Abstract
Rare M cells found in the lining of the gut and lungs provide gateways for foreign substances to enter the body and be delivered to the immune system. In this issue of Science , [ Kernéis et al .][1] describe a method of converting gut epithelial cells to M cells and begin to dissect the origins of the endogenous trigger for this process. Control of the flux of antigens across the gut lining would allow more efficient oral vaccination and immunization. [1]: http://www.sciencemag.org/cgi/content/short/277/5328/949