Nonetheless, oxygen susceptibility of regulatory immunocompetent cells as well as integrity of the mucosal barrier function may play an important role in protection and/or modification of the immune response including the integrity of epithelial tight junctions and M-cell related transcytosis of pathogens to highly organised lymphoid structures for effective immune responses [4; 12; 16]. A strong correlation between intestinal hypoxia during strenuous exercise and the magnitude of intestinal mucosa damage has been demonstrated by plasma levels of the surrogate parameter intestinal fatty acid binding protein (I-FABP), a specific biomarker for mucosal damage in the small intestine [4; 17].