Expression of thyroid transcription factor-1, surfactant proteins, type I cell-associated antigen, and Clara cell secretory protein in pulmonary hypoplasia.

Pulmonary hypoplasia (PH) is a developmental abnormality characterized by diminished distal lung parenchyma. Recent studies have demonstrated that thyroid transcription factor 1 (TTF-1), a member of NKx2 family of homeodomain transcription factors, plays an important role in lung organogenesis and lung epithelial gene expression. In order to evaluate whether abnormal expression of TTF-1 contributes to the pathophysiology of PH, we studied the expression of TTF-1, as well as that of the surfactant proteins (SPs), Clara cell secretory protein (CCSP), and type I cell-associated antigen (T1 cell-Ag), in PH. Immunolocalization patterns of these proteins were evaluated in 15 cases of PH with different associated diseases and compared with those of 14 matched controls. Our study demonstrated that the concentration gradient of TTF-1 along the proximal-distal axis in normal fetal lung is disrupted in PH after 24 weeks gestational age, while the expression of the SPs, CCSP, and T1 cell-Ag seemed to be preserved. We conclude that a normal TTF-1 expression pattern might be crucial in the control of distal lung development. Failure to switch off expression of TTF-1 in PH of more than 24 weeks gestational age may be a final common pathway leading to PH associated with the disease processes investigated in this study.

Expression of thyroid transcription factor-1 in congenital cystic adenomatoid malformation of the lung.

Congenital cystic adenomatoid malformation (CCAM) is an abnormality of branching morphogenesis of the lung. CCAM types 1, 2, and 3 exhibit a cellular composition that is different from that of CCAM type 4 when evaluated with bronchiolar and alveolar cell markers. Thyroid transcription factor 1 (TTF-1) regulates early lung development. To evaluate the potential role of TTF-1 in the development of CCAM, TTF-1 expression in CCAM was compared to that of fetal lungs at varying gestational ages. Twenty-three CCAM cases (17 type 1, two type 2, two type 3, and two type 4) and 11 fetal lungs (3 pseudoglandular, 4 canalicular, and 4 terminal sac stages) were analyzed using a rabbit polyclonal antiserum to rat TTF-1. Nuclear staining for TTF-1 was observed in ciliated and nonciliated cells of the bronchial and bronchiolar epithelia and in cells lining the distal air spaces by 12 weeks gestational age. By mid-gestation, proximal bronchial cells were TTF-1 negative, except for the basal cells, while TTF-1 staining was maintained in distal bronchiolar and alveolar cells. TTF-1 expression decreased in both bronchial, bronchiolar, and alveolar epithelia with advancing gestational age and cytodifferentiation. At term, TTF-1 expression persisted in a few bronchial and bronchiolar basal cells and in all alveolar type II cells, whereas type I cells were negative. In CCAM, TTF-1 was detected in the nuclei of epithelial cells lining the cysts. TTF-1 was expressed in a majority of the bronchiolar-like epithelial cells of the cysts in CCAM types 1, 2, and 3, where almost 100% of the cells were TTF-1 positive. In contrast, TTF-1 expression in the alveolar-like epithelium of CCAM type 4 cysts was restricted to type II cells and only 30%-60% of the lining cells were TTF-1 positive. These results support the hypothesis that CCAM types 1, 2, and 3 reflect abnormalities in lung morphogenesis and differentiation that are distinct from those for CCAM type 4. The role played by TTF-1 in the development of CCAM, if any, is not clear.

Congenital cystic adenomatoid malformation of the lung (CCAM): evaluation of the cellular components.

Congenital cystic adenomatoid malformation of the lung (CCAM) is a rare congenital lesion whose pathogenesis is not well defined. It is generally accepted that the various types of CCAMs originate at different levels of the tracheobronchial tree. To further define the pathogenesis of CCAM, we evaluated the cellular composition of different CCAM types by immunohistochemistry. Twenty-two CCAMs (17 CCAM type 1, two type 2, one type 3, and two type 4) were collected. The cellular composition was determined using immunohistochemical stains for type I cell-associated antigen (T1 cell-Ag), surfactant proteins and surfactant protein precursors (SP-A, SP-B, proSP-B, and proSP-C), neuroendocrine cells (GRP), Clara cells (UP-1), and the adhesion molecule CD44v6, a glycoprotein thought to be involved in cell-matrix and cell-cell interactions. Eleven fetal lungs also were analyzed to compare cytodifferentiation of the epithelial-lined cysts of the different types of CCAM with the stages of normal lung development. Our results indicate that CCAM is caused by an arrest in lung development, and, on the basis of cytodifferentiation, two major subtypes can be distinguished. One subtype consisting of CCAM types 1, 2, and 3 that shows a bronchiolar type of epithelium and a second subtype, consisting of CCAM type 4, that has an acinar-alveolar type of epithelium. Our findings also suggest that these two subtypes may arise at different stages of the branching of the bronchopulmonary tree, the first at the pseudoglandular stage and the second at the saccular stage.

Aberrant processing of surfactant protein C in hereditary SP-B deficiency.

Hereditary surfactant protein B (SP-B) deficiency causes lethal neonatal respiratory disease associated with abnormalities in pulmonary surfactant proteins and lipids. SP-C, a 4-kDa hydrophobic protein produced from a 21-kDa precursor, cooperates with SP-B to enhance the surface active properties of surfactant phospholipids. Anti-proSP-C polyclonal antisera were produced against fusion proteins containing 1) the amino terminus (amino acids 1-20), 2) the region carboxy-terminal to the mature SP-C peptide (amino acids 58-77), and 3) full-length 197-amino acid proSP-C and were characterized using immunoprecipitation, Western blot, and immunohistochemical techniques. Western blot analysis of bronchoalveolar lavage and amniotic fluid from hereditary SP-B-deficient patients allowed identification of a 12-kDa form of SP-C that contained epitopes consistent with the amino-terminal and active peptide regions of SP-C (amino acids 1-57). The 12-kDa SP-C peptide was not detected in bronchoalveolar lavage from healthy adults or adults with alveolar proteinosis or pneumonia. We conclude that SP-B deficiency is associated with the aberrant processing and secretion of an immature SP-C peptide, which may contribute to the respiratory failure associated with hereditary SP-B deficiency.