No abstract

Alveolar type II pneumocytes are thought to be progenitor cells capable of self-renewal and differentiation into type I pneumocytes. Nevertheless, the existence of an alveolar stem cell has been postulated. In lungs from patients with cystic fibrosis, the alveolar epithelium is damaged with ulceration and subsequent regeneration. We characterized alveolar modifications histologically and immunohistochemically in the pulmonary tissue of a patient homozygous for the DF508 mutation. Alveoli were of variable size and surrounded by an inflammatory infiltrate. They were lined by a continuous layer of cuboidal cells with very weak proliferative activity. These cells resembled type II pneumocytes. They expressed thyroid transcription factor-1, cystic fibrosis transmembrane conductance regulator, cytokeratin 7 and contained lamellar bodies. Weak expression of cytokeratin 5 considered to be a marker of progenitor cells of the bronchial and bronchiolar epithelium was detected. Explantation of this alveolar epithelium produced primary cultures and subcultures of epithelial cells that had acquired proliferative properties showing signs of dedifferentiation with a loss of lamellar bodies and a lack of expression of thyroid transcription factor-1. Persistence of the expression of cytokeratin 7 and a strong expression of cytokeratin 5 were observed. The culture conditions were thought to have circumvented the inhibition of proliferation observed in vivo due to the inflammatory peri-alveolar environment. They thus favored the multiplication of a population of cells co-expressing cytokeratin 5 and certain characteristics of type II pneumocytes. The presence of these cells of intermediate phenotype is indicative of the existence of immature precursors for type II pneumocytes.

Patients with cystic fibrosis homozygous for the AF508 mutation have marked disturbances in ion exchanges in a variety of tissues. Alterations in intra- or extracellular levels of Ca2+ and calcifications have been observed in numerous tissues from such patients, although the nature and origin of such calcifications have yet to be elucidated. In this study, we investigated the formation of calcifications in the respiratory tract of a AF508 homozygous child and attempted to establish their origin. Samples of bronchial epithelium from this patient were subjected to cytophysiological analysis ex vivo and in vitro. The defect of targeting of the cystic fibrosis transmembrane conductance regulator (CFTR) to the apical plasma membrane of epithelial cells was verified. Cytochemical and ultrastructural analysis revealed the presence of crystalline aggregates in fine needles in the respiratory tract. Cytochemical analysis, X-ray spectrometry, and electron diffraction showed that these aggregates corresponded to crystals of calcium phosphate in an apatite-like structure. Ultrastructural study of primary cultures of bronchial epithelium showed the presence of calcium phosphate crystals in granules from Golgi apparatus and in mitochondria. These observations indicated that modifications of ionic exchanges due to a defect in targeting of CFTR AF508 to the apical plasma membrane led to the formation of crystals of calcium phosphate in the cytoplasm of pulmonary cells. These crystals could enhance inflammation of the lung in patients with cystic fibrosis.