LILRB4 belongs to the subfamily B class of LIR receptors which contain two or four extracellular immunoglobulin domains, a transmembrane domain, and two to four cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). The receptor is expressed on monocytic cells and transduces a negative signal that inhibits stimulation of an immune response. The receptor can also function in antigen capture and presentation. It is thought to control inflammatory responses and cytotoxicity to help focus the immune response and limit autoreactivity. LILRB4 has also been proposed to be a potential target for tumor immunotherapy. It has been shown to express on tumor-associated macrophages and negatively regulate immune response in tumor. The expression of LILRB4 on monocytic myeloid leukemia cells supports infiltration and inhibits T cell proliferation.