CD18 expression and distribution of monocyte subsets in healthy controls (HCs) and patients with spondyloarthritis (SpA). (A) The cell membrane expression of CD18 on CD14+ CD16++ (non-classic) monocytes, CD14++ CD16+ (intermediate) monocytes, and CD14++ CD16- (classic) monocytes using peripheral blood mononuclear cells (PBMCs) from a representative HC with the gating strategy indicated. (B) The cell membrane expression of CD18 on non-classic monocytes, intermediate monocytes, and classic monocytes in PBMCs from 5 HCs and 10 patients with SpA. Bars indicate median and interquartile range. (C) The percentages of intermediate monocytes among all CD14+ monocytes in HLA-B27-positive SpA, HLA-B27-negative SpA, and HCs. PBMCs from the same 10 patients with SpA and 5 HCs were used. Bars indicate median and interquartile range. *P <0.05; **P <0.01; ****P <0.0001.