Pulmonary collectins and innate host defense of the lung

Surfactant proteins A and D (SP-A and SP-D) are members of the collectin family of polypeptides expressed in the respiratory tract that bind bacterial, fungal and viral pathogens, enhancing their opsonization and killing by phagocytic cells. Clearance of bacterial pathogens including group B streptococci, Haemophilus influenza, Pseudomonas aeruginosa and viral pathogens, respiratory syncytial virus, adenovirus and influenza A virus, was deficient in SP-A(-/-) mice. SP-A deficiency was associated with enhanced inflammation and synthesis of proinflammatory cytokines. SP-D(-/-) mice cleared these bacteria as efficiently as wild-type mice; however, clearance of viral pathogens was deficient in SP-D(-/-) mice and associated with increased inflammation. SP-A and SP-D play critical and distinct roles in the regulation of alveolar macrophage function and inflammation, contributing to innate defense of the lung.

[A case of severe Legionella pneumonia monitored with serum SP-A, SP-D, and KL-6]

A 67-year-old man was admitted for acute pneumonia on July 20th, 1999. Chest radiographs disclosed dense consolidation in the right lower lung fields. After admission, the pneumonia underwent rapid advance. On the basis of serological findings and cultures of pleural effusion and sputum, the patient was given a diagnosis of acute pneumonia caused by Legionella pneumophila 1 a. He gradually recovered from the pneumonia by means of chemotherapy using EM, RFP, Mino, gammaglobulins and steroids. The serum SP-A, SP-D, and KL-6 peaked on July 23rd, July 30th, and August 12th, respectively.

Deficiencies in lung surfactant proteins A and D are associated with lung infection in very premature neonatal baboons

Surfactant proteins A (SP-A) and D (SP-D) are important in the innate host defense against pathogenic microorganisms. A deficit in these proteins in premature infants, either because of immaturity or as a consequence of superimposed chronic lung disease (CLD), could increase their susceptibility to infection. The study reported here examined infection in CLD in the premature newborn baboon, and correlated it with the amounts of SP-A and SP-D in lung tissue and lavage fluid. Two groups of baboons were delivered prematurely, at 125 d gestational age (g.a.), and differed principally in whether they developed naturally acquired pulmonary infections and sepsis. Group I animals were ventilated with clinically appropriate oxygen for 6 d and 14 d without clinical incident. Group II animals were ventilated for 5 to 71 d, but differed from those in Group I in that most developed pulmonary infection and/or sepsis. In Group I animals, tissue pools of both SP-A and SP-D were equal to or exceeded those in adults, and lavage pools of SP-A increased progressively with the time of ventilation to about 35% of adult levels after 14 d. In contrast, most Group II animals had concentrations of lavage SP-A that were less than 20% of that in adult animals. A low concentration of lavage SP-A correlated with the release of interleukin-8, and with a high "infection index" based on histopathology, microbiologic cultures, and clinical indications of sepsis. Our data suggest that the amounts of SP-A and SP-D in lavage fluid are indicators of the risk of infection in the evolution of neonatal CLD. Deficits in the amount of lavage SP-A, even after 60 d of ventilation, may have inhibited the resolution of infection and thereby contributed to the developing injury among our Group II animals.

Surfactant proteins D and A in sputum

The surfactant proteins SP-D and SP-A are collectins and central components of the innate immune system of the peripheral lungs. They bind to carbohydrates on microorganisms and promote their removal. In the larger airways their role and concentrations are not yet known. Sputum may thus potentially be useful to characterize the collectins in this compartment. Induced sputum was obtained from healthy adults and spontaneous sputum from patients with cystic fibrosis. ELISA and carbohydrate binding assays were used to quantify the amount and functional capacity of the collectins in plugs or sol-fractions, prepared by centrifugation of the plugs. SP-D and SP-A were detectable in only about 50% of the sputum plugs. Varying the salt, detergent and calcium conditions of the assay did not improve the results. In samples with reproducibly detectable SP-D or SP-A, their carbohydrate binding capacity was zero. Sputum sol fraction and LPS inhibited the binding of the collectins to carbohydrate in the presence of calcium. Whereas SP-D and SP-A are abundant in the peripheral lung, their presence in sputum derived from the larger airways is variable and their carbohydrate binding capacity is lost.

Reduced proteolysis of surfactant protein A and changes of the bronchoalveolar lavage fluid proteome by inhaled alpha 1-protease inhibitor in cystic fibrosis

In cystic fibrosis (CF), the chronic neutrophilic inflammation of the airways results in proteolytic degradation of lung tissue early in the course of the disease. Inhalation of alpha 1-protease inhibitor (alpha 1-PI) may restore the protease-antiprotease imbalance and thus lead to less tissue damage. To monitor its impacts on bronchoalveolar lavage (BAL) fluid protein pattern (proteome) and on surfactant protein A (SP-A), eight young adults with CF inhaled 100 mg of alpha 1-PI twice daily over eight weeks. BAL fluids were obtained before and after inhalation. Total protein, the number and amount of proteins with a molecular mass < 20 kDa were reduced compared to pretreatment values. Degradation products of SP-A were shown by immunoblotting, being reduced after alpha 1-PI treatment. This pilot study demonstrates that inhalation of alpha 1-PI is associated with biochemical changes consistent with reduced proteolysis. The display of the BAL proteome by two-dimensional electrophoresis may be helpful to quantify the overall molecular changes associated with proteolytic or other lung injuries and offers the possibility to monitor directly therapeutic interventions.

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.

Intra-amniotic endotoxin accelerates lung maturation in fetal rabbits

The hypothesis that endotoxin in amniotic fluid accelerates fetal lung maturation was tested. On day 25 of gestation, LPS (5 microg/fetus) was injected intra-amniotically into one uterine horn of eight New Zealand white rabbits, whereas the contralateral amniotic sacs were injected with saline vehicle. The fetuses were delivered 48 h after LPS administration and their lungs were studied. One dam went into premature labor prior to the 48 h time point and was excluded from the study. Mean white cell counts in amniotic fluid and bronchoalveolar lavage fluid from LPS-treated fetuses were increased 3.2-fold (p = 0.04) and 9.9-fold (p = 0.04), respectively. Fetal weights and lung weights were not affected by LPS. Surfactant protein SP-A and SP-B mRNA expressions in LPS-treated fetuses were increased 2.3-fold (p = 0.03) and 1.4-fold (p = 0.04), respectively. Static lung compliance was increased in animals treated with LPS (p = 0.001). Lungs from LPS-treated animals had better aeration than those of controls. Mean volume of inflation-fixed lungs of LPS-treated fetuses was 1.7 times greater than that of controls (p = 0.03).

CONCLUSION

Intra-uterine exposure to LPS increases surfactant protein expression and improves lung stability and aeration in preterm animals.

Increased levels of nitrate and surfactant protein a nitration in the pulmonary edema fluid of patients with acute lung injury

Levels of nitrite (NO2-) and nitrate (NO3-) were measured in pulmonary edema fluid and plasma from 34 patients with early acute lung injury (ALI) and 20 patients with hydrostatic pulmonary edema. Pulmonary edema fluid from patients with ALI had significantly higher levels of NO2- + NO3- compared with pulmonary edema fluid from patients with hydrostatic pulmonary edema (108 +/- 13 microM versus 66 +/- 9 microM; means +/- SEM; p < 0.05). In addition, patients with shock had higher plasma NO2- + NO3- levels than those without shock (79 +/- 11 microM versus 53 +/- 12 microM, p < 0.05). Acidemia and increased anion gap, markers of systemic hypoperfusion, were also associated with twofold higher plasma NO2- + NO3- levels (p < 0.01). Increased levels of NO2- + NO3- in edema fluid samples were associated with slower rates of alveolar fluid clearance. Nitrated pulmonary surfactant protein A (SP-A) was also detected in the edema fluid of patients with ALI after immunoprecipitation with a specific antibody against this protein. Previously, we have shown that nitration of SP-A impairs its host- defense properties. In aggregate, the results of this study indicate that reactive oxygen-nitrogen species may play a role in the pathogenesis of human ALI.

