PRTN3 and rheumatoid arthritis: Unsurprisingly, compared with the other control groups, ACPA-positive/-negative RA, early/established RA synovium was highly infiltrated by various immune cells, including activated B cell, activated T cell, activated dendritic cell, and so on (Figure 2(b)), while the difference of immune cell infiltration among RA subgroups was not apparent, which suggested a microenvironment of excessive immune activation and synovial inflammation in RA.