Soluble CD40 ligand (sCD4OL) is reported to disrupt the blood-brain barrier (BBB). Cerebrospinal fluid (CSF) and serum sCD4OL levels were measured in 29 multiple sclerosis (MS), 29 neuromyelitis optica spectrum disorder (NMOSD), and 27 disease control (DC) patients. In MS, serum sCD4OL levels were higher than in DCs and positively correlated with the CSF/serum albumin ratio (Qalb). In NMOSD, CSF sCD4OL levels were significantly increased compared to DCs, and were correlated to Qalb, CSF cell counts, protein concentrations, and interleukin-6 levels. sCD4OL could be involved in BBB disruption in MS, whereas it may contribute to CNS inflammation in NMOSD. (C) 2017 Elsevier B.V. All rights reserved.