CD4 and rheumatoid arthritis: Tfh cell is a CD4 + T cell subset that promotes B cell maturation and differentiation, antibody production, and formation of germinal center in lymphoid follicles, and plays critical roles in the pathogenesis of many autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, SS, systemic sclerosis, etc. [25].