Study supported by a Grant from General Electric Healthcare and by FICYT (COF-08-20 and COF-11 40). AGL is the recipient of a grant from Universidad de Oviedo (UNOV-09-BECDOC). IUOPA is supported by Obra Social Cajastur. CIBER Enfermedades Respiratorias is supported by Instituto de Salud Carlos III. The authors would like to thank Ana Salas and Estela Rodríguez for their invaluable help with cytokine measurements, and Pablo Martinez Camblor for his help with the statistical analysis.