Surfactant protein A and lipid are internalized via the coated-pit pathway by type II pneumocytes

Surfactant protein (SP) A and SP-A-mediated lipid uptake by isolated type II cells were investigated with biochemical and morphological methods. Inhibition of coated-pit function by potassium depletion severely reduced both SP-A and SP-A-mediated lipid internalization. Lipid uptake in the absence of SP-A was not affected. With confocal laser scanning microscopy and immunoelectron microscopy, SP-A and lipid predominantly (60%) colocalized in intracellular vesicles carrying early endosomal markers (EEA1) 5 min after endocytosis but were negative for the late endosomal or lysosomal marker LAMP-1. As estimated by subcellular fractionation, at this time point, 23% of the internalized SP-A and 45% of internalized lipid were localized within light (<0.38 M sucrose) fractions, which contain lamellar bodies and are positive for EEA1. The remaining label was predominantly found within EEA1-positive and plasma membrane-containing subfractions (> or = 1 M sucrose). We suggest that in isolated type II cells in vitro, SP-A and lipid are taken up together via the coated-pit pathway and that at early time points, both components reside in the same early endosomal compartment.

Surfactant and surfactant inhibitors in meconium aspiration syndrome

Surfactant indices and inhibitors were measured in lung lavage fluid from 8 infants with meconium aspiration syndrome (MAS) who were receiving mechanical ventilation and 11 healthy control subjects. Surfactant phospholipid and surfactant protein A content in MAS was not different from that of control subjects, but concentrations of total protein, albumin, and membrane-derived phospholipid were elevated. All infants with MAS had hemorrhagic pulmonary edema. These findings reinforce the notion of MAS as a toxic pneumonitis with epithelial disruption and proteinaceous exudation.

Surfactant protein A recruits neutrophils into the lungs of ventilated preterm lambs

We tested the effects of surfactant protein A (SP-A) on inflammation and surfactant function in ventilated preterm lungs. Preterm lambs of 131 d gestation were ventilated for 15 min to initiate a mild inflammatory response, and were then treated with 100 mg/ kg recombinant human SP-C surfactant or with the same surfactant supplemented with 3 mg/kg ovine SP-A. Addition of SP-A to the SP-C surfactant did not change lung function. After 6 h of ventilation, cell numbers in the alveolar wash were 4.9 times higher in SP-A + SP-C-surfactant-treated animals. Cellular infiltrates consisted of neutrophils that produced less hydrogen peroxide than did cells from SP-C-surfactant-treated animals. Expression of adhesion molecules CD11b and CD44 was significantly greater after SP-A treatment, whereas the expression of CD14 was unchanged. Messenger RNAs (mRNAs) for the proinflammatory cytokines interleukin (IL)-1beta, IL-6, and IL-8, but not tumor necrosis factor-alpha, were increased in SP-A-treated lungs. Surfactant protein mRNAs and protein leakage into alveolar washes were not altered by SP-A, indicating that SP-A treatment produces no evidence of lung injury. The present study identifies an unanticipated role of SP-A in neutrophil recruitment in the lungs of preterm lambs.

Re-expression of pulmonary surfactant proteins following tracheal obstruction in fetal sheep

Increased fetal lung expansion, induced by tracheal obstruction (TO), is a potent stimulus for fetal lung growth, but rapidly reduces surfactant protein (SP) mRNA levels. Our aim was to determine the time course for the re-expression of the surfactant proteins in fetal lung tissue following the release of a TO and to relate these to the changes in lung liquid volume. Fetal sheep were exposed to either: (1) no treatment (controls); (2) 4 days of TO; (3) 4 days of TO, followed by release of the obstruction for 24 h; (4) 4 days of TO followed by release of the obstruction for 3 days. Four days of TO increased lung liquid volumes from 26.8 +/- 1.9 to 72.0 +/- 5.6 ml kg(-1) and reduced SP-A, SP-B and SP-C mRNA levels to 38.5 +/- 10.7, 56.8 +/- 10.3 and 18.3 +/- 5.3 % of control values, respectively. One day after TO release, lung liquid volumes were reduced to 17.4 +/- 5.3 ml kg(-1) (control 128 days, 31.0 +/- 3.8 ml kg(-1)) and SP-A and SP-B mRNA levels were not different from control levels. In contrast, SP-C mRNA levels only increased to 45.4 +/- 17.3 % of control. Three days after TO release, lung liquid volumes increased to 48.0 +/- 8.5 ml kg(-1) and SP-A and SP-B mRNA levels were reduced to 48.8 +/- 10.2 % and 71.5 +/- 19.8 % of control, respectively; SP-C mRNA levels remained at 35.3 +/- 12.3 % of control. Following the release of a TO, SP-A, SP-B and SP-C mRNA levels were closely and inversely related to the volume of lung liquid. Based on these relationships, the lung liquid volumes that equate to 100 % expression were considerably less than control lung volumes (< 10 vs. 30-40 ml kg(-1)) in fetuses of this age. Thus, the changes in fetal lung SP-A, SP-B and SP-C mRNA levels following the release of a TO are variable, differ between the proteins and are closely related to the changes in lung liquid volumes. We conclude that the re-expression of surfactant proteins following TO is variable and that the change in lung liquid volume is potentially a good indicator for surfactant protein re-expression. Experimental Physiology (2001) 86.1, 55-63.

Effects of intrauterine growth restriction on lung liquid dynamics and lung development in fetal sheep

OBJECTIVE

The aim of this study was to determine the effects of intrauterine growth restriction on fetal lung liquid and lung development.

STUDY DESIGN

Intrauterine growth restriction was induced in 7 fetal sheep from 120 to 140 days' gestation (term, approximately 147 days' gestation) by umbilicoplacental embolization. We used 6 control fetuses. Volumes and production rates of fetal lung liquid were measured, and lungs were removed post mortem (140 days' gestation) for analysis of concentrations of deoxyribonucleic acid, protein, and messenger ribonucleic acid for surfactant proteins A, B, and C.

RESULTS

Umbilicoplacental embolization induced fetal hypoxemia, hypoglycemia, and intrauterine growth restriction. At 140 days' gestation lung weight was reduced by 34%, and the fetal lung liquid production rate (15.9 +/- 1.8 mL/h for intrauterine growth restriction vs 24.8 +/- 3.9 mL/h for control) and volume (110.9 +/- 16.3 mL for intrauterine growth restriction vs 178.1 +/- 11.9 mL for control) were reduced in the intrauterine growth restriction group. After adjustment for body weight, however, values were not different from those in the control group. Pulmonary deoxyribonucleic acid and plasma cortisol concentrations were elevated by intrauterine growth restriction, but levels of messenger ribonucleic acid for surfactant proteins were unchanged.

CONCLUSION

In intrauterine growth restriction, lung liquid and lung growth were proportionate to body weight, and surfactant protein expression was unaffected. Alterations in lung deoxyribonucleic acid concentrations suggest that the lungs may be structurally immature.

