Orally inducible immune unresponsiveness is abrogated by IFN-gamma treatment.

The role of murine epithelial cells from small intestine (IEC) in orally induced immune unresponsiveness has been investigated. Murine IEC were shown to express a relatively low level of class II MHC Ag and were incapable of presenting BSA to Ag-specific Th cells. IFN-gamma treatment of the animals dramatically enhanced expression of class II MHC Ag by IEC enabling Ag presentation to Th cells. Ag-presenting function of IEC after IFN-gamma treatment was not affected by IEC panning on anti-IgG or anti-MAC-1-coated plates but it was blocked by a class II MHC-specific mAb. IFN-gamma-treated mice were responsive to parenteral BSA challenge after oral administration of the Ag, whereas untreated mice were immunosuppressed. Our data support the concept that poor expression of class II MHC Ag on IEC contributes to immunosuppression induced by oral administration of a protein Ag.