK cells). The flow cytometry analysis of the NK cells was at normal levels in peripheral blood lymphocytes with fewer CD56bright compared to the CD56dull NK cell subset when compared to blood from drug free donors. Furthermore, the cytolytic activity of in vitro patient NK cells analyzed was not lower, as would be expected from the regular expression of activating NK receptors for both subsets. Taken together, these data indicate that NK cells from opioid treated patients do not show any signs of NK cell immune-suppression. •Patients with chronic pain or mixed somatic component have been enrolled.•The aim is to evaluate the impact of opioid therapy on NK cells.•The phenotype and cytolytic activity of NK cells were evaluated.•Therapeutic doses of opioids do not alter the NK activity in suffering patients.