T cell activation via T cell receptor contact with antigen bound to MHC molecule on antigen presenting cell

Definition

Target type: biologicalprocess

The change in morphology and behavior of a mature or immature T cell resulting from exposure to an antigen for which its T cell receptor is specific bound to an MHC molecule on an antigen presenting cell, leading to the initiation or perpetuation of an immune response. [GOC:add, ISBN:0781735149]

T cell activation is a complex process that initiates an immune response upon encountering an antigen. The process begins when a T cell receptor (TCR) on the surface of a T cell recognizes and binds to an antigen presented by an MHC molecule on an antigen-presenting cell (APC). This interaction is highly specific, ensuring that T cells only respond to relevant threats.

The TCR is a heterodimer composed of alpha and beta chains, each containing variable regions that determine antigen specificity. The MHC molecule is a transmembrane protein that presents peptide fragments of antigens to T cells. There are two main classes of MHC molecules: MHC class I presents peptides derived from intracellular proteins, while MHC class II presents peptides derived from extracellular proteins.

Upon TCR binding to an antigen-MHC complex, the TCR initiates a signaling cascade that leads to T cell activation. This cascade involves a series of intracellular events, including phosphorylation of signaling molecules, activation of transcription factors, and gene expression changes.

Several co-receptors contribute to T cell activation. CD4+ T cells recognize antigens presented by MHC class II molecules, while CD8+ T cells recognize antigens presented by MHC class I molecules. These co-receptors amplify the TCR signal and contribute to T cell differentiation into specific effector cells.

Following activation, T cells undergo a process called clonal expansion, where they proliferate and differentiate into effector T cells. These effector cells are specialized to eliminate the antigen.

The overall process of T cell activation can be summarized as follows:

1. **Antigen presentation:** An APC captures an antigen, processes it, and presents it on its surface in association with an MHC molecule.
2. **TCR recognition:** A T cell with a TCR specific for the presented antigen recognizes and binds to the antigen-MHC complex.
3. **Signal transduction:** The TCR-mediated recognition triggers a signaling cascade within the T cell, leading to activation.
4. **T cell activation:** Activation results in clonal expansion and differentiation of T cells into effector T cells.
5. **Effector function:** Effector T cells eliminate the antigen and mediate immune responses.

This complex process ensures that T cells specifically target relevant antigens while avoiding autoimmune responses.'
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Proteins (2)

Compounds (17)