Mechanisms to explain surfactant responses

Pulmonary Surfactant: A Mighty Thin Film

Pulmonary surfactant is a critical component of lung function in healthy individuals. It functions in part by lowering surface tension in the alveoli, thereby allowing for breathing with minimal effort. The prevailing thinking is that low surface tension is attained by a compression-driven squeeze-out of unsaturated phospholipids during exhalation, forming a film enriched in saturated phospholipids that achieves surface tensions close to zero. A thorough review of past and recent literature suggests that the compression-driven squeeze-out mechanism may be erroneous. Here, we posit that a surfactant film enriched in saturated lipids is formed shortly after birth by an adsorption-driven sorting process and that its composition does not change during normal breathing. We provide biophysical evidence for the rapid formation of an enriched film at high surfactant concentrations, facilitated by adsorption structures containing hydrophobic surfactant proteins. We examine biophysical evidence for and against the compression-driven squeeze-out mechanism and propose a new model for surfactant function. The proposed model is tested against existing physiological and pathophysiological evidence in neonatal and adult lungs, leading to ideas for biophysical research, that should be addressed to establish the physiological relevance of this new perspective on the function of the mighty thin film that surfactant provides.

Surfactant and neonatal hemodynamics during the postnatal transition

Surfactant replacement therapy (SRT) has revolutionized the management of respiratory distress syndrome (RDS) in premature infants, leading to improved survival rates and decreased morbidity. SRT may, however, be associated with hemodynamic changes, which can have both positive and negative effects on the immature cardiovascular system, during the transitional adaptation from fetal to extrauterine environment. However, there is a relative paucity of evidence in this domain, with most of them derived from small heterogeneous observational studies providing conflicting results. In this review, we will discuss the hemodynamic changes that occur with surfactant administration during this vulnerable period, focusing on available evidence regarding changes in pulmonary and systemic blood flow, cerebral circulation and their clinical implications.

Exogenous pulmonary surfactant in COVID-19 ARDS. The similarities to neonatal RDS suggest a new scenario for an 'old' strategy

Acute respiratory distress syndrome (ARDS) related to SARS-CoV-2 infection has some unusual characteristics that differentiate it from the pathophysiology described in the more 'typical' ARDS. Among multiple hypotheses, a close similarity has been suggested between COVID-19 ARDS and neonatal respiratory distress syndrome (RDS). With this opinion paper, we investigated the pathophysiological similarities between infant respiratory diseases (RDS and direct neonatal ARDS (NARDS)) and COVID-19 in adults. We also analysed, for the first time, similarities in the response to exogenous surfactant administration in terms of improved static compliance in RDS and direct NARDS, and adult COVID-19 ARDS. In conclusion, we believe that if the pathological processes are similar both from the pathophysiological point of view and from the response in respiratory mechanics to a recruitment treatment such as surfactant, perhaps the latter could be considered a plausible option and lead to recruitment in clinical trials currently ongoing on patients with COVID-19.

"Optimal surfactant delivery protocol using the bovine lipid extract surfactant: a quality improvement study"

IMPORTANCE

Episodes of severe airway obstruction (SAO) are reported during surfactant administration.

OBJECTIVE

To evaluate adherence to and impact of a surfactant protocol on adverse events.

METHODS

An evidence-based protocol for surfactant administration was developed (2011), implemented (2012) and re-implemented (2014), including three major steps: lung recruitment, manual bagging, and bolus instillation. Three epochs were evaluated: E₀ (2010), E₁ (2015) and E₂ (2018). Adherence was defined as compliance with all steps. Adverse events such as hypoxia (<80%) and severe airway obstruction (SAO) were investigated.

RESULTS

197 infants (246 administrations) were included: E₀ 81 (110), E₁ 52 (63), and E₂ 64 (73). Adherence improved from 49% (E₁) to 67% (E₂). Full adherence to protocol significantly decreased SAO from 26% to 1.25% (E₂; p < 0.005) and hypoxia/bradycardia events (5 to 0% E₂; p < 0.005), without any side effects.

CONCLUSIONS

Adherence to a surfactant administration protocol improved over time and significantly decreased important adverse events.

