MINIREVIEW The Role of Endogenous Opioids and Their Receptors in the Immune System (433098)

he production and action of opioid peptides in the immune system has been extensively studied T beginning in the years 1979-1980 (1-3). The purpose of this review is to identify and highlight the accomplishments to date categorized into three major themes: (i) the action of opioids on immunocompe-tence in i i fro and in ri iv: (ii) the production of opioid peptides by cells of the immune system (immunocytes): and (iii) the identification and characterization of opioid receptors on immunocytes. Opioid peptides can be categorized into three groups: (i) the endorphins, which are encoded by the pro-opiomelanocortin (POMC) gene: ( i i) the enkephalins, which are encoded by proenkephalin: and (iii) the dynorphins, which are encoded by prodynorphin. As will be described in this review. the modulation by these peptides of immuno-competence is mediated through membrane bound re-ceptors classified into four types: 6, t. K. and p. Whereas the 6-. K-, and p-classes of receptors are sensitive to broad and selective opioid antagonists. the d i k e recep-tor is specific for?-endorphin. However. it would ap-pear that the t-like receptor does. in fact. share some features in common with other opioid receptors of immune and neuroendocrine origin. The role these molecules have in immune homeostasis and in the production of opioids by immunocytes implicates these peptides as important signal molecules within the im-mune system and between the immune and neuroen-docrine systems