Cell biology of tubotympanum in relation to pathogenesis of otitis media - a review

The sterility of the eustachian tube and tympanic cavity of normal individuals is maintained not only by the adaptive immune system, but also by the mucociliary system and the antimicrobial molecules of innate immunity. Mucin production and periciliary fluid homeostasis are essential for normal mucociliary function and dysfunction of this system is an important risk factor for otitis media. The secreted antimicrobial molecules of the tubotympanum include lysozyme, lactoferrin, beta defensins, and the surfactant proteins A and D (SP-A, SP-D). Defects in the expression or regulation of these molecules may also be the major risk factor for otitis media.

Pulmonary surfactant proteins A and D are potent endogenous inhibitors of lipid peroxidation and oxidative cellular injury

The lung is composed of a series of branching conducting airways that terminate in grape-like clusters of delicate gas-exchanging airspaces called pulmonary alveoli. Maintenance of alveolar patency at end expiration requires pulmonary surfactant, a mixture of phospholipids and proteins that coats the epithelial surface and reduces surface tension. The surfactant lining is exposed to the highest ambient oxygen tension of any internal interface and encounters a variety of oxidizing toxicants including ozone and trace metals contained within the 10 kl of air that is respired daily. The pathophysiological consequences of surfactant oxidation in humans and experimental animals include airspace collapse, reduced lung compliance, and impaired gas exchange. We now report that the hydrophilic surfactant proteins A (SP-A) and D (SP-D) directly protect surfactant phospholipids and macrophages from oxidative damage. Both proteins block accumulation of thiobarbituric acid-reactive substances and conjugated dienes during copper-induced oxidation of surfactant lipids or low density lipoprotein particles by a mechanism that does not involve metal chelation or oxidative modification of the proteins. Low density lipoprotein oxidation is instantaneously arrested upon SP-A or SP-D addition, suggesting direct interference with free radical formation or propagation. The antioxidant activity of SP-A maps to the carboxyl-terminal domain of the protein, which, like SP-D, contains a C-type lectin carbohydrate recognition domain. These results indicate that SP-A and SP-D, which are ubiquitous among air breathing organisms, could contribute to the protection of the lung from oxidative stresses due to atmospheric or supplemental oxygen, air pollutants, and lung inflammation.

[Surfactant protein and thyroid transcription factor 1 in pleuro-pulmonary neoplasia. Immunohistochemical study]

Aim of this work was to investigate the ability of the antibodies against Surfactant proteins (SP) and Thyroid transcription factor 1 (TTF-1) to distinguish primary neoplasms of the lung from metastatic carcinomas to the lung and pleural mesotheliomas. We evaluated the immunohistochemical expression of the antibodies anti SP-A, SP-B, pro SP-C, SP-D, and TTF-1 in a series of 56 primary lung carcinomas, 9 metastatic carcinomas to the lung, 5 pleural mesotheliomas and 8 non-pulmonary carcinomas. Among primary lung neoplasms, only adenocarcinomas immunostained for all SP (specificity = 1; total sensitivity = 0.52). TTF-1 had an excellent specificity (= 1), but a weak sensitivity (= 0.34) in recognizing primary lung carcinomas. TTF-1 was present in lung adenocarcinomas which were negative for SPs; however it failed to distinguish the subtypes. Pleural mesotheliomas, pulmonary metastases and non-pulmonary carcinomas were not immunoreactive for SP-A, SP-B, SP-D, and TTF-1. Pro SP-C was positive also in the adenocarcinomas of the large bowel and in their pulmonary and nodal metastases. These results demonstrate that the combined use of antibodies anti SP-A, SP-B and TTF-1 is the best association in distinguishing primary lung carcinomas from metastatic carcinomas to the lung and pleural mesotheliomas.

Interaction of surfactant protein A with lipopolysaccharide and regulation of inflammatory cytokines in the THP-1 monocytic cell line

Pulmonary surfactant protein A (SP-A) is involved in innate immunity in the lung. In this study we investigated the interaction of SP-A with different serotypes of lipopolysaccharide (LPS) on the regulation of inflammatory cytokines in vitro. In the human monocytic cell line, THP-1, combining SP-A with lipid A or rough LPS further enhanced lipid A- or rough LPS-stimulated tumor necrosis factor alpha (TNF-alpha) mRNA levels, while SP-A-elicited increases in TNF-alpha mRNA levels were partially neutralized. In contrast, the combination of smooth LPS and SP-A resulted in additive effects on TNF-alpha mRNA levels. We also demonstrated that there was cross-tolerance between SP-A and LPS in THP-1 cells. Pretreatment of THP-1 cells with LPS modestly inhibited the response of these cells to subsequent challenge with SP-A, with regard to the production of TNF-alpha, whereas there was no or little effect on the production of interleukin-1beta (IL-1beta) and IL-8. Conversely, pretreatment of THP-1 cells with SP-A markedly increased the response to subsequent challenge with LPS with regard to the production of IL-1beta and IL-8, although the production of TNF-alpha was modestly decreased. However, a synergistic stimulatory effect was observed when the two agents were added simultaneously to the cells. NF-kappaB formation was downregulated in SP-A- but not in LPS-induced tolerant cells. These results suggested that SP-A exhibits different interactions with distinct serotypes of LPS. In addition, SP-A is different from LPS with regard to the induction of cross-tolerance, and these actions may be mediated, at least in part, through different mechanisms.

Swim bladder gas gland cells produce surfactant: in vivo and in culture

Electron microscopical examination of gas gland cells of the physostome European eel (Anguilla anguilla) and of the physoclist perch (Perca fluviatilis) revealed the presence of significant numbers of lamellar bodies, which are known to be involved in surfactant secretion. In the perch, in which the gas gland is a compact structure and gas gland cells are connected to the swim bladder lumen via small canals, lamellar bodies were also found in flattened cells forming the swim bladder epithelium. Flat epithelial cells are absent in the eel swim bladder, in which the whole epithelium consists of cuboidal gas gland cells. In both species, Western blot analysis using specific antibodies to human surfactant protein A (SP-A) showed a cross-reaction with swim bladder tissue homogenate proteins of approximately 65 kDa and in the eel occasionally of approximately 120 kDa, probably representing SP-A-like proteins in a dimeric and a tetrameric state. An additional band was observed at approximately 45 kDa. Western blots using antibodies to rat SP-D again resulted in a single band at approximately 45 kDa in both species, suggesting that there might be a cross-reaction of the antibody to human SP-A with an SP-D-like protein of the swim bladder tissue. To localize the surfactant protein, eel gas gland cells were cultured on permeable supports. Under these conditions, the gas gland cells regain their characteristic polarity. Electron microscopy confirmed the presence of lamellar bodies in cultured cells, and occasionally, exocytotic events were observed. Immunohistochemical staining using an antibody to human SP-A demonstrated the presence of surfactant protein only in luminal membranes and in adjacent lateral membranes. Only occasionally, evidence was found for the presence of surfactant protein in lamellar bodies.

