CD55 and rheumatoid arthritis: Immunofluorescence staining of RA and Orth.A synovium also revealed colocalization of GSDME with CD55 in the lining area and THY-1 FLSs in the sublining area, suggesting a link between FLSs and GSDME-mediated pyroptosis in RA synovium as detected above (Figures 1C, Supplementary Figure S3).