Unconventional IELs present majority of IEL cells in intestinal epithelial layer and acquire their effector program after exiting thymus as naïve cells and encountering antigens in GALT. After such stimulation, unconventional IELs (mainly γδ T cells) reside in the intestinal epithelium. γδ T cells express TCR receptor made of γ and δ subunit and do not recognize antigen peptides presented in the MHC-bound form. The process of their activation is still largely unknown. Main property of γδ T cells is formation of long-lived memory populations in barrier tissues such as intestinal epithelium or in the skin. They perform immune memory in particular tissue even after clearance of pathogen or retreat of inflammation.