Appearance of paoproteins of pulmonary surfactant in human amniotic fluid

Preventing Respiratory Viral Diseases with Antimicrobial Peptide Master Regulators in the Lung Airway Habitat

The vast surface area of the respiratory system acts as an initial site of contact for microbes and foreign particles. The whole respiratory epithelium is covered with a thin layer of the airway and alveolar secretions. Respiratory secretions contain host defense peptides (HDPs), such as defensins and cathelicidins, which are the best-studied antimicrobial components expressed in the respiratory tract. HDPs have an important role in the human body's initial line of defense against pathogenic microbes. Epithelial and immunological cells produce HDPs in the surface fluids of the lungs, which act as endogenous antibiotics in the respiratory tract. The production and action of these antimicrobial peptides (AMPs) are critical in the host's defense against respiratory infections. In this study, we have described all the HDPs secreted in the respiratory tract as well as how their expression is regulated during respiratory disorders. We focused on the transcriptional expression and regulation mechanisms of respiratory tract HDPs. Understanding how HDPs are controlled throughout infections might provide an alternative to relying on the host's innate immunity to combat respiratory viral infections.

Differential Regulation of Human Surfactant Protein A Genes, SFTPA1 and SFTPA2, and Their Corresponding Variants

The human SFTPA1 and SFTPA2 genes encode the surfactant protein A1 (SP-A1) and SP-A2, respectively, and they have been identified with significant genetic and epigenetic variability including sequence, deletion/insertions, and splice variants. The surfactant proteins, SP-A1 and SP-A2, and their corresponding variants play important roles in several processes of innate immunity as well in surfactant-related functions as reviewed elsewhere [1]. The levels of SP-A have been shown to differ among individuals both under baseline conditions and in response to various agents or disease states. Moreover, a number of agents have been shown to differentially regulate SFTPA1 and SFTPA2 transcripts. The focus in this review is on the differential regulation of SFTPA1 and SFTPA2 with primary focus on the role of 5′ and 3′ untranslated regions (UTRs) and flanking sequences on this differential regulation as well molecules that may mediate the differential regulation.

Genetic Factors Contribute to Risk for Neonatal Respiratory Distress Syndrome among Moderately Preterm, Late Preterm, and Term Infants

OBJECTIVE

To determine the genetic contribution to risk for respiratory distress syndrome (RDS) among moderately preterm, late preterm, and term infants (estimated gestational age ≥32 weeks) of African- and European-descent.

STUDY DESIGN

We reviewed clinical records for 524 consecutive twin pairs ≥32 weeks gestation. We identified pairs in which at least 1 twin had RDS (n = 225) and compared the concordance of RDS between monozygotic and dizygotic twins. Using mixed-effects logistic regression, we identified covariates that increased disease risk. We performed additive genetic, common environmental, and residual effects modeling to estimate genetic variance and used the ratio of genetic variance to total variance to estimate genetic contribution to RDS disease risk.

RESULTS

Monozygotic twins were more concordant for RDS than dizygotic twins (P = .0040). Estimated gestational age, European-descent, male sex, delivery by cesarean, and 5-minute Apgar score each independently increased risk for RDS. After adjusting for these covariates, genetic effects accounted for 58% (P = .0002) of the RDS disease risk variance for all twin pairs.

CONCLUSIONS

In addition to environmental factors, genetic factors may contribute to RDS risk among moderately preterm, late preterm, and term infants. Discovery of risk alleles may be important for prediction and management of RDS risk.

Delivery and performance of surfactant replacement therapies to treat pulmonary disorders

Lung surfactant is crucial for optimal pulmonary function throughout life. An absence or deficiency of surfactant can affect the surfactant pool leading to respiratory distress. Even if the coupling between surfactant dysfunction and the underlying disease is not always well understood, using exogenous surfactants as replacement is usually a standard therapeutic option in respiratory distress. Exogenous surfactants have been extensively studied in animal models and clinical trials. The present article provides an update on the evolution of surfactant therapy, types of surfactant treatment, and development of newer-generation surfactants. The differences in the performance between various surfactants are highlighted and advanced research that has been conducted so far in developing the optimal delivery of surfactant is discussed.

Effects of nicotine on pulmonary surfactant proteins A and D in ovine lung epithelia

Maternal smoking during pregnancy increases the incidence and severity of respiratory infections in neonates. Surfactant proteins A and D (SP-A and SP-D, respectively) are components of pulmonary innate immunity and have an important role in defense against inhaled pathogens. The purpose of this study was to determine if nicotine exposure during the third trimester of pregnancy alters the expression of SP-A and SP-D of fetal lung epithelia. Pregnant ewes were assigned to four groups; a nicotine-exposed full-term and pre-term group, and control full-term and pre-term group. Lung tissue was collected for Western blot and IHC analysis of SP-A level, Western blot analysis of SP-D level and qPCR analysis of SP-A and SP-D mRNA expression. Exposure to nicotine significantly decreased SP-A gene expression (P = 0.01) and SP-A protein level in pre-term lambs. This finding suggests that maternal nicotine exposure during the last trimester of pregnancy alters a key component of lung innate immunity in offspring.

Genetic complexity of the human innate host defense molecules, surfactant protein A1 (SP-A1) and SP-A2--impact on function

Innate immunity mechanisms play a critical role in the primary response to invading pathogenic microorganisms and other insulting agents. The innate lung immune system includes lung surfactant, a lipoprotein complex that carries out a function essential for life, that is, reduction of the surface tension at the air-liquid interphase of the alveolar space. By means of this function, pulmonary surfactant prevents lung collapse, therefore ensuring normal lung function and lung health. Pulmonary surfactant contains a number of host-defense molecules that are involved in the elimination of pathogens, viruses, particles, allergens, and other insults, as well as in the control of inflammation. This review is concerned with one of the surfactant proteins, the human (h) surfactant protein A (hSP-A), which, in addition to its role in surfactant-related functions, plays an important role in the modulation of lung host defense. The hSP-A locus has been identified with extensive complexity that may have an impact on its function, structure, and regulation. In humans, two genes--SP-A1 (SFTPA1) and SP-A2 (SFTPA2)--encode SP-A, with SP-A2 gene products being more biologically active than SP-A1 in most of the in vitro assays investigated. Although the two hSP-A genes share a high level of sequence similarity, differences in the structure and function between SP-A1 and SP-A2 have been observed in recent studies. In this review, we discuss the human SP-A complexity and how this may affect SP-A function.

