Mucosal and Cutaneous Immunity Quiz
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Questions and Answers

What is one of the primary roles of enterocytes in the gut-associated lymphoid tissue (GALT)?

  • Transporting nutrients across the gut wall
  • Producing immune memory cells
  • Engaging PAMPs/DAMPs through PRRs (correct)
  • Secretion of antibodies

Which type of cells in the lamina propria is most abundant in response to pathogens?

  • Plasma cells
  • Mast cells
  • Memory T cells
  • Macrophages (correct)

What is the primary function of M cells in the gut?

  • Housing memory B cells
  • Secreting cytokines
  • Facilitating antigen transcytosis (correct)
  • Producing antimicrobial peptides

What cytokine response is typically elicited by PRR engagement in enterocytes?

<p>Cytokine secretion (B)</p> Signup and view all the answers

In the gut, which type of immune cell is primarily responsible for the first line of defense against pathogens?

<p>Natural killer (NK) cells (A)</p> Signup and view all the answers

What are the two major sections of the Gut-associated Lymphoid Tissue (GALT)?

<p>Gut epithelium and lamina propria (D)</p> Signup and view all the answers

Which type of cells predominates in the gut epithelium and is primarily responsible for nutrient absorption?

<p>Enterocytes (A)</p> Signup and view all the answers

What is the primary role of the mucus produced by goblet cells in the gut?

<p>Providing a barrier against pathogens (B)</p> Signup and view all the answers

Which structures form the brush border in the gut epithelium?

<p>Microvilli (C)</p> Signup and view all the answers

What type of cells are located at the bottom of intestinal crypts and produce antimicrobial peptides?

<p>Paneth cells (C)</p> Signup and view all the answers

How do commensal organisms in the gut contribute to pathogen defense?

<p>By competing for nutrients and producing toxins (B)</p> Signup and view all the answers

What is the function of the glycocalyx associated with the brush border?

<p>To provide a charged surface repelling pathogens (A)</p> Signup and view all the answers

Which cells in the gut epithelium are important in integrating internal and external signals and coordinating immune responses?

<p>Enterocytes (C)</p> Signup and view all the answers

Which epithelial cell type produces hormone-like molecules in the gut?

<p>Enteroendocrine cells (D)</p> Signup and view all the answers

What is a characteristic of follicle associated epithelium (FAE) in the gut?

<p>It contains M cells (D)</p> Signup and view all the answers

What is an example of an inductive site in the mucosa where a primary adaptive immune response is initiated?

<p>Peyer's patches (A)</p> Signup and view all the answers

Which cells are involved in the local production of lymphotoxin (LT) and IL-17 that drive the development of induced MALT (iMALT)?

<p>TH17 cells and lymphoid tissue inducer cells (B)</p> Signup and view all the answers

What defines the local immune response of both mucosal and cutaneous immunity?

<p>Activation occurring at the site where antigens are first encountered (C)</p> Signup and view all the answers

What term describes areas of induced MALT that can arise in the gut and lungs in response to infection and injury?

<p>Induced MALT (iMALT) (A)</p> Signup and view all the answers

Which type of mucosa is characterized by a single layer of columnar epithelium?

<p>Type 1 mucosae (A)</p> Signup and view all the answers

How do activated mucosal T and B cells reach various effector sites in the body?

<p>Via the lymphatic system and blood circulation (A)</p> Signup and view all the answers

What is a primary component of mucus that aids in immune function?

<p>Mucins (B)</p> Signup and view all the answers

What is the significance of the 'common mucosal immune system' concept?

<p>It indicates that antibody responses in one mucosal area can affect other distant mucosal sites. (A)</p> Signup and view all the answers

Which statement accurately describes the role of antimicrobial peptides in mucosal immunity?

<p>They prevent pathogen attachment and invasion. (A)</p> Signup and view all the answers

Which type of mucosal tissue is primarily associated with respiratory immunity?

<p>BALT (C)</p> Signup and view all the answers

What structure formed by the folding of the exterior surfaces of gut epithelium is key to nutrient absorption and pathogen defense?

<p>Microvilli (D)</p> Signup and view all the answers

Which of the following functions is primarily associated with the goblet cells in the gut epithelium?

<p>Producing mucus (D)</p> Signup and view all the answers

How do enterocytes contribute to the immune response in the gut?

<p>By integrating signals and coordinating responses with leukocytes (C)</p> Signup and view all the answers

What type of surface covers the apical surfaces of gut epithelial cells that acts against ingested pathogens?

<p>Glycocalyx (B)</p> Signup and view all the answers

Which of the following statements about the lamina propria is incorrect?

