**2.3 T cells**

Activated T cells comprise ≥50% of RA synovial cells, and majority are memory CD4 T cells. In terms of T cell subsets, the Th1(T helper 1) and Th17(T regulatory) are predominant, but lack Th2 subsets [5]. T cells release cytokines as their effector functions; Th1 release interferon gamma(IFN-γ), that further activate macrophages and increases its phagocytic activity. Likewise, effector cytokines of Th17 cells are IL-17A, IL-17F, IL-21, and IL-22, responsible for cell recruitment, secretion of proinflammatory cytokines, initiation of differentiation of B-cell, and activate NK cells [19]. IL-17 may emerge as a beneficial target for RA therapies.
