Veterinary Immunology and Serology

SPLEEN

• Lymph nodes filter antigen from lymph where as the spleen filters antigen from the blood.
• The spleen is the major site of immune responses to blood borne antigens.
• The filtering process removes both antigen particles and aged blood cells.
• Spleen stores red cells and platelets and produce blood cells in the fetus.
• Spleen is covered by a capsule and trabeculae pass into splenic pulp.
• The splenic pulp is divided into two compartments
  • Red pulp
  • white pulp

• The white pulp is circular in structure and is made up mainly of lymphocytes. It functions in a manner similar to the nodules of the lymph node.
• The red pulp surrounds the white pulp and contains mainly red blood cells and macrophages. The main function of the red pulp is to phagocytize old red blood cells

• The framework of the pulp is supported by the meshwork of reticular cells and fibres.
• Blood supply in spleen is by a single splenic artery that pierces the capsule at hilum and progressively divided into branches as trabecular artery.
• Small trabecular arterioles are surrounded by cuffs of lymphocytes (T cells and called T cell zone) in a cylindrical form and are called periarterial lymphoid sheath (PALS).
• Within these PALS, lymphoid follicles are present and some of which contain germinal centre.
• The follicles are in B cell zone.
• Germinal centres develop on antigenic stimulation and they are also called Malpighian corpuscles.
• A layer of T cells forming a mantle zone surrounds each follicle.
• The white pulp consists of periarteriolar sheath, the B cell follicle and the mantle zone.
• Trabecular artery in PALS is known as central artery and branches into many.
• Some supply terminates in marginal zone as sheathed artery or penicilli.
• White pulp and red pulp are separated by marginal zone, which is formed by fine spongy work of reticular cells and their fibres.
• Both T cells and B cells are present in this zone.
• The Red pulp is formed by cords of a meshwork of reticular cells and sinuses. All arterial blood vessels enter and terminate in cords. The cords contain RBCs, macrophages, platelets and plasma cells. The cords act as filter for RBCs, WBCs and sites for extra medulla hematopoiesis. Destruction of platelets and RBCs takes place in the red pulp and is referred to as hemocatharesis. The immune responses occur in the white pulp.
• Function - Site for the development of immune response. 2). Site for hematopoiesis (lymphopoiesis and erythropoiesis) .  3). Organ for filtration of RBCs and WBCs. 4).  Trap antigen and develop immune response.