Synovial tissue sections were dewaxed with 4% xylene and dehydrated with gradient alcohol.31 (link) For H&E staining, tissues were stained with H&E staining kit (toluidine blue, Keygen Biotech. Nanjing, China). For Masson, tissues were stained with Masson trichrome staining kit (toluidine blue, Keygen Biotech. Nanjing, China). For Safranin O staining, tissues were stained with Safranin O solution (ScyTek, Logan, UT, USA). All staining was performed according to the manufacturer’s instruction, and the morphological changes were observed with an optical microscope (BX51; Olympus Corp., Tokyo, Japan).