<p>It is primarily involved in nutrient absorption. (A)</p> Signup and view all the answers

What distinguishes mucosal immunity from systemic immunity?

<p>Mucosal immunity functions independently at the site of antigen encounter. (B)</p> Signup and view all the answers

Which of the following accurately describes a characteristic of type II mucosae?

<p>It includes tougher tissues required for protection in areas like the mouth and nose. (D)</p> Signup and view all the answers

What role do antimicrobial molecules such as lysozyme and lactoferrin serve in mucosal immunity?

<p>They break down bacterial cell walls and inhibit bacterial growth. (B)</p> Signup and view all the answers

What is the primary role of the brush border in the gut epithelium?

<p>Increasing the surface area for nutrient absorption and pathogen defense (B)</p> Signup and view all the answers

What is the primary function of the mucosa-associated lymphoid tissue (MALT)?

<p>Facilitating the activation of adaptive immune responses at mucosal sites. (B)</p> Signup and view all the answers

Which feature characterizes the lamina propria within the GALT?

<p>It lies between the gut epithelium and the muscle layer. (D)</p> Signup and view all the answers

Which statement best describes the relationship between MALT and SALT in the immune system?

<p>Both are independent arms of immunity that respond to local infections but can also activate systemic responses. (D)</p> Signup and view all the answers

Which of the following statements about the role of microbiota in the gut is accurate?

<p>Microbiota compete with pathogens for nutrients and space. (A)</p> Signup and view all the answers

Which cell type is responsible for the production of mucus in the gut epithelium?

<p>Goblet cells (B)</p> Signup and view all the answers

What characteristic of the glycocalyx is essential for its function in the gut?

<p>It provides a negative charge that repels pathogens. (B)</p> Signup and view all the answers

What primarily drives the ectopic development of lymphoid follicles and lymphatic vessels in induced MALT (iMALT)?

<p>Local production of lymphotoxin (LT) and IL-17 (C)</p> Signup and view all the answers

Which of the following best describes a characteristic of inductive sites in the mucosa?

<p>They initiate the primary adaptive immune response. (C)</p> Signup and view all the answers

How do effector lymphocytes migrate to various effector sites after activation in an inductive site?

<p>Through lymphatics and blood (C)</p> Signup and view all the answers

What is the primary distinguishing feature of regions of mucosal-associated lymphoid tissue (MALT) that are linked to type 1 mucosa?

<p>Higher density of dendritic cells and lymphocytes (A)</p> Signup and view all the answers

Which of the following statements accurately describes induced MALT (iMALT)?

<p>iMALT can develop in response to infection and tissue injury. (A)</p> Signup and view all the answers

Flashcards

Enterocytes' role in GALT

Enterocytes in the gut-associated lymphoid tissue (GALT) have Toll-like receptors (TLRs), NOD-like receptors (NLRs), and RIG-I-like receptors (RLRs) that respond to commensal bacteria or pathogens, initiating a cytokine response.

Cytokine secretion in GALT

The type of cytokine secreted by enterocytes depends on the specific pathogen or stimulus, and the surrounding microenvironment.

gd T cells in GALT

Gamma delta T cells in GALT produce antimicrobial peptides (defensins and cathelicidins) targeting pathogens.

NK and NKT cells' role

Natural killer (NK) and Natural Killer T (NKT) cells in GALT contribute to early gut defense.

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Lamina propria composition

The lamina propria contains macrophages, neutrophils, NKT cells, mast cells, immature dendritic cells (DCs), memory T and B cells, and TH17 cells.

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Intestinal follicles function

Intestinal follicles are structures in the lamina propria that can cluster or be isolated, acting as sites for lymphocyte activation and antibody production, especially IgA.

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Germinal centers in GALT

Germinal centers may form in the lamina propria when B cells are activated, giving rise to plasma cells producing antibodies, often IgA.

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Ag sampling in the gut

Follicle-associated epithelium (FAE) in the gut includes specialized cells called M cells, that efficiently take up antigens for immune response.

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GALT Components

The combination of gut epithelium and lamina propria that works together to protect against ingested pathogens and toxins.

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Gut Epithelium

The top layer of the gut, characterized by folds called crypts and villi, and specialized areas like follicle-associated epithelium containing M cells.

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Lamina Propria

Loose connective tissue between the gut epithelium and the muscle layer, containing immune cells.

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Enterocytes

The majority of gut epithelial cells responsible for nutrient absorption and integrating internal/external signals for immunity.

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Enteroendocrine Cells

Gut epithelial cells found on the villi that produce mucus and hormone-like molecules.

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Paneth Cells

Gut epithelial cells at the base of crypts that produce antimicrobial peptides.

