Target type: biologicalprocess
Any process that modulates the frequency, rate or extent of CD4-positive, alpha-beta T cell activation. [GOC:obol]
CD4-positive, alpha-beta T cell activation is a tightly regulated process that ensures an appropriate immune response to foreign antigens while preventing autoimmunity. The activation of these cells, also known as helper T cells, involves a complex interplay of signaling pathways, receptor interactions, and intracellular processes.
1. **Antigen Recognition and TCR Engagement:** The process begins with the recognition of a specific antigen presented by an antigen-presenting cell (APC), such as a dendritic cell or macrophage. The antigen is presented in the context of MHC class II molecules on the APC surface. The T cell receptor (TCR) on the CD4+ T cell, which consists of alpha and beta chains, interacts with the antigen-MHC complex, initiating the activation cascade.
2. **Co-stimulatory Signals:** TCR engagement alone is insufficient to activate a T cell. Co-stimulatory signals, such as those provided by CD28 on the T cell binding to CD80/CD86 (B7-1/B7-2) on the APC, are crucial for full activation. This signal ensures that the T cell response is specific and appropriate, preventing unwanted activation by self-antigens.
3. **Signal Transduction Pathways:** Upon TCR and co-stimulatory receptor engagement, intracellular signaling pathways are activated. Key pathways include:
- **The MAPK pathway:** Activated by the TCR complex, this pathway leads to the production of transcription factors like AP-1, which ultimately contribute to gene expression changes required for T cell activation.
- **The PI3K/AKT pathway:** Co-stimulatory signals activate this pathway, leading to the survival and proliferation of activated T cells.
- **The NF-κB pathway:** This pathway is crucial for the production of pro-inflammatory cytokines like TNF-α and IL-2.
4. **Cytokine Production:** Activated T cells release a variety of cytokines, including IL-2, IFN-γ, and TNF-α, that mediate different aspects of the immune response.
- **IL-2** is an important autocrine growth factor, promoting the proliferation and survival of activated T cells.
- **IFN-γ** has anti-viral and pro-inflammatory effects, contributing to the activation of other immune cells.
- **TNF-α** is a pro-inflammatory cytokine involved in inflammation and cell death.
5. **Differentiation and Effector Functions:** Activated CD4+ T cells differentiate into distinct subsets with specialized functions:
- **Th1 cells:** Primarily secrete IFN-γ and are involved in cell-mediated immunity, combating intracellular pathogens like viruses and bacteria.
- **Th2 cells:** Produce IL-4, IL-5, and IL-13, involved in humoral immunity, driving antibody production by B cells, and fighting extracellular parasites.
- **Th17 cells:** Secrete IL-17 and other cytokines, playing a role in inflammation and defense against extracellular bacteria and fungi.
- **Treg cells:** Act as suppressors of immune responses, preventing autoimmunity and maintaining immune homeostasis.
6. **Negative Regulation and Anergy:** Several mechanisms ensure that T cell activation is controlled and prevents excessive or inappropriate immune responses:
- **CTLA-4:** A negative regulator that binds to CD80/CD86 on APCs, preventing co-stimulation and suppressing T cell activation.
- **PD-1:** Another negative regulator that interacts with PD-L1 and PD-L2 on APCs, leading to T cell exhaustion and termination of immune responses.
- **Anergy:** A state of unresponsiveness induced by TCR engagement in the absence of co-stimulation, preventing activation by self-antigens.
The regulation of CD4+ T cell activation is a complex and finely tuned process, essential for maintaining immune homeostasis and providing appropriate responses to pathogens while preventing autoimmunity.'
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Protein | Definition | Taxonomy |
---|---|---|
Advanced glycosylation end product-specific receptor | An advanced glycosylation end product-specific receptor that is encoded in the genome of human. [PRO:DNx, UniProtKB:Q15109] | Homo sapiens (human) |
Compound | Definition | Classes | Roles |
---|---|---|---|
quinolinic acid | pyridinedicarboxylic acid : Any member of the class of pyridines carrying two carboxy groups. quinolinic acid : A pyridinedicarboxylic acid that is pyridine substituted by carboxy groups at positions 2 and 3. It is a metabolite of tryptophan. Quinolinic Acid: A metabolite of tryptophan with a possible role in neurodegenerative disorders. Elevated CSF levels of quinolinic acid are correlated with the severity of neuropsychological deficits in patients who have AIDS. | pyridinedicarboxylic acid | Escherichia coli metabolite; human metabolite; mouse metabolite; NMDA receptor agonist |
matrine | alkaloid | ||
vilazodone | vilazodone : A 1-benzofuran that is 5-(piperazin-1-yl}-1-benzofuran-2-carboxamide having a (5-cyanoindol-3-yl)butyl group attached at position N-4 on the piperazine ring. Used for the treatment of major depressive disorder. | 1-benzofurans; indoles; monocarboxylic acid amide; N-alkylpiperazine; N-arylpiperazine; nitrile | antidepressant; serotonergic agonist; serotonin uptake inhibitor |
fps-zm1 | FPS-ZM1: a neuroprotective agent and RAGE receptor antagonist; structure in first source | ||
n(delta)-(5-methyl-4-oxo-2-imidazolin-2-yl)ornithine | N(delta)-(5-methyl-4-oxo-2-imidazolin-2-yl)ornithine: RN given for (L)-isomer; structure in first source |