Amniotic fluid concentration of surfactant proteins in intra-amniotic infection

OBJECTIVE

Pulmonary surfactant is a complex molecule of lipids and proteins synthesized and secreted by type II alveolar cells into the alveolar epithelial lining. Both lipid and protein components are essential for lung function in postnatal life. Infection is a well-established cause of preterm delivery, and several inflammatory cytokines play a role in the mechanisms of preterm parturition. An increased concentration of inflammatory cytokines in amniotic fluid or fetal plasma has been linked to the onset of preterm parturition and fetal/neonatal injury, including cerebral palsy and chronic lung disease. Experimental evidence indicates that inflammatory mediators also regulate surfactant protein synthesis, and histologic chorioamnionitis is associated with a decreased incidence of hyaline membrane disease in neonates. This study was conducted to determine if amniotic fluid concentrations of surfactant protein (SP)-A, SP-B, and SP-D change in patients with and without intra-amniotic infection (IAI).

MATERIALS AND METHODS

A case-control study was conducted to determine amniotic fluid concentrations of SP-A, SP-B, SP-D, and total protein in patients who had an amniocentesis performed between 18 and 34 weeks of gestation for the detection of IAI in patients with spontaneous preterm labor with intact membranes (n = 42) and cervical insufficiency prior to the application of cerclage (n = 6). Amniotic fluid samples were selected from a bank of biological specimens and included patients with (n = 16) and without (n = 32) IAI matched for gestational age at amniocentesis. Intra-amniotic infection was defined as a positive amniotic fluid culture for microorganisms. Each group was further subdivided according to a history of corticosteroid administration within 7 days prior to amniocentesis into the following subgroups: (1) patients without IAI who had received antenatal corticosteroids (n = 21), (2) patients with IAI who had received antenatal corticosteroids (n = 9), (3) patients without IAI who had not received antenatal corticosteroids (n = 11), and (4) patients with IAI who had not received antenatal corticosteroids (n = 7). Amniotic fluid was obtained by transabdominal amniocentesis. SP-A, SP-B, and SP-D concentrations in amniotic fluid were determined by enzyme-linked immunosorbent assay (ELISA). Non-parametric statistics were used for analysis.

RESULTS

Women with IAI had a higher median amniotic fluid concentration of SP-B and of SP-B/total protein, but not other SPs, than those without IAI (both p = 0.03). Among patients who had received antenatal corticosteroids, the median amniotic fluid concentration of SP-B and of SP-B/total protein was significantly higher in patients with IAI than in those without IAI (SP-B, IAI: median 148 ng/mL, range 37.3-809 ng/mL vs. without IAI: median 7.2 ng/mL, range 0-1035 ng/mL; p = 0.005 and SP-B/total protein, IAI: median 14.1 ng/mg, range 4.3-237.5 ng/mg vs. without IAI: median 1.45 ng/mg, range 0-79.5 ng/mg; p = 0.003). Among women who had not received antenatal corticosteroids, the median amniotic fluid concentrations of SP-B and of SP-B/total protein were not significantly different between patients with and without IAI (SP-B, IAI: median 4 ng/mL, range 0-31.4 ng/mL vs. without IAI: median 3.4 ng/mL, range 0-37 ng/mL; p = 0.8 and SP-B/total protein, IAI: median 0.55 ng/mg, range 0-6.96 ng/mg vs. without IAI: median 0.59 ng/mg, range 0-3.28 ng/mg; p = 0.9). The median amniotic fluid concentrations of SP-A, SP-A/total protein, SP-D, and SP-D/total protein were not significantly different between patients with and without IAI whether they received antenatal corticosteroids or not (all p > 0.05).

CONCLUSIONS

IAI was associated with an increased amniotic fluid concentration of SP-B in patients who received antenatal corticosteroids within 7 days prior to amniocentesis.

The concentration of surfactant protein-A in amniotic fluid decreases in spontaneous human parturition at term

OBJECTIVE

The fetus is thought to play a central role in the onset of labor. Pulmonary surfactant protein (SP)-A, secreted by the maturing fetal lung, has been implicated in the mechanisms initiating parturition in mice. The present study was conducted to determine whether amniotic fluid concentrations of SP-A and SP-B change during human parturition.

STUDY DESIGN

Amniotic fluid SP-A and SP-B concentrations were measured with a sensitive and specific ELISA in the following groups of pregnant women: (1) mid-trimester of pregnancy, between 15 and 18 weeks of gestation (n = 29), (2) term pregnancy not in labor (n = 28), and (3) term pregnancy in spontaneous labor (n = 26). Non-parametric statistics were used for analysis.

RESULTS

SP-A was detected in all amniotic fluid samples. SP-B was detected in 24.1% (7/29) of mid-trimester samples and in all samples at term. The median amniotic fluid concentrations of SP-A and SP-B were significantly higher in women at term than in women in the mid-trimester (SP-A term no labor: median 5.6 microg/mL, range 2.2-15.2 microg/mL vs. mid-trimester: median 1.64 microg/mL, range 0.1-4.7 microg/mL, and SP-B term no labor: median 0.54 microg/mL, range 0.17-1.99 microg/mL vs. mid-trimester: median 0 microg/mL, range 0-0.35 microg/mL; both p < 0.001). The median amniotic fluid SP-A concentration in women at term in labor was significantly lower than that in women at term not in labor (term in labor: median 2.7 microg/mL, range 1.2-10.1 microg/mL vs. term no labor: median 5.6 microg/mL, range 2.2-15.2 microg/mL; p < 0.001). There was no significant difference in the median amniotic fluid SP-B concentrations between women in labor and those not in labor (term in labor: median 0.47 microg/mL, range 0.04-1.32 microg/mL vs. term no labor: median 0.54 microg/mL, range 0.17-1.99 microg/mL; p = 0.2).

