Major histocompatibility complex class II beta 2 domain (MHC II β2)

The Major Histocompatibility Complex (MHC) class II β2 domain is a conserved, non-polymorphic, membrane-proximal region of the MHC class II beta chain. It serves as the primary docking site for the CD4 co-receptor on T lymphocytes, which is essential for stabilizing the interaction between the T-cell receptor (TCR) and the MHC II-peptide complex during antigen presentation (Konig et al., 1992, Nature). Furthermore, this domain is the high-affinity binding site for the immune checkpoint protein Lymphocyte-activation gene 3 (LAG-3), which negatively regulates T-cell expansion and effector function (Huard et al., 1997, Proc. Natl. Acad. Sci. USA). In therapeutic contexts, the MHC II β2 domain is targeted by soluble LAG-3 fusion proteins like Eftilagimod alpha, which act as agonists to stimulate antigen-presenting cells and boost anti-tumor immunity (Brignone et al., 2007, J. Immunol.). Conversely, monoclonal antibodies such as Relatlimab block the interaction between LAG-3 and the β2 domain to restore the activity of exhausted T cells in the tumor microenvironment (Pardoll, 2012, Nat. Rev. Cancer). Dysregulation of this domain's interactions is implicated in immune evasion by tumors and the pathogenesis of various autoimmune and infectious diseases. The domain's structural integrity is vital for the proper assembly of the MHC II heterodimer and its subsequent transport to the cell surface.

Other names

MHC II beta-2 domainHLA class II beta 2 domainCD4-binding domain of MHC IILAG-3 binding site on MHC II

MHC class II agonism to activate antigen-presenting cells and blockade of the LAG-3/MHC II inhibitory pathway to restore T-cell function.