1 CEB-Centre of Biological Engineering, University of Minho, Campus de Gualtar, 4710-057 Braga Portugal; LABBELS-Associate Laboratory, Braga, Guimarães, Portugal. Electronic address: jazeredo@deb.uminho.pt.
2 Laboratory for Molecular and Cellular Technology, Queen Astrid Military Hospital, Brussels B-1120, Belgium. Electronic address: Jean-paul.pirnay@mil.be.