CONCLUSION

The amniotic fluid concentration of SP-A decreases in spontaneous human parturition at term.

Maternal alcohol ingestion reduces surfactant protein A expression by preterm fetal lung epithelia

In addition to neurodevelopmental effects, alcohol consumption at high levels during pregnancy is associated with immunomodulation and premature birth. Premature birth, in turn, is associated with increased susceptibility to various infectious agents such as respiratory syncytial virus (RSV). The initial line of pulmonary innate defense includes the mucociliary apparatus, which expels microorganisms trapped within the airway secretions. Surfactant proteins A and D (SP-A and SP-D, respectively) are additional components of pulmonary innate immunity and have an important role in pulmonary defense against inhaled pathogens. The purpose of this study was to determine if chronic alcohol consumption during the third trimester of pregnancy alters the function of the mucociliary apparatus and expression of SP-A and SP-D of fetal lung epithelia. Sixteen, date-mated ewes were assigned to two different groups; an ethanol-exposed group in which ewes received ethanol through surgically implanted intra-abomasal cannula during the third trimester of pregnancy, and a control group in which ewes received the equivalent amount of water instead of ethanol. Within these two groups, ewes were further randomly assigned to a full-term group in which the lambs were naturally delivered, and a preterm group in which the lambs were delivered prematurely via an abdominal incision and uterotomy. Ethanol was administered five times a week as a 40% solution at 1g/kg of body weight. The mean maternal serum alcohol concentration measured 6h postadministration was 16.3+/-4.36 mg/dl. Tracheas from six full-term lambs were collected to assess ciliary beat frequency (CBF). The lung tissue from all (24) lambs was collected for immunohistochemistry analysis of SP-A and SP-D protein production and fluorogenic real-time quantitative polymerase chain reaction analysis of SP-A and SP-D mRNA levels. Exposure to ethanol during pregnancy significantly blocked stimulated increase in CBF through ethanol-mediated desensitization of cAMP-dependent protein kinase. In addition, preterm born/ethanol-exposed lambs showed significantly decreased SP-A mRNA expression when compared with the preterm born/control group (P=.004); no significant changes were seen with SP-D. The full-term/ethanol-exposed lambs had no significant alterations in mRNA levels, but had significantly less detectable SP-A protein when compared with the full-term/control lambs (P=.02). These findings suggest that chronic maternal ethanol consumption during the third trimester of pregnancy alters innate immune gene expression in fetal lung. These alterations may underlie increased susceptibility of preterm infants, exposed to ethanol in utero, to RSV and other microbial agents.

Collectins and cationic antimicrobial peptides of the respiratory epithelia

The respiratory epithelium is a primary site for the deposition of microorganisms that are acquired during inspiration. The innate immune system of the respiratory tract eliminates many of these potentially harmful agents preventing their colonization. Collectins and cationic antimicrobial peptides are antimicrobial components of the pulmonary innate immune system produced by respiratory epithelia, which have integral roles in host defense and inflammation in the lung. Synthesis and secretion of these molecules are regulated by the developmental stage, hormones, as well as many growth and immunoregulatory factors. The purpose of this review is to discuss antimicrobial innate immune elements within the respiratory tract of healthy and pneumonic lung with emphasis on hydrophilic surfactant proteins and beta-defensins.

Regulation of surfactant protein and defensin mRNA expression in cultured ovine type II pneumocytes by all-trans retinoic acid and VEGF

Beta-defensins and surfactant proteins are components of the pulmonary innate immune system. Their gene expression is regulated by development, hormones, growth and immunoregulatory factors. It was our hypothesis that growth and differentiation factors such as all-trans retinoic acid (RA) and vascular endothelial growth factor (VEGF) may affect expression of selected innate immune genes by respiratory epithelial cells. Ovine JS7 cells (alveolar type II pneumocytes) were incubated in serum-free Dulbecco's modified Eagle's medium (DMEM) complete media that contained: no treatment (negative control), RA (500 nM), or VEGF (100 ng/ml) for 6, 12 or 24 h incubation. Total RNA was isolated, cDNA synthesized, and relative mRNA levels of surfactant protein A (SP-A) and SP-D, and sheep beta-defensin-1 (SBD-1) were determined by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Cells had significantly increased expression of SP-D mRNA at 6 h and 24 h, decreased expression of SP-A mRNA at 12 h, and unchanged levels of SBD-1 mRNA after the treatment with RA compared with their respective negative controls. VEGF did not alter the expression of the three innate immune genes. These findings suggest that SP-A and SP-D have different transcription regulation pathways, and that expression of SBD-1 is not inducible by RA similar to its human homolog HBD-1. The lack of changes induced by VEGF treatment suggests that VEGF does not have a direct effect on epithelial cells, but may affect gene expression indirectly.

Evolution of pulmonary surfactants for the treatment of neonatal respiratory distress syndrome and paediatric lung diseases

This review documents the evolution of surfactant therapy, beginning with observations of surfactant deficiency in respiratory distress syndrome, the basis of exogenous surfactant treatment and the development of surfactant-containing novel peptides patterned after SP-B. We critically analyse the molecular interactions of surfactant proteins and phospholipids contributing to surfactant function.

CONCLUSION

Peptide-containing surfactant provides clinical efficacy in the treatment of respiratory distress syndrome and offers promise for treating other lung diseases in infancy.

Testing for fetal lung maturation: a biochemical "window" to the developing fetus

Fetal lung maturity testing represents a major milestone in perinatology. This article critically evaluates specific controversies regarding the methodologies used to measure pulmonary surfactant in AF and how well each of these techniques performs both in principle and application. The clinical utility of fetal lung maturity testing as it applies to particularly difficult complications of pregnancy is discussed. These technical and clinical issues are framed by the scientific and empiric evidence that is used as the rationale for such testing and its implementation in the effective management of preterm delivery.

