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J. Exp. Med.,
Volume 188, Number 2, July 20, 1998 317-325
and µ Opiate Receptor-mediated
Heterologous Desensitization
By



From the * Laboratory of Molecular Immunoregulation, An intact chemotactic response is vital for leukocyte trafficking and host defense. Opiates are
known to exert a number of immunomodulating effects in vitro and in vivo, and we sought to determine whether they were capable of inhibiting chemokine-induced directional migration
of human leukocytes, and if so, to ascertain the mechanism involved. The endogenous opioid
met-enkephalin induced monocyte chemotaxis in a pertussis toxin-sensitive manner. Met-enkephalin, as well as morphine, inhibited IL-8-induced chemotaxis of human neutrophils and
macrophage inflammatory protein (MIP)-1
Intramural
Research Support Program, Science Applications International Corp. Frederick, Frederick, Maryland
21702; the § ABL-Basic Research Program, National Cancer Institute - Frederick Cancer Research
and Development Center, Frederick, Maryland 21702; the
Laboratory of Immunology, National
Institute on Aging, Baltimore, Maryland 21224; and the ¶ Department of Medicine, Duke University
Medical Center, Durham, North Carolina 27710
, regulated upon activation, normal T expressed
and secreted (RANTES), and monocyte chemoattractant protein 1, but not MIP-1
-induced
chemotaxis of human monocytes. This inhibition of chemotaxis was mediated by
and µ but
not
G protein-coupled opiate receptors. Calcium flux induced by chemokines was unaffected by met-enkephalin pretreatment. Unlike other opiate-induced changes in leukocyte
function, the inhibition of chemotaxis was not mediated by nitric oxide. Opiates induced
phosphorylation of the chemokine receptors CXCR1 and CXCR2, but neither induced internalization of chemokine receptors nor perturbed chemokine binding. Thus, inhibition of
chemokine-induced chemotaxis by opiates is due to heterologous desensitization through phosphorylation of chemokine receptors. This may contribute to the defects in host defense
seen with opiate abuse and has important implications for immunomodulation induced by several endogenous neuropeptides which act through G protein-coupled receptors.
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