The effect of ozone exposure on the ability of human surfactant protein a variants to stimulate cytokine production

Surfactant Protein-A and its immunomodulatory roles in infant respiratory syncytial virus infection: a potential for therapeutic intervention?

The vast majority of early-life hospital admissions globally highlight respiratory syncytial virus (RSV), the leading cause of neonatal lower respiratory tract infections, as the major culprit behind the poor neonatal outcomes following respiratory infections. Unlike those of older children and adults, the immune system of neonates looks rather unique, therefore mostly counting on the innate immune system and antibodies of maternal origins. The collaborations between cells and immune compartments during infancy inclines bias toward a T-helper 2 (Th2) immune profile and thereby away from a T-helper 1 (Th1) immune response. What makes it more problematic is that RSV infection also tends to elicit a stronger Th2-biased immune response and drive an aberrant allergy-like inflammation. It is thus evident how RSV infections potentially pave the way for wheezing recurrences and childhood asthma later in life. Surfactant, the essential lung substance for normal breathing processes in mammals, has immunomodulatory properties including lung collectins such as Surfactant Protein-A (SP-A), which is the most abundant protein component of surfactant, and also Surfactant Protein-D (SP-D). Deficiency of SP-A and SP-D has been found to be associated with impaired pathogen clearance and exacerbated immune responses during infections. We therefore conducted a review of the literature to describe pathomechanisms of RSV infections during blunted neonatal immunity potentially facilitating allergy-like inflammatory events within the developing lungs and highlight the potential protective role of the humoral collectin SP-A to mitigate these in the "early in life" pulmonary immune system.

Loss of Surfactant Protein A Alters Perinatal Lung Morphology and Susceptibility to Hyperoxia-Induced Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a condition of poor alveolar formation that causes chronic breathing impairment in infants born prematurely. Preterm lungs lack surfactant and are vulnerable to oxidative injuries driving the development of BPD. Our recent studies reported that surfactant protein A (SP-A) genetic variants influence susceptibility to neonatal lung disease. SP-A modulates activation of alveolar macrophages and parturition onset in late gestation. We asked whether a lack of SP-A alters alveolarization in a mouse model of hyperoxia-induced BPD. SP-A-deficient and control newborn mice were exposed to either clinically relevant 60% O2 hyperoxia or normoxia for 5-7 days. Alveolar formation was then assessed by mean linear intercept (MLI) and radial alveolar count (RAC) measurements in lung tissue sections. We report that the combination of SP-A deficiency and hyperoxia reduces alveolar growth compared to WT mice. The morphometric analysis of normoxic SP-A-deficient lungs showed lower RAC compared to controls, indicating reduced alveolar number. In the presence of hyperoxia, MLI was higher in SP-A-deficient lungs compared to controls. Differences were statistically significant for female pups. Spatial proteomic profiling of lung tissue sections showed that hyperoxia caused a 4-fold increase in the DNA damage marker γH2Ax in macrophages of SP-A-deficient lungs compared to normoxia. Our short report suggests an important role for SP-A in perinatal lung development and the protection of lung macrophages from oxidant injury. These studies warrant future investigation to discern the temporal interaction of SP-A, gender, oxidant injury, and lung macrophages in perinatal alveolar formation and development of BPD.

Genetic susceptibility to airway inflammation and exposure to short-term outdoor air pollution

BACKGROUND

Air pollution is a large environmental health hazard whose exposure and health effects are unequally distributed among individuals. This is, at least in part, due to gene-environment interactions, but few studies exist. Thus, the current study aimed to explore genetic susceptibility to airway inflammation from short-term air pollution exposure through mechanisms of gene-environment interaction involving the SFTPA, GST and NOS genes.

METHODS

Five thousand seven hundred two adults were included. The outcome measure was fraction of exhaled nitric oxide (FeNO), at 50 and 270 ml/s. Exposures were ozone (O₃), particulate matter < 10 µm (PM₁₀), and nitrogen dioxide (NO₂) 3, 24, or 120-h prior to FeNO measurement. In the SFTPA, GST and NOS genes, 24 single nucleotide polymorphisms (SNPs) were analyzed for interaction effects. The data were analyzed using quantile regression in both single-and multipollutant models.

