Expression of functional μ-opioid receptors during T cell development

We have examined the chemotactic responsiveness of thymocytes to selective mu-, kappa-, and delta -opioid agonists. Our results show that developing T cells migrate in response to mu- but not kappa- or delta -opioids. The mu -opioid response appears to be dependent on the classical mu -opioid receptor (MOR-1) since the chemotactic response is blocked by a selective mu -opioid antagonist, and is absent in thymocytes from MOR-l-deficient mice. Flow cytometric analysis of the mu -opioid responsive cells shows that these cells consist predominantly of highly immature CD4(-)CD8(-) T cells. These results represent the first demonstration of the functional expression of mu -opioid receptors by developing T cells. (C) 2001 Elsevier Science B.V. All rights reserved.