CTSK and rheumatoid arthritis: Interestingly, BMDMs treated with supernatant from ORF8-stimulated RA-hOBs exhibited enhanced expression of key osteoclast differentiation markers— osteoclast stimulatory transmembrane protein (OC-STAMP), dendrocyte expressed 7 transmembrane protein (DC-STAMP), nuclear factor of activated T cells 1 (NFATC1), RANK, CTSK, and calcitonin receptor (CALCR) — compared with BMDMs treated with supernatants from ORF8-stimulated H-hOBs (Figure 6B).