Natural cytotoxicity triggering receptor 2 is a protein that in humans is encoded by the NCR2 gene. NCR2 has also been designated as CD336 (cluster of differentiation 336). NKp44 is a natural cytotoxicity receptor that is is expressed on IL-2-activated human NK cells and may contribute to the increased efficiency of NK cells to mediate tumor cell lysis. NKp44 is composed of one Ig-like extracellular domain, a transmembrane segment, and a cytoplasmic domain. Prolactin up-regulates and cortisol down-regulates the surface expression of NKp44 at the transcriptional level. A cellular ligand for NKp44 (NKp44L) is expressed during HIV-1 infection and is correlated with the progression of CD4+ T cell depletion and an increase of viral load.