T-cell receptor–peptide–Major Histocompatibility Complex class II–CD4 complex (TCR–pMHCII–CD4 complex)

The T-cell receptor–peptide–Major Histocompatibility Complex class II–CD4 complex is a fundamental multi-protein assembly essential for the initiation of the adaptive immune response (Glassman et al., 2018, Science). This complex forms when a T-cell receptor (TCR) on a CD4+ helper T cell recognizes a specific antigenic peptide presented by a Major Histocompatibility Complex class II (MHC II) molecule on an antigen-presenting cell (UniProt P01730, P04440). The CD4 co-receptor stabilizes this interaction by binding to a conserved region of the MHC II molecule, which simultaneously recruits the Src family kinase Lck to the TCR complex to initiate intracellular signaling (PubMed: 29880686). This assembly is the primary trigger for T-cell activation, proliferation, and differentiation into various effector lineages (StatPearls: T-cell activation). Dysregulation of this complex is central to the pathogenesis of autoimmune diseases, where self-peptides are recognized, and in infectious diseases or cancer, where immune evasion may occur (NIH: Immune System Disorders). Therapeutic strategies targeting this complex include monoclonal antibodies that block CD4 or TCR components, such as Teplizumab or Ibalizumab, as well as MHC II-binding peptides like Glatiramer acetate designed to compete with pathogenic antigens (PubChem: Glatiramer). Understanding the structural dynamics of this complex is crucial for developing precise immunomodulators that can either suppress unwanted immune responses or enhance T-cell activity against tumors.

Other names

TCR-CD4-pMHCII complexCD4-TCR-MHCII complexAntigen-presenting complexT-cell receptor signaling complexMHC II-peptide-TCR-CD4 quaternary complex

Drugs targeting this complex typically act by blocking the physical interaction between the TCR and pMHCII, inhibiting the co-receptor function of CD4, or modulating the downstream signaling initiated by the CD3 subunits of the TCR complex.