Technische Universität München

The Entrepreneurial University

Opioid receptors participate in the function of immune cells. Opioid receptors have been found on the surface of different immune cells. Opioids modulate both innate and acquired immune responses. 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 would be mediated by the nervous system. Thus, opioid modulation of the immune response is mediated, in part, directly through the interaction with opioid receptors expressed by several populations of immune cells, but the influence of opioids on the immune response is also the result of the effects of these drugs on both the central nervous system and the hypothalamic-pituitary-adrenal axis.
Several investigations have demonstrated that the capacity of both peritoneal macrophages and neutrophils to phagocytose the yeast Candida albicans is inhibited following in vivo administration of morphine. The decrease in the phagocyte capacity may be particularly dangerous for athletes during exercise, because in this situation the stimulation of innate immune responses can be crucial for preventing the entry and the maintenance of microorganism in the body. The effects of narcotics on other populations of immune cells are also inhibitory, for example:
  • Suppression of the cytotoxic activity of natural killer cells; enhancing the growth of implanted tumours
  • Depression of lymphocyte responsiveness to mitogen stimulation
  • Thymus gland atrophy
  • Decrease of T-lymphocyte numbers
  • Decrease of T-cell function
  • Inhibition of antibody production
  • Inhibition of B-cell activity
  • Decrease the levels of interferon  
Furthermore, narcotics are involved in the increased incidence of infections and probably in the development of tumors. This may be particularly important in athletes during competitions, in which temporary immunosuppression is frequent.