Treys in cancer and autoimmunity Robbins based md pathology exam answer
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"Regulatory T Cells"[MeSH Terms] AND cancer
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Robbins pathology regulatory T cells cancer autoimmunity FOXP3 CTLA4 IL-10 TGF-beta
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"Regulatory T Cells"[MeSH Terms] AND autoimmunity
Regulatory T cells (Tregs) in cancer and autoimmunity
Definition: Tregs are a subset of CD4+ T lymphocytes that suppress immune responses and maintain self-tolerance. They are typically characterized by CD4+, CD25high, FOXP3+ phenotype.
Key molecular features and mechanisms
| Feature | Role |
|---|---|
| FOXP3 | Master transcription factor required for Treg development and suppressive function |
| CD25 | High-affinity IL-2 receptor alpha chain. Tregs consume IL-2, limiting IL-2 availability for activated effector T cells |
| CTLA-4 | Removes or blocks B7 costimulatory molecules on antigen-presenting cells, preventing CD28-mediated T-cell activation |
| IL-10 and TGF-beta | Immunosuppressive cytokines that inhibit activation and effector functions of T cells and other immune cells |
Robbins describes Tregs as CD4+ cells that inhibit lymphocyte activation following recognition of self or foreign antigen. Their function depends on FOXP3, CTLA-4, IL-2 signaling, and suppressive cytokines. Robbins & Kumar Basic Pathology, chapter on immune tolerance.
Role in autoimmunity
Normal role
Tregs prevent autoimmune disease by suppressing potentially self-reactive lymphocytes in peripheral tissues. Thus, they are a major mechanism of peripheral self-tolerance.
Failure of Tregs
Deficient number or function of Tregs permits activation of autoreactive T cells, leading to chronic inflammation and autoimmune disease.
Important examples
- FOXP3 mutation causes IPEX syndrome: immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome.
- Features include early-onset severe autoimmunity, enteropathy, type 1 diabetes, eczema, and endocrinopathies.
- Mutations affecting CTLA4, IL-2 receptor alpha chain (CD25), IL-10, or the IL-10 receptor can also impair immune regulation and predispose to autoimmunity.
Exam line:
Treg deficiency results in loss of peripheral tolerance and uncontrolled activation of self-reactive lymphocytes, causing autoimmunity.
Role in cancer
Tumor-promoting action
In cancer, Tregs are usually harmful to the host because they suppress antitumor immune responses. Tumors recruit and expand Tregs within the tumor microenvironment.
Tregs inhibit:
- Tumor-specific CD8+ cytotoxic T cells
- CD4+ helper T-cell responses
- NK-cell activity
- Antigen presentation and dendritic-cell activation
This enables tumor immune evasion, tumor persistence, and progression. A high density of tumor-infiltrating FOXP3+ Tregs is often associated with poor prognosis, although the association varies by tumor type.
Therapeutic relevance
Checkpoint inhibitors can improve antitumor immunity:
- Anti-CTLA-4 therapy reduces inhibitory signaling and can enhance T-cell activity.
- Anti-PD-1/PD-L1 therapy reverses inhibitory signaling affecting antitumor T cells.
However, removing these immune brakes may also break self-tolerance and produce immune-related autoimmune toxicities, such as colitis, dermatitis, hepatitis, thyroiditis, or hypophysitis.
Exam line:
In cancer, Tregs favor tumor growth by suppressing tumor-specific immune responses; in autoimmunity, Tregs are protective because they suppress self-reactive immune responses.
Cancer versus autoimmunity: high-yield comparison
| Situation | Treg activity | Outcome |
|---|---|---|
| Normal immune homeostasis | Balanced | Maintains self-tolerance while allowing protective immunity |
| Autoimmunity | Decreased or defective | Loss of tolerance and tissue damage by autoreactive lymphocytes |
| Cancer | Increased, especially in tumor microenvironment | Suppression of antitumor T-cell responses and immune escape |
| Checkpoint inhibitor treatment | Functional suppression is reduced | Better tumor killing but increased risk of autoimmunity |
One-paragraph MD pathology answer
Regulatory T cells are CD4+, CD25high, FOXP3+ lymphocytes that maintain peripheral tolerance by suppressing activation of other lymphocytes. They act through CTLA-4-mediated reduction of B7 costimulation on antigen-presenting cells, consumption of IL-2 through high CD25 expression, and secretion of IL-10 and TGF-beta. In autoimmunity, defective Treg development or function causes loss of self-tolerance; FOXP3 mutations cause IPEX syndrome, and defects in CTLA4, CD25, IL-10, or IL-10 receptor may also lead to autoimmunity. In cancer, accumulation of Tregs in the tumor microenvironment suppresses tumor-specific T-cell and NK-cell responses, facilitating immune evasion and tumor progression. Thus, Tregs protect against autoimmunity but can promote cancer by inhibiting antitumor immunity.
Recent reviews support the clinical relevance of tumor-associated Tregs, but their prognostic value differs across cancers, including NSCLC (PMID 39272135).
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