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 systembut they can alsomodulatemany 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 possiblemechanisms
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 ofmacrophages
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.
opiates, morphine, heroin, methadone, substitution treatment, immune system.