128 ANTIGEN TRANSPORT AND PROCESSING ACROSS IFNγ-TREATED HT29-19A INTESTINAL CELLS.

Abstract

The main function of Major Histocompatibility Complex class II (MHC II) molecules is to present antigenic peptides produced in antigen presenting cells to T lymphocytes. During intestinal inflammation, an overexpression of MHC II molecules in enterocytes is associated with an increased macromolecular transport. This study examines the relationship between MHC II expression and transepithelial transport and processing of an exogenous protein, horseradish peroxidase (HRP). Transwell-grown HT29-19A intestinal cells were treated on their basal or apical side with IFNγ (10 to 100 U/ml). After 48 hours, intracellular and surface expression of MHC II molecules as well as the lysosomal proteolytic activity (cathepsin B and D) were assessed. Transepithelial transport and processing of 3H-HRP were measured in HT29-19A cell monolayers mounted in Ussing chambers and ionic conductance (G) and 22Na and 14C-mannitol fluxes were used as markers of the paracellular pathway. HT29-19A cells did not express MHC II molecules in basal conditions. IFNγ induced an increase in MHC II molecules, but their transfer to the external membrane was small. The stimulation of MHC II molecules expression was not associated with a change in proteolytic cathepsin B or D activity. When IFNγ was placed on the basal compartment of intestinal monolayers, G, 22Na, 14C-mannitol and intact-HRP fluxes rose significantly (G: 7.2±0.2 vs 22.7±4.3 mS/cm2, 22Na: 63±2 vs 184±24 μg/h.cm2, 14C-Mannitol: 5.6±0.3 vs 25±5 μg/h.cm2, intact HRP: 31±4 vs 193±56 ng/h.cm2 in control vs IFNγ-treated cells) suggesting a paracellular leakage. Degraded-3H-HRP fluxes, reflecting a transcellular pathway, were also significantly increased in IFNγ-treated cells compared to controls. No such changes in permeability were observed when IFNγ was applied in the apical compartment. The chromatographic profiles of the tritiated peptides released in the basal compartment of Ussing chambers after transcytosis of 3H-HRP, were not strickingly different between control and IFNγ-treated intestinal cells. In the HT29-19A intestinal model stimulated by IFNγ, no direct relationship is found between MHC II molecules expression by enterocytes and the transepithelial transport and processing of exogenous antigens.