CD158f, also known as KIR2DL5, is a polymorphic 60 kDa transmembrane glycoprotein with two Ig-like extracellular domains by which it recognize HLA class I molecules. Its long intracellular domain contains immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that upon extracellular ligand-mediated phosphorylation serve as docking sites for inhibitory phosphatases, which results in blocking natural cytotoxicity as well as antibody-dependent cytotoxicity of the particular NK cell, and its adhesion toward target cells. Together with other killer inhibitory receptors CD158f is important for immunological tolerance to discriminate between normal and abnormal cells. Besides NK cells it is expressed on a small population of cytotoxic T cells. Expression of CD158f alleles is highly variable in the population.