1. Immunology Area, Pediatric Hospital Bambino Gesù, Viale San Paolo 15, 00146 Rome, Italy
2. Department of Experimental Medicine-Section of Histology, University of Genova, Via G.B. Marsano 10, 16132 Genova, Italy
3. Department of Medicine, University of Verona, Piazzale L.A. Scuro 10, 37134 Verona, Italy