Mouse thymocytes incubated in vitro with increasing concentrations of interleukin-1 (IL-1) in the presence of phytohemagglutinin (PHA) exhibited a dose-dependent increase in cell proliferation, as measured by [3H]thymidine incorporation. Under these conditions, there was a parallel dosedependent increase in specific [3H]morphine binding, with a maximum increase of approximately 5-fold over basal levels. The binding sites differ from classical opioid receptors in that they are not stereo-selective. Interleukin-2 was ineffective in promoting either cell proliferation or enhanced opioid binding, but the effects of IL-1 could be mimicked by phorbol myristate acetate (PMA), suggesting the involvement of tyrosine phosphorylation. These results indicate that morphine-binding sites on immune cells can be regulated by cytokine activation.
Bibliographical noteFunding Information:
Acknow/edger?lents: This worh was supported by NIDA Research grants DA06011 (N.M.L.) and DA00564 (H.H.L.). and by Retearch Scientist Awards DA-00020 (N.M.L.) and DA-70554 (H.H.L.).
- Cell proliferation
- Opioid binding
- Phorbol ester