Maternal tobacco smoking and lung epithelium-specific proteins in amniotic fluid

The bronchiolar 16 kD Clara cell secretory protein (CC16) and the alveolar surfactant-associated protein A (SP-A) are secreted in the amniotic fluid (AF), where they reflect the growth and the maturity of the fetal lung. To evaluate the possible effects of in utero tobacco smoke exposure upon infant bronchoalveolar epithelium function and maturity, CC16 and SP-A levels were determined in AF obtained at term (36-41 wk) from 28 nonsmoking, 18 smoke-exposed, and 28 smoking mothers with uncomplicated pregnancies. Tobacco smoke exposure was assessed by questionnaire and the assay in AF and maternal urine of cotinine, a stable nicotine metabolite. The specificity of the changes of CC16 and SP-A concentrations in AF was assessed by comparison with nonpulmonary proteins of high- (albumin and transferrin) or low-molecular weight (beta2-microglobulin, retinol binding protein, cystatin-C). Pulmonary and nonpulmonary AF proteins were also compared by two-dimensional gel electrophoresis between smoking and nonsmoking mothers. The levels of CC16 and SP-A as well as low- and high-molecular-weight proteins were not significantly different between the three smoking categories. The protein pattern of AF, established by two-dimensional gel electrophoresis, did not reveal any quantitative or qualitative difference between nonsmoking (n = 10), smoke-exposed (n = 5), and smoking mothers (n = 5). By multiple regression analysis of possible determinants, tobacco smoke did not emerge as a significant predictor of CC16 and SP-A concentrations in AF. SP-A level was dependent only on gestational age at birth (r2 = 0.1, p = 0.001), whereas CC16 correlated only with the levels of low-molecular weight proteins (r2 = 0.2, p = 0.0001). The latter correlation suggests that CC16 enters AF not only as a result of its secretion at the surface of the respiratory tract but also partly following its elimination by the fetal kidney. This study suggests that maternal smoking during pregnancy is not associated with alterations of the secretory functions of the epithelium of the distal airways and the alveoli at term.

Surfactant protein A (SP-A): the alveolus and beyond

Surfactant protein A (SP-A) is the major protein component of pulmonary surfactant, a material secreted by the alveolar type II cell that reduces surface tension at the alveolar air-liquid interface. The function of SP-A in the alveolus is to facilitate the surface tension-lowering properties of surfactant phospholipids, regulate surfactant phospholipid synthesis, secretion, and recycling, and counteract the inhibitory effects of plasma proteins released during lung injury on surfactant function. It has also been shown that SP-A modulates host response to microbes and particulates at the level of the alveolus. More recently, several investigators have reported that pulmonary surfactant phospholipids and SP-A are present in nonalveolar pulmonary sites as well as in other organs of the body. We describe the structure and possible functions of alveolar SP-A as well as the sites of extra-alveolar SP-A expression and the possible functions of SP-A in these sites.

Surfactant protein-A: new insights into an old protein--II

Pulmonary surfactant is a lipoprotein substance that lines the lungs and helps reduce surface tension. Surfactant associated protein-A (SP-A) is the most abundant non-serum protein in pulmonary surfactant. This complex glycoprotein aids in the synthesis, secretion and recycling of surfactant phospholipids, and facilitates the reduction of surface tension by surfactant phospholipids. Recent evidence has highlighted the role of SP-A in the innate immune system present in the lung. SP-A may play a major role in defense against pathogens by interacting with both infectious agents and the immune system. Factors that affect fetal lung maturation, e.g. gestational age and hormones regulate SP-A gene expression. Mediators of immune function also regulate SP-A levels. A number of lung disorders, including infectious diseases and respiratory distress syndrome are associated with abnormal alveolar SP-A levels. SP-A can no longer be called a lung-specific protein, since it has recently been detected in other tissues. In most species, SP-A is encoded by a single gene, however in humans it is encoded by two, very similar genes. Models for the structure of the human SP-A protein molecule have been proposed, suggesting that the mature alveolar SP-A molecule is composed of both gene products. The study of SP-A may provide information helpful in understanding disease processes and formulating new treatment modalities.

Immunohistochemical localization of surfactant apoproteins in usual interstitial pneumonia associated with pulmonary carcinoma

Surfactant apoproteins A and B (SP-A and SP-B) are antigenic determinants of pulmonary surfactant complexes. The role and functional significance of these proteins are largely unknown and the pattern of expression is probably related to the functional maturation of type II pneumocytes. Differential expression of SP-A and SP-B was reported in the developing human lung but little is known of their expression in the chronic injury. We studied 5 surgical cases of usual interstitial pneumonia (UIP) associated with carcinoma to evaluate the expression of pulmonary surfactant apoproteins. These cases were immunohistochemically examined by the streptavidin-biotin complex method using monoclonal antibodies HS-1 and HS-2 against pulmonary surfactant apoprotein A (SP-A) and B (SP-B), respectively. In UIP, SP-B was expressed strongly in type II pneumocytes and Clara cells but bronchiolar epithelium and metaplastic squamous cell lines in the honeycomb lesion were non-reactive. SP-A showed a similar pattern but much weaker reactivity when compared to that of SP-B. Type II pneumocytes in normal lung tissue exhibited weak immunoreactivity and no difference in the intensity of staining between SP-A and SP-B. Neither carcinomatous area nor metaplastic lining cells at honeycomb lesion show immunoreactivity to SP-A and SP-B. These results suggest that type II pneumocytes in the UIP are functionally immature in their expression of the apoprotein types and the metaplastic squamous cells or neoplastic transformed cells do not have molecular characteristics of type II pneumocytes.

Collectins: collectors of microorganisms for the innate immune system

Collectins are a group of multimeric proteins mostly consisting of 9-18 polypeptides organised into either 'bundle-of-tulips' or 'X-like' overall structures. Each polypeptide contains a short N-terminal segment followed by a collagen-like sequence and then by a C-terminal lectin domain. A collectin molecule is assembled from identical or very similar polypeptides by disulphide bonds at the N-terminal segment, formation of triple helices in the collagen-like region and clusters of three lectin domains at the peripheral ends of triple helices. These proteins can bind to sugar residues on microorganisms via the peripheral lectin domains and subsequently interact, via the collagen-like triple-helices, with receptor(s) on phagocytes and/or the complement system to bring about the killing and clearance of the targets without the involvement of antibodies. The collectins can also bind to phagocyte receptor(s) to enhance phagocytosis mediated by other phagocytic receptors. Lack, or low levels, of collectin expression can lead to higher susceptibility to infections, especially during childhood when specific immunity has not fully developed. Therefore, the collectins play important roles in the enhancement of innate immunity.

