Antigènes alimentaires, barrière intestinale et immunité muqueuse

The intestine absorbs nutrients but also samples luminal macromolecules (food antigens, bacteria) in view of developing tolerogenic or inflammatory immune responses. Two distinct pathways are implicated: the paracellular and transcellular transport pathways. Tight junctions between epithelial cells determine paracellular permeability and in steady-state condition small molecules only are permeable. Food antigens cannot diffuse along tight junctions, they are sampled by transcytosis across enterocytes, partially degraded into peptides that bind to the enterocyte MHC class II molecules and are secreted in the form of antigen presenting vesicules called exosomes. Luminal content can also be sensed through the transport of immune-complexes, IgE in food allergy, IgA in celiac disease and sometimes IgG. These immune complexes allow protective responses towards pathogenic bacteria but induce deleterious immune responses when food antigens are concerned (food allergy, celiac disease).