[Opioids and their immunomodulatory properties]

Opiates have been recently used for suppression of the neuropathic pain or to relieve pain in patients with cancer diseases. However, opiates are also used by drug abusers to achieve feeling of euphoria. These drugs influence not only the nervous system but they can also modulate many other physiological functions including those of the immune system. Since opioid receptors have been found on the surface of cells of the immune system, two possible mechanisms of opiate actions have to be considered. The first one represents a direct action of the opiates through the opioid receptors on immune cells; the second mechanism is mediated by the nervous system. The immunomodulatory properties of the opiates have been demonstrated in numerous models. Especially the enhanced sensitivity to viral and bacterial infections, observed in drug abusers, is accounted to the side effects of opiates. Experimental animal models have shown even more complex actions of opiates, which can lead to suppression as well as to stimulation of individual immunological parameters. Although proliferation of lymphocytes tested in vitro after application of opiates in vivo is generally reduced, production of the pro-inflammatory cytokines and some functions of macrophages can be enhanced. Effects of opiate action depend on the experimental model used, the drug dose, way of drug application, time of testing and on the tested immunological parameter. This article summarizes recent knowledge of effects of opiates on the functions of cells of the immune system. It also refers global problems of exploitation of illegal drugs and the importance of methadone in the substitution treatment.