Stem cell dysfunction represents a new domain of investigation. Alveolar epithelium regeneration and repair requires activation and proliferation of tissue-resident (progenitor) cells and their differentiation to replace the damaged cells [48] . However, unlike cancer cells, stem cells are not immortal and display decreasing telomere length with aging [49] . Telomere shortening has been documented to be associated with reduced capacity for stem cell renewal, and decreased activity of telomerase, the polymerase responsible for telomere maintenance. The stem cells of the alveolar epithelium are the type 2 AEC, and expression of telomerase has been documented in these cells [48] . Experimental studies have also indicated that telomerase is expressed mainly during lung development with a peak expression before birth followed by a decrease to nearly undetectable levels in mature alveolar epithelium. Interestingly, telomerase expression and activity could be reinduced in normal quiescent type 2 AEC exposed to oxidative stress [50] . The current understanding is that a population of type 2 AEC may have the capacity to survive injury through telomerase activation, and consequently may be responsible for repopulation of the damaged alveolar epithelium. On the basis of reports of pulmonary disorders in dyskeratosis congenita (a rare hereditary disease of poor telomere maintenance), recent and exciting findings have documented mutations in the telomerase gene in familial idiopathic pulmonary fibrosis [51] . In addition, it is likely that environmental factors such as inflammation, oxidative stress, or virus infection may modify telomerase activity and account for the development of organ-specific disease associated with telomerase dysfunction. In this view, new data in chronic respiratory diseases support the concept that alveolar stem cell dysfunction may play an important role in the rate of progression or severity in ILD [52] . The question whether telomerase mutations or telomere dysfunction may be implicated in pediatric ILD needs to be addressed in prospective studies, one possible tool being determination of telomere length in circulating leukocytes.