Leukocyte immunoglobulin-like receptors (LILRs) are inhibitory, stimulatory or soluble receptors encoded within the leukocyte receptor complex. Some LILRs are extensively polymorphic, and exhibit evidence for balancing selection and association with disease susceptibility. LILRA1 (LIR-6) can recognize MHC (major histocompatibility complex) class I or class I-like molecules, and high levels of sequence similarity among LILRA1, LILRA2 (ILT1), LILRA3 (ILT6) and LILRB1/B2.