KLRK1 and viral infectious disease: Previous studies documented that the expression of NKG2D ligands are up-regulated through a variety of stimuli that have been collectively termed “cellular stress”, such as cellular transformation, viral infection, and/or DNA damage [25,26], and the upregulation of MICA/B in distressed cells may alert the immune system that the cells are undergoing pathological changes and enhance the innate immune function.