CD319 is a single-pass type-1 335 aa transmembrane glycoprotein and expressed on NK cells, subsets of mature dendritic cells, activated B cells, cytotoxic lymphocytes but not in promyelocytic, B- or T-cell lines. Expression is high in spleen, lymph node, periperal blood leukocytes and lowest in bone marrow. Expression is in small intestine, stomach, appendix, lung and trachea. CD319 is tyrosine phosphorylated in activated NK cells and is associated with 19- and 39 kD proteins. CD319 has a homology with the CD2 family of receptors within the Ig superfamily. Some of the CD2 members stimulate cytotoxicity through the CD319 associated protein.