Inflammatory Response

Overview

• Non-specific defense mechanism against tissue damage.
• Initiated by injured tissue cells releasing chemical signals.

Activation of Endothelial Cells

• Chemical signals activate endothelial cells of nearby capillaries.
• Selectins (adhesion molecules) displayed on activated endothelial cells.

Role of Neutrophils

• Selectins attract neutrophils, slow them down, and cause rolling along endothelium.
• Neutrophils encounter chemicals activating integrins (adhesion receptors).
  • Integrins tightly attach to adhesion receptor molecules on endothelial cells.
• Neutrophils stick to endothelium and stop rolling, known as margination.

Inflammatory Mediators

• Released by injured tissue, induce mast cell degranulation.
• Histamine release leads to:
  • Vasodilation.
  • Opening of junctions between endothelial cells.
  • Allows fluid and leukocytes to leave capillary into infected tissue.

Extravasation Process

• Neutrophils change shape and pass through endothelial wall into interstitial tissue fluid (extravasation).

Chemotaxis and Phagocytosis

• Neutrophils (followed by other phagocytes) attracted to damage site by chemotactic substances.
• Ingestion and destruction of invading bacteria by phagocytes.