CD274 and rheumatoid arthritis: Studies have shown that PD‐1 and PD‐L1 expression is upregulated in RA synovial tissues (the lining of the joints), suggesting that the PD‐1/PD‐L1 axis is involved in the pathogenesis of RA by modulating T‐cell responses and promoting inflammation (Canavan et al. 2021; Raptopoulou et al. 2010; Luo et al. 2018).