10.1 Mucosal-associated lymphoid tissue (MALT)
3 min read•july 25, 2024
is your body's first line of defense against invaders. It's found in places like your gut and lungs, where germs often try to enter. MALT has special cells that catch bad guys and alert your immune system.
MALT is like a neighborhood watch for your body. It has different parts working together to keep you safe. Some cells sample what's in your gut, while others produce antibodies to fight off threats. It's a complex system that helps you stay healthy.
Structure and Function of Mucosal-Associated Lymphoid Tissue
Structure of mucosal-associated lymphoid tissue
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- MALT forms diffuse lymphoid tissue found in mucosal surfaces throughout body
- Located in (lungs, nasal passages), (stomach, intestines), and (bladder, urethra)
- Components of MALT work together to provide immune defense:
- Epithelial layer contains specialized M cells that sample antigens from lumen
- Lamina propria houses diverse immune cells (, , ) that respond to threats
- Organized lymphoid structures like and isolated lymphoid follicles coordinate immune responses
- Cellular composition includes:
- T lymphocytes (both CD4+ helper and CD8+ cytotoxic)
- B lymphocytes that can differentiate into antibody-producing plasma cells
- that present antigens to activate T cells
- that phagocytose pathogens and present antigens
- MALT produces as primary mucosal antibody
- IgA dimers secreted across epithelium to provide protection in lumen
Role of lymphoid organs in immunity
- Peyer's patches in small intestine ileum serve as
- Contain germinal centers where B cells proliferate and mature
- Sample antigens from gut lumen to initiate immune responses
- in pharynx act as first line respiratory/digestive defense
- Palatine, lingual, and pharyngeal tonsils trap pathogens
- Produce antibodies against inhaled or ingested antigens (dust, pollen, bacteria)
- Appendix at small/large intestine junction maintains gut health
- Houses beneficial bacteria to repopulate gut after illness
- Contains high concentration of lymphoid tissue for local immunity
Inductive vs effector sites
- Inductive sites like Peyer's patches initiate immune responses
- Organized lymphoid structures present antigens to naive lymphocytes
- Include isolated lymphoid follicles and mesenteric lymph nodes
- carry out activated immune responses
- Diffuse distribution throughout lamina propria and epithelium
- Activated lymphocytes migrate here to fight pathogens
- Lymphocytes travel between sites via lymphatics and blood
- Allows coordinated across mucosal surfaces
Importance of microfold cells
- M cells sample and transport antigens across epithelial barrier
- Located in follicle-associated epithelium overlying lymphoid tissue
- Lack absorptive microvilli found on other epithelial cells
- Have folded basolateral membrane to increase surface area
- Antigen sampling occurs through several steps:
- Endocytosis of antigens from lumen
- Transport across cell in vesicles
- Release to antigen-presenting cells beneath
- M cells bridge lumen and immune system
- Enable immune surveillance of mucosal surfaces
- Crucial for initiating responses to pathogens
- Help maintain tolerance to commensal microbes
Key Terms to Review (24)
Antigen Presentation: Antigen presentation is the process by which immune cells display antigens on their surface to enable T cells to recognize and respond to pathogens or infected cells. This crucial mechanism bridges innate and adaptive immunity, allowing for a targeted immune response against specific threats.
B cells: B cells are a type of white blood cell that plays a crucial role in the adaptive immune response by producing antibodies. They originate from hematopoietic stem cells in the bone marrow and are essential for recognizing and responding to specific pathogens, thereby providing long-lasting immunity.
Dendritic Cells: Dendritic cells are a type of immune cell that play a crucial role in the body's immune response by capturing, processing, and presenting antigens to T cells. These cells serve as a bridge between the innate and adaptive immune systems, facilitating the activation of T cells and promoting the development of adaptive immunity.
Effector sites: Effector sites are specific locations in the body where immune responses are carried out, particularly involving the action of immune cells like T cells and B cells. These sites are crucial for executing the immune functions necessary for controlling infections and maintaining homeostasis, especially in the context of mucosal-associated lymphoid tissue (MALT) that serves as a key player in protecting mucosal surfaces.
Flow cytometry: Flow cytometry is a powerful analytical technique used to measure the physical and chemical characteristics of cells or particles as they flow in a fluid stream through a laser beam. This method enables the identification and quantification of various cell types, allowing researchers to gain insights into cellular functions and interactions, which are crucial for understanding immune responses, differentiation processes, and tumor behavior.
Gastrointestinal tract: The gastrointestinal tract is a complex system of hollow organs that extends from the mouth to the anus, responsible for digestion and absorption of nutrients. It plays a crucial role in processing food, breaking it down into essential nutrients, and eliminating waste. This system is closely linked to the immune system, particularly through its interaction with mucosal-associated lymphoid tissue (MALT), which monitors and responds to pathogens in the gut.
Gut-brain axis: The gut-brain axis refers to the complex communication network linking the gastrointestinal tract and the brain, involving biochemical signaling between the gut microbiota, the immune system, and the central nervous system. This interaction plays a crucial role in regulating emotional behavior, cognitive function, and overall health, highlighting how gut health can influence mental well-being and vice versa.
Histological Analysis: Histological analysis is the study of the microscopic structure of tissues, allowing researchers to examine cell types, organization, and the overall architecture of tissues. This method is crucial in understanding how different tissues interact with immune responses, particularly in structures like mucosal-associated lymphoid tissue (MALT), which plays a vital role in the immune defense of mucosal surfaces.
Immune Response: The immune response is the complex biological process through which the body identifies and eliminates pathogens, such as bacteria, viruses, and parasites. This response involves various cells and signaling molecules, coordinated primarily within primary and secondary lymphoid organs, enabling the body to recognize and remember specific invaders for faster responses in the future. The immune response is crucial for maintaining health and preventing disease, as it adapts to effectively combat a wide range of infectious agents.