Immunohistochemical investigation of pulmonary surfactant in perinatal fatalities

In order to verify forensic pathological significance of immunohistochemical investigation of pulmonary surfactant, 11 forensic and 16 clinico-pathological cases of perinatal death were comparatively examined. Surfactant appeared in some infants of 31-32 weeks gestation and was usually positive thereafter, indicating maturity of fetal lungs, although it may not have fully developed until about the 36th week of gestation. It was negative in all cases of the hyaline membrane disease except for a full-term infant (secondary respiratory distress syndrome). In usual cases, surfactant coating the expanded alveolar epithelia with its diffuse deposit in the intra-alveolar spaces was considered to indicate duration of hypoxia under persistent respiration (agonal state). Such finding was most intensely observed in asphyxia and in severe respiratory failure from intrinsic causes in the infants over ca. 36 weeks of gestation. With reference to pulmonary micromorphology, the amount of intra-alveolar surfactant seemed to be most closely related to the alveolar septal (interstitial) edema.

Analysis of dipalmitoyl phosphatidylcholine in amniotic fluid by enzymatic hydrolysis and high-performance thin-layer chromatography reflectance spectrodensitometry

A novel test for the determination of dipalmitoyl phosphatidylcholine (DPPC) in amniotic fluid (AF) as free dipalmitoylglycerol (DPG), is described. Aliquots of amniotic fluid were hydrolyzed with Bacilus cereus phospholipase C, and the resulting diglycerides analyzed by AgNO3-modified high-performance thin-layer chromatography (HPTLC)-reflectance spectrodensitometry. This HPTLC system provided resolution of DPG and palmitoylpalmitoleoylglycerol (POG) from other 1,2-diglycerides and cholesterol. The turn-around analysis time for triplicate aliquots of amniotic fluid was 40 min. Recoveries ranged between 90 and 98%. In summary, this method provides a quantitative, specific, highly reproducible, and fast turn-around means of analysis of DPPC in amniotic fluid.

Stable microbubble test for predicting the risk of respiratory distress syndrome: I. Comparisons with other predictors of fetal lung maturity in amniotic fluid

With the advent of surfactant replacement therapy, there is an increasing need for a rapid test of predicting the development of respiratory distress syndrome (RDS). We evaluated the clinical usefulness of the stable microbubble (SM) test in predicting the development of RDS by comparison with other tests in amniotic fluid samples obtained within 12 h before delivery from 40 pregnancies between 23-35 weeks of gestation. These tests included the lecithin/sphingomyelin (L/S) ratio, disaturated phosphatidylcholine/sphingomyelin (DSPC/S) ratio, concentrations of lecithin, DSPC, and surfactant-associated proteins A and B, C (SP-A, SP-B,C). The cut-off value of each test for predicting RDS was determined at a point of maximum diagnostic accuracy. The overall diagnostic accuracy of the SM test was similar to that of other tests. However, both the SM test and the SP-B,C concentration had positive predictive values of 100%. We conclude that the rapid (< 10 min) and reliable information obtained by this test should encourage its use in defining a population of neonates with surfactant deficiency in a multicentre trial of prophylactic surfactant therapy.

Immunoassay for the determination of surfactant apoprotein (SP-A) in human amniotic fluid: comparison with other indices of assessing foetal lung maturity

The concentration of the major surfactant-associated protein SP-A (28-36 kDa) was determined in 73 amniotic fluid samples obtained from normal (n = 40) and complicated (n = 33) pregnancies. Lecithin/sphingomyelin (L/S) ratio and phosphatidylglycerol (PG) levels were also determined in all the samples by one-dimensional step-wise thin-layer chromatography. An enzyme-linked immunosorbent assay was used to determine human lung surfactant apoprotein SP-A. The amount of SP-A in human amniotic fluid increased as a function of gestational age from 8 mg l-1 at 36 weeks to 11.75 mg l-1 at 40-41 weeks of gestation. There was a significant difference (p less than 0.01) in amniotic fluid SP-A concentration from female (9.93 +/- 0.60 micrograms ml-1) compared to male (9.10 +/- 0.52 micrograms ml-1) foetuses. In amniotic fluid samples obtained from a group of complicated pregnancies, SP-A levels were significantly lower than in the normal group when adjusted for gestational age and sex of the foetus (p less than 0.05).

Surfactant protein A in the course of respiratory distress syndrome

Surfactant-associated protein (SP-A) was measured in tracheal aspirates of ventilated infants with (n = 51) and without (n = 21) respiratory distress syndrome (RDS). SP-A concentrations in samples collected after birth were significantly lower in RDS than in infants ventilated for other reasons than RDS (median 0.03 vs. 1.60 micrograms/ml). As a biochemical test to diagnose RDS early after birth, the sensitivity of measuring SP-A in tracheal aspirates was 87% and specificity 81%. SP-A content in tracheal aspirates of infants with RDS was monitored during the first 7 days of life. A significant (P less than 0.001) increase within the first 4 days was found in those infants who survived, whereas no such change was found in those infants who died.

