Chronic Inflammation

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Intro & Causes - The Slow Burn

  • Inflammation of prolonged duration (weeks to months).
  • Characterized by co-existing:
    • Active inflammation
    • Tissue destruction
    • Repair attempts (angiogenesis, fibrosis)
  • Onset:
    • May follow unresolved acute inflammation.
    • May begin insidiously (de novo).
  • Principal Causes:
    • Persistent infections (e.g., Mycobacterium tuberculosis, Treponema pallidum, fungi, viruses).
    • Hypersensitivity diseases (e.g., autoimmune: RA, IBD; allergic: asthma).
    • Prolonged exposure to toxic agents (exogenous: silica; endogenous: cholesterol). Acute vs Chronic Inflammation Comparison

⭐ Infiltration with mononuclear cells (macrophages, lymphocytes, plasma cells) is a hallmark of chronic inflammation.

Cellular Players - The Chronic Crew

Persistent inflammation is orchestrated by a specialized cellular cast (📌 MLP-EM: Macrophages, Lymphocytes, Plasma cells, Eosinophils, Mast cells). These cells interact, releasing mediators sustaining the response and influencing tissue injury/repair.

CellOrigin/Key FeaturesKey Functions in Chronic Inflammation
MacrophagesMonocytes; M1 (classical), M2 (alternative)Phagocytosis, Ag presentation, cytokines (TNF, IL-1, IL-6), growth factors
LymphocytesT-cells (CD4+, CD8+), B-cellsBidirectional macrophage activation (IFN-γ, IL-12); adaptive immunity
Plasma CellsDifferentiated B-lymphocytesProduce antibodies against persistent antigens/autoantigens
EosinophilsGranulocytes; recruited by eotaxinHelminth defense; IgE-mediated allergic reactions (MBP release)
Mast CellsTissue-resident; surface IgE receptorsRelease histamine, leukotrienes, proteases, cytokines; modulate inflammation

⭐ Epithelioid cells in granulomas are activated macrophages with abundant pink cytoplasm, resembling epithelial cells, key for granulomatous inflammation.

Mediators & Mechanisms - Fueling the Fire

  • Key Mediators:
    • Cytokines: Pro-inflam: TNF, IL-1, IL-6; IFN-γ (T-cell driven macrophage activation); IL-10 (anti-inflam), TGF-β (fibrosis).
    • Chemokines: Attract specific leukocytes (e.g., MCP-1).
    • Growth Factors: PDGF, FGF, TGF-β stimulate angiogenesis & fibrosis.
  • Mechanisms:
    • Persistent stimuli (microbes, irritants).
    • Macrophage-Lymphocyte interactions: Bidirectional activation.
    • Concurrent tissue injury & attempted repair (fibrosis). Mediators and resolution of inflammation

⭐ IFN-γ, produced by NK cells and T lymphocytes (Th1, CD8+), is the most potent endogenous macrophage-activating cytokine.

Granulomatous Inflammation - Walling Off Trouble

  • Hallmark: Aggregates of activated macrophages (epithelioid cells), often with a collar of lymphocytes; may fuse to form multinucleated giant cells (e.g., Langhans, foreign body type).
  • Purpose: To contain or "wall off" an offending agent that is difficult to eradicate.

Granuloma with Langhans giant cell

TypeMechanismKey MediatorsExamples
ImmunePersistent T-cell (Th1) response to antigen (Ag)IFN-γ (activates Mφ)Tuberculosis (caseating), Sarcoidosis (non-caseating), Leprosy, Fungal inf., Crohn's d.
Foreign BodyInert material; direct Mφ activation-Sutures, talc, silica, asbestos, beryllium (can also be immune-mediated)

Systemic Effects & Outcomes - The Body's Burden

  • Fever: Persistent low-grade; IL-1, TNF mediated.
  • Acute Phase Response:
    • Liver: ↑CRP, SAA, Fibrinogen (IL-6 driven).
    • Results in ↑ESR.
  • Leukocytosis: ↑WBC count; pattern indicates etiology (e.g., neutrophilia, lymphocytosis).
  • Anemia of Chronic Disease (ACD):
    • IL-6 → ↑Hepcidin → ↓iron absorption & release.
  • Cachexia: TNF-α (cachectin) causes muscle/fat loss.
  • Secondary (AA) Amyloidosis: Chronic inflammation → ↑SAA → organ deposition.

⭐ ACD: Characterized by ↓ serum iron, ↓ TIBC, and normal/↑ ferritin.

High‑Yield Points - ⚡ Biggest Takeaways

  • Chronic inflammation is characterized by prolonged duration and co-existing active inflammation, tissue injury, and healing attempts.
  • Key cellular players are macrophages, lymphocytes (T and B cells), and plasma cells.
  • Tissue destruction is often mediated by inflammatory cells and their products.
  • Repair involves angiogenesis and fibrosis (scarring).
  • Granulomatous inflammation (e.g., TB, sarcoidosis) features epithelioid macrophages and giant cells.
  • Mediators include cytokines (e.g., TNF, IL-1, IFN-γ) and growth factors.
  • Potential long-term sequelae include loss of function, fibrosis, and neoplastic transformation (e.g., chronic gastritis and cancer).

Practice Questions: Chronic Inflammation

Test your understanding with these related questions

The characteristic cell of a granulomatous reaction is:

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Flashcards: Chronic Inflammation

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Acute inflammation arises in response to _____ or tissue necrosis

TAP TO REVEAL ANSWER

Acute inflammation arises in response to _____ or tissue necrosis

infection

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