1. Division of Mucosal Immunology, Research Center Borstel, Parkallee 22, 23845 Borstel, Germany, Institute of Infectiology, University of Münster, von-Esmarch-Strasse 56, 48149 Münster, Germany, and Department of Analytical Biotechnology, Veterinary Research Institute, Hudcova 70, 621 32 Brno, Czech Republic