A FAMILY OF HUMAN LYMPHOID AND MYELOID IG-LIKE RECEPTORS, SOME OF WHICH BIND TO MHC CLASS-I MOLECULES

Leukocyte Ig-like receptors (LIRs) are a newly discovered family of im munoreceptors expressed on monocytes and B cells and at lower levels o n dendritic cells and NK cells. The amino acid sequences in the extrac ellular regions of eight of these receptors show between 63 and 84% id entity to the prototypic LIR-1 sequence, LIRs contain either two or fo ur Ig domains and fall into three classes: those with cytoplasmic doma ins containing two, three, or four immunoreceptor tyrosine-based inhib itory motif-like motifs; those with a short cytoplasmic domain and no immunoreceptor tyrosine-based inhibitory motif-like motifs; and those with no transmembrane domain represented by a single LIR molecule that is presumably secreted. The LIRs are structurally related to the huma n Fc alpha R and the killer inhibitory receptors and map to the same r egion of chromosome 19 as these genes, Like killer inhibitory receptor s, at least hva LIRs bind to MHC class I Ags, but their different cell ular distribution suggests a distinct role in immune system modulation .