EXPRESSION OF OPIOID RECEPTORS MESSENGER-RNAS IN IMMUNE CELLS

Multiple reports indicate interactions between opioids and the immune system. Opioids call have immunosuppressive or immunoenhancing effects depending on the in vivo or the in vitro models used. Moreover, reported in vivo effects of opioids on immune responses may be direct or indirect. Pharmacological studies aimed at characterizing opioid receptors on immune cells have brought confusing and controversial data, due in part to the low number of receptors on these cells and also to the presence of ''non-opioid'' receptors, i.e. receptors that cannot be blocked by ''classical'' opioid ligands such as naloxone. The first molecular cloning of an opioid receptor was reported recently for the mouse delta receptor (1,2). Subsequently, the cDNAs for the mu and kappa receptors were cloned by several groups. We used a reverse-transcriptase-polymerase chain reaction (RT-PCR) strategy for detecting expression of the three cloned opioid receptors on immune cells. The human immune cells tested express no or low level of message for the delta and kappa receptors and undetectable mRNA for the mu receptor. The murine immune cells tested show variable levels of message for the delta receptor and undetectable mRNA for the mu and kappa receptors.