1. Departamento de Inmunologı́a, Microbiologı́a y Parasitologı́a, Facultad de Medicina y Odontologı́a,1 and
2. Departamento de Enfermerı́a I,2 Universidad del Paı́s Vasco, E-48080 Bilbao, Vizcaya, Spain, and
3. Department of Oral Surgery, Oral Medicine and Oral Pathology, School of Dental Science, Trinity College, University of Dublin, Dublin 2, Republic of Ireland3