Killer-Cell Immunoglobulin-Like Receptors (KIRs) are important cells of the immune system. KIRs are a family of Natural Killer (NK) Cells surface glycoproteins. KIRs control the killing function of these cells by interacting with MHC class I molecules. This interaction allows KIRs to identify virally infected cells or tumor cells by the distinctive low level of Class I MHC on their surface. The majority of KIRs are inhibitory, their recognition of MHC suppresses the cytotoxic activity of their NK cell. Only a limited number of KIRs have the capacity to activate cells. KIR2DL3 is an inhibitory Killer Cell Ig-like Receptor. KIR2DL3 recognizes class I MHC molecules (HLA-Cw1, -Cw3, -Cw7, and Cw8). KIR2DL3 inhibits the activity of NK cells thus preventing cell lysis.