On the other hand, functionally intact IgG that remains in the intestinal lumen might be expected to bind antigens and participate in protection of the tissue through immune exclusion. The intestinal mucus layer does provide an important protective barrier in the interactions of the intestinal tissue with microbes [179] . Interestingly, an IgG Fc binding site has been identified in association with the intestinal mucus [180] [181] [182] . This IgG Fc binding protein is distinct from the FcRn receptor. The Fc binding protein may block passage of IgG-antigen complexes to the enterocyte surface, thereby blocking their uptake and transport to the lamina propria, and perhaps allowing the complexes to be degraded in the intestinal lumen and excreted [169, 182] .