PRTN3 and rheumatoid arthritis: Furthermore, studies have shown circulatory cytokine differences with an increase in levels of CXCL13 and CXCL12 in ACPA+ compared to ACPA− RA patients, with a recent study demonstrating an increase in CXCR3+ CD4 T cells in the synovial fluid compared to the periphery, irrespective of ACPA status [11,13,15].