Term
Mucosal Immunology Background |
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Definition
-The mucosal immune system exists as a separate entity to the peripheral immune system.
-It represents a well structured, two part defense.
one is structured and localized to the mucosal tissues.
one is more diffuse.
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Term
Structured Tissue Defenses |
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Definition
- in the structured tissues, foreign antigens are encountered and selectively taken up to initiate immune responses
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Term
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Definition
-collections of effector cells (B and T cells), differentiated plasma cells, antigen presenting cells (APCs) in the tissue are involved in the protective phase of the response.
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Term
Why two separate systems? |
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Definition
-This separate and sophisticated system likely evolved as a defense mechanism against mucosally-encountered agents.
-Protection of mucosal surfaces present unique demands – the human GI tract alone is larger than 300 m2.
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Term
Organization of the Mucosal
Immune System
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Definition
GALT – Gut-Associated Lymphoid Tissues.
Lymphoid tissues associated with the gastrointestinal tract.
BALT – Bronchus-Associated Lymphoid Tissues.
Lymphoid tissues associated with the airway branches of the lungs.
NALT – Nasopharyngeal-Associated Lymphoid Tissues.
Lymphoid tissues associated with the upper regions of the respiratory and gastrointestinal tracts.
MALT – Mucosal-Associated Lymphoid Tissues
The total collection of mucosal lymphoid tissues, acting as a network.
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Term
Gut-associated Lymphoid Tissues (GALT)
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Definition
-Gut-associated lymphoid tissue. lymphoid structures — Peyer's patches and isolated lymphoid follicles (ILFs) — and diffuse lamina propria.
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Term
Peyer's patches and isolated lymphoid follicles |
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Definition
-are composed of a specialized follicle-associated epithelium (FAE) containing M cells, a subepithelial dome (SED) rich in dendritic cells (DCs), and B-cell follicle(s) that contain germinal centers (GCs), where follicular B cells efficiently undergo class-switch recombination (CSR) and somatic hypermutation (SHM).
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Term
Migration of T and B cells into the mucosa |
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Definition
-takes place through high endothelial venules (HEVs), located in the interfollicular regions of Peyer's patches, which contain mostly T cells.
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Term
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Definition
- diffuse tissue that contain a large number of immunoglobulin A (IgA)+ plasma cells, activated T and B cells, macrophages, dendritic cells (DCs) and stromal cells (SCs).
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Term
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Definition
-may process antigens from the lumen and present them directly to T cells and B cells, which can induce IgA class-switching and differentiation in situ. However, these Ag-loaded DCs will migrate to MLNs
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Term
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Definition
-is transported across the epithelium, where it serves as a first line of defense against pathogens and for the maintenance of gut-flora homeostasis. ILFs)
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Term
Distinction Between Mucosal and
Peripheral Immune Systems
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Definition
-The epithelial cell network is termed the Follicle-associated Epithelium” (FAE).
-MALT contains organized regions including a subepithelial area (termed Dome).
-MALT contains B cell zones (the germinal centers) containing IgA-committed B cells and adjacent T cell regions with antigen presenting cells (APCs) and high endothelial venules (HEVs).
-Like peripheral lymph nodes, naïve T and B cells enter the MALT through the HEVs.
-Antigen-activated and memory T and B cells emigrate from the inductive environment via lymphatic drainage, circulate through the blood stream, and home to mucosal effector sites.
-The effector sites include diffuse tissue, where T and B cells reside and perform their effector functions.
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Term
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Definition
-Mucosal epithelium (separating the tissue from the lumen of the organ) contains specialized cells termed “M cells”.
- M cells are closely associated with lymphocytes and dendritic cells.
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Term
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Definition
Inductive Sites of GALT
Peyer’s Patches
Appendix
Individual lymphoid nodules/follicles
Inductive Sites of NALT
Tonsils
Adenoids
Inductive Sites of BALT
Mediastinal Lymph Nodes
Cervical Lymph Nodes
Individual lymphoid nodules
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Term
Effector Mechanisms Protecting
Mucosal Sites
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Definition
● CD8+ T cells – Cytolytic T Lymphocytes (CTL) – protection against viral pathogens.
● CD4+ T cells – expressing cytokine functions involved in protective cellular responses, including IL-2, IFN-g and TNF-b – a Th1-response.
● CD4+ T cells – expressing cytokine functions involved in B cell responses, including IL-4, IL-5, IL-6 and IL-13 – a Th2-response.
● CD4+ T cells - cytokines involved in the regulation of immunity, including IL-10 and TGF-b – regulatory cells.
● B cells/plasma cells secreting IgG1 or IgA.
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