Immunogenicity of surfactant. I. Human alveolar surfactant

A risk-benefit assessment of natural and synthetic exogenous surfactants in the management of neonatal respiratory distress syndrome

Alveolar surfactant is central to pulmonary physiology. Quantitative and qualitative surfactant abnormalities appear to be the primary aetiological factors in neonatal respiratory distress syndrome (RDS) and exogenous replacement of surfactant is a rational treatment. Available exogenous surfactants have a natural (mammal-derived lung surfactants) or synthetic origin. Pharmacodynamic and clinical studies have demonstrated that exogenous surfactants immediately improve pulmonary distensibility and gas exchange; however, this is achieved more slowly and with more failures with synthetic surfactants. The ensuing advantageous haemodynamic effects are not so striking and they include an inconvenient increased left to right ductal shunt. Two strategies of administration have been used: prophylactic or rescue therapy to treat declared RDS. All methods of instillation require intubation. In addition to the early benefits (improved gas exchange and reduced ventilatory support) the incidence of classical complications of RDS, especially air leak events, is decreased except for the uncommon problem of pulmonary haemorrhage. The incidence of bronchopulmonary dysplasia is neither uniformly nor significantly reduced although the severity appears to be lessened. The overall incidence of peri-intraventricular haemorrhages is not diminished although separate trials have shown a decreased rate. The most striking beneficial effect of exogenous surfactants is the increased survival (of about 40%) of treated very low birthweight neonates. A small number of adverse effects has been described. The long term outcome of survivor neonates with RDS treated with surfactants versus control neonates with RDS not treated with surfactants is similar in terms of physical growth, at least as good in terms of respiratory status, with a similar or slightly better neurodevelopmental outcome. There is not clear benefit of exogenous surfactant therapy in extremely premature infants (< 26 weeks gestational age, birthweight < 750 g). The potential risks of contamination, inflammatory and immunogenic reaction and the inhalation of platelet activating factor remain a theoretical concern of surfactant therapy which has not been confirmed in clinical practice. The optimal timing of treatment favours prophylaxis over rescue treatment and early rescue treatment rather than delayed therapy. Meta-analyses suggest the clinical superiority of natural surfactant extracts over a synthetic one (colfosceril palmitate). The economic impact of surfactant therapy is favourable and the costs per quality-adjusted life year (QALY) for surviving surfactant treated infants are low. In conclusion, the mid and long term benefit/risk ratio clearly favours the use of exogenous surfactants to prevent or to treat RDS in neonates who have a gestational age of > 26 weeks or a birthweight of > 750 g, especially with the prophylactic strategy using natural surfactant extracts.

[Natural or artificial surfactants? Arguments in favour of natural surfactants]

The use of exogenous surfactant (ES) is an essential component for prevention and treatment of hyaline membrane disease (HMD). The ES available for clinical use are of two therapeutic classes: natural surfactants prepared from mammalian lung and artificial surfactants. The choice between these two classes of ES is controversial. In this overview, we present the arguments in favour of the preferential use of natural ES. The presence of hydrophobic specific proteins (SP-B and SP-C) provides to natural ES better surface tension properties than artificial ES. The in vitro greater efficacy of natural ES has been confirmed in vivo in experimental models of surfactant deficiency, human pharmacodynamic studies, and comparative clinical trials. Furthermore, the excellent clinical tolerance and harmlessness of natural ES has been firmly established. A meta-analysis of the comparative clinical trials between natural ES and one artificial ES (enrolling as many as 4400 babies treated for HMD) suggests that the use of natural ES compared to this artificial ES significantly reduces the neonatal mortality by 20%. In conclusion, all these arguments are in favor of the preferential use of natural ES for prevention and treatment of HMD.

In vitro and in vivo transfer and expression of human surfactant SP-A- and SP-B-associated protein cDNAs mediated by replication-deficient, recombinant adenoviral vectors

