IL17A and Autoimmunity: Given that the survival of immune cells may be affected differentially by the surrounding environment where the resident tissue cells provide survival factors, the shifting of IL-17+ cell or IFN γ+ cell changes from 1 year of age to 2 years of age is presumably affected by the (1) pathogenic increase of autoimmunity, (2) age-dependent cellular senescence, or (3) different survival rates based on where they reside.