Surfactant protein A differentially regulates IFN-gamma- and LPS-induced nitrite production by rat alveolar macrophages

Although several studies have demonstrated that the pulmonary collectins surfactant protein (SP)-A and SP-D contribute to innate immunity by enhancing pathogen phagocytosis, the role of SP-A and SP-D in regulating production of free radicals and cytokines is controversial. We hypothesized that the state and mechanism of activation of the immune cell influence its response to SP-A. The effects of SP-A and SP-D on production of nitric oxide (NO) and inducible nitric oxide synthase (iNOS) were assessed in isolated rat alveolar macrophages activated with lipopolysaccharide (LPS), interferon gamma (IFN-gamma), or both agonists. SP-A inhibited production of NO and iNOS in macrophages stimulated with smooth LPS, which did not significantly bind SP-A, or rough LPS, which avidly bound SP-A. In contrast, SP-A enhanced production of NO and iNOS in cells stimulated with IFN-gamma or INF-gamma plus LPS. Neither SP-A nor SP-D affected baseline NO production, and SP-D did not significantly affect production of NO in cells stimulated with either LPS or IFN-gamma. These results suggest that SP-A contributes to the lung inflammatory response by exerting differential effects on the responses of immune cells, depending on their state and mechanism of activation.

KGF regulates pulmonary epithelial proliferation and surfactant protein gene expression in adult rat lung

Keratinocyte growth factor (KGF, FGF-7) is a potent mitogen for epithelial cells. We instilled recombinant human KGF to determine the effects of KGF on alveolar epithelial cells. Left lungs of adult rats were instilled intrabronchially with KGF (5 mg/kg) or normal saline. KGF instillation resulted in epithelial cell hyperplasia, and the alveolar bromodeoxyuridine (BrdU) labeling index peaked at 35% on day 2 after instillation. The mRNA levels for the surfactant proteins (SPs) SP-A, SP-B, and SP-D were increased in whole lung tissue on days 1 and 2 after KGF treatment and then returned to control levels on days 3-7. SP-C mRNA levels were increased on days 2-5 after KGF instillation. However, all surfactant protein mRNAs were reduced in type II cells isolated from rats instilled with KGF 2 or 3 days before isolation. These observations were confirmed by in situ hybridization. Instillation of KGF also increased the amount of SP-A and SP-D in lavage fluid. Transcripts for CC10, the 10-kDa Clara cell protein, were decreased. KGF increases the mRNA for the surfactant proteins per lung because of type II cell hyperplasia, but the mRNA per cell is slightly diminished as measured in isolated cells or estimated by in situ hybridization.

The role of surfactant proteins in DPPC enrichment of surface films

A pressure-driven captive bubble surfactometer was used to determine the role of surfactant proteins in refinement of the surface film. The advantage of this apparatus is that surface films can be spread at the interface of an air bubble with a different lipid/protein composition than the subphase vesicles. Using different combinations of subphase vesicles and spread surface films a clear correlation between dipalmitoylphosphatidylcholine (DPPC) content and minimum surface tension was observed. Spread phospholipid films containing 50% DPPC over a subphase containing 50% DPPC vesicles did not form stable surface films with a low minimum surface tension. Addition of surfactant protein B (SP-B) to the surface film led to a progressive decrease in minimum surface tension toward 1 mN/m upon cycling, indicating an enrichment in DPPC. Surfactant protein C (SP-C) had no such detectable refining effect on the film. Surfactant protein A (SP-A) had a positive effect on refinement when it was present in the subphase. However, this effect was only observed when SP-A was combined with SP-B and incubated with subphase vesicles before addition to the air bubble containing sample chamber. Comparison of spread films with adsorbed films indicated that refinement induced by SP-B occurs by selective removal of non-DPPC lipids upon cycling. SP-A, combined with SP-B, induces a selective adsorption of DPPC from subphase vesicles into the surface film. This is achieved by formation of large lipid structures which might resemble tubular myelin.

Structural characterisation of human proteinosis surfactant protein A

Human surfactant protein-A (SP-A) has been purified from a proteinosis patient and characterised by a combination of automated Edman degradation and mass spectrometry. The complete protein sequence was characterised. The major part of SP-A was shown to consist of SP-A2 gene product, and only a small amount of SP-A1 gene product was shown to be present. A cysteine extension to the N-terminal was indicated by sequence data, but was not definitely proven. All proline residues in the Y position of Gly-X-Y in the collagen-like region were at least partially modified to hydroxy-proline, but no lysine residues were found to be modified. A complex N-linked glycosylation was found on Asn-187 showing great heterogeneity as variants from a mono-antennary to penta-antennary glycosylation with varying amounts of attached pentose were identified. The disulfide bridges in the carbohydrate recognition domain were identified to be in the 1-4, 2-3 pattern common for collectins. Interchain disulfide bridges were discovered between two Cys-48 residues and cysteine residues in the N-terminal region. However, the exact disulfide bridge connections within the bouquet-like ultrastructure could not be established.

Complement-mediated host defense in the lung

Complement is a system of plasma proteins that aids in the elimination of pathogens from the body. We hypothesized that there is a functional complement system present in the lung that aids in the removal of pathogens. Western blot analysis revealed complement proteins of the alternative and classical pathways of complement in bronchoalveolar lavage fluids (BALF) from healthy volunteers. Functional classical pathway activity was detected in human BALF, but there was no significant alternative pathway activity in lavage fluid, a finding that correlates with the low level of the alternative pathway protein, factor B, in these samples. Although the classical pathway of complement was functional in lavage fluid, the level of the classical pathway activator C1q was very low. We tested the ability of the lung- specific surfactant proteins, surfactant protein A (SP-A) and surfactant protein D (SP-D), to substitute for C1q in classical pathway activation, since they have structural homology to C1q. However, neither SP-A nor SP-D restored classical pathway activity to C1q-depleted serum. These data suggest that the classical pathway of complement is functionally active in the lung where it may play a role in the recognition and clearance of bacteria.

Expression of intrapulmonary surfactant apoprotein-A in autopsied lungs: comparative study of cases with or without pulmonary hypoplasia

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: -, +/-, 1+, 2+. The staining intensity of SP-A was high at 1+ 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 = 0.039 and p = 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.

Pulmonary surfactant protein A interacts with gel-like regions in monolayers of pulmonary surfactant lipid extract

Epifluorescence microscopy was used to investigate the interaction of pulmonary surfactant protein A (SP-A) with spread monolayers of porcine surfactant lipid extract (PSLE) containing 1 mol % fluorescent probe (NBD-PC) spread on a saline subphase (145 mM NaCl, 5 mM Tris-HCl, pH 6.9) containing 0, 0.13, or 0.16 microg/ml SP-A and 0, 1.64, or 5 mM CaCl(2). In the absence of SP-A, no differences were noted in PSLE monolayers in the absence or presence of Ca(2+). Circular probe-excluded (dark) domains were observed against a fluorescent background at low surface pressures (pi approximately 5 mN/m) and the domains grew in size with increasing pi. Above 25 mN/m, the domain size decreased with increasing pi. The amount of observable dark phase was maximal at 18% of the total film area at pi approximately 25 mN/m, then decreased to approximately 3% at pi approximately 40 mN/m. The addition of 0.16 microg/ml SP-A with 0 or 1.64 mM Ca(2+) in the subphase caused an aggregation of dark domains into a loose network, and the total amount of dark phase was increased to approximately 25% between pi of 10-28 mN/m. Monolayer features in the presence of 5 mM Ca(2+) and SP-A were not substantially different from those spread in the absence of SP-A, likely due to a self-association and aggregation of SP-A in the presence of higher concentrations of Ca(2+). PSLE films were spread on a subphase containing 0.16 microg/ml SP-A with covalently bound Texas Red (TR-SP-A). In the absence of Ca(2+), TR-SP-A associated with the reorganized dark phase (as seen with the lipid probe). The presence of 5 mM Ca(2+) resulted in an appearance of TR-SP-A in the fluid phase and of aggregates at the fluid/gel phase boundaries of the monolayers. This study suggests that SP-A associates with PSLE monolayers, particularly with condensed or solid phase lipid, and results in some reorganization of rigid phase lipid in surfactant monolayers.

