Immunological Mechanisms Involved in MS and effects of LDN β-endorphin is an opioid peptide, synthesized by cells of the central nervous system (arcuate nucleus) and immune system (lymphocytes, thymocytes, monocytes and splenocytes). This peptide is decreased in concentration in peripheral blood mononuclear cells (PBMC) of MS patients, with the lowest concentrations linked to the progressive forms of the disease. Furthermore increased concentrations of β-endorphin are found during interferon beta treatment and following clinical relapses. In the animal model of MS, experimental autoimmune encephalitis, β-endorphin blockade worsens disability.