CD5 and inflammatory bowel disease: Based on the level of CD5 expression, reflecting developmentally acquired intrinsic affinity of TCR for self-ligands, we were able to classify naive CD8+ T cell pools to define CD5lo cells as high Tc17 producers and CD5hi cells (especially Ly6C+ cells) as poor Tc17 producers, which is a crucial mechanistic basis for severe inflammatory diseases in the IBD and GVHD settings.