CD4 and rheumatoid arthritis: Specifically, IL-27 signaling may impact the development of RA by modulating CD4 + T cell differentiation, suppressing monocytes/macrophages and osteoclasts within the joint cavity, disrupting interactions between synovial ectopic lymphoid structures (ELS) and Th17 cells, and regulating inflammation mediated by RA synovial fibroblasts (RA-FLS) [38, 39].