To investigate the functional maturity of the lungs of infants with pulmonary hypoplasia, we measured the expression of surfactant apoprotein-A (SP-A) in the autopsied lungs. Autopsied lungs were taken from 16 infants who died at birth or soon after. A lung-to-body weight ratio of less than 1.2% was defined as pulmonary hypoplasia. Eight infants were classified as belonging to the normal group, and eight as belonging to the pulmonary hypoplasia group. Many of the pulmonary hypoplasia group were complicated not only by pulmonary hypoplasia, but also by amniotic fluid volume abnormalities or an anatomical malformation. We measured the expression of SP-A immunologically using murine anti-human SP-A MAb in the autopsied lung tissue, and subjected the tissue to SP-A staining by the direct staining method. The expression of SP-A was assessed as one of four grades: Ϫ, Ϯ, 1ϩ, 2ϩ. The staining intensity of SP-A was high at 1ϩ or stronger in five infants of the normal group. SP-A expression was significantly reduced, however, in all infants of the pulmonary hypoplasia group except for one infant with normal amniotic fluid volume and relatively mild pulmonary hypoplasia. There was a significant negative correlation between the staining intensity of SP-A and two factors: pulmonary hypoplasia and abnormal amniotic fluid volume (p ϭ 0.039 and p ϭ 0.0063, respectively). In the present study, we demonstrated that SP-A expression was significantly reduced in infants with pulmonary hypoplasia. We speculate that the functional maturity of the lungs of infants with pulmonary hypoplasia is also suppressed. The alveolar lining is composed of type I and type II epithelial cells. Human pulmonary surfactants are lipid-protein complexes (lipoproteins) synthesized in type II cells. These surfactants are secreted into the alveolar space in order to cover the surface of alveoli and thus reduce alveolar surface tension. The functional expression of pulmonary surfactants requires specific proteins (apoproteins). To date, four types of surfactant apoproteins (SP) have been identified: SP-A, SP-B, SP-C, and SP-D. Of these, SP-A is the most prevalent form of SP (1). SP-A is a hydrophilic glycoprotein with a molecular weight of approximately 28 -36 kD, and the level of SP-A in the amniotic fluid, gastric juice, and respiratory aspirate is a useful indicator of the functional maturity of fetal and neonatal lung tissue (2, 3).In the present study, to assess the functional maturity of the lungs of infants with pulmonary hypoplasia, we measured the expression of SP-A immunohistologically using murine antihuman SP-A MAb in the autopsied lungs of infants who died at birth or soon after.
METHODS
Subjects.Autopsied lungs were taken from 16 infants at some point during a 21-y period between November 1976 and February 1998. Of the 16 infants, 14 came from the Division of Neonatal Intensive Care or the Department of Gynecology and Obstetrics at our hospital. These subjects had died at birth or within 5 d of birth. The remaining two infants came from the Neo...