Institute of Virology, Charité - Universitätsmedizin Berlin, Freie Universität Berlin, Humboldt-Universität zu Berlin, Berlin Institute of Health, Berlin, Germany. Electronic address: guenther.schoenrich@charite.de. Institute of Virology, Charité - Universitätsmedizin Berlin, Freie Universität Berlin, Humboldt-Universität zu Berlin, Berlin Institute of Health, Berlin, Germany. Section Molecular Immunology, Institute of Immunology, Heidelberg University Hospital, Heidelberg, Germany. Electronic address: yvonne.samstag@urz.uni-heidelberg.de.