Major histocompatibility complex class II–peptide complex (pMHCII)

The Major Histocompatibility Complex class II (MHC II)–peptide complex is a fundamental molecular assembly essential for the initiation and regulation of the adaptive immune response [1]. Expressed primarily on professional antigen-presenting cells like dendritic cells, MHC II molecules present exogenous peptide fragments to the T-cell receptors (TCRs) of CD4+ helper T cells [1, 5]. This interaction, often referred to as the "first signal" of T-cell activation, determines the specificity of the immune response against pathogens or tumors [1]. In autoimmune diseases, MHC II complexes may inappropriately present self-antigens, leading to tissue destruction, while in cancer, their downregulation can facilitate immune evasion [2, 3]. Therapeutic strategies targeting this complex include peptide analogs that compete for MHC binding, such as glatiramer acetate, and TCR-like antibodies that specifically recognize disease-associated peptide-MHC combinations [2, 4]. Additionally, checkpoint molecules like LAG-3 interact with MHC II to modulate T-cell exhaustion, making this complex a pivotal node for immunomodulatory drug development [3].

Other names

HLA class II–peptide complexMHC II–antigen complexpMHCII complexMHCII-peptide interactionHLA-DR/DQ/DP-peptide complex

Competitive inhibition of peptide binding to the MHC II groove, blockade of MHC II interaction with the LAG-3 inhibitory receptor, or modulation of the TCR-MHC II immunological synapse to induce tolerance or activation.