Lung deposition of nebulized surfactant in newborn piglets: Nasal CPAP vs Nasal IPPV

BACKGROUND

Nasal continuous positive airway pressure support (nCPAP) is the standard of care for prematurely born infants at risk of neonatal respiratory distress syndrome (nRDS). However, nasal intermittent positive pressure ventilation (NIPPV) may be an alternative to nCPAP in babies requiring surfactant, and in conjunction with surfactant nebulization, it could theoretically reduce the need for invasive mechanical ventilation. We compared lung deposition of nebulized poractant in newborn piglets supported by nCPAP or NIPPV.

METHODS

Twenty-five sedated newborn piglets (1.2-2.2 kg) received either nCPAP (3 cmH2 O, n = 12) or NIPPV (3 cmH2 O positive end expiratory pressure+3 cmH2 O inspiratory pressure, n = 13) via custom-made nasal prongs (FiO2 0.4, Servo-i ventilator). Piglets received 200 mg kg-1 of technetium-99m-surfactant mixture continuously nebulized with a customized eFlow-Neos investigational vibrating-membrane nebulizer system. Blood gases were taken immediately before, during, and after nebulization. The deposition was estimated by gamma scintigraphy.

RESULTS

Mean surfactant deposition in the lungs was 15.9 ± 11.9% [8.3, 23.5] (mean ± SD [95% CI]) in the nCPAP group and 21.6 ± 10% [15.6, 27.6] in the NIPPV group (P = .20). Respiratory rates were similar in both groups. Minute volume was 489 ± 203 [360, 617] in the nCPAP group and 780 ± 239 [636, 924] mL kg-1  min-1 in the NIPPV group (P = .009). Blood gases were comparable in both groups.

CONCLUSION

Irrespective of the noninvasive ventilatory support mode used, relatively high lung deposition rates of surfactant were achieved with nebulization. The amounts of deposited surfactant might suffice to elicit a pulmonary function improvement in the context of nRDS.

Impact of Body Position on Lung Deposition of Nebulized Surfactant in Newborn Piglets on Nasal Continuous Positive Airway Pressure

INTRODUCTION

The ideal body position during surfactant nebulization is not known.

OBJECTIVE

The aim of this study was to determine whether body positioning during surfactant nebulization influences surfactant distribution and deposition in the lungs.

METHODS

Twenty-four 12- to 36-h-old full-termpiglets (1.3-2.2 kg) on nasal continuous positive airway pressure (nCPAP) were randomized into four groups: lateral decubitus with right or left side up, prone or supine positions (n = 6 each). All animals received 200 mg kg-1 of poractant alfa mixed with 200 MBq of 99mtechnetium-nanocolloid via a customized eFlow-Neos investigational vibrating-membrane nebulizer. Surfactant deposition (percentage of the administered dose) was measured by gamma scintigraphy.

RESULTS

Comparing all groups, the mean total lung surfactant deposition was significantly higher in the prone position (32.4 ± 7.7%, p = 0.03). The deposition in this group was higher in the right lung (21.0 ± 8.6 vs. 11.3 ± 5.7%, p = 0.04). When nebulization was performed in the lateral decubitus, most of the surfactant was found in the dependent lung, regardless of which side the piglet lay on (right side up 15.3 ± 1.0 vs. 3.4 ± 1.0%, p = 0.06, and left side up 11.2 ± 9.8 vs. 1.8 ± 0.7%, p = 0.04).

CONCLUSIONS

In spontaneously breathing animals on nCPAP, the prone position yielded the highest lung dose. Higher deposition rates in the dependent lung while on lateral decubitus indicates that deposition was also influenced by gravity.

Beractant and poractant alfa in premature neonates with respiratory distress syndrome: a systematic review of real-world evidence studies and randomized controlled trials

Findings from previous meta-analyses of randomized clinical trials (RCTs) in premature infants with respiratory distress syndrome (RDS) varied as to whether clinical outcomes differed by type of animal-derived pulmonary surfactant; real-world evidence (RWE) was excluded. We extracted study characteristics and outcomes from full-text articles from a systematic search for studies that compared beractant with poractant alfa for RDS in preterm infants. RWE data were tabulated; RCT data were subjected to meta-analyses. Designs, patient characteristics, and follow-up durations varied widely among studies (4 RWE, 15 RCT). RWE studies with adjusted odds ratios (ORs) found no statistically significant between-treatment differences in outcomes. In RCT meta-analyses, no statistically significant between-treatment differences were observed for death (OR [95% confidence interval], 1.35 [0.98-1.86]), bronchopulmonary dysplasia (1.25 [0.96-1.62]), pneumothorax (1.21 [0.72-2.05]), and air leak syndrome (2.28 [0.82-6.39]). Collectively, outcomes were similar with beractant and poractant alfa in RWE studies and pooled RCTs.

