CD4 and infection: Of note, although far less studied than their CD8+ T counterparts, gut CD4+ Trm cells have been also efficiently induced in infection models, with the two populations displaying both shared as well as unique phenotypic characteristics, for example, CD4+ and CD8+ Trm cells expressed high levels of CD69, while CD4+ expressed lower level of CD103 compared to CD8+ Trm cells [13].