Activated transcriptional profile in lining macrophages at the onset of AIA and CXCL1 expression in the lining. (A) GO analysis of differentially expressed genes in lining and sublining macrophages at 4 h after mBSA challenge (n = 3). FDR, false discovery rate. (B) GO analysis of differentially expressed genes in lining and sublining macrophages from PBS control knees (n = 3). (C) Confocal images of the knee immunostained for CXCL1 at 4 h p.c. (large panel; VSIG4, magenta; CXCL1, green; CD68, cyan; CD31, red; nuclei, gray; scale bar = 100 µm). Zoomed region of the lining shows expression of CXCL1 in various cells (middle panel, scale bar = 10 µm), whereas further enlargement demonstrates colocalization of CXCL1 and VSIG4 (right panel, scale bar = 3 µm). (D) Quantification of CXCL1 distribution in the synovium in additional mice from two independent experiments; Each violin plot represents one to two knee sections of a single mouse with median and interquartile range indicated. F, femur; FP, fat pad; M, meniscus; T, tibia.