"Lymph Node" - what is it, definition of the term
A lymphatic gland is a compact, encapsulated organ of the immune system positioned along lymphatic vessels; it consists of a cortex rich in B‑cell lymphocytes, a paracortex populated by T‑cell lymphocytes, and a medullary region containing macrophages and plasma cells, functioning to filter lymph, trap pathogens and particulate matter, and provide a site where antigens are presented to lymphocytes, thereby initiating adaptive immune responses.
Detailed information
The lymphatic gland is a small, encapsulated organ situated along the network of vessels that return interstitial fluid to the circulatory system. Its outer capsule consists of dense connective tissue, beneath which a cortex houses densely packed lymphocytes organized into follicles. Deeper within, the medulla contains cords of immune cells and sinusoids that permit filtered fluid to exit toward larger ducts. Blood supply arrives via arterioles that penetrate the capsule, while efferent vessels transport processed lymph away from the node.
When a blood‑feeding arthropod such as a tick, a biting insect, a louse, or a flea penetrates the skin, microbial agents and foreign proteins are introduced into the surrounding tissue. The nearest lymphatic gland detects these antigens through resident dendritic cells that capture and present them to T lymphocytes in the cortex. Activation of T cells triggers proliferation within germinal centers, leading to the generation of effector cells that migrate to the site of the bite. Concurrently, B lymphocytes differentiate into plasma cells that secrete antibodies targeting the introduced pathogens.
Key immunological events following an ectoparasite bite:
- Antigen capture by resident antigen‑presenting cells
- Migration of these cells to the nodal cortex
- Presentation of peptide fragments to naïve T cells
- Clonal expansion of specific T‑cell subsets
- Activation of B cells within germinal centers
- Production of pathogen‑specific immunoglobulins
Clinical relevance includes the enlargement of these glands, known as reactive lymphadenopathy, which often signals a localized infection or an allergic response to arthropod saliva. Persistent enlargement may warrant diagnostic imaging or fine‑needle aspiration to exclude malignant transformation. In cases of tick‑borne diseases, the node can serve as a reservoir for spirochetes, facilitating systemic dissemination if not promptly treated.
Therapeutic considerations focus on eliminating the arthropod, managing inflammation, and, when indicated, administering antimicrobial agents specific to the suspected pathogen. Monitoring the size and tenderness of the gland provides a practical indicator of disease progression or resolution.