**Abstract**

Multiple sclerosis (MS) is accompanied by decreases in serum endogenous enkephalin/endorphins and alterations in inflammatory cytokines. This retrospective analysis of serum levels was conducted in 53 patients with established relapsing-remitting MS treated with the disease-modifying therapies (DMT) glatiramer acetate, dimethyl fumarate or with the biotherapeutic low dose naltrexone (LDN) to elevate enkephalins, an off-label alternative. Opioid growth factor (OGF), an inhibitory endogenous opioid involved in modulating cellular replication, was measured and correlated to serum β-endorphin, IL-17A and TNFα. Results revealed that MS leads to a significant reduction in OGF levels in subjects on DMTs, but patients on LDN had OGF levels comparable to non-MS controls. Individuals on DMTs had significantly elevated TNFα levels, while IL-17A levels were significantly elevated only in patients taking dimethyl fumarate. A direct correlation was established between OGF and IL17A indicating a potential interaction between the OGF-OGFr axis and pro-inflammatory T-helper cells providing insight into the disease etiology.

**Keywords:** relapsing-remitting multiple sclerosis, serum cytokines, opioid growth factor, low-dose naltrexone, biomarkers
