Leukocyte immunoglobulin (Ig)-like receptor B4 (LILRB4) is a member of leukocyte Ig-like receptors (LILRs). LILRB4 is encoded in the leukocyte receptor cluster, which is on human chromosome 19q13.4. The structure and function of LILRs are similar to those of other leukocyte receptor cluster receptors, such as killer cell immunoglobulin-like receptors. Leukocyte immunoglobulin-like receptor (LILRB4) is a kind of inhibitory receptor that plays a key role in immune checkpoint pathways. Inhibitory receptors also participate in achieving balance between activating and inhibitory actions to ensure immune responses to pathogens in the immune system. However, they not only protect the host from autoimmune responses, but also preserve peripheral tolerance. LILRB4 also regulates immune responses, and its role in regulating immune responses is mostly controlled by its ligands.