Chronic Inflammation and Granulomatous Inflammation Flashcards
Discuss three characteristics of chronic inflammation.
(1) Infiltration with mononuclear cells: This includes macrophages, lymphocytes and plasma cells.
(2) Tissue destruction: this is largely induced by the products of the inflammatory cells. The persistent presence of these cells and their secreted substances can lead to ongoing tissue damage.
(3) Repair: This involves new vessel proliferation (angiogenesis) and fibrosis. Fibrosis involves the formation of scar tissue to replace damaged tissue.
State three causes of chronic inflammation.
(1) Persistent infections by microbes that are difficult to eradicate e.g. mycobacteria, treponema pallidum, and certain viruses and fungi, which tend to establish persistent infections and elicit a T lymphocyte-mediated immune response called delayed-type hypersensitivity.
(2) Immune-mediated inflammatory diseases (hypersensitivity diseases)
(3) Prolonged exposure to potentially toxic agents. Examples include non-degradable exogneous materials such as inhaled particulate silica.
What happens to monocytes when they reach the extravascular tissue during acute inflammation?
Monocytes transform into larger macrophages, which have longer half-lives and a greater capacity for phagocytosis than blood monocytes.
Macrophages may become activated in extravascular tissue. What are characteristics of activated macrophages?
increased cell size, higher content of lysosomal enzymes, more active metabolism, greater microbicidal activity
Briefly outline macrophage activation signals.
◾ microbial products e.g. bacterial endotoxins
◾ cytokines e.g. IFN-γ
◾ inflammatory mediators e.g. prostaglandins, leukotrienes
◾ extracellular matrix proteins e.g. fibronectin
Briefly discuss the formation of giant cells.
Under the influence of IFN-γ, macrophages can fuse to form large, multinucleated cells called giant cells. These cells are often seen in chronic inflammatory conditions and granulomas.
How do mast cells contribute to allergic reactions?
In atopic individuals, mast cells are “armed” with IgE antibodies specific for certain environmental antigens. When these antigens are encountered, the IgE-coated mast cells release histamines and arachidonic acid (AA) metabolites.
What is granulomatous inflammation?
Granulomatous inflammation is a distinctive pattern of chronic inflammation characterized by aggregates of activated macrophages that assume an epithelioid appearance.
Besides tuberculosis, what are other examples of granulomatous infections?
(1) Sarcoidosis
(2) Cat-scratch disease
(3) Lymphogranuloma inguinale
(4) Leprosy
(5) Brucellosis
(6) Mycotic infections
(7) Parasitic infections
Further notes:
Sarcoidosis: an inflammatory disease characterized by the formation of tiny clumps of inflammatory cells in various organs, most commonly the lungs and lymph nodes
Cat-scratch disease: an infectious disease caused by the bacterium Bartonella henselae, typically transmitted through a scratch or bite from a cat
Lymphogranuloma inguinale/venereum: this is a sexually transmitted infection caused by certain strains of Chlamydia trachomatis
Brucellosis: a bacterial infection that spreads from animals to humans, often through the consumption of unpasteurized dairy products or contact with infected animals
What are two types of granulomas?
(1) Foreign body granulomas
(2) Immune granulomas
What are the histological features of a granuloma?
🔥 Granulomas contain epithelioid cells, which are activated macrophages with pink, granular cytoplasm and indistinct cell boundaries. Their nuclei are typically elongated or oval, vesicular and often have a single prominent nucleolus.
🔥 The aggregates of epithelioid macrophages are surrounded by a collar of lymphocytes. These lymphocytes secrete cytokines and this results in continuous activation of macrophages.
🔥 In some granulomas, macrophages fuse to form multinucleated giant cells, which are a hallmark of granulomatous inflammation.
🔥 Older granulomas may have a rim of fibroblasts and connective tissue, indicating the progression of the inflammatory response and the attempt to contain the persistent stimulus.
What causes caseous necrosis in granulomas, and how does it appear?
In granulomas associated with certain infectious organisms, such as the tubercle bacillus, a combination of hypoxia and free-radical injury leads to a central zone of necrosis. This necrotic tissue has a granular, cheesy appearance, which is why it is called caseous necrosis.
