Cells, tissues, and organs composing the
immune system, including the
bone marrow,
thymus,
spleen, and
lymph nodes. The most highly organized components are the thymus and lymph nodes, and the least organized are the cells that wander in the loose
connective-tissue spaces under membranes lining most body systems, where they can establish lymph nodules (local
lymphocyte production centre) in response to
antigens. The most common lymphoid tissue cell is the lymphocyte. Others are macrophages, which engulf foreign materials and probably alter them to initiate the immune response, and reticular cells, which produce and maintain thin networks of fibres as a framework for most lymphoid organs.
See also immunity;
lymphatic system.
For more information on lymphoid tissue, visit Britannica.com.