Congenital pulmonary alveolar proteinosis (CPAP) is a fatal disease of full-term infants that is unresponsive to current medical therapy. It is now recognized that at least some forms of this disorder are associated with a deficiency of SP-B, one of the surfactant-associated proteins, as well as probable aberrations in the surfactant-associated proteins SP-A and SP-C. Given these developments, it is logical to hypothesize that CPAP may be amenable to gene therapy, in which the human SP-B cDNA, and possibly the cDNAs of the other surfactant associated proteins, are transferred to the epithelium of the lower respiratory tract. We constructed replication-deficient, recombinant adenovirus vectors in which a constitutive viral promoter drives the expression of the DNAs for the surfactant-associated proteins, SP-B (AdCMV.SP-B) and SP-A (AdCMV.SP-A). Following infection of the human lung A549 epithelial cell line with these vectors in vitro, the appropriately sized mRNAs for these cDNAs were detected, whereas cells infected with a control virus or uninfected cells produced none. Western blots demonstrated expression of these proteins, including appropriate processing of the hydrophobic protein, SP-B. Following in vivo intratracheal infection of rats with these vectors, Northern analysis of the lungs revealed appropriately sized mRNAs for these cDNAs whereas rats infected with control virus or uninfected rats show no hybridization with the human surfactant-associated protein probes. In the AdCM-V.SP-A-infected rats, Western blots confirmed the overproduction of the human SP-A protein in both the bronchoalveolar lavage and lung homogenates compared to controls. Thus, it is feasible to utilize adenovirus vectors to transfer and express the human surfactant associated protein cDNAs in vitro and in vivo, presenting a possible mode of therapy for CPAP, as well as other surfactant deficiency states such as the neonatal respiratory distress syndrome and possibly the adult respiratory distress syndrome.

Evidence for the existence of ganglioside molecules on Pneumocystis carinii from human lungs

This study was undertaken to assess whether glycolipid antigens (particularly gangliosides) are associated with Pneumocystis carinii obtained from human lungs. Gangliosides were extracted, purified in high performance thin-layer chromatography and stained with resorcinol. Two resorcinol-positive bands, co-migrating with GM1 and GD1a were demonstrated, suggesting the existence of ganglioside molecules on P. carinii. No resorcinol-positive bands were revealed in the pulmonary control tissue. In addition, an antiserum obtained from rabbits immunized with P. carinii antigen reacted with gangliosides GM1 and GD1a, as revealed by a dot immunobinding assay. This reactivity was inhibited by first incubating the antiserum with ganglioside micelles. Furthermore, anti-glycosphingolipid antibodies (aGM1) reacted with the bands of 200 and 55 kDa of P. carinii antigen. These results suggest that ganglioside antigens expressed on P. carinii can trigger specific immune responses.

Identification of a cell membrane protein that binds alveolar surfactant

Alveolar surfactants are complex mixtures of proteins and phospholipids produced by type II alveolar cells and responsible for lowering pulmonary surface tension. The process by which surfactant is produced and exported and by which its production by pulmonary cells is regulated are not well understood. This study was designed to identify a cellular receptor for surfactant constituents. To do so, monoclonal anti-idiotypic antibodies directed against antibodies to porcine and rabbit surfactant proteins were prepared. These monoclonal anti-idiotypic antibodies bind both alveolar lining and bronchial epithelial cells in rabbit, porcine, and human lungs. Macrophages and other nonepithelial cells do not react with these antibodies. Western blot analysis indicates that both A2R and A2C recognize the same proteins in both pig and rabbit lungs: a 30-kd protein and additional proteins at 52 and 60 kd. Preincubating lung wash cells with A2C or A2R prevents binding of porcine or rabbit surfactant preparations, respectively, by these cells. Preincubating frozen sections of lung tissue with surfactant inhibits binding of A2R and A2C to the lung. Antibody directed to a cell membrane protein that recognizes alveolar surfactant may be useful in elucidating the structure and function of this receptor and in understanding the cellular physiology and pathophysiology of the surfactant system.

Immunogenicity of surfactant. II. Porcine and bovine surfactants

Protein-containing surfactants of human and animal origin are being used increasingly to treat neonatal and adult respiratory distress syndromes. This trend led us to examine the antigenicity of two important preparations of animal surfactant, cow lung surfactant extract (CLSE) and a porcine surfactant preparation, Curosurf. We describe here 15 monoclonal antibodies against Curosurf and four against CLSE. Antibodies were studied by Western blot analysis to determine their ability to recognize protein components of their respective surfactant preparations. They were also tested for their ability to inactivate surfactant in vitro, assayed using the pulsating bubble surfactometer. Several antibodies directed against CLSE or Curosurf functionally inactivate the surfactant to which they were raised. We determined the degree of immunologic cross-reactivity between antibodies directed to CLSE and Curosurf against the other surfactant and also against human surfactant, both by Western blot and by examining functional inactivation in vitro. Antibodies to these animal surfactants that are commonly used therapeutically may inactivate the specific animal surfactant to which they were raised, as well as human and other surfactants. Generally, when antibodies inactivate surfactant from more than one animal species, they inactivate heterologous surfactants comparably to the extent to which they inactivate the surfactant to which they are directed. Immune complexes between anti-surfactant antibodies and surfactant have been described in the course of neonatal respiratory distress syndrome. The potential pathophysiological importance of anti-surfactant antibodies may therefore lie in their ability to inactivate administered surfactant, other similar surfactants and endogenous surfactant. In so doing, these antibodies may potentiate surfactant deficiency or pulmonary injury initiated by other stimuli.