HLA-C and rheumatoid arthritis: The majority of antigen-presenting cells (APCs) in the inflamed RA synovium are fully differentiated DCs expressing high levels of class I and II major histocompatibility complex (MHC) and several T-cell costimulatory molecules.34 In summary, the role of DCs in the pathogenesis of RA is complex and dichotomous, and DCs may induce either tolerance or autoimmunity based on the integrated signals received in the microenvironment of synovial joints.