Characterization of the lymphocyte activation gene 3-encoded protein. A new ligand for human leukocyte antigen class II antigens.

Abstract

SummaryThe lymphocyte activation gene 3 (LAG-3), expressed in human activated T and natural killer (NK) cells, is closely related to CD4 at the gene and protein levels. We report here the initial characterization of the LAG-3-encoded protein. We have generated two monoclonal antibodies after immunization of mice with a 30-amino acid peptide that corresponds to an exposed extra loop region present in the LAG-3 immunoglobulin-like first domain. The reactivity of these reagents is directed against LAG-3 since they recognize both membrane-expressed and soluble recombinant LAG-3 molecules produced in a baculovirus expression system. The two antibodies are likely to react with the same or closely related epitope (termed LAG-3.1) exposed on the LAG-3 first domain extra loop, as assessed in competition experiments on LAG-3-expressing activated lymphocytes. Cellular distribution analysis indicated that the LAG-3.1 epitope is expressed on activated T (both CD4 + and CD8 + subsets) and NK cells, and not on activated B cells or monocytes. In immunoprecipitation experiments performed on activated T and NK cell lysates, a 70-kD protein was detected after SDS-PAGE analysis. 45-kD protein species were also immunoprecipitated. Both the 70-and 45-kD proteins were shown to be N-glycosylated. In Western blot analysis, only the former molecule was recognized by the anti-LAG-3 antibodies, demonstrating that it is LAG-3 encoded. These anti-LAG-3 antibodies were used to investigate whether the LAG-3 protein interacts with the CD4 ligands. By using a high-level expression cellular system based on COS-7 cell transfection with recombinant CDM8 vectors and a quantitative cellular adhesion assay, we demonstrate that rosette formation between LAG-3-transfected COS-7 cells and human leukocyte antigen (HLA) class II-bearing B lymphocytes is specifically dependent on LAG-3/HLA class II interaction. In contrast to CD4, LAG-3 does not bind the human immunodeficiency virus gp120. This initial characterization will guide further studies on the functions of this molecule, which may play an important role in immune responses mediated by T and NK lymphocytes.

The Upregulation of LAG-3 on T Cells Defines a Subpopulation with Functional Exhaustion and Correlates with Disease Progression in HIV-Infected Subjects

“…As is known, activated T cells also express MHC II molecules (40,41), which in turn may bind to LAG-3 on the same T cells and control their activities after those T cells are activated by APCs (21,29,42); this is particularly important when those activated T cells contact somatic cells carrying MHC class I (MHC I) but not MHC II molecules and screen for pathogen-derived epitopes in the context of MHC I complexes. The self-carrying MHC II molecules on T cells may generate a threshold for the initiation of activated T cell-mediated killing, preventing the occurrence of autoimmune activities when no pathogen-derived epitopes are present in the binding groove of MHC I molecules.…”

A Soluble Lymphocyte Activation Gene-3 Molecule Used as a Vaccine Adjuvant Elicits Greater Humoral and Cellular Immune Responses to Both Particulate and Soluble Antigens

“…The lymphocyte activation gene-3 (LAG-3) 3 molecule is related to CD4 at the gene and protein levels (1,2). LAG-3 is expressed in activated CD4 ϩ and CD8 ϩ T lymphocytes where it is associated with the CD3/TCR complex at the cell surface (3,4).…”

Expression of lymphocyte activation gene 3 (LAG-3) on B cells is induced by T cells

“…Lymphocyte activation gene 3 (LAG-3/CD223) was first identified as a cell surface molecule selectively expressed in activated human NK and T lymphocytes [1,2]. Interestingly, it was found to be closely related to CD4 [1].…”