Acts as soluble receptor for class I MHC antigens. Binds both classical and non-classical HLA class I molecules but with reduced affinities compared to LILRB1 or LILRB2. Binds with high affinity to the surface of monocytes, leading to abolish LPS-induced TNF-alpha production by monocytes. Detected in B-cells, and at lower levels in natural killer (NK) cells. Detected in peripheral blood monocytes and lung. N-glycosylation is required for ligand binding.