1. Department of Bacteriology, Swedish Institute for Infectious Disease Control, S-171 82 Solna, Sweden
2. Microbiology and Tumor Biology Center, Karolinska Institute, S-171 77 Stockholm, Sweden
3. Department of Cell and Molecular Biology, Box 596, The Biomedical Center, Uppsala University, S-751 24 Uppsala, Sweden
4. LEO Pharma, DK-2750 Ballerup, Denmark