ABSTRACT
The main sites of entry for microbes into the body are through mucosal surfaces. It is therefore not surprising that more than 50% of the total body lymphoid mass is associated with these surfaces. These are collectively called mucosa-associated lymphoid tissues (MALT) and include NALT, BALT, GALT, and lymphoid tissue associated with the genitourinary system (Section O). There are two main kinds of mucosal lymphoid tissue: (i) aggregates of subepithelial lymphocytes “organized” into follicles often with overlying specialized epithelial cells (microfold or M cells—see below); (ii) “diffuse” lymphoid tissue (separate cell populations) within the lamina propria below the epithelial cell layer of the various tracts.
