TYK2 and rheumatoid arthritis: JAK/STAT pathway is considered as the initial driver of the proinflammatory response in RA [235] and it consists of four receptor-associated kinases, JAK1, JAK2, JAK3, and tyrosine kinase 2 (TYK2), which activate STAT family (STAT1, STAT2, STAT3, STAT5A/B, STAT6).