CD244 is a 70 kDa type I transmembrane glycoprotein containing four ITSM domains in its cytoplasmic part, serving as docking sites for both activating and inhibitory signaling molecules. Its extracellular ligand is CD48. CD244 is involved in non-MHC restricted cytotoxic activity of NK cells and acts as a costimulatory ligand for both NK cells and T cells. Interaction of CD244 with CD48 on T cells leads to the activation of both, but interaction with CD48 on other cells (e.g. tumor cells) can lead to inhibition of NK cell functions.