Purification, characterization and cDNA cloning of human lung surfactant protein D

Human pulmonary surfactant protein D (SP-D) was identified in lung lavage by its similarity to rat SP-D in both its molecular mass and its Ca(2+)-dependent-binding affinity for maltose [Persson, Chang & Crouch (1990) J. Biol. Chem. 265, 5755-5760]. For structural studies, human SP-D was isolated from amniotic fluid by affinity chromatography on maltose-Sepharose followed by f.p.l.c. on Superose 6, which showed it to have a molecular mass of approx. 620 kDa in non-dissociating conditions. On SDS/PAGE the human SP-D behaved as a single band of 150 kDa or 43 kDa in non-reducing or reducing conditions respectively. The presence of a high concentration of glycine (22%), hydroxyproline and hydroxylysine in the amino acid composition of human SP-D indicated that it contained collagen-like structure. Collagenase digestion yielded a 20 kDa collagenase-resistant globular fragment which retained affinity for maltose. Use of maltosyl-BSA as a neoglycoprotein ligand in a solid-phase binding assay showed that human SP-D has a similar carbohydrate-binding specificity to rat SP-D, but a clearly distinct specificity from that of other lectins, such as conglutinin, for a range of simple saccharides. Amino acid sequence analysis established the presence of collagen-like Gly-Xaa-Yaa triplets in human SP-D and also provided sequence data from the globular region of the molecule which was used in the synthesis of oligonucleotide probes. Screening of a human lung cDNA library with the oligonucleotide probes, and also with rabbit anti-(human SP-D), allowed the isolation of two cDNA clones which overlap to give the full coding sequence of human SP-D. The derived amino acid sequence indicates that the mature human SP-D polypeptide chain is 355 residues long, having a short non-collagen-like N-terminal section of 25 residues, followed by a collagen-like region of 177 residues and a C-terminal C-type lectin domain of 153 residues. Comparison of the human SP-D and bovine serum conglutinin amino acid sequences indicated that they showed 66% identity despite their marked differences in carbohydrate specificity.

Implication of surfactant apoprotein in otitis media with effusion

A two-site simultaneous immunoassay using monoclonal antibodies against human surfactant apoprotein (SAP) was used to measure SAP in middle ear effusions (MEEs). In 130 MEE samples from children with otitis media with effusion, SAP was detected in 54 samples (SAP-positive cases, 41.5%). In the remainder, the SAP concentration was below the sensitivity of the immunoassay (SAP-negative cases, 58.5%). A significant difference in periods of observation was found between the SAP-positive cases (17.3 +/- 16.8 months) and the SAP-negative cases (26.2 +/- 22.5 months) (p less than .01). The percentage of positive cases was highest in the serous MEE group (81.2%) and decreased in the purulent MEE group (57%), the mucoid MEE group (30%), and the hyperviscous MEE group (13.6%), in that order. In the purulent MEE group and the mucoid MEE group, the period of observation was significantly shorter in the SAP-positive cases (18.3 +/- 20.4 months and 20.2 +/- 19.4 months) than in the SAP-negative cases (35.9 +/- 24.5 months and 25.4 +/- 18.7 months) (p less than .05). These results suggest that SAP is present in the middle ear cleft and may be a good prognostic predictor of otitis media with effusion in children.

Hormonal and developmental regulation of pulmonary surfactant synthesis in fetal lung

Pulmonary surfactant, a unique developmentally regulated, phospholipid-rich lipoprotein, is synthesized by the type II cells of the pulmonary alveolus, where it is stored in organelles termed lamellar bodies. The principal surface-active component of surfactant, dipalmitoylphosphatidylcholine, a disaturated form of phosphatidylcholine, acts in concert with the surfactant-associated proteins to reduce alveolar surface tension. Relatively large amounts of phosphatidylglycerol also are present in lung surfactants of a number of species, including man. The role of phosphatidylglycerol in surfactant function has not been elucidated; however, its presence in increased amounts in pulmonary surfactant is correlated with enhanced fetal lung maturity. Surfactant glycerophospholipid synthesis in fetal lung tissue is regulated by a number of hormones and factors, including glucocorticoids, prolactin, insulin, oestrogens, androgens, thyroid hormones, and catecholamines acting through cyclic AMP. In studies with human fetal lung in organ culture, we have observed that glucocorticoids, in combination with prolactin and/or insulin, increase the rate of lamellar body phosphatidylcholine synthesis and alter lamellar body glycerophospholipid composition to one reflective of surfactant secreted by the human fetal lung at term. Four surfactant-associated proteins, SP-A, SP-B, SP-C and SP-D, have recently been characterized. Recognition of their potential importance in the reduction of alveolar surface tension and in endocytosis and reutilization of secreted surfactant by type II cells has stimulated rapid advancement of knowledge concerning the structures of the surfactant proteins and their genes, as well as their developmental and hormonal regulation in fetal lung tissue. The genes encoding SP-A, SP-B and SP-C are expressed in a cell-specific manner and are independently regulated in fetal lung tissue during development. SP-A gene expression occurs exclusively in the type II cell and is initiated after 75% of gestation is complete. In the human fetus, expression of the SP-B and SP-C genes is detectable much earlier in development than SP-A, before the time of appearance of differentiated type II cells. It is apparent from studies using human and rabbit fetal lung in culture that cyclic AMP and glucocorticoids serve important roles in the regulation of SP-A gene expression. While the effects of cyclic AMP are exerted primarily at the level of gene transcription in human fetal lung tissue, glucocorticoids have stimulatory effects on SP-A gene transcription and inhibitory effects on SP-A mRNA stability. In addition, cyclic AMP and glucocorticoids act synergistically to increase SP-A gene transcription in human fetal lung in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of cell-specific markers for alveolar epithelium in fetal rat lung

In adults, the alveolar epithelium is composed of types I and II cells which differ structurally and functionally although they appear to belong to the same cell lineage. Using cell-specific markers (type I cells, monoclonal antibody; type II cells, Maclura pomifera lectin [MPA]), we have determined when and in what pattern their binding sites occur during development of the fetal rat lung. Rather than first appearing on days 19 to 20, when morphogenesis of type I cells occurs and lamellar bodies provide positive identification of type II cells, the markers appeared on day 15 (for type I cell marker) and day 16 (for type II cell marker). The type I cell marker was widespread by day 17 and was sufficiently abundant to be detected on a Western blot. MPA binding appeared more gradually and was often found on isolated cells. On serial sections of day 20 lung, the markers appeared to be localized to the same cells. The early appearance of cell-specific markers suggests an early onset of the developmental program that leads to full differentiation of types I and II cells. Co-expression of both cell-specific markers suggest that fetal cell lineage may differ from the scheme proposed by others that type II cells serve as type I cell precursors during development.

