Granulomatous Inflammation : Definition, Causes, Pathenogenesis, Diseases, Types, Morphology

Granulomatous Inflammation: Understanding Key Concepts

Overview of Granulomatous Inflammation

• Granulomatous inflammation is a specialized type of chronic inflammation that occurs when the body cannot eliminate an offending agent, such as in tuberculosis.

• While neutrophils are predominant in acute inflammation, macrophages play a crucial role in chronic inflammation.

Role and Activation of Macrophages

• Macrophages are key components of the mononuclear phagocyte system, which includes blood monocytes and tissue macrophages. Tissue macrophages originate from blood monocytes that migrate into tissues.

• The transformation from monocyte to macrophage is influenced by various chemicals like adhesion molecules and cytokines. Different tissues have specific names for macrophages (e.g., Kupffer cells in the liver).

• Activated macrophages perform two main functions: eliminating injurious agents through secretion of reactive oxygen species and initiating repair processes via growth factors.

Chronic Inflammation Characteristics

• Unlike acute inflammation where macrophages disappear post-injury, they accumulate during chronic inflammation due to continuous recruitment and local proliferation at the site. This accumulation can lead to tissue destruction due to their secretions.

Pathogenesis of Granulomatous Inflammation

• Granulomas form when macrophages become epithelioid cells, enhancing microbial killing ability against resistant agents. A granuloma consists mainly of these epithelioid cells surrounded by lymphocytes, with possible multinucleated giant cells present.

• Eosinophils may also be found in granulomas during parasitic infections; giant cells result from the fusion of multiple epithelioid cells.

Types of Granulomas

Foreign Body vs Immune Granulomas

• Foreign Body Granulomas: Occur when materials (like talc or sutures) cannot be engulfed by a single macrophage; no immune response is involved, allowing identification of foreign agents at the center.

• Immune Granulomas: Formed against poorly degradable agents; involve T lymphocytes that secrete cytokines activating more lymphocytes and enhancing macrophage activity through gamma interferon secretion.

Cell Types in Granulomatous Inflammation

Epithelioid Cells and Giant Cells

• Epithelioid cells arise from activated tissue macrophages; they exhibit increased synthetic activity but reduced phagocytic ability compared to regular macrophages while having enhanced secretory capabilities for microbial killing.

• Various types of giant cells include Langhans giant cells (peripheral nuclei resembling horseshoes), foreign body type giant cells (randomly arranged nuclei), and counting giant cells formed from foamy macrophages in fat necrotic tissues.

Morphological Patterns in Granulomas

Necrosis Types

• Caseating Necrosis: Characteristic center necrosis seen commonly in tuberculosis cases within granulomas.

• Non-necrotizing Granuloma: No central necrosis observed; associated with conditions like sarcoidosis.

• Suppurative Necrosis: Presence of neutrophils leading to purulent centers seen in cat-scratch disease or fungal infections, occasionally tuberculosis as well.

This concludes our overview on granulomatous inflammation, highlighting its mechanisms, cell types involved, and morphological patterns observed during this inflammatory response process.