The Significance Of SP-A And SP-D Phase Expression In Human Fetal Lung Tissues

Pulmonary surfactant associated protein A (SP-A) and pulmonary surfactant associated protein D (SP-D) distributing on bronchus or interface of aero-fluid in pulmonary alveolus, are mainly secreted by Alveolar epithelia cell II (ACE II) and members of collectin family. SP-A and SP-D are the important innate immune defense molecules in lung local tissue, and are involved not only clearance of pathogens but also in accommodation of immune, inflammation and allergic responses. Both of them are regarded as the clinical indicator of fetal lung development and pulmonary diseases.This study aims at the general rules of human fetal lung tissue, along with SP-A and SP-D protein synthesis and secretion of different phases, for discussing the relation of fetal lung maturity with SP-A and SP-D expression. According to the analysis of these immune defense factor and immunoregulator (SP-A and SP-D) in fetal lung, it is helpful to interpret the pathophysiologic mechanism of pulmonary infection and local immune defense in pre-mature and newborn, and provides the theoretic basis of SP-A and SP-D replacement therapy.Material and MethodsForty cases of fetus by water-sac induced labor during 10-week to 3 6-week gestation, 5 cases of normal new-born and 2 cases of normal adult were collected, whose lung tissue were fixed, embedded into paraffin for section. Their lung developmental maturity was assayed by hematoxylin and eosin (HE) staining, and thephase feature of SP-A and SP-D protein expression was detected by immunohistochemistry.Meantime, the co-expression of SP-A and SP-D at one of human lung tissue section was tested under light microscopy by dual-staining immunohistochemistry.Forty-six whole fetal lungs, as well as 5 new-born lungs, were respectively lavaged with 30 ml saline, and their bronchoalveolar lavage fluid (BALF) was collected at mean rate of 85. 6+13. 1%.The total protein in BALF of fetal or newborn lungs was respectively quantified with BCA protein detection kit, among which the quantity of SP-A and SP-D was respectively detected with semi-quantity reverse indirect hemagglutination test (RIHA) and ELISA (enzyme linked immunosorbent assay) at the same time.ResultsThe SP-A protein existed in human fetal lung tissue since 10 weeks, as well as SP-D protein since 12 weeks. Both of them located in bronchial epithelium and cellular plasm of AECII in fetal lung, whose expession gradually strenthened during ductular and vesicle phases of lung deveopment; meantime drifted from promixal bronchia to AEC II . They had stably expressed in AEC II from late lung development to birth.We found SP-A and SP-D distribution had the overlapping feature in protein existing time and place. In detail, both of them could nearly at the same time express in cellular plasm. However, their expression in primitive alveolar epithelia cells had indistinctively improved before birth, then the two kind of proteins synthesized and secreted more after birth.The BCA assay also suggested the total protein concentration in BALF gradually improved since 10-week gestation with fetal lung development to peak at the time of birth. The methods of RIHA and ELISA detected that SP-A and SP-D content changed under this law, and their concentrations were respectively 0.34+ 0.07ug/ml, 0.05 ± 0.0lug/ml when 10-week gestation, upregulated into 6.42 + 0.36ug/ml, 1.22 ± 0.13ug/ml before birth.ConclusionsThe study is the first time domestic report that detects the protein expression, distribution, and content change of SP-A and SP-D in human fetal lung development with several methods. It suggests SP-A and SP-D expression gradually strengthened with fetal lung development. The SP-A and SP-D positive cells began to exist in fetal bronchial epithelial cells, located in ACE II. With fetus growth and fetal lung development, the protein secreted more in BALF, and SP-A and SP-D synthesis and secretion reached the peak when birth. The ACE II stimulated by kinetical factors(such as alveolar charging or drag) after birth, could rapidly synthesis and secret SP molecules. The phase expression of SP-A and SP-D was important indicator of fetal lung maturity. All of findings are hopeful of revealing pathologic mechanism of abnormal pulmonary surfactant synthesis for premature; moreover provide data about SP-A or SP-D related pulmonary diseases for newborn, specially premature.