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Goblet Cells

Gut epithelial cells producing mucus and antimicrobial molecules.

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Mucus Barrier

A physical and chemical barrier in the gut, preventing pathogens from harming the system.

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Brush Border

The folded exterior surface of gut epithelium containing microvilli covered by glycocalyx.

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Glycocalyx

Thick, glue-like layer on the brush border with negative charge, repelling pathogens and containing enzymes.

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Microbiota

Beneficial microorganisms living in the gut.

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Mucosal Immunity

The immune system's response to pathogens that enter through mucosal surfaces (like the gut or lungs).

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MALT

Mucosa-Associated Lymphoid Tissue; a collection of immune cells beneath mucosal surfaces.

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GALT

Gut-Associated Lymphoid Tissue; MALT found in the intestines.

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SALT

Skin-Associated Lymphoid Tissue; immune cells in the skin.

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Type I Mucosa

Single layer columnar epithelium in the intestines and lungs.

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Type II Mucosa

Squamous epithelium where tougher tissue is required (e.g., mouth, nose, vagina).

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Mucus

Viscous solution of polysaccharides in water, a key barrier in the body.

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Antibodies in Mucus

Immunoglobulin A(IgA) mainly, and IgG in type II mucosae present in mucus.

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Antimicrobial Molecules

Substances like lysozyme and lactoferrin, that kill or inhibit bacteria in mucus.

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Mucosal Immune System

A specialized immune system that defends mucosal surfaces like the gut, lungs, and urogenital tract against pathogens.

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Inductive Site (MALT)

A location where the body first encounters an antigen, initiating an adaptive immune response.

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Peyer's Patches (PPs)

Specialized areas in the small intestine acting as inductive sites for immune responses.

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Effector Site (MALT)

Part of the mucosa where activated immune cells execute the response to an antigen.

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iMALT (Induced MALT)

Specialized patches of lymphoid tissue generated in response to infection, injury, or inflammation in the gut, lungs.

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Common Mucosal Immune System

The characteristic that antibodies generated in one mucosal site can be produced and detected in other distant mucosal sites.

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Lymphotoxin (LT)

A factor involved in tissue development, including the formation of lymphoid follicles and lymphatic vessels.

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IL-17

A cytokine involved in the development of lymphoid tissues, especially in response to inflammation.

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TH17 Cells

A type of T cell that produces IL-17, aiding in the formation of lymphoid tissue.

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LTi cells

Cells that produce lymphotoxin, helping to create lymphoid tissues.

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Gut epithelium structure

Folds of crypt and villus structures, and specialized areas like follicle-associated epithelium (FAE) containing M cells.

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Lamina propria function

Loose connective tissue supporting the epithelium and containing immune cells, below the gut lining.

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Enterocytes role

Absorb nutrients and relay internal/external signals to coordinate immune responses in GALT.

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Enteroendocrine cells

Epithelial cells on villi producing mucus and hormone-like molecules.

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Paneth cells

Epithelial cells at crypt base, producing antimicrobial peptides.

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Goblet cells

Epithelial cells producing mucus and antimicrobial molecules, located on the side of crypts.

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Mucus barrier

Protective layer in the gut with physical and antimicrobial properties.

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Brush border structure

Folded exterior surfaces of gut epithelium forming microvilli.

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Glycocalyx function

Thick layer with negative charge on the brush border, repelling pathogens and containing enzymes.

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Microbiota role

Beneficial bacteria in the gut that can compete with pathogens for resources.

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Mucosal Immunity

The immune response to pathogens entering through mucosal surfaces, like the gut or lungs, distinct from systemic responses.

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MALT

Mucosa-Associated Lymphoid Tissue; a collection of immune cells beneath mucosal surfaces.

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GALT

Gut-Associated Lymphoid Tissue; a type of MALT found in the intestines.

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SALT

Skin-Associated Lymphoid Tissue; immune cells in the skin.

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Type I Mucosa

Single layer columnar epithelium found in the intestines and lungs.

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Type II Mucosa

Squamous epithelium found in areas like the mouth, nose, and vagina.

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Mucus

A viscous solution of polysaccharides in water, forming a physical barrier and containing antimicrobial molecules.

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Antibodies in Mucus

Predominantly IgA in type I mucosae (e.g., gut), and IgG in type II mucosae (e.g., mouth).

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Antimicrobial Molecules

Substances like lysozyme (breaks down bacterial walls) and lactoferrin (sequesters iron).

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Mucosal Immunity

The immune system's response to pathogens entering mucosal surfaces (e.g., gut, lungs).

