Objective Recent evidence has suggested the importance of an aberrantly activated monocyte system in amyotrophic lateral sclerosis (ALS) pathogenesis. However, the roles of each monocyte subset, namely CD14+CD16-classical monocytes, CD14dimCD16+ non-classical monocytes and CD14+CD16+ intermediate monocytes, in ALS remain unknown. We aimed to clarify the alterations in the monocyte subset proportions and the surface marker expressions on each monocyte subset in ALS. Methods Blood samples were collected from 19 ALS patients and 28 healthy controls (HC). The surface expressions of CCR2, CX3CR1, CD64 and CD62L were measured in the three monocyte subsets (classical, non-classical and intermediate) by flow cytometry. Results The percentages of CCR2 and CD62L on CD14+CD16-classical monocytes were significantly lower in ALS patients than in HC (P = 0.0012 and P = 0.0296, respectively). No differences were found in CX3CR1 and CD64 on each monocyte subset. The percentage of intermediate monocytes showed a significant negative correlation with the revised ALS functional rating scale score (r =-0.631, P = 0.0038). Conclusions Reductions in chemotaxis-and adhesion-related molecules on classical inflammatory monocytes are present in ALS, further suggesting the involvement of an aberrant innate immune system in ALS pathogenesis.
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