Cyclophosphamide prevents systemic keratinocyte growth factor-induced up-regulation of surfactant protein A after allogeneic transplant in mice

We reported that systemic keratinocyte growth factor (KGF) given before bone marrow transplantation (BMT) prevents allogeneic T cell-dependent lung inflammation assessed on Day 7 post-BMT, but the antiinflammatory effects of KGF were impaired in mice injected with both T cells and conditioning regimen of cyclophosphamide (Cy). Intratracheal KGF is known to stimulate the expression of surfactant protein A (SP-A), an oxidant-sensitive T cell immunomodulator produced by alveolar type II cells. We hypothesized that systemic KGF up-regulates SP-A after allogeneic BMT, and the addition of Cy may interfere with the ability of KGF to enhance SP-A production. The subcutaneous administration of recombinant human KGF (5 mg/kg on Days -6, -5, and -4 pre-BMT) increased SP-A protein and mRNA in allogeneic T cell-recipient irradiated mice measured on Day 7 post-BMT. In contrast, the same KGF treatment in irradiated mice given T cells and Cy failed to up-regulate SP-A mRNA and protein expression. In mixed lymphocyte reaction experiments designed to simulate the in vivo model, the addition of human SP-A (5-50 microg) to alloactivated T cells suppressed the production of interleukin-2 in a dose-dependent fashion. We conclude that the systemic pre-BMT injection of KGF in recipients of allogeneic T cells up-regulates SP-A, which may contribute to the early antiinflammatory effects of KGF. The protective KGF-mediated SP-A production is abolished in mice given alloreactive T cells plus Cy.

Increased levels of surfactant protein A and D in bronchoalveolar lavage fluids in patients with bronchial asthma

Surfactant proteins (SP)-A and SP-D are collagen-like glycoproteins belonging to the "collectin" class of C-type lectins, which are primarily synthesized in type II cells. Recent studies reported the possibility of local production of SP-A and SP-D in the airways, but the amounts of surfactant proteins in patients with bronchial asthma have not been studied. The composition of surfactant proteins in mild, stable asthmatics in the first lavage as bronchial lavage (BL) and the second and third lavages consecutively as alveolar lavages (AL) were therefore, analysed separately. The co-relationships in the BL between the amounts of surfactant proteins and those of fucose, which is one of the markers of submucosal secretion were also analysed. Increased amounts of SP-A in BL and AL of in asthmatics were found as compared with those in controls. A high concentration of SP-D in the AL asthma patients was also found. The levels of SP-A correlated with those of fucose in patients with bronchial asthma (r=0.849, p<0.01). The observations in the present study suggested that surfactant protein A may be secreted from the airways with allergic inflammation in a different manner from the alveoli. The increased levels of surfactant proteins A and D may play a protective role in an allergic inflammation in the pathogenesis of bronchial asthma.

Effects of intrauterine IL-6 and IL-8 on the expression of surfactant apoprotein mRNAs in the fetal rat lung

OBJECTIVE

The purpose of this study was to investigate the effect of interleukin-6 (IL-6) and interleukin-8 (IL-8), whose concentrations are elevated with chorioamnionitis, on the expression of surfactant apoprotein mRNAs in fetal rat lung.

STUDY DESIGN

We employed an animal model in which we were able to administer substances continuously into the cavity between the fetal membranes and endometrium using a miniosmotic pump. Lipopolysaccharide (LPS), IL-6, or IL-8 was administered to timed pregnant rats for 3 days (day 16-19), and fetal lung expression of surfactant apoprotein mRNAs for SP (surfactant apoprotein)-A, SP-B, and SP-C was evaluated by Northern blot hybridization.

RESULTS

Continuous administration of LPS increased the expression of each surfactant apoprotein mRNA, but the expression of mRNAs was not dose-dependent. On the other hand, continuous IL-6 or IL-8 administration increased the expression of each surfactant apoprotein mRNA in a dose-dependent manner.

CONCLUSION

Fetal lung maturation may be promoted by either IL-6 or IL-8 produced in response to chorioamnionitis.

Very low surfactant protein C contents in newborn Belgian White and Blue calves with respiratory distress syndrome

We have studied a respiratory distress syndrome (RDS) occurring in newborn calves of the Belgian White and Blue (BWB) breed that represents the large majority of beef cattle in Belgium. Pulmonary surfactant isolated from 14 BWB newborn calves that died from RDS and from 7 healthy controls was analysed for composition and surface activity. An extremely low content or, in some instances, an absence of surfactant protein C (SP-C) was detected in the RDS samples by Western blotting and differential amino acid analysis [0.03+/-0.01% (w/w) relative to total phospholipids, compared with 0.39+/-0.06% for healthy controls (means+/-S.E.M., P < 0.001)]. The contents of surfactant protein B (SP-B) were similar in RDS and control samples. The crude surfactant samples isolated from RDS calves had higher ratios of total protein to total phospholipid, altered phospholipid profiles and lower SP-A contents. Both crude and organic extracts of RDS surfactant samples showed increased dynamic surface tension compared with healthy controls when evaluated with a pulsating-bubble surfactometer. The addition of purified SP-C to organic extracts of RDS surfactant samples lowered surface tension. Strongly decreased levels of mature SP-C associated with fatal RDS and altered surface activity in vitro have, to the best of our knowledge, not been previously reported. The mechanisms underlying RDS and the decrease in SP-C in BWB calves remain to be established.

Surfactant proteins A and B as interactive genetic determinants of neonatal respiratory distress syndrome

Prematurity is the most important risk factor predisposing to neonatal respiratory distress syndrome (RDS). Genetic factors are likely to contribute to the risk of this complex disease. The present study was designed to investigate whether the surfactant protein B (SP-B) gene or interaction between the SP-A and SP-B genes has a role in the genetic susceptibility to RDS. The genotype analyses were performed on 684 prematurely born neonates, of whom 184 developed RDS. Of the two SP-B polymorphisms genotyped, the Ile131Thr variation affects a putative N-terminal N:-linked glycosylation site of proSP-B and the length variation of intron 4 has previously been suggested to associate with RDS. Neither of the two SP-B polymorphisms associated directly with RDS or with prematurity. Instead, our data show that the previously identified association between SP-A alleles and RDS was dependent on the SP-B Ile131Thr genotype. On the basis of chi(2) and logistic regression analyses, the SP-A allele, haplotype and genotype distributions differed significantly between the RDS infants and controls only when the SP-B genotype was Thr/Thr. Among the infants born before 32 weeks of gestation and having the SP-B genotype Thr/Thr, the SP-A1 allele 6A(2) was over-represented in RDS group compared with controls (P = 0.001, OR = 4.7, CI 1.8-12.2). In the same comparison, the SP-A1 allele 6A(3) was under-represented in RDS (P = 0.001, OR = 0.2, CI 0.1-0.6). We propose that the SP-B Ile131Thr polymorphism is a determinant for certain SP-A alleles as factors causing genetic susceptibility to RDS (6A(2), 1A(0)) or protection against it (6A(3), 1A(2)).

