Leukocyte immunoglobulin (Ig)-like receptor B1 (LILRB1) is a member of leukocyte Ig-like receptors (LILRs), also known as CD85j, ILT2, LIR1, and MIR7, contains four extracellular immunoglobulin domains, and four intracellular ITIMs. It is expressed on monocytes, macrophages, DCs, eosinophils and basophils, B cells, T cells, and natural killer (NK) cells, as well as on in vitro cultured cord blood-derived progenitor mast cells and osteoclasts. The interactions between LILRB1 and HLA-I molecule are dependent on the non-polymorphic α3 domain of the heavy chain and β2 microglobulin. LILRB1 additionally interacts with the UL18 molecules from human cytomegalovirus (HCMV), which is an HLA-I homolog, RIFIN molecules from Plasmodium falciparum, Dengue virus through an unidentified ligand, and the damage associated molecular pattern proteins S100A8 and S100A9. Recent studies suggest that LILRB1 on tumor cells stimulates immune responses in certain situations.