Lymphatic System

Lymphatic follicles

Lymphatic follicles (lymphatic nodules) are spherical or ovoid structures composed of aggregated lymphocytes and a meshwork of reticular cells. Lymphatic follicles lack capsule, and they typically populate the lamina propria of the mucous membranes in the alimentary (gut-associated lymphoid tissue, GALT) and respiratory tracts (bronchus-associated lymphoid tissue, BALT). Primary follicles are mostly composed of small lymphocytes, while secondary follicles contain a central light zone, the germinal center that is formed by activated, large lymphocytes. Mucous membrane may contain solitary lymphatic follicles or aggregated follicles that often elevate the mucous membrane forming tonsils. These aggregated follicles also appear in the vermiform appendix and the Peyer’s patches in the ileum.