Morphine stimulates phagocytosis of Mycobacterium tuberculosis by human microglial cells: involvement of a G protein-coupled opiate receptor

Phillip K. Peterson, Genya Gekker, Shuxian Hu, Wen Sheng, Thomas W Molitor, Chun C. Chao

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37 Scopus citations


Opiate-induced immunosuppression has been implicated in the pathogenesis of infections caused by a variety of microorganisms, including human immunodeficiency virus (HIV). Although effects of opiates on lymphocyte function have been studied more extensively, morphine also has been shown to inhibit several functional activities of mononuclear phagocytes (e.g. chemotaxis, respiratory burst activity and phagocytosis). Opiate addiction has been identified as a risk factor for clinical tuberculosis prior to the HIV epidemic, and macrophages are a key cell in the pathogenesis of Mycobacterium tuberculosis. Thus, the hypothesis was tested in the present study that morphine would suppress phagocytosis of M. tuberculosis by human microglial cells, the resident macrophages of the brain. Contrary to this hypothesis, treatment of human fetal microglial cell cultures with morphine (10-8m) was found to stimulate phagocytosis of nonopsonized M. tuberculosis H37Rv. The stimulatory effect of morphine was blocked by naloxone and the μ opiate receptor selective antagonist β-funaltrexamine. Also, morphine-induced increase in phagocytic activity was markedly inhibited by pertussis toxin and was unaffected by cholera toxin, suggesting the mechanism of morphine's stimulatory effect on microglial cell phagocytosis involves a Gi protein-coupled μ opiate receptor. The results of this in vitro study support the concept that exogenous and endogenous opioids play an immunomodulatory role within the central nervous system through their interaction with G protein-coupled receptors on microglial cells.

Original languageEnglish (US)
Pages (from-to)299-309
Number of pages11
JournalAdvances in Neuroimmunology
Issue number3
StatePublished - 1995

Bibliographical note

Funding Information:
This work was supported by National Institutes of Health grant DA 04381. We thank Dr Fred Kravitz for his invaluable assistance and Stacey Larson for help in preparation of the manuscript.

Copyright 2014 Elsevier B.V., All rights reserved.


  • G protein
  • Microglia
  • Mycobacterium tuberculosis
  • morphine
  • opiate receptors


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