Lung injury after asphyxia and hemorrhagic shock in newborn piglets: Analysis of structural and inflammatory changes

OBJECTIVE

Asphyxia of newborns is a severe and frequent challenge of the peri- and postnatal period. The purpose of this study was to study early morphological, immunological and structural alterations in lung tissue after asphyxia and hemorrhage (AH).

METHODS

44 neonatal piglets (age 32 hrs) underwent asphyxia and hemorrhage (AH) and were treated according to the international liaison committee of resuscitation (ILCOR) guidelines. For this study, 15 piglets (blood transfusion (RBC) n = 9; NaCl n = 6, mean age 31 hrs) were randomly picked. 4 hours after ROSC (return of spontaneous circulation), lung tissue and blood samples were collected.

RESULTS

An elevation of myeloperoxidase (MPO) activity was observed 4 hrs after AH accompanied by an increase of surfactant D after RBC treatment. After AH tight junction proteins Claudin 18 and junctional adhesion molecule 1 (JAM1) were down-regulated, whereas Occludin was increased. Furthermore, after AH and RBC treatment dephosphorylated active form of Connexin 43 was increased.

CONCLUSIONS

AH in neonatal pigs is associated with early lung injury, inflammation and alterations of tight junctions (Claudin, Occludin, JAM-1) and gap junctions (Connexin 43) in lung tissue, which contributes to the development of lung edema and impaired function.

[Intervention and role of the paediatrician in the delivery room]

Some newborns require the presence of a paediatrician in the delivery room, for emergency care. This generally leads to hospitalisation in neonatal intensive care or neonatology. Prematurity and respiratory distress are the main causes. These unexpected situations are a source of anxiety for the parents. It is essential that the multidisciplinary team draws on both its technical and relational expertise, in order to provide optimal treatment to the infant while supporting the parents with the necessary empathy.

Folding sticky elastica: dynamics and reversibility of folds in Langmuir monolayers

Lipid monolayers at the air/water interface are often subject to large mechanical stresses when compressed laterally. For large enough compression they fold in the out-of-plane direction to relax stress. The repetitive folding and unfolding of lung surfactant monolayers during breathing plays a critical role in conserving monolayer material at the air/water interface lining the lung. Although the mechanisms behind the folding have been explored recently, relatively little information exists regarding the implications of folding dynamics on the long-term stability of the monolayer. We address this question by investigating the dynamical effect of folding rate in a lipid monolayer containing nano-particles, using a combination of analytic theory, simulation and experiment. We find that the presence of adsorbed particles are essential for monolayer rupture during unfolding. These particles act as linkers pinning the folds shut. The rate of folding affects reversibility as well. We construct a reversibility phase diagram spanned by the compression period and the size of the adsorbed particles showing the complex interaction of fold morphology, particle diffusion, and linker unbinding that results in reversible or irreversible folding.

Parental preferences regarding administration of an animal-derived versus a synthetic medication to newborn infants

AIM

We examined the perceptions of parents with regard to animal-derived versus synthetic medications of comparable efficacy. We hypothesized that this issue is a concern in neonatal care and that the perceptions of parents from one geographical location would be similar to those of another.

METHODS

A survey was distributed to parents of neonates admitted to a neonatal intensive care unit of a southeastern hospital.

RESULTS

Of 153 parents surveyed, 150 (98%) responded. More mothers than fathers completed the surveys (113 vs. 34). Fifty-six percent of participants indicated a college or higher education; 40% had an income of $51,000/yr or higher. Thirty-four percent of parents had concerns about animal-derived medications, 41% preferred a synthetic medication of equivalent efficacy, and 69% would like to be informed if a medication was animal-derived.

CONCLUSION

Parents have concerns about exposing neonates to animal-derived medication and wish to be informed if an animal-derived medication is being considered.

Surfactant

Exogenous pulmonary surfactant, widely used in neonatal care, is one of the best-studied treatments in neonatology, and its introduction in the 1990s led to a significant improvement in neonatal outcomes in preterm infants, including a decrease in mortality. This chapter provides an overview of surfactant composition and function in health and disease and summarizes the evidence for its clinical use.

