Summary of Mechanism of Diseases: Chronic Inflammation

Acute Inflammation

  • Rapid tissue response to injury.

  • Macroscopic Signs: Redness, swelling, heat, pain, loss of function.

  • Microscopic Changes: Vascular dilation, exudate leakage, neutrophil emigration.

  • Controlled by short-lived chemical mediators; some drug-manipulable.

  • Neutrophils act as fast, short-lived phagocytes, engulfing bacteria and dead tissue.

  • Phagocytosis enhanced by opsonization (e.g., antibodies).

  • Oxygen-dependent bacterial killing; defects increase infection susceptibility.

Chronic Inflammation

  • Prolonged response (weeks/months) with inflammation, tissue injury, and repair attempts.

  • Can arise from:

    1. Transition from acute inflammation.

    2. De novo (autoimmune conditions; chronic infections).

    3. Coexisting with acute inflammation.

  • Effects: Fibrosis, impaired function, atrophy, immune response stimulation.

Causes

  1. Persistent infections (e.g., mycobacteria).

  2. Hypersensitivity diseases (e.g., rheumatoid arthritis).

  3. Prolonged exposure to toxic agents (exogenous or endogenous).

Morphological Features

  • Infiltration with mononuclear cells (macrophages, lymphocytes).

  • Tissue destruction and healing attempts (angiogenesis, fibrosis).

Cells and Mediators

  • Macrophages: Dominant in chronic inflammation; secrete cytokines, destroy pathogens.

    • Two activation pathways: Classical (M1, microbicidal) and Alternative (M2, repair).

  • Lymphocytes: Amplify chronic inflammation; three subsets (TH1, TH2, TH17).

  • Eosinophils: Involved in allergic and parasitic reactions.

  • Mast Cells: Release mediators in allergic reactions.

  • Neutrophils: Persist in chronic inflammation (e.g., osteomyelitis).

Granulomatous Inflammation

  • Characterized by activated macrophages; forms in response to persistent agents.

  • Types:

    • Immune granulomas (persistent microbes).

    • Foreign body granulomas (inert materials).

Clinical Examples

  • Chronic cholecystitis, gastric ulceration, inflammatory bowel disease, liver cirrhosis, thyrotoxicosis, rheumatoid arthritis.

Systemic Effects

  • Fever, acute-phase proteins (e.g., CRP), leukocytosis, and other systemic responses.