LILRB3, also known as ILT5, LIR3, and CD85a (PIR-B in mouse and rat), is an immune regulatory protein that is expressed on peripheral monocytes, neutrophils, eosinophils, basophils, and mast cell progenitors. Triggering of LILRB3 inhibits the activation of macrophages, mast cells, neutrophils, basophils, and B cells. On osteoclast precursors, LILRB3 ligation inhibits RANK L/TRANCE or M-CSF induced differentiation. LILRB3 can also bind to ligands exposed on necrotic tumor cells, S. aureus, and Angiopoietin-like 7. In the mouse CNS, PIR-B functions as a receptor for the myelin proteins Nogo, MAG, and OMgp and mediates their inhibitory action on neurite outgrowth and axon regeneration.