The observation of the immunomodulatory effects of opioid drugs opened the discussion about possible mechanisms of action and led researchers to consider the presence of opioid receptors (OR) in cells of the immune system. To date, numerous studies analyzing the expression of OR subtypes in animal and human immune cells have been performed. Some of them confirmed the expression of OR at both the mRNA and protein level, while others did not detect the receptor mRNA either. Although this topic remains controversial, further studies are constantly being published. The most recent articles suggested that the expression level of OR in human peripheral blood lymphocytes could help to evaluate the success of methadone maintenance therapy in former opioid addicts, or could serve as a biomarker for chronic pain diagnosis. However, the applicability of these findings to clinical practice needs to be verified by further investigations.

• Keywords
• addiction, chronic pain, immune cells, opioid drugs, opioid receptors, stem cells,
• MeSH
• Biomarkers MeSH
• Chronic Pain drug therapy   etiology   metabolism   MeSH
• Immune System drug effects   immunology   metabolism   MeSH
• Stem Cells drug effects   metabolism   MeSH
• Humans MeSH
• Analgesics, Opioid pharmacology   MeSH
• Receptors, Opioid genetics   metabolism   MeSH
• Gene Expression Regulation * MeSH
• Inflammation complications   etiology   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Biomarkers MeSH
• Analgesics, Opioid MeSH
• Receptors, Opioid MeSH