1. Institute of Pathology and Molecular Immunology of the University of Porto; Rua Dr Roberto Frias s/n 4200-465 Porto Portugal
2. Institute of Biomedical Science Abel Salazar; University of Porto; Portugal
3. Hospital Veterinario do Porto; Travessa Silva Porto, 174 4200-465 Porto Portugal
4. Rohm and Haas Research Laboratories; 85W Stratford Avenue Lansdowne PA 19050-1946 USA