Lymph Nodes: Function, Location & Importance for Immunity

Lymph nodes are small, bean-shaped secondary lymphoid organs strategically distributed along lymphatic vessels. Major clusters: cervical, axillary, inguinal, mesenteric, mediastinal.

Core Functions

1. Filtration & Surveillance: Lymph percolates through cortical sinuses; dendritic cells present antigens to naïve T/B cells.
2. Lymphocyte Activation & Clonal Expansion: Antigen-specific T and B cells proliferate in paracortex and follicles.
3. Effector Differentiation: B cells → plasma cells (antibodies); T cells → cytotoxic/Th1/Th2/Th17/Tfh subsets.
4. Memory Formation: Long-lived memory B/T cells persist for rapid secondary responses.
5. Immune Cell Reservoir: Macrophages, dendritic cells, NK cells, follicular dendritic cells.
6. Fluid Homeostasis: Return filtered lymph to venous circulation via thoracic duct.
7. Tolerance Induction: Regulatory T cells prevent autoimmunity to self-antigens.

Clinical Relevance

Lymphadenopathy signals infection, malignancy (lymphoma, metastasis), autoimmune disease, or drug reactions. Pattern, consistency, and associated symptoms guide diagnosis.