– 2B4 (CD244) is expressed by memory-phenotype CD8() T cells and all natural killer (NK) cells. The ligand for 2B4, CD48, is expressed on hematopoietic cells. 2B4 is conserved in humans and mice, and a number of reports have linked 2B4 with activation of lymphocytes.Engagement of 2B4 on NK cell surfaces with specific antibodies or CD48 can trigger cell mediated cytotoxicity, interferon γ secretion, phosphoinositol turnover and NK cell invasiveness.