Lymphoid and haematopoietic system

The lymphoid and haematopoietic system is composed of multiple organs and tissues distributed throughout the body and is responsible for the development of the immune response, and the production of the blood's cellular components. The primary lymphoid organs are the bone marrow and thymus, responsible for production and maturation of the B- and T- lymphocytes respectively. The secondary lymphoid organs, the lymph nodes, spleen and mucosa-associated lymphoid tissues maintain populations of mature lymphocytes and are the sites of antigenic stimulation and clonal expansion. The mucosa associated lymphoid tissue (MALT) represents dispersed aggregates of nonencapsulated lymphoid tissue along the surface of mucosal tissues and they act to protect the mucosae against infectious agents. The thymus is a primary immune organ, in which T-cells are produced without the need for antigenic stimulation. The bone marrow is the primary site for haematopoiesis and is a primary lymphoid tissue.