IL17A and colitis: We therefore transferred naïve WT or Tec−/− naïve CD4+ T cells from IL-17A fate mapping mice into Rag2−/− mice and analyzed the small intestine and colon for appearance of preconversion (Th17) and postconversion (exTh17) effector cells 3 weeks after transfer by monitoring eYFP+ cells (Figure 5A; Supplementary Figure S9A), a time frame which corresponds to the onset of colitis disease (47), as exemplified by similar colon lengths between control and treated groups (Supplementary Figure S9B).