LILRB1, also known as CD85j and ILT2, is a transmembrane glycoprotein in the LILR immunoregulatory protein family. LILRB1 is expressed on NK cells that have expanded in response to acute HCMV infection. LILRB1 exhibits considerable diversity in the population, and polymorphisms in the LILRB1 gene have been associated with susceptibility to rheumatoid arthritis and weakly associated with HCMV disease in a subset of patients with HIV. The regulation of phagocytosis by macrophages is an additional key role of LILRB1 signaling. LILRB1 recognizes a wide variety of HLA haplotypes due to its interaction with the invariant β2M subunit of MHC class I, which suggests that this signaling axis is relevant across diverse patient populations.