NICU bedside caregivers sustain process improvement and decrease incidence of bronchopulmonary dysplasia in infants < 30 weeks gestation

BACKGROUND

The objective of this study was to investigate whether a respiratory care bundle, implemented through participation in the Vermont Oxford Network-sponsored Neonatal Intensive Care Quality Improvement Collaborative (NIC/Q 2005) and primarily dependent on bedside caregivers, resulted in sustained decrease in the incidence of bronchopulmonary dysplasia (BPD) in infants < 30 wk gestation.

METHODS

A retrospective cohort study was conducted. Infants inborn between 23 wk and 29 wk + 6 d of gestation were included. Patients with congenital heart disease, significant congenital or lung anomalies, or death before intubation were excluded. Four time periods (T1-T4) were identified: T1: September 1, 2002 to August 31, 2004; T2: September 1, 2004 to August 31, 2006; T3: September 1, 2006 to August 31, 2008; T4: September 1, 2008 to August 31, 2010.

RESULTS

A total of 1,050 infants were included in the study. BPD decreased significantly in T3 post-implementation of the respiratory bundle compared with T1 (29.9% vs 51.2%, respectively; adjusted odds ratio [aOR] = 0.06 [95% CI 0.03-0.13], P = < .001). The decrease was not sustained into T4. There was a significant increase in the rate of BPD-free survival to discharge in T3 compared with T1 (53.1% vs 47%; aOR = 1.68 [95% CI 1.11-2.56], P = .01) that was also not sustained. The rate of infants requiring O2 at 28 d of life decreased significantly in T3 versus T1 (40.3% vs 69.9%, respectively; aOR = 0.12 [95% CI 0.07-0.20], P = < .001). Increases in the rate of surfactant administration by 1 h of life and rate of caffeine use were observed in T4 versus T1, respectively. There was a significant decrease in median ventilator days and a significant increase in the median number of noninvasive CPAP days throughout the study period.

CONCLUSIONS

In this study, implementation of a respiratory bundle managed primarily by nurses and respiratory therapists was successful in increasing the use of less invasive respiratory support in a consistent manner among very low birthweight infants at a single institution. However, this study and others have failed to show sustained improvement in the incidence of BPD despite sustained process change.

Prematurity and congenital heart disease

Significant advances in technology and therapy have led to dramatic improvements in the survival of preterm babies over the last 2 decades. Similarly, improvements in surgical and cardiac intensive care techniques have increased the feasibility of supporting even very small babies to the point of surgical repair, leading some to adopt an approach of early and complete surgical repair in preterm infants, with the aim of minimizing potential preoperative morbidity associated with extended medical management or surgical palliation. (1,2) However, multiple diagnostic and therapeutic challenges complicate the care of premature infants. Major errors in echocardiography are more common in neonates weighing less than 2.5 kg, (3) and the ideal timing and type of surgical intervention in premature infants remains unknown. These problems are compounded by the need for critical care practices that optimize management of immature cardiopulmonary, gastrointestinal, and neurological systems. This review will summarize some of the recent advances in neonatal and perinatal medicine, which have the potential to contribute to improved management of preterm infants with critical cardiac disease.

Lung protective ventilation in extremely preterm infants

The lungs of an extremely preterm infant ≤28 weeks gestation are structurally and biochemically immature and vulnerable to injury from positive pressure ventilation. A lung protective approach to respiratory support is vital, aiming to ventilate an open lung, using the lowest pressure settings that maintain recruitment and oxygenation and avoiding hyperinflation with each tidal breath. For infants with severe respiratory distress syndrome and persistent atelectasis, lung protective ventilation requires recruitment using stepwise pressure increments, followed by reduction in ventilator pressures in search of an optimal point at which to maintain ventilation. Several studies, including a single randomised controlled trial, have found this lung protective strategy to be more effectively administered using high-frequency oscillatory ventilation rather than conventional ventilation. Many extremely preterm infants have minimal atelectasis and low oxygen requirements in the first days of life, and the ventilatory approach in this case should be one of avoidance of factors including overdistension that are known to contribute to later pulmonary deterioration. From a practical perspective, this means setting positive end-expiratory pressure at the lowest value that maintains oxygenation and restricting tidal volume using a volume-targeted mode of ventilation.

Surfactant for bacterial pneumonia in late preterm and term infants

BACKGROUND

Pulmonary surfactant is an important part of the host defence against respiratory infections. Bacterial pneumonia in late preterm or term newborn infants often leads to surfactant deficiency or dysfunction, as surfactant is either inactivated or peroxidated. Studies of animal models of pneumonia and clinical case reports suggest that exogenous surfactant might be beneficial to infants with bacterial pneumonia.

