Peyer's patch, showing germinal center, mantle zone, and marginal zone of larger cells with irregular nuclei and a moderate amount of pale cytoplasm. Specialized lymphoid tissue is found in association with certain epithelia, in particular the naso- and oro-pharynx (Waldeyer's ring: adenoids, tonsils), the gastrointestinal tract (gut-associated lymphoid tissue: Peyer's patches of the distal ileum, mucosal lymphoid aggregates in the colon and rectum), and lung (bronchus-associated lymphoid tissue). Collectively, this is known as mucosa-associated lymphoid tissue (MALT). These tissues tend to have prominent B cell follicles, but also may have discrete T cell zones, similar to the paracortex of lymph nodes. MALT is thought to function in response to intraluminal antigens and the generation of mucosal immunity. Lymphoid cells that respond to antigen in the MALT acquire homing properties that enable them to return to these tissues.