1. Facultad de Ciencias, Universidad Nacional Autónoma de México, México DF, México;
2. Instituto Nacional de Enfermedades Respiratorias “Ismael Cosío Villegas,” México DF, México; and
3. Dorothy P. and Richard P. Simmons Center for Interstitial Lung Disease, Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania