<P> Pathogenic microorganisms and other antigens entering the intestinal tract encounter macrophages, dendritic cells, B - lymphocytes, and T - lymphocytes found in Peyer's patches and other sites of gut - associated lymphoid tissue (GALT). Peyer's patches thus act for the gastrointestinal system much as the tonsils act for the respiratory system, trapping foreign particles, surveilling them, and destroying them . </P> <P> Peyer's patches are covered by a special follicle - associated epithelium that contains specialized cells called microfold cells (M cells) which sample antigen directly from the lumen and deliver it to antigen - presenting cells (located in a unique pocket - like structure on their basolateral side). Dendritic cells and macrophages can also directly sample the lumen by extending dendrites through transcellular M cell - specific pores . At the same time the paracellular pathway of follicle - associated epithelium is closed tightly to prevent penetration of antigens and continuous contact with immune cells . T cells, B - cells and memory cells are stimulated upon encountering antigen in Peyer's patches . These cells then pass to the mesenteric lymph nodes where the immune response is amplified . Activated lymphocytes pass into the blood stream via the thoracic duct and travel to the gut where they carry out their final effector functions. The maturation of B - lymphocytes takes place in the Peyer's patch . </P> <P> Although important in the immune response, excessive growth of lymphoid tissue in Peyer's patches is pathologic, as hypertrophy of Peyer's patches has been closely associated with idiopathic intussusception . </P> <P> The hypertrophy of Peyer's patches has also been associated with susceptibility to transmissible spongiform encephalopathies (commonly known as prion diseases). </P>

What is the function of the diffuse lymphatic tissue