OBJECTIVES

To assess the effect of exogenous surfactant treatment on mortality and pulmonary complications in infants with bacterial pneumonia.

SEARCH METHODS

We used standard Cochrane Collaboration methodology to conduct our search of databases. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 6); MEDLINE (accessed via Ovid SP June 2011); EMBASE (via Ovid SP 1980 to June 2011); and CINAHL Plus (accessed via EBSCOHost June 2011).

SELECTION CRITERIA

We limited our search to randomised and quasi-randomised trials of surfactant replacement therapy in infants > 35 weeks gestation with bacterial pneumonia in the first 28 days of life. The primary outcome measures were death, time to resolution of pneumonia, incidence of chronic lung disease, pneumothoraces and pulmonary haemorrhage.

DATA COLLECTION AND ANALYSIS

We assessed all studies with predefined criteria as to whether they were eligible for inclusion. We extracted data using RevMan 5 (RevMan 2011). We used the standard Cochrane Collaboration methodology for data collection and analysis to assess risk of bias, heterogeneity, treatment effect, missing data and reporting bias where appropriate.

MAIN RESULTS

We did not identify any studies that met our inclusion criteria.

AUTHORS' CONCLUSIONS

There is no evidence from randomised controlled trials (RCTs) to support or refute the efficacy of surfactant in near-term and term infants with proven or suspected bacterial pneumonia. RCTs are still required to answer this question.

Noninvasive ventilation for respiratory distress syndrome: a randomized controlled trial

CONTEXT

Strategies for reducing exposure to endotracheal ventilation through the use of early noninvasive ventilation has proven to be safe and effective, but the option with the greatest benefits needs to be determined.

OBJECTIVE

To determine, in infants with respiratory distress syndrome, if early nasal intermittent positive-pressure ventilation (NIPPV) compared with nasal continuous positive airway pressure (NCPAP) decreases the need for mechanical ventilation.

PATIENTS AND METHODS

In this single-center, randomized controlled trial, infants (gestational ages 26 to 33/7 weeks) with respiratory distress syndrome were randomly assigned to receive early NIPPV or NCPAP. Surfactant was administered as rescue therapy. The primary outcome was the need for mechanical ventilation within the first 72 hours of life.

RESULTS

A total of 200 infants, 100 in each arm, were randomly assigned. Rates of the primary outcome did not differ significantly between the NIPPV (25%) and NCPAP (34%) groups (relative risk [RR]: 0.71 [95% confidence interval (CI): 0.48–1.14]). In posthoc analysis, from 24 to 72 hours of life, significantly more infants in the NIPPV group remained extubated compared with those in the NCPAP groups (10 vs 22%; RR: 0.45 [95% CI: 0.22–0.91]). This difference was also noted in the group of infants who received surfactant therapy, NIPPV (10.9%), and NCPAP (27.1%) (RR: 0.40 [95% CI: 0.18–0.86]).

CONCLUSIONS

Early NIPPV did not decrease the need for mechanical ventilation compared with NCPAP, overall, in the first 72 hours of life. However, further studies to assess the potential benefits of noninvasive ventilation are warranted, especially for the most vulnerable or preterm infants.

An overview of pulmonary surfactant in the neonate: genetics, metabolism, and the role of surfactant in health and disease

Pulmonary surfactant is a complex mixture of phospholipids (PL) and proteins (SP) that reduce surface tension at the air-liquid interface of the alveolus. It is made up of about 70-80% PL, mainly dipalmitoylphosphatidylcholine (DPPC), 10% SP-A, B, C and D, and 10% neutral lipids, mainly cholesterol. Surfactant is synthesized, assembled, transported and secreted into the alveolus where it is degraded and then recycled. Metabolism of surfactant is slower in newborns, especially preterm, than in adults. Defective pulmonary surfactant metabolism results in respiratory distress with attendant morbidity and mortality. This occurs due to accelerated breakdown by oxidation, proteolytic degradation, inhibition or inherited defects of surfactant metabolism. Prenatal corticosteroids, surfactant replacement, whole lung lavage and lung transplantation have yielded results in managing some of these defects. Gene therapy could prove valuable in treating inherited defects of surfactant metabolism.

