Acute vs Chronic Inflammation

Overview

• Acute Inflammation: Short-term and often rapidly resolves.

  • Predominantly involves neutrophils.
  • Characterized by vascular changes, neutrophil recruitment, and vasodilation.
  • Leads to symptoms like heat, redness, swelling, pain, and loss of function.

• Chronic Inflammation: Long-term and persistent.

  • Mainly involves macrophages.
  • Features include angiogenesis, mononuclear cell infiltration, and fibrosis.
  • Can lead to tissue scarring and loss of function.

Key Differences

Acute Inflammation

• Cells Involved: Neutrophils are the primary responders.
• Process:
  • Neutrophil recruitment and extravasation.
  • Vascular changes, including vasodilation.
  • Eventual resolution with clearance of injurious stimuli and restoration of normal function.
• Symptoms: Heat, redness, swelling, pain, and potential loss of function.
• Mechanism:
  • Platelet aggregation leads to clot formation.
  • Neutrophils secrete molecules to recruit more immune cells.
  • Respiratory burst generates reactive oxygen species (ROS) to kill pathogens.

Chronic Inflammation

• Cells Involved: Macrophages and plasma cells are central.
• Features:
  • Angiogenesis and mononuclear cell infiltration.
  • Scar formation and potential loss of function.
• Examples:
  • Persistent infections like tuberculosis (granulomatous inflammation) and prolonged H. pylori infections.
  • Autoimmune diseases like rheumatoid arthritis.
  • Chronic exposure to irritants like silica.
• Macrophage Role:
  • Origin from bone marrow, developing into macrophages in the tissue.
  • M1 macrophages: Pro-inflammatory, involved in engulfing pathogens and secreting pro-inflammatory cytokines.
  • M2 macrophages: Anti-inflammatory, involved in tissue repair and fibrosis.
  • Activation pathways: Classical for M1, alternative for M2.
• Cytokine and Immune Response:
  • M1 macrophages activate T cells, promoting Th1 and Th17 subtypes.
  • Th1 cells secrete interferon gamma, reinforcing M1 macrophage differentiation.
  • Plasma cells produce antibodies.
  • Neutrophils and eosinophils have minor roles compared to macrophages.

Conclusion

• Chronic inflammation can result in detrimental outcomes like tissue scarring and neoplastic transformation, e.g., untreated H. pylori leading to gastric adenocarcinoma.
• Understanding the differences and processes in acute vs chronic inflammation is crucial, especially for medical exams like USMLE Step 1.