Surfactant protein genetic marker alleles identify a subgroup of tuberculosis in a Mexican population

Pulmonary surfactant and its components are essential for normal lung function and are involved in local host defense. Surfactant protein (SP)-A and SP-D bind to and modulate phagocytosis of Mycobacterium tuberculosis by macrophages. Frequency comparisons of SP marker alleles in tuberculosis patients and healthy control subjects (tuberculin-skin test positive or general population) were performed. Regression analyses of the tuberculosis and the tuberculin-skin test positive groups revealed, on the basis of odds ratios, tuberculosis susceptibility (DA11_C and GATA_3) and protective (AAGG_2) marker alleles. Similarly, between tuberculosis patients and general population control subjects, susceptibility 1A(3), 6A(4), and B1013_A and protective AAGG_1, and AAGG_7 marker alleles were observed. Moreover, interactions were seen between alleles 6A(2) and 1A(3) (P=.0064) and between 1A(3) and B1013_A (P=. 036). The findings indicate a possible involvement of SP alleles in tuberculosis pathogenesis.

Chorioamnionitis decreased incidence of respiratory distress syndrome by elevating fetal interleukin-6 serum concentration

Respiratory distress syndrome (RDS) of newborns is one of the most important factors determining neonatal morbidity and mortality. The interleukin-6 (IL-6) titre in cord sera of RDS-free neonates born to mothers with histological chorioamnionitis was significantly higher than that in RDS-complicated neonates without chorioamnionitis. Maternal administration of glucocorticoid suppressed the IL-6 concentrations in the cord sera of fetuses with chorioamnionitis. The fetuses without chorioamnionitis who suffered from RDS even after maternal glucocorticoid administration showed a similar IL-6 titre to that of RDS-affected neonates without chorioamnionitis. Examination of the mechanism by which IL-6 decreased the incidence of fetal RDS revealed that H441-4, a human pulmonary adenocarcinoma cell line, stimulated with recombinant (r)-IL-6 started the synthesis of mRNA and protein of pulmonary surfactant protein (SP)-A. The present study shows that IL-6 elevation in fetuses with chorioamnionitis promotes fetal lung maturation by inducing SP-A synthesis, thereby decreasing the incidence of RDS in the preterm neonates.

Altered airway surfactant phospholipid composition and reduced lung function in asthma

Pulmonary surfactant in bronchoalveolar lavage fluid (BALF) and induced sputum from adults with stable asthma (n = 36) and healthy controls (n = 12) was analyzed for phospholipid and protein compositions and function. Asthmatic subjects were graded as mild, moderate, or severe. Phospholipid compositions of BALF and sputum from control subjects were similar and characteristic of surfactant. For asthmatic subjects, the proportion of dipalmitoyl phosphatidylcholine (16:0/16:0PC), the major phospholipid in surfactant, decreased in sputum (P < 0.05) but not in BALF. In BALF, mole percent 16:0/16:0PC correlated with surfactant function measured in a capillary surfactometer, and sputum mole percent 16:0/16:0PC correlated with lung function (forced expiratory volume in 1 s). Neither surfactant protein A nor total protein concentration in either BALF or sputum was altered in asthma. These results suggest altered phospholipid composition and function of airway (sputum) but not alveolar (BALF) surfactant in stable asthma. Such underlying surfactant dysfunction may predispose asthmatic subjects to further surfactant inhibition by proteins or aeroallergens in acute asthma episodes and contribute to airway closure in asthma. Consequently, administration of an appropriate therapeutic surfactant could provide clinical benefit in asthma.

Differential effects of surfactant protein A on regional organization of phospholipid monolayers containing surfactant protein B or C

Epifluorescence microscopy combined with a surface balance was used to study monolayers of dipalmitoylphosphatidylcholine (DPPC)/egg phosphatidylglycerol (PG) (8:2, mol/mol) plus 17 wt % SP-B or SP-C spread on subphases containing SP-A in the presence or absence of 5 mM Ca(2+). Independently of the presence of Ca(2+) in the subphase, SP-A at a bulk concentration of 0.68 microg/ml adsorbed into the spread monolayers and caused an increase in the molecular areas in the films. Films of DPPC/PG formed on SP-A solutions showed a pressure-dependent coexistence of liquid-condensed (LC) and liquid-expanded (LE) phases. Apart from these surface phases, a probe-excluding phase, likely enriched in SP-A, was seen in the films between 7 mN/m < or = pi < or = 20 mN/m. In monolayers of SP-B/(DPPC/PG) spread on SP-A, regardless of the presence of calcium ions, large clusters of a probe-excluding phase, different from probe-excluding lipid LC phase, appeared and segregated from the LE phase at near-zero surface pressures and coexisted with the conventional LE and LC phases up to approximately 35 mN/m. Varying the levels of either SP-A or SP-B in films of SP-B/SP-A/(DPPC/PG) revealed that the formation of the probe-excluding clusters distinctive for the quaternary films was influenced by the two proteins. Concanavalin A in the subphase could not replace SP-A in its ability to modulate the textures of films of SP-B/(DPPC/PG). In films of SP-C/SP-A/(DPPC/PG), in the absence of calcium, regions consisting of a probe-excluding phase, likely enriched in SP-A, were detected at surface pressures between 2 mN/m and 20 mN/m in addition to the lipid LE and LC phases. Ca(2+) in the subphase appeared to disperse this phase into tiny probe-excluding particles, likely comprising Ca(2+)-aggregated SP-A. Despite their strikingly different morphologies, the films of DPPC/PG that contained combinations of SP-B/SP-A or SP-C/SP-A displayed similar distributions of LC and LE phases with LC regions occupying a maximum of 20% of the total monolayer area. Combining SP-A and SP-B reorganized the morphology of monolayers composed of DPPC and PG in a Ca(2+)-independent manner that led to the formation of a separate potentially protein-rich phase in the films.

Distinct effects of surfactant protein A or D deficiency during bacterial infection on the lung

Mice lacking surfactant protein (SP)-A (SP-A-/-) or SP-D (SP-D-/-) and wild-type mice were infected with group B streptococcus or Haemophilus influenzae by intratracheal instillation. Although decreased killing of group B streptococcus and H. influenzae was observed in SP-A-/- mice but not in SP-D-/- mice, deficiency of either SP-A or SP-D was associated with increased inflammation and inflammatory cell recruitment in the lung after infection. Deficient uptake of bacteria by alveolar macrophages was observed in both SP-A- and SP-D-deficient mice. Isolated alveolar macrophages from SP-A-/- mice generated significantly less, whereas those from SP-D-/- mice generated significantly greater superoxide and hydrogen peroxide compared with wild-type alveolar macrophages. In SP-D-/- mice, bacterial killing was associated with increased lung inflammation, increased oxidant production, and decreased macrophage phagocytosis. In contrast, in the absence of SP-A, bacterial killing was decreased and associated with increased lung inflammation, decreased oxidant production, and decreased macrophage phagocytosis. Increased oxidant production likely contributes to effective bacterial killing in the lungs of SP-D-/- mice. The collectins, SP-A and SP-D, play distinct roles during bacterial infection of the lung.

Immunohistochemistry of pulmonary surfactant apoprotein A in forensic autopsy: reassessment in relation to the causes of death

To reassess the immunohistochemical distribution of pulmonary surfactant apoprotein A (SP-A) in relation to the causes of death, 282 forensic autopsy cases were reviewed. The most intense and dense granular immunostaining of intra-alveolar SP-A was observed in the hyaline membrane syndrome from various traumas, protracted death from drowning, and perinatal aspiration of amniotic fluid. Similar granular staining pattern was found in fatal poisoning by a muscle relaxant and organophosphate pesticides. An evident increase of intra-alveolar granular staining was noted in most fatalities from mechanical asphyxia and drowning, and some cases of fire death. SP-A staining was usually very weak or sparse in alcohol intoxication, poisoning by hypnotics and also carbon monoxide poisoning. These findings suggest that the amount of intra-alveolar granular SP-A staining may be a possible indicator of severity and duration of respiratory distress (agony) from peripheral (non-central nervous system) origin and alveolar damage.

