Identification of the CD85 antigen as ILT2, an inhibitory MHC class I receptor of the immunoglobulin superfamily

The CD85 molecule was originally defined at the Fifth. Workshop on Leucocyt e Antigens in 1993 by two monoclonal antibodies, VMP55 and GHI/75. This cel l-surface glycoprotein is expressed on B cells, monocytes, and subpopulatio ns of T and natural killer (NIC) cells, and particularly high levels are ex pressed by normal and neoplastic plasma cells and by hairy cell leukemia B cells. We affinity purified the CD85 antigen and obtained tryptic peptide s equence which indicated that this molecule might be ILT2, a recently descri bed inhibitory major histocompatibility complex class I receptor of the imm unoglobulin superfamily. This was confirmed by showing that both of the ori ginal anti-CD85 mAbs stained ILT2 transfectants. The cell signaling role de monstrated for ILT2 is consistent with the previously reported involvement of CD85 in T cell activation.