25.6 : 二次リンパ器官

Secondary lymphoid organs, such as the spleen, lymph nodes, and mucosa-associated lymphoid tissues or MALT, are the sites where lymphocytes first encounter antigens and become activated.

The spleen, the largest lymphoid organ, is located on the left side of the abdominal cavity, below the diaphragm. Histologically, it is divided into white and red pulp.

The white pulp consists of lymphocytes and is the site for immune function. On the other hand, the red pulp is rich in macrophages and is responsible for the destruction of worn-out red blood cells and pathogens.

Lymph nodes are small, bean-shaped structures found near the surface of the body in the inguinal, axillary, and cervical regions.

In addition to lymphocyte activation, lymph nodes cleanse the lymph of pathogens and cellular debris, preventing their entry into the blood.

MALT is distributed throughout the mucous membranes of the body, protecting against pathogens.

Peyer's patches, found in the distal portion of the small intestine, and tonsils, which form a ring of lymphoid tissue around the pharynx, are the two notable examples of MALT.