Alterations in chemokine receptor expressions on peripheral blood monocytes in multiple sclerosis and neuromyelitis optica

Objectives Human peripheral blood monocytes comprise three different subtypes: CD14+CD16- (classical type), CD14^lowCD16+ (non-classical type) and CD14+CD16+ (intermediate type). These subsets are known to have different functions, but little is known about their roles in multiple sclerosis (MS), especially for maintaining remission. We aimed to clarify the alterations in monocyte subsets in patients with MS and neuromyelitis optica (NMO)/NMO spectrum disorder (NMOSD) in the remission phase. Methods Blood samples were collected from 19 MS patients and 10 NMO/NMOSD patients in the remission phase, and 42 healthy controls (HC). The surface expressions of CCR2, CX3CR1, CD64 (FcγR1) and CD62L were analyzed in the monocyte subsets by flow cytometry. Results CCR2 expression was significantly decreased in classical monocytes from MS patients, regardless of interferon-β (IFN-β) treatment, but not in those from NMO/NMOSD patients. CX3CR1 expression was also decreased in all monocyte subsets from MS patients receiving IFN-β, whereas CX3CR1 expression in classical monocytes was only decreased in NMO/NMOSD patients receiving prednisolone. In NMO/NMOSD patients on prednisolone, the percentages of CD14+CD16+ intermediate monocytes, CD14^lowCD16+ non-classical monocytes and CD64+CD14+CD16+ monocytes among total monocytes were significantly lower than in HC. CD62L expression on the monocyte subsets showed no significant differences among the patients and HC. Conclusions Our findings suggest that alterations in chemokine receptor expressions on peripheral blood monocytes can occur in MS and NMO/NMOSD during the remission phase. Down-modulation of CCR2 in MS, and CX3CR1 in MS and NMO/NMOSD could partly contribute to sustained remission by preventing monocyte infiltration into the central nervous system.