Inductive sites: Inductive sites are specialized areas within the immune system where immune responses are initiated, particularly in the context of mucosal-associated lymphoid tissue (MALT). These sites, such as the tonsils and Peyer's patches, play a crucial role in the activation and differentiation of lymphocytes upon encountering antigens, thereby contributing to the overall mucosal immunity.
Inflammatory bowel disease: Inflammatory bowel disease (IBD) refers to a group of chronic inflammatory conditions of the gastrointestinal tract, primarily including Crohn's disease and ulcerative colitis. These diseases are characterized by inflammation that can lead to various symptoms such as abdominal pain, diarrhea, and weight loss, significantly affecting the quality of life. The immune system plays a critical role in the pathogenesis of IBD, with dysregulation contributing to the persistent inflammation observed in affected individuals.
Macrophages: Macrophages are large immune cells that play a crucial role in the body's defense mechanisms by engulfing and digesting cellular debris, pathogens, and foreign substances. They originate from monocytes in the blood and are pivotal in both the innate and adaptive immune responses, acting as key players in inflammation, antigen presentation, and tissue repair.
MALT lymphoma: MALT lymphoma, or mucosa-associated lymphoid tissue lymphoma, is a type of non-Hodgkin lymphoma that originates in the mucosal tissues, primarily affecting sites like the gastrointestinal tract, lungs, and salivary glands. This cancer arises from the B-cells of the immune system and is closely linked to chronic inflammatory conditions such as infection by Helicobacter pylori in the stomach. Understanding MALT lymphoma involves recognizing its association with mucosal-associated lymphoid tissue, which plays a crucial role in the immune response at mucosal surfaces.
Microfold cells (M cells): Microfold cells, commonly referred to as M cells, are specialized epithelial cells found in the mucosal surfaces of the gastrointestinal tract, particularly in Peyer's patches. They play a critical role in the immune response by facilitating the transport of antigens from the gut lumen to underlying immune cells, thus acting as a bridge between the intestinal lumen and the immune system.
Mucosal immunity: Mucosal immunity refers to the specialized immune responses that occur at mucosal surfaces, which include the gastrointestinal tract, respiratory tract, and urogenital tract. This form of immunity is crucial for protecting the body against pathogens that enter through these surfaces while maintaining tolerance to non-harmful antigens, such as food proteins and commensal bacteria. Mucosal immunity involves various immune cells and molecules, primarily located in mucosal-associated lymphoid tissue (MALT), ensuring effective responses to infections while preventing unnecessary inflammation.
Mucosal-associated lymphoid tissue (MALT): Mucosal-associated lymphoid tissue (MALT) refers to a collection of lymphoid tissues found at mucosal surfaces, which play a crucial role in the immune system's response to pathogens. MALT is strategically located in areas like the gastrointestinal tract, respiratory tract, and urogenital tract, enabling it to effectively monitor and respond to antigens entering through these surfaces. Its unique structure supports the generation of immune responses and the development of immunological memory against mucosal pathogens.
Oral tolerance: Oral tolerance is a specific immune response that occurs when the immune system becomes unresponsive to antigens encountered via the gastrointestinal tract, leading to a state of immune acceptance rather than activation. This process is crucial for maintaining immune homeostasis and preventing inappropriate responses to dietary antigens and commensal microbes, which are abundant in mucosal environments.
Peyer's patches: Peyer's patches are specialized lymphoid tissues located in the mucosal lining of the small intestine, particularly the ileum. They play a crucial role in the immune system by monitoring intestinal bacteria and generating immune responses, thus maintaining gut homeostasis. Their structure includes follicles that house B cells and other immune cells, making them essential for the development of mucosal immunity.
Plasma Cells: Plasma cells are specialized B cells that produce large quantities of antibodies, playing a crucial role in the immune response. They are formed from activated B cells following exposure to antigens, and their primary function is to secrete antibodies that target specific pathogens, helping to neutralize infections and promote clearance.
Respiratory tract: The respiratory tract is a system of passages that facilitate the exchange of gases between the external environment and the lungs. It begins at the nose and mouth, extending through the pharynx, larynx, trachea, bronchi, and into the lungs, playing a crucial role in respiration and protecting against pathogens.
Secretory IgA: Secretory IgA (sIgA) is an antibody that plays a crucial role in the immune defense of mucosal surfaces, such as those in the gastrointestinal, respiratory, and urogenital tracts. It is produced by plasma cells in mucosal-associated lymphoid tissue (MALT) and is unique because it exists in a dimeric form, allowing it to effectively neutralize pathogens and prevent their adherence to epithelial cells.
T cells: T cells, or T lymphocytes, are a type of white blood cell that plays a central role in the adaptive immune response. They originate from hematopoietic stem cells in the bone marrow but mature in the thymus, where they develop the ability to recognize specific antigens presented by other cells. T cells are crucial for cell-mediated immunity, helping to eliminate infected or cancerous cells and orchestrating the immune response.
Tonsils: Tonsils are lymphoid tissues located at the back of the throat that play a critical role in the immune system by helping to filter out pathogens and prevent infections. They are part of the body's first line of defense against inhaled or ingested foreign substances, making them an essential component of mucosal-associated lymphoid tissue (MALT). Tonsils can become swollen during infections, reflecting their active involvement in immune responses.
Urogenital tract: The urogenital tract refers to the combined system of organs responsible for the production and excretion of urine and the reproductive functions in both males and females. This tract includes structures such as the kidneys, ureters, bladder, urethra, and in females, the vagina and uterus, and in males, the penis and prostate. Understanding this system is crucial as it plays a significant role in maintaining homeostasis and is a site for various immunological interactions.