Inflammation Overview and Types

Inflammation Overview

• Inflammation is a local vascular and cellular response of living tissue to an injurious agent.
• Aims of inflammation include fighting bacteria, localizing infection, and removing damaged tissue.
• Causes of inflammation include allergic reactions, chemical irritants, infections, trauma, injury, burns, lacerations, cuts, wounds, frostbite, and various diseases (e.g., cardiovascular disease, neurological disease, autoimmune diseases, cancer, lupus, and fibromyalgia).
• Types of inflammation include acute and chronic inflammation.

Acute Inflammation

• Onset is fast, typically within minutes to hours.
• Cellular infiltrate is primarily neutrophils.
• Tissue injury and fibrosis are usually mild and self-limited.
• Local and systemic signs are prominent.

Chronic Inflammation

• Onset is slow, often over days.
• Cellular infiltrate includes monocytes, macrophages, and lymphocytes.
• Tissue injury and fibrosis are often severe and progressive.
• Local and systemic signs are less prominent.

Cells in Acute and Chronic Inflammation

• Acute: neutrophils (phagocytosis, pus cells)
• Chronic: lymphocytes (chronic), plasma (chronic), histiocytes (chronic phagocytosis, monocytes), eosinophils (allergy, parasitic), mast cells (allergy - histamine, serotonin), and giant cells (phagocytosis, histiocytes).

Local Signs of Inflammation

• Heat
• Redness
• Swelling
• Pain
• Loss of function

Systemic Effects of Inflammation

• Fever
• Leukocytosis
• Malaise
• Nausea
• Anorexia
• Lymphoid hyperplasia
• CRP and ESR raised

Main Events of Inflammation

• Vascular response
• Inflammatory fluid exudate
• Inflammatory cellular exudate

Vascular Response

• Changes in vascular flow and caliber: vasodilation (histamine), stasis (increased viscosity, swollen ends, open capillaries).
• Increased permeability: histamine, kinins, endothelial "gaps", direct endothelial injury.

Inflammatory Fluid Exudate

• Formation: increased vascular dilation and permeability, interstitial osmotic pressure, and reduced hydrostatic pressure.
• Function: diluting toxins, bringing antibodies, supplying nutrition, supplying fibrinogen (for localization and movement of inflammatory cells and fibroblasts).

Composition of Exudate

• Appearance: turbid (like pus)
• Consistency: viscous
• Protein content: high (4-8 gm)
• Specific gravity: high (above 1018)
• Cell content: numerous neutrophils
• On standing: clots

Cellular Exudate

• Extravasation of neutrophils (Margination, Rolling, Adhesion, Transmigration - Diapedesis)
• Chemotaxis (directed movement of neutrophils and macrophages to the inflamed area)
• Activation of leukocytes: produce eicosanoids, undergo degranulation, secrete cytokines
• Phagocytosis (ingestion and destruction of bacteria, necrotic debris, and foreign particles)

Opsonization and Phagocytosis (Cellular Responses)

• Recognition (Opsonins - Immunoglobulins, complement)
• Engulfment
• Killing (oxidative and non-oxidative)

Chemical Mediators

• Cellular: histamine, serotonin, eicosanoids, nitric oxide, platelet activating factor (PAF)
• Plasma: complement, kinins, clotting factors, fibrinolytic

Outcomes of Acute Inflammation

• Resolution
• Regression & Healing
• Progression & spread
• Progression & Chronicity

Summary of Sequence of Events

• Vasodilation → Increased vascular permeability → Leakage of exudate, stasis → Extravasation, margination, rolling, adhesion, transmigration (diapedesis) → Chemotaxis → PMN activation → Phagocytosis: recognition, attachment, engulfment, killing → Termination → 100% resolution, scar, or chronic inflammation

Types of Acute Inflammation

• Suppurative
  • Localized: Abscess, Furuncle, Carbuncle
  • Diffuse: Cellulitis
• Non-Suppurative

Types of Acute Non-Suppurative Inflammation

• Catarrhal
• Serous
• Fibrinous
• Membranous
• Hemorrhagic
• Necrotizing
• Serofibrinous (various infections)

Chronic Inflammation

• Causes: persistence of infection, prolonged exposure to insult
• Types: non-specific, specific (granuloma)

Granulomas

• Definition: chronic, specific inflammation with nodular collection of epithelioid cells, lymphocytes, and giant cells
• Etiology:
  • Infective (bacteria, parasites, fungi)
  • Non-infective (selososis, foreign bodies)
  • Unknown (Crohn's, sarcoidosis)
• Components: histiocytes, epithelioid cells, giant cells (Langhans), lymphocytes, fibroblasts
• Classification: with or without caseation, suppurative, foreign body