IL17A and cholangiocarcinoma: Multiple other cell types in the tumor stroma, including blood platelets, T helper cells [Th, responsible for immune surveillance such as interleukin-17 (IL17)-producing T cells (Th17 cells) associated with autoimmunity], and Tregs (that inhibit the activity of Th cells) produce transforming growth factor (TGF) β and other factors that act on the CCA cells [20].