Overview over important activatory, inhibitory, and costimulatory NK cell receptors. NK cells integrate various signals in response to leukemic cells. The precise function of some of the receptors is not yet well known, and some activatory receptors might be costimulatory, and vice versa. Note that recent evidence suggests that NKG2D and NKp46 are co-stimulatory receptors because they are not able to induce NK cell activity on their own.⁴  In addition, KIR2DL4 is, to date, considered to convey activatory rather than inhibitory signals.⁴  Many other receptors, including cytokine, chemotactic, and adhesion molecule receptors, as well as other costimulatory receptors, are not shown. Ligands are shown in parentheses. AICL; activation-induced C-type lectin; BAT-3, HLA-B-associated transcript 3; CD16, FcRIII receptor; LFA-1, leukocyte functional antigen 1; MICA/B, MHC class I–related chain A/B; NTB, natural killer T- and B-cell antigen; PCNA, proliferating cell nuclear antigen; ULBPs, UL-16 binding proteins.