The lymph nodes are major components of the lymphatic system clustered in small groups or chains at strategic locations, where they drain the lymphatic vessels of various anatomic regions. The drainage involves not only the mechanical filtration of the foreign bodies in the lymph but also the recognition and processing of antigens. The lymph nodes exhibit a complex architecture in which a variety of cell populations are arranged in distinct interfacing compartments. This provides a favorable environment in which the various cellular components can process antigens, interact, and generate the immune response.