A new method for measurement of surfactant specific apoprotein in amniotic fluid

A simple and rapid method for the quantitative measurement of surfactant specific apoprotein concentration in amniotic fluid was developed using the measurement of immunological reactions by the nephelometric technique. Use of this method made it possible to measure 0.5-8.0 micrograms apoproteins per ml within approximately 70 min. Surfactant specific apoproteins in 54 samples of amniotic fluid were measured using the method. The surfactant specific apoprotein concentration in amniotic fluid increased from 1.03 +/- 0.51 micrograms/ml (mean +/- S.D.) at 26-30 weeks of gestation to 4.45 +/- 2.08 micrograms/ml at 36 weeks of gestation or more. Among premature infants, who were delivered within 24 h afer amniocentesis, surfactant specific apoprotein concentration was less than 1.5 micrograms/ml in three infants with respiratory distress syndrome (RDS), and more than 2.1 micrograms/ml in six without RDS. The results indicated that the quantitative measurement of surfactant specific apoprotein in amniotic fluid is effective in predicting the fetal lung maturity, and that simplicity and rapidity make our method useful for clinical application.

Prenatal relationship of surfactant lipid and protein constituents in infants with respiratory distress syndrome: a preliminary communication

The prenatal relationships between surfactant disaturated phosphatidylcholine (DSPC) and surfactant-associated proteins of preterm infants with respiratory distress syndrome (RDS) have not been well documented. In the present study we measured the concentration of DSPC, surfactant glycoproteins (GP), and surfactant proteolipids (PLP) in amniotic fluids obtained within 6 hours prior to delivery of 16 newborn infants with gestational ages between 27 and 32 weeks. In control infants of 27-32 weeks gestation without RDS, the values of DSPC, GP, and PLP per milliliter of amniotic fluid were 20 +/- 2.9 micrograms, 684 +/- 115.3 ng and 289 +/- 62.5 ng, respectively. These values were significantly higher, threefold for PLP, fourfold for DSPC, and fivefold for GP, than amniotic fluid levels in infants with RDS. The findings support the concept that immaturity of surfactant in RDS involves both phospholipids and surfactant-associated proteins. Measurements of surfactant lipid-protein complex appear to enhance the reliability for identifying prenatally, infants at risk of developing hyaline membrane disease. More extensive studies are warranted to assess the usefulness of these assays for clinical application.

Rat pulmonary surfactant protein A is expressed as two differently sized mRNA species which arise from differential polyadenylation of one transcript

In rat, the surfactant-associated glycoprotein A, SP-A, is encoded by two mRNA species of 0.9 and 1.6 kb. Each transcript is polyadenylated and is found in approximately the same ratio in total cellular RNA isolated from either alveolar type II cells or from whole lung. The two mRNA species have identical coding regions and differ only in the length of the 3' untranslated sequences. Restriction analysis and partial sequence analysis of rat genomic clones indicate that each mRNA species arises from one gene, with the difference in size most easily accounted for by differential polyadenylation. During fetal development, the accumulation of mRNA encoding SP-A is detectable by day 18 but increases many-fold on day 19. However, there are no apparent alterations in the prevalence of either mRNA species during fetal development or in the early postnatal period.

Surfactant proteins in the diagnosis of fetal lung maturity. I. Predictive accuracy of the 35 kD protein, the lecithin/sphingomyelin ratio, and phosphatidylglycerol

The concentration of the major surfactant protein with a molecular weight of 35 kD was determined in 469 amniotic fluid specimens from 284 pregnancies by the two-site simultaneous immunoassay with monoclonal antibodies. The predictive accuracy of the 35 kD protein was compared with that of the lecithin/sphingomyelin ratio and phosphatidylglycerol (the lung profile). Immature levels of 35 kD protein (less than 0.6 micrograms/ml) predicted 59% of all cases of respiratory distress syndrome (RDS) with an accuracy of 91%, and mature levels of 35 kD protein (greater than 3.0 micrograms/ml) predicted 68% of all infants who did not have RDS with an accuracy of 100%. The overall accuracy of the 35 kD protein in predicting the risk of developing respiratory distress syndrome was similar to that of the lung profile. In addition, testing with 35 kD protein improved the predictive value of an indeterminate lung profile (lecithin/sphingomyelin ratio of 1:1.9 and no phosphatidylglycerol) from 52% to 74%. The present results show that the lecithin/sphingomyelin ratio, phosphatidylglycerol, and 35 kD apoprotein have additive effects in improving the accuracy of the diagnosis of lung maturity.

Detection of the type II cell or its precursor before week 20 of human gestation, using antibodies against surfactant-associated proteins

The present study was performed to find out whether the type II alveolar epithelial cell or its precursor (an approximately cuboidal cell lacking multilamellar bodies) is present before the twentieth week of human gestation. For this purpose we used an antibody, SALS-Hu(E), which recognizes the human type II cell on the basis of surfactant-associated proteins. Application of SALS-HuE (by indirect immunofluorescence) to acetone-fixed frozen sections of fetal lung tissue gave a distinct staining of the cuboidal or low columnar epithelial cells lining the end-pieces of the tubular system of fetal lung (initially only a few): this staining started around weeks 10 to 12 after conception. Around week 16 some of the labeled epithelial cells appeared to be rather flat and by week 19 a combined cellular and linear fluorescence pattern was seen. Columnar epithelial cells of the prospective bronchial portion did not show this specific staining. Our results indicate that the type II cell or its precursor cell is indeed present in the pseudoglandular period of human lung development, i.e., starting around the tenth to twelfth week. This cell type lines the acinar tubule, the basic structure of the pulmonary acinus. Transformation of this cell type into the type I alveolar epithelial cell seems to start in week 16.

