CD4 and rheumatoid arthritis: Although conventional T cell subsets, particularly CD4+ and CD8+ T cells, have long been implicated in RA immunopathology (8–10), recent studies have underscored the critical contributions of unconventional T cells, also referred to as innate-like T cells, including natural killer T (NKT) cells, mucosal-associated invariant T (MAIT) cells, and gamma delta T (γδ T) cells (11, 12).