Chemical Mediators in Inflammation

Chemical Mediators in Inflammation

• Chemical mediators are substances that initiate and regulate the inflammatory response.
• Histamine is found in granules of platelets, basophils, and mast cells. It causes vasodilation (widening of blood vessels) and increased permeability of capillaries, a key early step in inflammation.

Prostaglandins

• Prostaglandins are lipid-soluble molecules derived from arachidonic acid. They are found in various foods like poultry, meat, fish, and eggs.
• They contribute to vasodilation, increased capillary permeability, pain, and fever.
• Aspirin inhibits prostaglandin production, reducing inflammation.
• Glucocorticoids decrease arachidonic acid availability, also reducing prostaglandin production.

Plasma Proteins

• Plasma proteins include kinins, activated complement proteins, and clotting factors.
• Bradykinin dilates blood vessels, increases capillary permeability, and causes pain.
• The complement system is a group of proteins that work together in the inflammatory response, including killing microorganisms directly.

Clotting System

• The clotting system forms a fibrinous meshwork at the inflamed site.
• This traps exudates, microorganisms, and foreign bodies.
• This prevents the spread of infection and inflammation to adjacent tissues, and keeps microorganisms close to phagocytes.
• It forms a clot, stopping bleeding and providing structure for future repair.

Leukotrienes

• Leukotrienes are produced from arachidonic acid in leukocytes and mast cells.
• They promote leukocyte margination and chemotaxis (movement of cells).
• Some leukotrienes cause vasodilation.

Platelet-Activating Factor

• Platelet-activating factor induces platelet aggregation (sticking together) during clotting.
• It activates neutrophils and provides chemotactic signals to eosinophils.

Cytokines

• Cytokines are produced by numerous cells like lymphocytes, macrophages, and others.
• Interleukins (some are pyrogens) are a type of cytokine.
• Interferons interfere with viruses infecting nearby cells, and other cytokines have related functions.

Acute Inflammation

• Acute inflammation has a rapid onset with minimal damage and rapid resolution.
• Exudates, of diverse types, are formed.
• Serous exudate: watery, low protein.
• Hemorrhagic exudate: bloody, high protein, due to leakage of red blood cells.
• Fibrinous exudate: thick, sticky, meshwork from fibrinogen.
• Purulent exudate: pus, degraded white blood cells, proteins, and cellular debris.

Chronic Inflammation

• Chronic inflammation may last for weeks, months, or years.
• It may arise from recurrent acute inflammation or low-grade responses.
• Macrophages and lymphocytes replace neutrophils.
• Fibroblast proliferation causes scarring and tissue distortion.
• Chronic inflammation can result from exposure to various substances such as talc, asbestos, silica, surgical sutures and microorganisms.
• Nonspecific and Granulomatous are two types of chronic inflammation.

Chronic Inflammation: Granulomatous Lesion

• A granuloma is a small (1-2mm) lesion.
• Macrophage infiltration, surrounded by lymphocytes, is a hallmark feature.
• Granulomas result from contact with substances like sutures, splinters, silica, asbestos, and microorganisms causing tuberculosis or syphilis.
• These substances are hard to digest.
• The immune response forms a mass of macrophages (epithelioid cells) around the foreign material, encapsulated by connective tissue.
• A tubercle is a granuloma associated with Mycobacterium tuberculosis infection.