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GALT Components

The combination of gut epithelium and lamina propria that works together to protect against ingested pathogens and toxins.

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Gut Epithelium

The top layer of the gut, characterized by folds called crypts and villi, and specialized areas like follicle-associated epithelium containing M cells.

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MALT

Mucosa-Associated Lymphoid Tissue; immune cell collections under mucosal surfaces.

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Lamina Propria

Loose connective tissue between the gut epithelium and the muscle layer, containing immune cells.

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GALT

Gut-Associated Lymphoid Tissue; MALT found in the intestines.

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Enterocytes

The majority of gut epithelial cells responsible for nutrient absorption and integrating internal/external signals for immunity.

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Inductive Site (MALT)

Location where the body first encounters an antigen, starting an adaptive immune response.

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Enteroendocrine Cells

Gut epithelial cells found on the villi that produce mucus and hormone-like molecules.

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Peyer's Patches

Specialized areas in the small intestine acting as inductive sites for immune responses; part of the GALT.

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Paneth Cells

Gut epithelial cells at the base of crypts that produce antimicrobial peptides.

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Effector Site (MALT)

Part of the mucosa where activated immune cells execute the response to an antigen.

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Goblet Cells

Gut epithelial cells producing mucus and antimicrobial molecules, located on the side of crypts.

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iMALT

Patches of lymphoid tissue generated in response to infection, injury, or inflammation; a form of induced mucosa-associated lymphoid tissue.

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Common Mucosal Immune System

Antibodies generated in one mucosal site can be produced and detected in other distant mucosal sites; a key feature of mucosal immunity.

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Mucus Barrier

A physical and chemical barrier in the gut, preventing pathogens from harming the system.

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Lymphotoxin (LT)

A factor involved in tissue development, including lymphoid follicle and lymphatic vessel formation.

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Brush Border

The folded exterior surface of gut epithelium forming microvilli.

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Glycocalyx

Thick layer with negative charge on the brush border, repelling pathogens and containing enzymes.

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IL-17

A cytokine involved in the development of lymphoid tissues (particularly in response to inflammation).

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Microbiota

Beneficial bacteria in the gut that can compete with pathogens for resources.

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TH17 Cells

A type of T cell that produces IL-17, aiding in the formation of lymphoid tissue.

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M cells

Specialized cells in the follicle-associated epithelium that take up antigens for immune responses.

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LTi cells

Cells that produce lymphotoxin, helping to create lymphoid tissues.

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Study Notes

Mucosal and Cutaneous Immunity

  • Most human and animal pathogens enter the body through skin or mucosal surfaces.
  • Mucosa-associated lymphoid tissue (MALT) and skin-associated lymphoid tissue (SALT) are collections of antigen-presenting cells (APCs) and lymphocytes.
  • These tissues function independently and induce mucosal and cutaneous immune responses.

Mucosal Immunity Overview

  • Mucosal Immunity is the immune response mounted at mucosal surfaces.
  • The response is distinct from systemic immune responses and occurs locally where the antigen (Ag) is first encountered, without involvement of a draining lymph node).
  • The effector cells can enter the lymphatic system or circulation but home to mucosal or cutaneous tissues.

Mucosal Immunity and Cutaneous Immunity

  • Mucosal and cutaneous immune responses are different from systemic responses.
  • The responses occur at the site of initial exposure to an Ag (antigen).
  • Effector cells that are generated can enter efferent lymphatics or circulation, but they will specifically return to mucosal or cutaneous tissues to perform their effector functions.
  • A systemic immune response can be triggered when antigen-bearing APCs of MALT or SALT migrate to local lymph nodes and activate naive B and T cells in that location.

Epithelial and Immune Function

  • Mucosae come in two types:
    • Type 1: Occurs in the intestine and lungs; composed of a single layer of columnar epithelium
    • Type 2: Found in the mouth, nose, and vagina; uses squamous epithelium for a tougher tissue structure.
  • Both types of mucosa produce mucus, which is a viscous solution of polysaccharides in water.

Mucus Composition

  • Mucus contains various antibodies (Abs), mostly IgA in type 1 mucosae and IgG in type 2 mucosae.
  • Contains antimicrobial molecules such as lysozyme (breaks down bacterial cell wall components) and lactoferrin (sequesters iron needed for bacterial growth).

MALT (Mucosa-Associated Lymphoid Tissue)

  • MALT is a constantly being defended against pathogen assaults from immune responses mounted in MALT.

Inductive and Effector Sites

  • An inductive site is an area in a mucosa where an antigen is encountered, leading to a primary adaptive immune response. (e.g. Peyer's Patches (PPs), in the gut)
  • An effector site is an area where effector lymphocytes are dispatched. This could be an exocrine gland (e.g., salivary glands or lacrimal glands).

