ANTIGEN SAMPLING ACROSS EPITHELIAL BARRIERS AND INDUCTION OF MUCOSAL IMMUNE-RESPONSES

Epithelial barriers on mucosal surfaces at different sites' in the bod y differ dramatically in their cellular organization, and antigen samp ling strategies at diverse mucosal sites are adapted accordingly. In s tratified and pseudostratified epithelia, dendritic cells migrate to t he outer limit of the epithelium, where they sample antigens for subse quent presentation in local or distant organized lymphoid tissues. In simple epithelia, specialized epithelial M cells (a phenotype that occ urs only in the epithelium over organized lymphoid follicles) deliver samples of foreign material by transepithelial transport from the lume n to organized lymphoid tissues within the mucosa. Certain pathogens e xploit the M cell transport process to cross the epithelial barrier an d invade the mucosa. Here we review the features of M cells that deter mine antigen and pathogen adherence and transport into mucosal lymphoi d tissues.