Induction and characterization of the major surfactant apoprotein during rabbit fetal lung development

Antibodies directed against the major apoprotein associated with rabbit lung surfactant were used to characterize the induction and cellular localization of this protein during rabbit fetal lung development. In lung tissues from rabbits of 26 days gestational age and older, discrete epithelial type II cells were stained positively using the peroxidase antiperoxidase technique. The content of the major protein in homogenates of fetal lung tissue was analyzed using an immunoblotting technique. A protein of about 29 kDa, pI less than or equal to 5.6, was first detectable in fetal lung tissue on day 24 of gestation. The 29-36 kDa, mature form of the surfactant apoprotein was first detectable in lung homogenates from 30-day gestational age fetal rabbits. Treatment of homogenates of day 26 and 31 fetal lung tissues with endoglycosidase F, yielded, in both cases, an immunoreactive triplet with more neutral isoelectric points than the proteins in the untreated homogenates. By immunoblot analysis, we found that only the 29-36 kDa, mature form of the surfactant apoprotein was present in lamellar bodies purified from lung tissues of fetuses of 28 and 31 days and from day 2 neonates. These findings are suggestive that only the mature, 29-36 kDa form of the surfactant apoprotein is associated with lamellar bodies during fetal lung type II cell differentiation in vivo.

Regulation of pulmonary surfactant apoprotein SP 28-36 gene in fetal human lung

Pulmonary surfactant stabilizes lung alveoli, preventing respiratory failure and hyaline membrane disease in premature infants. In addition to lipids, surfactant contains apoproteins that are thought to be critical for normal surfactant function. We have examined the ontogeny and regulation of the major surfactant-associated protein of molecular mass 28-36 kDa (SP 28-36) in human fetal lung. SP 28-36 was not detected in tissue from second trimester abortuses by either immunoblot analysis or enzyme-linked immunosorbent assay (less than 0.02 microgram per mg of DNA). Levels of mRNA for SP 28-36, assayed by cDNA hybridization, were low or undetectable in all preculture specimens. The concentration of saturated phosphatidylcholine in lung tissue was 30% of the adult value with no apparent increase between 15 and 24 weeks gestation. SP 28-36 content increased during explant culture in the absence of serum and hormones, exceeding adult levels (3.2 +/- 1.0 micrograms per mg of DNA) after 5 days. In cultures treated with triiodothyronine (2 nM) and dexamethasone (10 nM), hormones that regulate phosphatidylcholine synthesis, the increase in SP 28-36 was accelerated (treated/control ratio was 7.1 and 3.4 at 3 and 5 days, respectively). Levels of mRNA for SP 28-36 also increased during culture and were stimulated by hormones (treated/control = 8.6 and 1.9 at 3 and 5 days, respectively). SP 28-36 and its mRNA increased similarly in the presence of dexamethasone alone, whereas triiodothyronine alone had no apparent effect. The molecular weight and charge pattern was similar for SP 28-36 of adult and cultured fetal tissue. These findings indicate that expression of the SP 28-36 gene is low during the second trimester, increases during explant culture, and is accelerated by glucocorticoid treatment.

Post-translational modification of the major human surfactant-associated proteins

The major protein in human pulmonary surfactant is a sialoglycoprotein of 32-36 kDa (PSP-A) that has been shown by translation of lung mRNA in vitro to be derived from precursor molecules of 29-31 kDa [Floros, Phelps & Jaeusch (1985). J. Biol. Chem. 260, 495-500]. We show here that two-dimensional gel patterns of PSP-A similar to that of the primary translation products are obtained by incorporation of [35S]methionine in the presence of tunicamycin or by N-glycanase digestion of the 32-36 kDa group. Additional gel patterns are also observed in which the isoelectric-point heterogeneity is similar to that of either tunicamycin-treated tissue or primary translation products, but with higher molecular masses. The gel patterns showing higher-molecular-mass components are obtained when terminal sialic acid addition is prevented by the incubation of lung tissue with monensin or when terminal sialic acids are digested from the fully processed protein with neuraminidase. The 32-36 kDa forms have been shown to contain [14C]mannose. Pulse-chase experiments indicate that the acidic isoforms in the protein group arise from basic isoforms that are detectable within 10 min.

Analysis of proteins in rabbit pulmonary surfactant using monoclonal antibodies

We have used monoclonal antibodies developed against the apolipoproteins associated with pulmonary surfactant purified from rabbit lavage fluid to study the expression of epitopes common to these proteins. The pulmonary surfactant contained nearly 20 proteins, of which at least 10 were not derived from serum. Electrophoresis, with sulfhydryl reduction of these proteins indicated apparent molecular weights of approximately 155, 135, 125, and 115 X 10(3) (high-molecular-weight group); 80, 70, and 60 X 10(3) (intermediate group); and 18 through 10 X 10(3) (low-molecular-weight group). Two-dimensional polyacrylamide gel electrophoresis, in which the proteins were electrophoresed without reduction in the first dimension, but with sulfhydryl reduction in the second dimension, revealed that the 80, 70, and 60 X 10(3) proteins dissociated into proteins of nominal molecular weights of 40, 35, and 30 X 10(3), respectively. In contrast, the 125 and 115 X 10(3) proteins of the high-molecular-weight group contained a protein which could only be reduced to a minimum molecular weight of 55 to 60 X 10(3). Monoclonal antibodies generally were of three types: those that reacted strongly with the high-molecular-weight group and weakly with the intermediate group; those that reacted conversely; and those that reacted only with the low-molecular-weight group. Our results indicate that at least two different surfactant apolipoproteins, with differing minimum molecular weights in SDS-polyacrylamide gel electrophoresis, have common epitopes. Although these results cannot certify a physiological relationship between these proteins, they suggest that the intracellular synthesis or extracellular processing of surfactant apolipoproteins may be more complicated than predicted by the findings of previous experiments, perhaps involving the posttranslational assembly of one surfactant protein into oligomers which resist dissociation under the conditions used for the analyses.

The proteins of human lung surfactant

Human pulmonary surfactant was purified from bronchoalveolar lavage of patients. The proteins present in surfactant were analyzed by SDS-polyacrylamide gel electrophoresis into serum and non-serum components. One non-serum surfactant protein (Mr = 43 000) was then identified in the 100 000 X g supernatant of a lung homogenate on the basis of phospholipid binding. This lung protein was purified and partially characterized. The presence of 3-methyl histidine and reaction in Western blot analysis with antibody against chicken muscle actin both strongly suggested that the 43 000 Da protein of human surfactant is indeed cytoplasmic actin. It is proposed that this surfactant protein is involved in the secretion and not necessarily in the function of surfactant.