Novel approach to quantitative reverse transcription PCR assay of mRNA component in autopsy material using the TaqMan fluorogenic detection system: dynamics of pulmonary surfactant apoprotein A

A novel approach to quantitative reverse transcription (RT)-PCR assay of mRNA component using fluorescent TaqMan methodology and a new instrument (ABI Prism 7700 sequence detection system) was developed for autopsy materials. Pulmonary surfactant apoprotein A (SP-A) mRNA from a cadaveric lung was quantitated in real-time. The target SP-A gene and the endogenous reference of glyceraldehyde-3-phosphate (GAPDH) were amplified in the same tube, and an amount of the target was normalized to the reference. This assay had a high reproducibility and discrimination even in forensic autopsy materials up to 96 h postmortem. Elevated SP-A expressions were determined in some cases. This system without post-PCR sample handling would be a very useful tool in pathological diagnosis and DNA analysis.

Composition of alveolar surfactant changes with training in humans

OBJECTIVE

We test the hypothesis that the changes we observed previously in the relative amounts of disaturated phospholipids (DSP), cholesterol (CHOL), and surfactant protein-A (SP-A) in human alveolar surfactant in response to acute exercise, and which were related to fitness, can be induced by training.

METHODOLOGY

We examine the effect of 7 weeks' training on these major surfactant components, together with surfactant protein-B (SP-B), in bronchoalveolar lavage fluid harvested from 17 males, both at rest and after acute exercise. Fitness was assessed as workload/heart rate achieved during cycling for 30 min at 90% of theoretical maximal heart rate, and was increased in all subjects following training (mean increase 22.2+/-3.91%; P = 0.001).

RESULTS

Training significantly increased the SP-A/DSP, SP-B/DSP, SP-A/CHOL and SP-A/SP-B ratios in whole surfactant harvested from subjects both at rest and immediately following exercise. Training also increased the SP-B/CHOL ratio at rest. Changes were particularly marked at rest in the SP-A/DSP, SP-A/CHOL, and SP-B/CHOL ratios in the tubular myelin-rich fraction, and after exercise in the SP-A/DSP, SP-A/CHOL, and SP-A/SP-B ratios in the tubular myelin-poor fraction.

CONCLUSION

We conclude that training markedly alters the composition of alveolar surfactant both at rest and with exercise; the physiological significance of these changes remains to be determined.

Polymorphisms of human SP-A, SP-B, and SP-D genes: association of SP-B Thr131Ile with ARDS

An allele association study of 19 polymorphisms in surfactant proteins SP-A1, SP-A2, SP-B, and SP-D genes in acute respiratory distress syndrome (ARDS) was carried out. Trend-test analysis revealed differences (p < 0.05) in the frequency of alleles for some of the microsatellite markers flanking SP-B, and for one polymorphism (C/T) at nucleotide 1580 [C/T (1580)], within codon 131 (Thr131Ile) of the SP-B gene. The latter determines the presence or absence of a potential N-linked glycosylation site. Multivariate analysis revealed significant differences only for the C/T (1580) polymorphism. When the ARDS population was divided into subgroups, idiopathic (i.e., pneumonia, etc.) or exogenic (i.e., trauma, etc.), significant differences were observed for the C/T (1580), for the idiopathic ARDS group, and the frequency of the C/C genotype was increased in this group. Based on the odds ratio, the C allele may be viewed as a susceptibility factor for ARDS. Although the expression of both C and T alleles occurs in heterozygous individuals, it is currently not known whether these alleles correspond to similar levels of SP-B protein. These data suggest that SP-B or a linked gene contributes to susceptibility to ARDS.

Effect of surfactant protein A (SP-A) on the production of cytokines by human pulmonary macrophages

Surfactant protein A (SP-A) is thought to play a role in the modulation of lung inflammation during acute respiratory distress syndrome (ARDS). However, SP-A has been reported both to stimulate and to inhibit the proinflammatory activity of pulmonary macrophages (Mphi). Because of the interspecies differences and heterogeneity of Mphi subpopulations used may have influenced previous controversial results, in this study, we investigated the effect of human SP-A on the production of cytokines and other inflammatory mediators by two well-defined subpopulations of human pulmonary Mphi. Surfactant and both alveolar (aMphi) and interstitial (iMphi) macrophages were obtained from multiple organ donor lungs by bronchoalveolar lavage and enzymatic digestion. Donors with either recent history of tobacco smoking, more than 72 h on mechanical ventilation, or any radiological pulmonary infiltrate were discarded. SP-A was purified from isolated surfactant using sequential butanol and octyl glucoside extractions. After 24-h preculture, purified Mphi were cultured for 24 h in the presence or absence of LPS (10 microg/mL), SP-A (50 microg/mL), and combinations. Nitric oxide and carbon monoxide (CO) generation (pmol/microg protein), cell cGMP content (pmol/microg protein), and tumor necrosis factor alpha (TNFalpha), interleukin (IL)-1, and IL-6 release to the medium (pg/microg protein) were determined. SP-A inhibited the lipopolysaccharide (LPS)-induced TNFalpha response of both interstitial and alveolar human Mphi, as well as the IL-1 response in iMphi. The SP-A effect on TNFalpha production could be mediated by a suppression in the LPS-induced increase in intracellular cGMP. In iMphi but not in aMphi, SP-A also inhibited the LPS-induced IL-1 secretion and CO generation. These data lend further credit to a physiological function of SP-A in regulating alveolar host defense and inflammation by suggesting a fundamental role of this apoprotein in limiting excessive proinflammatory cytokine release in pulmonary Mphi during ARDS.

Surfactant metabolism in SP-D gene-targeted mice

Mice with surfactant protein (SP)-D deficiency have three to four times more surfactant lipids in air spaces and lung tissue than control mice. We measured multiple aspects of surfactant metabolism and function to identify abnormalities resulting from SP-D deficiency. Relative to saturated phosphatidylcholine (Sat PC), SP-A and SP-C were decreased in the alveolar surfactant and the large-aggregate surfactant fraction. Although large-aggregate surfactant from SP-D gene-targeted [(-/-)] mice converted to small-aggregate surfactant more rapidly, surface tension values were comparable to values for surfactant from SP-D wild-type [(+/+)] mice. (125)I-SP-D was cleared with a half-life of 7 h from SP-D(-/-) mice vs. 13 h in SP-D(+/+) mice. Although initial incorporation and secretion rates for [(3)H]palmitic acid and [(14)C]choline into Sat PC were similar, the labeled Sat PC was lost from the lungs of SP-D(+/+) mice more rapidly than from SP-D(-/-) mice. Clearance rates of intratracheal [(3)H]dipalmitoylphosphatidylcholine were used to estimate net clearances of Sat PC, which were approximately threefold higher for alveolar and total lung Sat PC in SP-D(-/-) mice than in SP-D(+/+) mice. SP-D deficiency results in multiple abnormalities in surfactant forms and metabolism that cannot be attributed to a single mechanism.

