T cell activation

Definition

Target type: biologicalprocess

The change in morphology and behavior of a mature or immature T cell resulting from exposure to a mitogen, cytokine, chemokine, cellular ligand, or an antigen for which it is specific. [GOC:mgi_curators, ISBN:0781735149]

T cell activation is a complex and tightly regulated process that involves a series of steps leading to the differentiation and proliferation of T cells in response to specific antigens. It is a crucial element of adaptive immunity, enabling the immune system to target and eliminate pathogens and aberrant cells.

1. **Antigen Recognition:** T cell activation begins with the recognition of antigen presented by antigen-presenting cells (APCs), such as dendritic cells, macrophages, or B cells. APCs capture antigens, process them, and display them on their surface in the context of major histocompatibility complex (MHC) molecules.

2. **MHC-Antigen Complex Interaction:** T cell receptors (TCRs) on the surface of T cells specifically recognize and bind to the MHC-antigen complex. This interaction initiates a cascade of signaling events.

3. **Costimulatory Signals:** In addition to antigen recognition, T cell activation requires costimulatory signals delivered by APCs. These signals, provided by molecules like CD80/CD86 on APCs and CD28 on T cells, ensure that T cells are activated only in the presence of a genuine threat, preventing inappropriate activation.

4. **Signal Transduction:** Upon TCR and costimulatory signal engagement, a complex intracellular signaling cascade is triggered. Key signaling molecules include kinases (like Lck and ZAP-70), adaptor proteins (like LAT and SLP-76), and second messengers (like calcium and diacylglycerol). These signaling pathways lead to the activation of transcription factors, such as NF-κB, NFAT, and AP-1.

5. **Transcriptional Activation:** Activated transcription factors translocate to the nucleus and initiate the transcription of genes essential for T cell activation and differentiation. These genes encode for cytokines, chemokines, growth factors, and other proteins that promote T cell proliferation, differentiation, and effector function.

6. **T Cell Differentiation:** Activated T cells undergo differentiation into effector T cells, specialized for different functions. Helper T cells (Th cells) secrete cytokines that help activate other immune cells, while cytotoxic T cells (CTLs) directly kill infected or cancerous cells.

7. **Effector Function:** Effector T cells carry out their specific functions, contributing to the elimination of pathogens or aberrant cells. Th cells help activate B cells to produce antibodies, while CTLs directly kill infected or cancerous cells via the release of cytotoxic molecules.

8. **Memory Cell Formation:** After an infection is cleared, a subset of activated T cells differentiate into memory T cells. Memory T cells persist in the body, providing long-term immunity to specific pathogens. They can rapidly respond to a subsequent infection with the same antigen, allowing for a faster and more effective immune response.

The process of T cell activation is tightly regulated to ensure appropriate immune responses and prevent autoimmunity. Dysregulation of T cell activation can contribute to various diseases, including autoimmune disorders and cancer.'
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Proteins (18)

Compounds (357)