The red and white pulp of the spleen (100X)

The white pulp consists of lymphoid tissue surrounding central arteries, organized into lymphoid follicles that include a periarteriolar lymphoid sheath (PALS) predominantly made up of T lymphocytes. Surrounding the PALS are germinal centers, which primarily contain B lymphocytes and macrophages. This area plays a crucial role in the immune response by producing lymphocytes and antibodies, with germinal centers serving as sites for B cell proliferation and differentiation.

The red pulp is characterized by a network of sinusoids (venous sinuses) and splenic cords (cords of Billroth). The sinusoids are lined by endothelial cells with a discontinuous basal lamina, allowing the free passage of blood cells. The splenic cords comprise reticular cells and fibers, containing erythrocytes, macrophages, lymphocytes, plasma cells, and other blood cells. This region is responsible for filtering blood, removing old and damaged red blood cells, recycling iron, and serving as a reservoir for blood and platelets. Macrophages in the red pulp phagocytose cellular debris and pathogens.