Opioid receptor blockade increases the number of lymphocytes without altering T cell response in draining lymph nodes in vivo

A number of studies have been dedicated to estimate the consequences on immunity of the clinical use of opioids by focusing on mitogen-induced polyclonal proliferation of T cells from blood or spleen. Here we examined, under physiological conditions, the contribution of endogenous opioids in the development of a CD4(+) T cell response within draining lymph nodes. We show in OVA-primed DOI 11.10 mice that delta-opioid receptors were upregulated upon Tcell activation in vivo and that opioid receptor neutralization increased the number of specific anti-OVAT lymphocytes without promoting their capacity to proliferate. The sensitivity to Fas-mediated apoptosis of T lymphocytes and the synthesis of homeostatic lymphoid chernokines were not either affected suggesting that opioids operate mainly before the entry of T lymphocytes into lymph nodes. (c) 2007 Elsevier B.V. All rights reserved.