Lymph node
Clinical significance
The B cells migrate to the nodular cortex and medulla. The T cells migrate to the deep cortex. This is a region of a lymph node called the paracortex that immediately surrounds the medulla. Because both naive T cells and dendritic cells express CCR7, they are drawn into the paracortex by the same chemotactic factors, increasing the chance of T cell activation. Both B and T lymphocytes enter lymph nodes from circulating blood through specialized high endothelial venules found in the paracortex. Lymph node enlargement or swelling is known as lymphadenopathy. Swelling may be due to many causes, including infections, tumors, autoimmune disease, drug reactions, diseases such as amyloidosis and sarcoidosis, or because of lymphoma or leukemia. Depending on the cause, swelling may be painful, particularly if the expansion is rapid and due to an infection or inflammation. Lymph node enlargement may be localised to an area, which might suggest a local source of infection or a tumour in that area that has spread to the lymph node. It may also be generalised, which might suggest infection, connective tissue or autoimmune disease, or a malignancy of blood cells such as a lymphoma or leukaemia. Rarely, depending on location, lymph node enlargement may cause problems such as difficulty breathing, or compression of a blood vessel (for example, superior vena cava obstruction).
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