The direct actions of opiates on the mammalian immune system depend on the existence of
ligand binding sites either on the surface of the affected cell or in the interior of the cell. With
the cloning of various opiate receptors from neuronal tissue, numerous researchers have
screened leukocyte cDNA libraries for the expression of these receptors with some positive
results. However, the pattern of expression of neuronal opiate receptors in the cellular
immune system does not completely explain the biological action of opiates there. Several …