Extramural tumor deposits without a lymph node structure in T1 sigmoid colon cancer

Lymph nodes are the sentinels of the immune system that control the surfaces of the body to the outside (skin, lung, gut) and the tissues, whereas the spleen monitors the inside surface (vasculature) and the blood. Lymph nodes are both matchmakers and copy shops. They are matchmakers because they bring together antigens with antigen-specific B lymphocytes and T lymphocytes. This is a major challenge since antigens can enter and develop at any site of the body while the average frequency of antigen-specific B cells and T cells is in the range of only 1 in 100 000. Lymph nodes solve this problem by concentrating antigen-containing lymph and attracting huge numbers of B cells and T cells from the blood. Lymph nodes are copy shops because they provide a microenvironment that facilitates an enormous expansion of B cells and T cells bearing receptors specifically directed against the cognate antigen. Due to their huge number, these antigen-specific B cells and T cells are now able to successfully protect the body. This article describes the anatomical structures allowing the lymph node to be a matchmaker and a copy shop.