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Process by which immune cells display antigens to T cells

Antigen presentation is a crucial process in the immune system that involves the display of antigens on the surface of antigen-presenting cells (APCs) to be recognized by T cells. This process is essential for the activation of T cells and the initiation of the adaptive immune response.

Mechanism

Antigen presentation involves the processing of antigens and their presentation on major histocompatibility complex (MHC) molecules. There are two main pathways of antigen presentation: the MHC class I pathway and the MHC class II pathway.

MHC Class I Pathway

Diagram of MHC Class I antigen processing

The MHC class I pathway presents endogenous antigens, which are typically derived from proteins synthesized within the cell. These antigens are processed by the proteasome into peptide fragments. The peptides are then transported into the endoplasmic reticulum by the TAP complex, where they bind to MHC class I molecules. The peptide-MHC class I complexes are transported to the cell surface, where they can be recognized by CD8+ T cells.

MHC Class II Pathway

Diagram of MHC Class II antigen processing

The MHC class II pathway presents exogenous antigens, which are typically derived from extracellular proteins. These antigens are taken up by APCs through endocytosis or phagocytosis and are processed in endosomes and lysosomes. The resulting peptides are loaded onto MHC class II molecules within the endosomal compartments. The peptide-MHC class II complexes are then transported to the cell surface, where they can be recognized by CD4+ T cells.

Antigen-Presenting Cells

The primary antigen-presenting cells are dendritic cells, macrophages, and B cells. Each of these cell types has specialized functions in antigen presentation and T cell activation.

• Dendritic cells are the most potent APCs and are essential for the initiation of T cell responses. They capture antigens in peripheral tissues and migrate to lymph nodes to present antigens to T cells.
• Macrophages are involved in the presentation of antigens to T cells in tissues and are important for the activation of helper T cells.
• B cells can present antigens to T cells, particularly in the context of humoral immunity.

Role in Immune Response

Antigen presentation is critical for the activation of T cells, which are central to the adaptive immune response. The recognition of peptide-MHC complexes by T cell receptors (TCRs) leads to T cell activation, proliferation, and differentiation into effector cells. This process is essential for the clearance of pathogens and the development of immunological memory.

Related pages

• Major histocompatibility complex
• T cell receptor
• Adaptive immune system
• Dendritic cell

Gallery

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  Diagram of antigen presentation
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  Diagram of MHC Class I antigen processing
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  Diagram of MHC Class II antigen processing

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