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What role do high endothelial venules play in lymph nodes?

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Diagram of the human lymphatic system highlighting lymphatic vessels and major lymphoid organs, including lymph nodes, adenoids, tonsils, thymus gland, spleen, appendix, bone marrow, and ducts. — lymphatic system The human lymphatic system, showing the lymphatic vessels and lymphoid organs.

High endothelial venules (HEVs) serve as the primary entry point for lymphocytes traveling from the bloodstream into the lymph node.

These specialized blood vessels are characterized by a single layer of large endothelial cells equipped with surface receptors specifically designed to recognize and bind B and T lymphocytes. As these immune cells pass through the HEVs, they adhere to these receptors and are effectively recruited into the paracortex of the lymph node. Once inside, the lymphocytes can migrate to their respective functional areas—T cells remain in the paracortex to encounter antigens, while B cells move into the outer cortex—to participate in the body's immune response.12