Serum surfactant proteins A and D as prognostic factors in idiopathic pulmonary fibrosis and their relationship to disease extent

Idiopathic pulmonary fibrosis (IPF) is a progressive, life-threatening, interstitial lung disease of unknown etiology. For optimal therapeutic management of IPF an accurate tool is required for discrimination between reversible and irreversible types of the disease. However, such noninvasive tools are few, and even with high-resolution computed tomography (HRCT), which is the most trusted method for doing so, the nature of the disease activity in IPF cannot always be accurately predicted. The aims of the present study were to assess the values of surfactant protein (SP)-A and SP-D in semiquantifying the extent of disease in IPF and in predicting deterioration in restrictive pulmonary function and survival over a follow-up period of 3-yr. SP-A and SP-D in sera were measured with enzyme-linked immunosorbent assays as previously described. Fifty-two IPF patients were studied to evaluate the association between serum SP-A and SP-D and disease extent on HRCT, deterioration in pulmonary function, and survival during 3 yr of follow-up. Both SP-A and SP-D concentrations were significantly correlated with the extent of alveolitis (a reversible change), whereas they did not correlate with the progression of fibrosis (an irreversible change). The SP-D concentration, unlike that of SP-A, was also related to the extent of parenchymal collapse and the rate of deterioration per year in pulmonary function. The concentrations of SP-A and SP-D in patients who died within 3 yr were significantly higher than in patients who were still alive after 3 yr. We propose that assays of SP-A and SP-D in sera from IPF patients are useful tools for understanding some pathologic characteristics of the disease, that SP-D may be a good predictive indicator of the rate of decline in pulmonary function, and that a combination of the assays for SP-A and SP-D may be helpful in predicting the outcome of patients with IPF.

Two rat surfactant protein A isoforms arise by a novel mechanism that includes alternative translation initiation

A single gene for rat surfactant protein A (SP-A) encodes two isoforms that are distinguished by an isoleucine-lysine-cysteine (IKC) N-terminal extension (SP-A and IKC-SP-A). Available evidence suggests that the variants are generated by alternative signal peptidase cleavage of the nascent polypeptide at a primary site (Cys(-)(1)-Asn(1)) and a secondary site (Gly(-)(4)-Ile(-)(3)). In this study, we used site-directed mutagenesis and heterologous expression in vitro and in insect cells to the examine mechanisms that may lead to alternative signal peptidase cleavage including alternative translation initiation at two in-frame AUGs (Met(-)(30) and Met(-)(20)), a suboptimal context for hydrolysis at the primary cleavage site, or cotranslational protein modifications that expose an otherwise cryptic secondary cleavage site. In vitro translation of a rat cDNA for SP-A resulted in both 28 and 29 kDa primary translation products on SDS-PAGE analysis, while translation of cDNAs encoding Met-30Ala and Met-20Ala mutations resulted in only the single 28 and 29 kDa molecular mass species, respectively. These data are consistent with translation initiation at both Met(-)(30) and Met(-)(20) during in vitro synthesis of SP-A. The Met-30Ala mutation reduced expression of the longer isoform in insect cells, indicating that the Met(-)(30) site also contributes to eucaryotic protein expression. Forcing translation initiation at Met(-)(30) by optimizing the Kozak consensus sequence surrounding that codon or by mutating the Met(-)(20) codon resulted in preferential expression of the longer SP-A isoform but reduced overall expression of the protein almost 10-fold. Both isoforms were generated to some degree whether translation was initiated at the codon for Met(-)(30) or Met(-)(20), indicating that the site of translation initiation is not the sole determinant of isoform generation and suggesting that either the context of the primary cleavage site is suboptimal or that cotranslational modifications affect cleavage. Preventing N-terminal glycosylation at Asn(1) did not affect the site of signal peptidase cleavage. Disruption of interchain disulfide formation at Cys(-)(1) by substitution with serine markedly enhanced cleavage at the Gly(-)(4)-Ile(-)(3) bond, but substitution with alanine enhanced cleavage at the Cys(-)(1)-Asn(1) bond. We conclude that rat SP-A isoforms arise by a novel mechanism that includes both alternative translation initiation at two in-frame AUGs and a suboptimal context for signal peptidase hydrolysis at the primary cleavage site.

Factors influencing pulmonary surfactant protein A levels in cord blood, maternal blood and amniotic fluid

The purpose of this study was to evaluate factors that influence pulmonary surfactant protein A (SP-A) levels in cord blood, maternal blood and amniotic fluid, as well as to establish the normal range of serum SP-A. Labor significantly influenced cord blood SP-A levels. The SP-A levels in maternal blood after delivery were correlated with, but higher than those before delivery. There was a correlation between SP-A levels in amniotic fluid and cord blood. Neonatal serum SP-A was not correlated with maternal SP-A levels. The normal range of SP-A in cord blood was 2.7-21.7 ng/ml following cesarean section without labor, 4.8-50.2 ng/ml after labor at gestational weeks 36-38, and 12.2-44.6 ng/ml at gestational weeks 39-41. SP-A levels in maternal blood before and after delivery and amniotic fluid were 6. 0-74.0, 9.6-73.6 and 403.4-24,540 ng/ml, respectively.

Metabolism of phosphatidylglycerol by alveolar macrophages in vitro

In whole animal studies, it has been shown that turnover of surfactant dipalmitoylphosphatidylglycerol (DPPG) is faster than that of dipalmitoylphosphatidylcholine (DPPC). The goal of this investigation was to characterize the metabolism of DPPG by alveolar macrophages and to determine whether they contribute to the faster alveolar clearance of DPPG. Isolated rat alveolar macrophages were incubated with liposomes colabeled with [(3)H]DPPG and [(14)C]DPPC. Macrophages internalized both lipids in a time- and temperature-dependent manner. The uptake of both lipids was increased by surfactant protein (SP) A and by adherence of the macrophages to plastic slides. The isotope ratio of DPPC to DPPG internalized by macrophages in suspension in the absence of SP-A was significantly lower than the isotope ratio in liposomes, suggesting that macrophages preferentially internalize DPPG when SP-A is absent. Phospholipase activity in macrophage homogenate was higher toward sn-2-labeled DPPG than toward sn-2-labeled DPPC. These studies show that alveolar macrophages play an important role in catabolizing surfactant lipids and may be partially responsible for the relatively faster clearance of DPPG from the lung.

Activation of surfactant protein-B transcription: signaling through the SP-A receptor utilizing the PI3 kinase pathway

This study describes receptor-activated signaling initiated by surfactant protein-A (SP-A), and the means by which it activates transcription of surfactant protein-B. Pulmonary surfactant is a mixture of lipids and associated proteins produced by type II pneumocytes. Interaction of SP-A with its cognate receptor (SPAR) on type II cells is involved in regulating surfactant secretion. This interaction also increases transcription of surfactant proteins and several other genes. To study SP-A cytokine activity, we used as a model surfactant-protein (SP-B) transcription, the activators of which have been characterized. HNF-3 and TTF-1 transcription factors are known to stimulate SP-B transcription. SP-A caused increased phosphorylation and nuclear localization of both. Corresponding increases in protein binding to the SP-B promoter were demonstrated by gel shift analysis. SP-A increased protein binding to HNF-3 and TTF-1 consensus recognition elements. Footprinting analysis indicated that SP-A-induced protein binding to SP-B promoter was greater in amount, but not different in location, from that seen in control cells, which normally transcribe SP-B. SP-A caused transient increases in PI3 kinase localization at the plasma membrane, and SP-A signaling to elicit increased SP-B transcription was blocked by LY294002, an inhibitor of PI3 kinase. Therefore, SP-A signals through PI3 kinase to increase SP-B transcription in type II pneumocytes by enhancing TTF-1 and HNF-3 activation of the SP-B promoter. SP-A activation of this signaling pathway, which affects many cellular functions and has not previously been implicated in type II cell transcriptional activity, has profound import for understanding type II cell biology.