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    Related Topics

    From Lymphatic System

    Bronchomediastinal Trunk
    Drains lymph from thoracic organs.
    NALT
    Nasal-associated lymphoid tissue.
    SALT
    Skin-associated lymphoid tissue.
    Lymphatic Capillaries
    Initial lymphatic vessels that collect interstitial fluid.
    Central Axillary Nodes
    Located centrally in the armpit.
    Para-aortic Lymph Nodes
    Drain abdominal viscera and lower limbs.
    Lumbar Trunk
    Drains lower limbs and pelvic organs.
    Lateral Axillary Nodes
    Located along the humerus in the axilla.
    Appendix
    Lymphoid-rich structure of the large intestine.
    Retroaortic Nodes
    Located behind the aorta.
    Cisterna Chyli
    Dilated sac at the start of the thoracic duct.
    Superficial Cervical Lymph Nodes
    Drain superficial structures of the head and neck.
    Subscapular Axillary Nodes
    Located along the posterior chest wall.
    Pharyngeal Tonsil
    Located in the nasopharynx (adenoids).
    Supraclavicular Lymph Nodes
    Located above the clavicle; key in thoracic drainage.
    Thymus
    Primary lymphoid organ for T-cell maturation.
    Subclavian Trunk
    Drains lymph from the upper limbs.
    Tubal Tonsils
    Near openings of the auditory tubes.
    Right Lymphatic Duct
    Drains right upper quadrant of the body.
    Mastoid Lymph Nodes
    Drain the posterior scalp and ear.
    MALT
    Mucosa-associated lymphoid tissue.
    Preaortic Nodes
    Located in front of the aorta.
    Paratracheal Nodes
    Located lateral to the trachea.
    Iliac Lymph Nodes
    Include external, internal, and common iliac nodes.
    Popliteal Lymph Nodes
    Drain the foot and leg.

    BALT

    Reviewed by our medical team

    Bronchus-associated lymphoid tissue.

    1. Overview

    Bronchus-associated lymphoid tissue (BALT) is a subtype of mucosa-associated lymphoid tissue (MALT) located within the respiratory tract, primarily around the bronchi and bronchioles. It functions as an immune surveillance site that protects the lungs and lower airways against inhaled pathogens, environmental antigens, and particulates. While BALT is usually sparse or absent in healthy adult lungs, it becomes more prominent in response to infection or inflammation, playing a key role in mucosal immunity of the respiratory system.

    2. Location

    BALT is situated in the mucosa and submucosa of the lower respiratory tract, most commonly in:

    • The walls of bronchi and bronchioles

    • Peribronchial connective tissue

    • Bronchial bifurcations and branching points of the airway

    It is more developed in children and young animals and tends to regress or remain dormant in healthy adults unless stimulated by chronic infection, irritation, or autoimmune disease. In such conditions, BALT can reappear or expand—a phenomenon referred to as “inducible BALT” (iBALT).

    3. Structure

    BALT is composed of both diffuse and organized lymphoid tissues. Its key structural components include:

    • Lymphoid follicles: Primarily composed of B lymphocytes, often with active germinal centers.

    • Perifollicular T cell zones: Surround the B-cell follicles and contain T lymphocytes and antigen-presenting dendritic cells.

    • Follicle-associated epithelium (FAE): May contain specialized M cells that sample antigens from the airway lumen, similar to GALT in the intestine.

    • High endothelial venules (HEVs): Specialized vessels that allow naive lymphocytes from the bloodstream to enter BALT and participate in immune responses.

    In inflamed lungs or in chronic conditions, BALT may become hyperplastic and resemble secondary lymphoid organs, complete with germinal centers and memory cell populations.

    4. Function

    The primary function of BALT is to initiate and regulate immune responses to antigens entering the lungs via inhalation. Specific functions include:

    • Antigen sampling and processing: Captures inhaled pathogens or allergens through M cells and antigen-presenting cells.

    • Lymphocyte activation: Activates naive B and T cells to respond to respiratory pathogens or environmental antigens.

    • Antibody production: Supports the class switching of B cells to IgA-secreting plasma cells that provide local mucosal protection.

    • Immunological memory formation: Facilitates long-term defense by forming memory lymphocytes specific to previously encountered respiratory antigens.

    5. Physiological Role(s)

    BALT contributes to both immune defense and immunoregulation in the respiratory system. Its physiological roles include:

    • First-line immune defense: Rapid detection and response to inhaled viruses, bacteria, and fungi before systemic spread.

    • Maintenance of pulmonary homeostasis: Balances immune activation with tolerance to harmless antigens like dust or pollen.

    • Regulation of inflammation: Helps resolve immune responses to avoid excessive lung damage, although this can be dysregulated in disease.

    • Developmental role: In neonates and children, BALT may contribute to the maturation of the immune system and help educate lymphocytes to common respiratory antigens.

    6. Clinical Significance

    Respiratory Infections

    BALT becomes highly active during acute and chronic respiratory infections. It contributes to:

    • Clearance of pathogens: Such as influenza virus, Mycobacterium tuberculosis, and respiratory syncytial virus (RSV).

    • Formation of inducible BALT (iBALT): In response to infection, inflammation, or vaccination, leading to enhanced local immunity.

    Autoimmune and Inflammatory Lung Diseases

    Excessive or dysregulated BALT formation has been implicated in several chronic lung conditions, including:

    • Chronic obstructive pulmonary disease (COPD): BALT-like lymphoid aggregates may contribute to chronic airway inflammation.

    • Rheumatoid arthritis-associated interstitial lung disease: BALT structures are often found in affected lungs.

    • Sarcoidosis and hypersensitivity pneumonitis: Characterized by exaggerated immune responses, sometimes involving BALT hyperplasia.

    BALT Lymphoma

    Extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) can arise from chronically stimulated BALT. Although rare, this type of pulmonary lymphoma often presents with persistent cough, dyspnea, or lung nodules on imaging and may be associated with autoimmune disease or chronic infection.

    Vaccination and Immunotherapy

    Targeting BALT or inducing iBALT has been proposed as a strategy for improving vaccine efficacy against respiratory pathogens. Intranasal or inhaled vaccines can stimulate BALT directly, leading to robust mucosal immunity and IgA production.

    Diagnostic Considerations

    BALT is not normally visible on routine imaging, but when hyperplastic, it may be detected as nodular or reticulonodular opacities on chest X-rays or CT scans. Bronchoscopy or lung biopsy may be required for histological evaluation in suspected lymphoma or chronic inflammatory disease.

    Did you know? Lymphatic capillaries, the smallest of the lymphatic vessels, are extremely thin-walled and allow for the uptake of interstitial fluid.