Appendix ('gut-associated lymphatic tissue' or GALT) (human)

A large nodule in the appendix extends through the proper lamina (1) and submucosa. The nodule is similar to that found in a lymph node with germinal centre (2) and darker-stained cap (crescent) (3) orientated towards the lumen of the gut showing a flattened dome area covered with discontinuous epithelial lining (4). Short crypts of Lieberkhn with columnar mucous epithelial cells (5) flank the dome area. (6) Connective tissue of submucosal layer. The follicles mostly contain B cell types while T cells are spread throughout the interfollicular areas. Plasma cells here produce largely dimeric IgA to be transported through the epithelial cells towards the lumen.