Immune Cells Release Natural Painkilling Peptides Through Opioid Receptors to Relieve Nerve Pain
Immune cells at injury sites release the body's own opioid peptides — Met-enkephalin, β-endorphin, and dynorphin A — through a calcium-regulated signaling pathway to produce pain relief.
Quick Facts
What This Study Found
Opioid receptors on immune cells (leukocytes) can trigger the release of three opioid peptides — Met-enkephalin, β-endorphin, and dynorphin A (1-17) — which then act on nearby nerve cell receptors to relieve neuropathic pain. This challenges the classical view that opioid pain relief works only through receptors on neurons.
The researchers mapped the complete signaling pathway: activation of leukocyte opioid receptors triggers a Gαi/o-Gβγ protein cascade through phospholipase C and IP3 receptors, releasing intracellular calcium, which drives opioid peptide secretion. When leukocytes were depleted, pain relief from exogenous opioids was significantly reduced and could only be restored by transplanting wild-type immune cells — not those lacking opioid receptors.
Key Numbers
3 opioid peptides released (Met-enkephalin, β-endorphin, dynorphin A) · δ-, μ-, and κ-opioid receptor subtypes involved · Gαi/o-Gβγ-PLC-IP3-Ca²⁺ signaling pathway
How They Did This
Researchers used a mouse model of neuropathic pain created by chronic constriction injury of the sciatic nerve. They injected opioid receptor agonists at the damaged nerve site and measured pain relief using von Frey filaments (which test sensitivity to touch). They systematically blocked or removed components of the signaling pathway — depleting leukocytes, using genetic knockouts, and applying pharmacological inhibitors — to identify the mechanism. They also tested opioid peptide release from immune cells ex vivo.
Why This Research Matters
This research reveals that immune cells are active participants in pain control, not just bystanders. By showing that opioid receptors on leukocytes drive the release of the body's own painkilling peptides, this work opens a fundamentally new approach to pain management — one that could potentially harness the immune system's natural analgesic capacity rather than relying solely on drugs that act on nerve cells.
The Bigger Picture
The opioid crisis has driven intense interest in understanding exactly how pain relief works at the molecular level. This research reveals that immune cells aren't just passive targets of opioid drugs — they actively participate in pain modulation by releasing the body's own opioid peptides. This could lead to entirely new pain management strategies that enhance the immune system's natural analgesic function rather than flooding neuronal receptors with synthetic opioids.
What This Study Doesn't Tell Us
This was a mouse study, so findings need to be confirmed in humans. The chronic constriction injury model, while well-established, may not fully replicate all forms of human neuropathic pain. The relative contributions of different leukocyte subtypes to opioid peptide release were not fully characterized.
Questions This Raises
- ?Could therapies that enhance leukocyte opioid peptide release provide pain relief with fewer side effects than traditional opioids?
- ?Do different types of immune cells contribute differently to opioid peptide release at injury sites?
- ?Is this immune-mediated pain relief pathway impaired in chronic pain conditions that resist conventional opioid treatment?
Trust & Context
- Key Stat:
- 3 opioid peptides released by immune cells Met-enkephalin, β-endorphin, and dynorphin A are secreted by leukocytes at nerve injury sites to produce local analgesia
- Evidence Grade:
- This is a preclinical animal study with rigorous mechanistic investigation including genetic knockouts, pharmacological blockade, cell transfer experiments, and ex vivo validation. The evidence is strong for the mouse model but requires human translation.
- Study Age:
- Published in 2016, this study established a key mechanism in immune cell-mediated analgesia. Subsequent research has likely built on these findings in the active field of neuroimmune pain modulation.
- Original Title:
- Leukocyte opioid receptors mediate analgesia via Ca(2+)-regulated release of opioid peptides.
- Published In:
- Brain, behavior, and immunity, 57, 227-242 (2016)
- Authors:
- Celik, Melih Ö(4), Labuz, Dominika(7), Henning, Karen, Busch-Dienstfertig, Melanie, Gaveriaux-Ruff, Claire, Kieffer, Brigitte L, Zimmer, Andreas, Machelska, Halina
- Database ID:
- RPEP-02889
Evidence Hierarchy
Frequently Asked Questions
What are opioid peptides and why do immune cells release them?
Opioid peptides are small proteins naturally produced by the body that act as painkillers by binding to opioid receptors. This study showed that immune cells called leukocytes, which gather at injury sites, have their own opioid receptors. When these receptors are activated, the immune cells release opioid peptides like Met-enkephalin and β-endorphin, which then act on nearby nerves to reduce pain.
Could this research lead to new pain treatments?
Potentially, yes. Understanding that immune cells actively participate in pain relief by releasing opioid peptides opens the possibility of developing treatments that boost this natural process. Such therapies might provide pain relief with fewer of the side effects and addiction risks associated with traditional opioid medications.
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Cite This Study
https://rethinkpeptides.com/research/RPEP-02889APA
Celik, Melih Ö; Labuz, Dominika; Henning, Karen; Busch-Dienstfertig, Melanie; Gaveriaux-Ruff, Claire; Kieffer, Brigitte L; Zimmer, Andreas; Machelska, Halina. (2016). Leukocyte opioid receptors mediate analgesia via Ca(2+)-regulated release of opioid peptides.. Brain, behavior, and immunity, 57, 227-242. https://doi.org/10.1016/j.bbi.2016.04.018
MLA
Celik, Melih Ö, et al. "Leukocyte opioid receptors mediate analgesia via Ca(2+)-regulated release of opioid peptides.." Brain, 2016. https://doi.org/10.1016/j.bbi.2016.04.018
RethinkPeptides
RethinkPeptides Research Database. "Leukocyte opioid receptors mediate analgesia via Ca(2+)-regu..." RPEP-02889. Retrieved from https://rethinkpeptides.com/research/celik-2016-leukocyte-opioid-receptors-mediate
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkPeptides research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.