Major histocompatibility complex class I molecule, Major histocompatibility complex class II molecule, and T-cell receptor (MHC class I, MHC class II, TCR)

Major histocompatibility complex class I and class II molecules (MHC class I, MHC class II) are cell surface glycoproteins essential for antigen presentation to T-cell receptors (TCRs), which mediate adaptive immunity. MHC class I molecules are expressed on all nucleated cells and present intracellular (endogenous) peptides to cytotoxic CD8+ T cells, facilitating recognition and elimination of infected or malignant cells[6][4][2]. MHC class II molecules are primarily expressed on antigen-presenting cells (dendritic cells, macrophages, B cells), present extracellular (exogenous) peptides, and activate CD4+ T helper cells, orchestrating broader immune responses[4][3][2]. The T-cell receptor is a multimeric cell surface receptor found on T lymphocytes; it binds to antigenic peptides displayed by MHC molecules, triggering T cell activation, proliferation, and effector function[2][3]. These complexes are central to immune surveillance, transplant compatibility, and the development of therapies for cancer, autoimmune diseases, and infection, but are also associated with risks such as autoimmunity and transplant rejection[6][7].

Other names

HLA class IHLA class IIHuman leukocyte antigen class I/IIT lymphocyte antigen receptor

Blockade or modulation of immune checkpoints controlling T-cell responses (e.g., anti-PD-1/PD-L1, anti-CTLA-4 inhibitors enhance T cell recognition and response to antigens presented by MHC molecules) Immunosuppression via inhibition of T cell activation (e.g., reduced TCR signaling) Enhancement of antigen presentation or immune activation (e.g., therapies increasing MHC expression)