Components of GALT (Gut-Associated Lymphoid Tissue)

  • GALT provides effective immune defense against ingested pathogens and toxins.
  • Has two major sections: gut epithelium and lamina propria.
  • Gut epithelium is folded into crypts and villi, and normal gut epithelium has follicle-associated epithelial (FAE) cells
  • Lamina propria is loose connective tissue between the basolateral surfae of the epithelium and the muscle layer.

Elements of Gut Epithelium

  • Enterocytes: Major portion, responsible for nutrient absorption.
  • Enteroendocrine cells: Found in villi, produce mucus and hormone-like molecules.
  • Paneth cells: Located in intestinal crypts, produce antimicrobial peptides.
  • Goblet cells: Located on the sides of intestinal crypts, produce mucus and antimicrobial molecules.

Functions of GALT Components

  • Mucus in GALT forms a strong physical barrier and antimicrobial defense.
  • Gut epithelial cells' apical surfaces are protected by non-induced innate barriers.
  • Commensal organisms compete for nutrients and space, limiting pathogenic encroachment.
  • Beneficial microbiota secrete toxins that hinder pathogens and positively affect the underlying mucus layer.
  • Brush border within GALT contains glycocalyx, which is a negative charge and repels pathogens
  • TLRs, NLRs, and RLRs on enterocytes in GALT can respond to commensals or stress conditions through cytokine secretion.
  • Additional innate defense in GALT is provided by γδ T cells within or near the epithelium; these cells produce antimicrobial peptides.
  • NK cells and NKT cells in GALT participate in first-line defense.

Lamina Propria Components

  • Lamina propria contains macrophages, neutrophils, NKT cells, mast cells, and immature DCs.
  • Memory αβ T cells (both CD4+ and CD8+), memory B cells, and TH17 effectors are abundant.
  • Some lymphocytes are diffusely distributed, while others organize into follicles.

Antigen Sampling in the Gut

  • Follicle-associated epithelium (FAE) specializes in Ag capture.
  • M cells, within FAE, directly transcytose antigens to other APCs in the dome.
  • Interfollicular areas of FAE contain mature αβ T cells.
  • Apical surfaces of M cells lack glycocalyx and have a thick brush border, which facilitates endocytosis of antigens.

GALT DCs

  • Several DC subsets exist in mice, with CX3CR1+ DCs found throughout the gut.
  • CX3CR1+ DCs directly sample Ag from the gut lumen and from M cells, while CCR6+ DCs mainly sample Ag from transcytosed M cells.

Immune Response Types

  • In healthy conditions, GALT DCs will often provide tolerance or apoptosis for naïveT cells that respond to food antigens and promote Treg differentiation.
  • During inflammation, GALT DCs mature and activate antigen-specific T cells. Activated DCs can migrate to draining lymph nodes to stimulate systemic immune responses.

NALT and BALT (Nasal-Associated Lymphoid Tissue and Bronchial-Associated Lymphoid Tissue)

  • NALT and BALT defend against inhaled air substances and pathogens.
  • NALT includes nasal submucosal glands, tonsils, and the epithelial layers lining the nasopharynx.
  • BALT includes bronchial submucosal glands, epithelial layers lining the trachea, bronchi, and lungs, plus follicles and diffuse collections of lymphocytes beneath the epithelium.
  • NALT and BALT have structures resembling those in the gut.

NALT and BALT Structure and Antigen Sampling

  • Components of the upper respiratory system, like nose hairs and cillia in the nasal passages, provide non-induced innate barriers.
  • Nasopharyngeal epithelial cells secrete sIgA, lactoferrin, lysozyme, and other antimicrobial molecules and maintain a normal microbiota.
  • Under stress conditions, epithelial cells in NALT and BALT produce cytokines, which summon innate leukocytes.
  • Unlike GALT, the uptake of antigens in NALT and BALT is easier due to a lack of harsh enzymes or low pH present in the gut.

Antigen Sampling and Response Types

  • Antigen sampling in tonsils using M cells.
  • Antigen sampling and responses in the airway that may use dendritic cells to convey antigens in the airway to the inductive sites.
  • Dendritic cells that commence maturation can return to underlying lymphoid tissue or may migrate to more distant lymph nodes to induce a systemic response.

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Lecture 27: Mucosal and Cutaneous Immunity PDF

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Test your knowledge on mucosal and cutaneous immunity, key concepts of how the body responds to pathogens that enter through skin or mucosal surfaces. Understand the roles of MALT and SALT, as well as the differences between local immune responses and systemic reactions.

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