IL21 and type 1 diabetes mellitus: Taken together, these findings indicate that CCR9+ Th cells in the inflamed lesions of the pancreas in NOD mice are phenotypically related to GIT residing CCR9+ Tfh cells, supporting the notion that IL-21-producing CCR9+ Th cells that are critical for the development of T1D may emerge from Tfh cells in the GIT or a common GIT-residing precursor population.