1. Department of Immunology and Gnotobiology, Institute of Microbiology ASCR, v.v.i., Vídeňská 1083, 142 20 Prague 4, Czech Republic, and Department of Biomedical Polymers, Institute of Macromolecular Chemistry ASCR, v.v.i., Heyrovský Square 2, 162 06 Prague 6, Czech Republic