Interferon-β suppresses inflammatory pain through activating µ-opioid receptor

Area of Science:

• Neuroscience
• Immunology
• Pain Research

Background:

• Interferons (IFNs) are cytokines with diverse biological roles beyond antiviral defense.
• Type I IFNs, including IFN-β, have demonstrated neuroprotective and anti-inflammatory properties.
• IFN-β's role in pain modulation, particularly in inflammatory pain conditions, requires further investigation.

Purpose of the Study:

• To investigate the potential of IFN-β in alleviating mechanical allodynia associated with Complete Freund's Adjuvant (CFA)-induced inflammatory pain in rats.
• To determine the underlying mechanisms of IFN-β's antinociceptive effects, focusing on spinal cord pathways.

Main Methods:

• Intrathecal administration of IFN-β in rats with CFA-induced inflammatory pain and in naïve rats.
• Behavioral assessments including paw withdrawal threshold and latency.
• Western blot and immunohistochemical analyses of spinal cord tissue to examine opioid receptor expression and localization.

Main Results:

• Intrathecal IFN-β administration significantly increased the paw withdrawal threshold and latency in both naïve and CFA-treated rats.
• A neutralizing IFN-β antibody reduced these measures, indicating a tonic inhibitory role of endogenous IFN-β in pain signaling.
• IFN-β's analgesic effect was dose-dependent, transient, and reversed by naloxone, suggesting involvement of central opioid receptors.
• Increased expression of phosphorylated µ-opioid receptors and co-localization of µ-opioids with IFN-α/β receptors were observed in the spinal cord dorsal horn.

Conclusions:

• IFN-β exhibits significant antinociceptive effects against inflammatory pain in rats.
• The analgesic action of IFN-β is mediated through the activation of µ-opioid receptors in the spinal cord.
• Endogenous IFN-β plays a tonic role in inhibiting pain signaling in the spinal cord.