The killer cell inhibitory receptor genomic region on human chromosome 19q13.4

Multiple genes encoding type I transmembrane molecules and belonging to the immunoglobulin superfamily have recently been localized to human chromosome 19q13.4. These include a family of genes encoding killer cell inhibitory receptors (KIR) expressed on natural killer (NK) cells and subsets of T-lymphocytes, immunoglobulin-like transcripts (ILT-1, -2 and 3) expressed on myeloid cells and subsets of lymphoid cells, the gp49 family of receptors expressed on mast cells and NK cells and the gene encoding human myeloid immunoglobulin A Fc receptor (CD89). The receptors have one to four extracellular immunoglobulin domains, and the ligands are known for some of these molecules. This includes the Fc alpha R and KIRs of the p58/p50 and p70/p70 delta, but the ligands for many others are unknown. Except for CD89, each subfamily of receptors exist, in two forms, of which one has a long cytoplasmic domain containing one to four immunoreceptor tyrosine-based inhibitory motifs (ITIM) and another form with a short cytoplasmic tail without ITIMs. ITIM-containing receptors can recruit cytoplasmic tyrosine phosphatases and provide inhibitory signals for cell activation, whereas receptors with a "short" tail induce activating signals. The 19q13.4 chromosomal region is therefore now emerging as the immunoglobulin superfamily linkage group of genes differentially expressed on hematopoietic cell lineages and encoding pairs of receptors with opposing effects on signal transduction pathways and effector functions in hematopoietic cells.