PDCD1 and rheumatoid arthritis: Transcriptomics analysis by RNA-Seq on synovial tissue biopsies from healthy donors (n = 28), osteoarthritis (OA, n = 22), ACPA+ve RF+ve arthralgia (n = 10), IA/UA (n = 6), early RA (n = 57), and established RA (n = 95) patients revealed that PDCD1 (encoded PD-1), CD274 (encoded PD-L1) and PDCD1LG2 (encoded PD-L2) expression was not increased in OA compared to healthy controls (Fig 1A).