alpha-beta T cell proliferation

Definition

Target type: biologicalprocess

The expansion of an alpha-beta T cell population by cell division. [GOC:ai]

Alpha-beta T cell proliferation is a complex process that involves the activation, clonal expansion, and differentiation of T cells in response to antigen presentation. It is a critical component of adaptive immunity, allowing the immune system to specifically target and eliminate pathogens. Here is a detailed description of the process:

1. **Antigen Presentation:** T cell activation begins with the presentation of antigen by antigen-presenting cells (APCs), such as dendritic cells, macrophages, and B cells. APCs capture and process antigens, displaying peptide fragments on their surface bound to major histocompatibility complex (MHC) molecules.

2. **T Cell Receptor (TCR) Engagement:** T cells express TCRs on their surface, which recognize specific antigen-MHC complexes. When a TCR on a naïve T cell encounters its cognate antigen-MHC complex on an APC, it initiates a signaling cascade.

3. **Signal 1: TCR-MHC Interaction:** The TCR-MHC interaction triggers the activation of intracellular signaling pathways, including the MAPK and PI3K pathways. These pathways lead to the phosphorylation and activation of transcription factors, such as NF-κB, AP-1, and NFAT.

4. **Signal 2: Costimulatory Signals:** In addition to TCR engagement, T cells require costimulatory signals from APCs to become fully activated. These signals are provided by molecules such as CD80 and CD86 on APCs, which interact with CD28 on T cells. Costimulation is essential for preventing T cell anergy and promoting full activation.

5. **T Cell Activation and Clonal Expansion:** Upon receiving both signal 1 and signal 2, T cells become activated. Activated T cells undergo clonal expansion, proliferating rapidly to generate a large population of antigen-specific T cells.

6. **Differentiation into Effector Cells:** During clonal expansion, activated T cells differentiate into effector cells, specialized to perform specific immune functions. CD4+ T cells differentiate into helper T cells (Th), which secrete cytokines that activate other immune cells. CD8+ T cells differentiate into cytotoxic T lymphocytes (CTLs), which directly kill infected or cancerous cells.

7. **Effector Function:** Effector T cells migrate to sites of infection or inflammation, where they perform their specific functions. Th cells secrete cytokines that recruit and activate macrophages, neutrophils, and other immune cells. CTLs release cytotoxic granules containing perforin and granzyme, which induce apoptosis in target cells.

8. **Memory T Cell Formation:** Following the clearance of an infection, a subset of activated T cells differentiate into memory T cells. These cells are long-lived and can quickly respond to re-exposure to the same antigen, providing long-lasting immunity.

9. **T Cell Homeostasis:** After an immune response, T cell numbers decline through apoptosis, resulting in a return to a state of homeostasis. Memory T cells, however, are maintained to provide long-term immunity.

10. **Regulation of T Cell Proliferation:** Tight regulation of T cell proliferation is essential for preventing excessive immune responses and autoimmune disease. Regulatory T cells (Tregs) play a crucial role in suppressing T cell activation and proliferation, maintaining immune tolerance.'
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