Treating pain with Endorphins: Endorphin-based activation of the PD-1 pathway for Pain therapy: β-Endorphin, an endogenous opioid neuropeptide and peptide hormone known to play a role in hunger, thrill, pain, maternal care, reward, and cognition, increases the expression of PD-L1, attenuates acutes and chronic pain, and suppresses mechanical and thermal hypersensitivity and inhibits nociceptive neuron excitability via up-regulation of its target gene, 14/April/2018, 11.47 pm