How do lymph nodes help lymphocytes encounter foreign antigens?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

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.

Lymph nodes facilitate the encounter between lymphocytes and foreign antigens by acting as specialized filtration centers within the lymphatic system.1

Antigens enter the node via lymphatic vessels, while naive B and T cells arrive through specialized blood vessels known as high endothelial venules (HEVs). Once inside, the node’s structural organization ensures these cells meet their targets:1

B cells: These migrate to the outer cortex to form follicles. Within these structures, they interact with dendritic cells and macrophages that present foreign antigens. Upon activation, they form germinal centres for maturation.1
T cells: These remain in the paracortex, where cortical macrophages and dendritic cells present antigenic peptides to them, stimulating their activation into helper or cytotoxic T lymphocytes.1

By concentrating both the foreign material and the immune cells in these specific microenvironments, lymph nodes maximize the efficiency of the immune system in detecting and responding to threats.1