DPP4 and rheumatoid arthritis: In order to obtain more insight into CXCL10 processing and the role of CXCL10 and CD26/DPP IV in various rheumatic diseases, including psoriatic arthritis (PsA), ankylosing spondylitis (AS) and RA, the synergistic interaction between cytokines to regulate CXCL10 and CD26/DPP IV expression in fibroblasts and endothelial cells was investigated.