FAP and rheumatoid arthritis: Multicolor immunofluorescence analyses revealed that the most significant marker genes identified (ferroptosis-sensitive fibroblast subset: Mfap4, ferroptosis-resistant fibroblast subset: Sparcl1) could distinguish different subsets among FAPα+ fibroblasts in the synovium of RA patients and CIA mice (Supplementary Fig. 4, Fig. 3d, e).