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    Related Topics

    From Lymphatic System

    Jugular Trunk
    Drains lymph from the head and neck.
    Submental Lymph Nodes
    Drain the floor of the mouth and central lower lip.
    Popliteal Lymph Nodes
    Drain the foot and leg.
    Waldeyer’s Ring
    Ring of lymphoid tissue surrounding the naso- and oropharynx.
    Lymphatic Capillaries
    Initial lymphatic vessels that collect interstitial fluid.
    Preaortic Nodes
    Located in front of the aorta.
    Retroaortic Nodes
    Located behind the aorta.
    NALT
    Nasal-associated lymphoid tissue.
    Lingual Tonsils
    Located at the base of the tongue.
    Thoracic Duct
    Main lymphatic duct draining most of the body.
    SALT
    Skin-associated lymphoid tissue.
    Deep Cervical Lymph Nodes
    Located along internal jugular vein; receive lymph from head and neck.
    BALT
    Bronchus-associated lymphoid tissue.
    Thymus
    Primary lymphoid organ for T-cell maturation.
    Tracheobronchial Nodes
    Drain lungs and bronchi.
    Submandibular Lymph Nodes
    Drain the face, mouth, and pharynx.
    Posterior Mediastinal Nodes
    Drain posterior thoracic structures.
    Lymph Nodes
    Small structures that filter lymph and store immune cells.
    Iliac Lymph Nodes
    Include external, internal, and common iliac nodes.
    Subscapular Axillary Nodes
    Located along the posterior chest wall.
    Anterior Mediastinal Nodes
    Drain anterior thoracic structures.
    Mastoid Lymph Nodes
    Drain the posterior scalp and ear.
    Apical Axillary Nodes
    Located at the apex of the axilla.
    Palatine Tonsils
    Located on each side of the oropharynx.
    Supraclavicular Lymph Nodes
    Located above the clavicle; key in thoracic drainage.

    MALT

    Reviewed by our medical team

    Mucosa-associated lymphoid tissue.

    1. Overview

    Mucosa-associated lymphoid tissue (MALT) refers to a collection of diffuse and organized lymphoid tissues located within mucosal surfaces throughout the body. As part of the immune system, MALT plays a crucial role in defending against pathogens that enter through mucosal barriers such as the respiratory, gastrointestinal, and genitourinary tracts. It houses immune cells that detect, respond to, and eliminate invading microorganisms while helping maintain immune tolerance to harmless antigens like food and commensal bacteria.

    2. Location

    MALT is distributed throughout various mucosal sites of the body, forming the largest component of the lymphatic system. It is categorized based on its location:

    • GALT (Gut-associated lymphoid tissue): Found in the gastrointestinal tract (e.g., Peyer’s patches, appendix, tonsils, isolated lymphoid follicles).

    • BALT (Bronchus-associated lymphoid tissue): Located in the respiratory tract, especially around bronchi and bronchioles.

    • NALT (Nasal-associated lymphoid tissue): Present in the nasal passages, particularly in the adenoids.

    • VALT (Vulvovaginal-associated lymphoid tissue): Found in the female reproductive tract.

    • Other locations: Salivary glands, lacrimal glands, conjunctiva, and urinary tract mucosa.

    Unlike lymph nodes, MALT is not always encapsulated and may appear as diffuse lymphoid aggregates interspersed within the mucosal epithelium and lamina propria.

    3. Structure

    MALT includes both organized and diffuse lymphoid tissues, structurally designed to interact closely with the mucosal surface. Its components include:

    • Epithelium-associated lymphocytes: Lymphocytes scattered within or beneath the mucosal epithelium.

    • Lymphoid follicles: Contain B cells in germinal centers surrounded by T cells and antigen-presenting cells (e.g., dendritic cells, macrophages).

    • Specialized epithelial cells: M cells (microfold cells) transport luminal antigens across the epithelium into lymphoid tissue below.

    • Plasma cells: Produce immunoglobulin A (IgA), which is secreted into the mucosal surface to neutralize pathogens.

    MALT lacks a fibrous capsule (unlike lymph nodes) and is instead closely integrated with the mucosal epithelium, allowing immediate immune responses to local stimuli.

    4. Function

    MALT functions as the body’s first line of defense at mucosal surfaces. Its major functions include:

    • Antigen sampling: M cells and dendritic cells capture pathogens and antigens from the mucosal surface and deliver them to immune cells.

    • Immune response initiation: Activates T and B lymphocytes in response to foreign antigens.

    • Antibody production: Promotes class switching of B cells to secrete IgA, which is critical for mucosal immunity.

    • Maintenance of immune tolerance: Helps suppress immune responses to non-threatening antigens like food proteins and commensal microbes.

    5. Physiological Role(s)

    MALT plays vital roles in both immunity and immune regulation, especially at mucosal interfaces. These roles include:

    • Barrier immunity: Prevents pathogen entry by initiating rapid localized immune responses at mucosal surfaces.

    • Regulation of inflammation: Balances pro-inflammatory and anti-inflammatory signals to protect mucosal tissues from chronic damage.

    • Oral tolerance: Facilitates immunological unresponsiveness to harmless antigens, preventing allergic or autoimmune reactions.

    • Immune education: Particularly during childhood, MALT exposes immune cells to diverse antigens, helping shape immune memory.

    6. Clinical Significance

    Infections

    MALT is a primary site of defense against mucosal pathogens, including viruses, bacteria, and parasites. Dysfunction or depletion of MALT (e.g., in HIV infection) compromises mucosal immunity, increasing susceptibility to infections in the gut, lungs, and genital tract.

    Autoimmune and Inflammatory Disorders

    • Inflammatory bowel disease (IBD): Aberrant activation of GALT contributes to the pathogenesis of Crohn’s disease and ulcerative colitis.

    • Celiac disease: Loss of tolerance to gluten in GALT results in villous atrophy and chronic inflammation of the small intestine.

    • Asthma and allergic rhinitis: BALT and NALT play roles in hypersensitivity reactions to inhaled allergens.

    MALT Lymphoma

    MALT lymphomas are extranodal marginal zone B-cell lymphomas that arise from chronic antigenic stimulation in MALT. Common sites include:

    • Stomach: Associated with chronic Helicobacter pylori infection.

    • Salivary glands: Linked to Sjögren’s syndrome.

    • Thyroid: Often related to Hashimoto’s thyroiditis.

    Treatment often includes eradication of the underlying infection or autoimmune trigger, in addition to radiation or immunotherapy.

    Vaccination and Immunotherapy

    MALT is an important target for mucosal vaccines, such as oral polio vaccine and nasal influenza vaccines. These vaccines stimulate MALT directly to produce localized immunity, especially secretory IgA, enhancing protection at pathogen entry points.

    Did you know? Lymphangitis is an inflammation of the lymphatic vessels that often occurs due to an infection.