IFN-gamma-producing dendritic cells are important for priming of gut intraepithelial lymphocyte response against intracellular parasitic infection.

The importance of intraepithelial lymphocytes (IEL) in immunoprotection against orally acquired pathogens is being increasingly recognized. Recent studies have demonstrated that Ag-specific IEL can be generated and can provide an important first line of defense against pathogens acquired via oral route. However, the mechanism involved in priming of IEL remains elusive. Our current study, using a microsporidial model of infection, demonstrates that priming of IEL is dependent on IFN-gamma-producing dendritic cells (DC) from mucosal sites. DC from mice lacking the IFN-gamma gene are unable to prime IEL, resulting in failure of these cells to proliferate and lyse pathogen-infected targets. Also, treatment of wild-type DC from Peyer's patches with Ab to IFN-gamma abrogates their ability to prime an IEL response against Encephalitozoon cuniculi in vitro. Moreover, when incubated with activated DC from IFN-gamma knockout mice, splenic CD8(+) T cells are not primed efficiently and exhibit reduced ability to home to the gut compartment. These data strongly suggest that IFN-gamma-producing DC from mucosal sites play an important role in the generation of an Ag-specific IEL response in the small intestine. To our knowledge, this report is the first demonstrating a role for IFN-gamma-producing DC from Peyer's patches in the development of Ag-specific IEL population and their trafficking to the gut epithelium.