Role of vagal innervation on pulmonary surfactant system during fetal development

Vagally mediated afferent feedback and compliant lungs (surfactant system) play vital roles in the establishment of adequate alveolar ventilation and pulmonary gas exchange at birth. Although the significance of vagal innervation in the establishment of normal breathing patterns is well recognized, the precise role of lung innervation in the maturation of the surfactant system remains unclear. The specific aim of the present study was to investigate whether vagal denervation compromises the surfactant system during fetal development. Experiments were performed on 12 time-dated fetal sheep: 8 underwent cervical vagal denervation, and 4 were sham operated. Vagal denervation was performed at 110–113 days gestation. Fetal lambs were instrumented in utero to record arterial pH and blood-gas tensions. The animals were delivered by cesarean section under general anesthesia between 130 and 133 days gestation (term ∼147 days). Lung samples were collected for wet-to-dry ratios, light and electron microscopy, and overall lung morphology. In addition, total proteins, total phospholipids, and surfactant proteins A and B were analyzed in both lung tissue and bronchoalveolar lavage fluid. Vagal denervation had no effect on alveolar architecture, including type II cells or the morphology of lamellar bodies within them. Furthermore, surfactant proteins A and B and total phospholipids were similar in lung tissue and bronchoalveolar lavage fluid between the two groups. A significant correlation was observed between circulating cortisol concentrations and surfactant proteins in the bronchoalveolar lavage fluid and lung tissue. We provide definitive evidence that vagal innervation at midgestation is not required for maturation of the pulmonary surfactant system during fetal development.

The role of surfactant treatment in preterm infants and term newborns with acute respiratory distress syndrome

Surfactant treatment in preterm infants and term newborns with (acute respiratory distress syndrome) ARDS-like severe respiratory failure has become part of an individualized treatment strategy in many intensive care units around the world. These babies constitute heterogeneous groups of gestational ages, lung maturity, as well as of the underlying disease processes and postnatal interventions. The pathophysiology of respiratory failure in preterm infants is characterized by a combination of primary surfactant deficiency and surfactant inactivation as a result of plasma proteins leaking into the airways from areas of epithelial disruption and injury. Various pre- and postnatal factors, such as exposure to chorioamnionitis, pneumonia, sepsis and asphyxia, induce an injurious inflammatory response in the lungs of preterm infants, which may subsequently affect surfactant function, synthesis and alveolar stability. Surfactant inactivation--and dysfunction--is also a hallmark in newborns with meconium aspiration syndrome (MAS), pneumonia and other disorders affecting the pulmonary function. Although for the majority of suggested indications no data from randomized controlled trials exist, a surfactant replacement that counterbalances surfactant inactivation seems to improve oxygenation and lung function in many babies with ARDS without any apparent negative side effects. Newborns with MAS will definitely benefit from a reduced need for extracorporeal membrane oxygenation (ECMO). Clinical experience seems to justify surfactant treatment in neonates with ARDS.

Macrophage dysfunction and susceptibility to pulmonary Pseudomonas aeruginosa infection in surfactant protein C-deficient mice

To determine the role of surfactant protein C (SP-C) in host defense, SP-C-deficient (Sftpc-/-) mice were infected with the pulmonary pathogen Pseudomonas aeruginosa by intratracheal injection. Survival of young, postnatal day 14 Sftpc-/- mice was decreased in comparison to Sftpc+/+ mice. The sensitivity to Pseudomonas bacteria was specific to the 129S6 strain of Sftpc-/- mice, a strain that spontaneously develops interstitial lung disease-like lung pathology with age. Pulmonary bacterial load and leukocyte infiltration were increased in the lungs of Sftpc-/- mice 24 h after infection. Early influx of polymorphonuclear leukocytes in the lungs of uninfected newborn Sftpc-/- mice relative to Sftpc+/+ mice indicate that the lack of SP-C promotes proinflammatory responses in the lung. Mucin expression, as indicated by Alcian blue staining, was increased in the airways of Sftpc-/- mice following infection. Phagocytic activity of alveolar macrophages from Sftpc-/- mice was reduced. The uptake of fluorescent beads in vitro and the number of bacteria phagocytosed by alveolar macrophages in vivo was decreased in the Sftpc-/- mice. Alveolar macrophages from Sftpc-/- mice expressed markers of alternative activation that are associated with diminished pathogen response and advancing pulmonary fibrosis. These findings implicate SP-C as a modifier of alveolar homeostasis. SP-C plays an important role in innate host defense of the lung, enhancing macrophage-mediated Pseudomonas phagocytosis, clearance and limiting pulmonary inflammatory responses.