Opening the crypt: current facts and hypotheses on the function of cryptopatches.

Cryptopatches, small aggregates of lymphoid cells found in the intestinal lamina propria, have been assigned many functions specific to gut immunity. Populated with seemingly immature lymphoid cells and dendritic cells, it has been suggested that cryptopatches maturate intraepithelial lymphocytes, Th17 cells, IL-22-producing NKp46(+) cells, and lymphoid tissues in response to the gut microbiota. Some of these issues, however, remain hotly debated. Therefore, cryptopatches are coming to the forefront of gut immunology and warrant a comprehensive discussion of their role in the development of the immune system.