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    Related Topics

    From Lymphatic System

    Lymphatic Capillaries
    Initial lymphatic vessels that collect interstitial fluid.
    Mastoid Lymph Nodes
    Drain the posterior scalp and ear.
    Sacral Lymph Nodes
    Drain the pelvic floor and rectum.
    Iliac Lymph Nodes
    Include external, internal, and common iliac nodes.
    Preaortic Nodes
    Located in front of the aorta.
    Parotid Lymph Nodes
    Drain the lateral face and scalp.
    Spleen
    Filters blood and initiates immune response.
    Jugular Trunk
    Drains lymph from the head and neck.
    BALT
    Bronchus-associated lymphoid tissue.
    Peyer’s Patches
    Lymphoid nodules in the small intestine.
    Deep Cervical Lymph Nodes
    Located along internal jugular vein; receive lymph from head and neck.
    Right Lymphatic Duct
    Drains right upper quadrant of the body.
    Paratracheal Nodes
    Located lateral to the trachea.
    Occipital Lymph Nodes
    Drain the back of the scalp.
    Inguinal Lymph Nodes
    Drain the lower limbs and external genitalia.
    Lymphatic Collecting Vessels
    Carry lymph through lymph nodes.
    Thoracic Duct
    Main lymphatic duct draining most of the body.
    Submandibular Lymph Nodes
    Drain the face, mouth, and pharynx.
    Axillary Lymph Nodes
    Drain the upper limbs and chest wall.
    Lumbar Trunk
    Drains lower limbs and pelvic organs.
    Pharyngeal Tonsil
    Located in the nasopharynx (adenoids).
    NALT
    Nasal-associated lymphoid tissue.
    Supraclavicular Lymph Nodes
    Located above the clavicle; key in thoracic drainage.
    Subclavian Trunk
    Drains lymph from the upper limbs.
    Apical Axillary Nodes
    Located at the apex of the axilla.

    SALT

    Reviewed by our medical team

    Skin-associated lymphoid tissue.

    1. Overview

    Skin-associated lymphoid tissue (SALT) is a specialized component of the immune system that operates at the body’s largest organ— the skin. As a form of peripheral or mucosa-associated lymphoid tissue (MALT), SALT serves as a frontline defense system against pathogens entering through the skin. It contains a diverse network of immune cells and plays an essential role in immune surveillance, inflammation, and homeostasis. SALT is especially important in mediating both innate and adaptive immune responses at cutaneous sites.

    2. Location

    SALT is widely distributed throughout all layers of the skin, particularly in the epidermis and dermis. Key locations include:

    • Epidermis: Contains specialized immune cells such as Langerhans cells (dendritic cells) and resident memory T cells.

    • Dermis: Contains a variety of immune cells including dermal dendritic cells, mast cells, macrophages, natural killer (NK) cells, and a dense network of T lymphocytes.

    • Skin-draining lymph nodes: Although not part of SALT directly, these nodes receive antigen-presenting cells that migrate from the skin and are essential in initiating systemic immune responses.

    SALT is functionally integrated with the lymphatic vessels of the dermis and subcutaneous tissue, allowing antigen-presenting cells to transport captured antigens to regional lymph nodes.

    3. Structure

    Unlike traditional lymphoid organs, SALT is not encapsulated and does not have a distinct follicular architecture. Instead, it consists of diffusely distributed immune cells organized into functional zones. Its components include:

    • Langerhans cells: Specialized dendritic cells located in the epidermis that capture and process antigens.

    • Dermal dendritic cells: Located in the dermis, they help present antigens to T cells and support immune responses.

    • Resident T cells: Include CD4+ helper T cells and CD8+ cytotoxic T cells, particularly memory T cells that remain in the skin long-term.

    • Mast cells and macrophages: Contribute to innate immune responses and inflammation.

    • Keratinocytes: Though not classical immune cells, they produce cytokines and chemokines that shape immune responses.

    These elements are supported by a network of capillaries and lymphatic vessels that facilitate cell migration and immune communication with systemic lymphoid organs.

    4. Function

    SALT plays several key roles in cutaneous immune defense. Major functions include:

    • Antigen detection: Langerhans cells and dermal dendritic cells detect and process microbial and environmental antigens.

    • Immune response initiation: Antigen-presenting cells activate T lymphocytes either locally or in skin-draining lymph nodes.

    • Memory formation: Skin-resident memory T cells are formed following antigen exposure, enabling rapid recall responses to repeat challenges.

    • Inflammation regulation: Cytokines and chemokines produced by keratinocytes and immune cells modulate local inflammation and recruit additional immune effectors.

    • Barrier integrity support: Immune cells within SALT help maintain the structural and microbial balance of the epidermal barrier.

    5. Physiological Role(s)

    SALT is critical for maintaining skin immune equilibrium and providing site-specific immunity. Its physiological roles include:

    • Defense against pathogens: First responder to bacteria, viruses, fungi, and parasites that breach the epidermis.

    • Wound healing: Immune cells assist in tissue repair by clearing debris and promoting angiogenesis and epithelial regeneration.

    • Tumor surveillance: T cells and NK cells monitor and eliminate cells with malignant potential.

    • Microbiome interaction: Helps maintain a balanced relationship with skin commensals by regulating immune tolerance and inflammation.

    • Environmental response: Reacts to allergens, UV radiation, and irritants, which can lead to immune tolerance or hypersensitivity depending on context.

    6. Clinical Significance

    Inflammatory Skin Diseases

    Dysregulation of SALT contributes to several chronic inflammatory conditions, including:

    • Psoriasis: Involves excessive activation of dendritic cells and T cells, resulting in epidermal hyperplasia and chronic inflammation.

    • Atopic dermatitis: Characterized by barrier dysfunction and Th2-dominant immune responses within SALT.

    • Contact dermatitis: Caused by overactivation of SALT in response to allergens (Type IV hypersensitivity reaction).

    Cutaneous Infections

    SALT is essential in defending against infections such as:

    • Staphylococcus aureus skin infections

    • Herpes simplex virus reactivation

    • Fungal infections like dermatophytosis

    Immunodeficiencies or local immune suppression can lead to severe or recurrent skin infections due to impaired SALT function.

    Skin-Resident Memory T Cells

    These long-lived T cells remain in the epidermis after primary exposure and enable rapid and localized immune responses on re-exposure to the same antigen—vital for vaccine strategies and skin-targeted immunotherapies.

    Skin Cancer Surveillance

    SALT contributes to immunosurveillance against developing skin tumors such as melanoma or squamous cell carcinoma. Loss of immune regulation or immune evasion by tumor cells can allow progression.

    Vaccination and Immunotherapy

    SALT is a target for transcutaneous or intradermal vaccination techniques that aim to activate local immunity and generate systemic responses (e.g., smallpox or BCG vaccines).

    Transplant and Autoimmune Relevance

    In graft-versus-host disease (GVHD) and autoimmune blistering disorders (e.g., pemphigus vulgaris), aberrant T cell activation in SALT contributes to tissue damage and systemic inflammation.

    Did you know? The lymphatic system consists of lymph, lymph nodes, tonsils, spleen, and thymus.