RESULTS

Significant interactions between SNPs and air pollution were found for six SNPs (p < 0.05): rs4253527 (SFTPA1) with O₃ and NO_x, rs2266637 (GSTT1) with NO₂, rs4795051 (NOS2) with PM₁₀, NO₂ and NO_x, rs4796017 (NOS2) with PM₁₀, rs2248814 (NOS2) with PM₁₀ and rs7830 (NOS3) with NO₂. The marginal effects on FeNO for three of these SNPs were significant (per increase of 10 µg/m³):rs4253527 (SFTPA1) with O₃ (β: 0.155, 95%CI: 0.013-0.297), rs4795051 (NOS2) with PM₁₀ (β: 0.073, 95%CI: 0.00-0.147 (single pollutant), β: 0.081, 95%CI: 0.004-0.159 (multipollutant)) and NO₂ (β: -0.084, 95%CI: -0.147; -0.020 (3 h), β: -0.188, 95%CI: -0.359; -0.018 (120 h)) and rs4796017 (NOS2) with PM₁₀ (β: 0.396, 95%CI: 0.003-0.790).

CONCLUSIONS

Increased inflammatory response from air pollution exposure was observed among subjects with polymorphisms in SFTPA1, GSTT1, and NOS genes, where O₃ interacted with SFTPA1 and PM10 and NO₂/NO_x with the GSTT1 and NOS genes. This provides a basis for the further exploration of biological mechanisms as well as the identification of individuals susceptible to the effects of outdoor air pollution.

Ozone effect on the inflammatory and proteomic profile of human macrophages and airway epithelial cells

Ozone (O₃) is one of the most harmful urban pollutants, but its biological mechanisms have not been fully elucidated yet. Human bronchial epithelial cells (HBEpC) and human macrophage cells (differentiated human monocytic cell line) were exposed to O₃ at the concentration of 240 μg/m³ (120 ppb), corresponding to the European Union alert threshold. Cell viability, reactive oxygen species (ROS) production, and pro-inflammatory cytokines release (IL-8 and TNF-α) were evaluated. Results indicated that O₃ exposure increases ROS production in both cell types and enhances cytokines release in macrophages. O₃ stimulated IL-8 and TNF-α in HBEpC when the cells were pretreated with Lipopolysaccharide, used to mimic a pre-existing inflammatory condition. Proteomics analysis revealed that, in HBEpC, O₃ caused the up-regulation of aldo-keto reductase family 1 member B10, a recognized critical protein in lung carcinogenesis. In conclusion, our results show that 120 ppb O₃ can lead to potential damage to human health suggesting the need for a revision of the actual alert levels.

The Lung Alveolar Cell (LAC) miRNome and Gene Expression Profile of the SP-A-KO Mice After Infection With and Without Rescue With Human Surfactant Protein-A2 (1A0)

Human surfactant protein (SP)-A1 and SP-A2 exhibit differential qualitative and quantitative effects on the alveolar macrophage (AM), including a differential impact on the AM miRNome. Moreover, SP-A rescue (treatment) of SP-A-knockout (KO) infected mice impoves survival. Here, we studied for the first time the role of exogenous SP-A protein treatment on the regulation of lung alveolar cell (LAC) miRNome, the miRNA-RNA targets, and gene expression of SP-A-KO infected mice of both sexes. Toward this, SP-A-KO mice of both sexes were infected with Klebsiella pneumoniae, and half of them were also treated with SP-A2 (1A⁰). After 6 h of infection/SP-A treatment, the expression levels and pathways of LAC miRNAs, genes, and target miRNA-mRNAs were studied in both groups. We found 1) significant differences in the LAC miRNome, genes, and miRNA-mRNA targets in terms of sex, infection, and infection plus SP-A2 (1A⁰) protein rescue; 2) an increase in the majority of miRNA-mRNA targets in both study groups in KO male vs. female mice and involvement of the miRNA-mRNA targets in pathways of inflammation, antiapoptosis, and cell cycle; 3) genes with significant changes to be involved in TP-53, tumor necrosis factor (TNF), and cell cycle signaling nodes; 4) when significant changes in the expression of molecules from all analyses (miRNAs, miRNA-mRNA targets, and genes) were considered, two signaling pathways, the TNF and cell cycle, referred to as “integrated pathways” were shown to be significant; 5) the cell cycle pathway to be present in all comparisons made. Because SP-A could be used therapeutically in pulmonary diseases, it is important to understand the molecules and pathways involved in response to an SP-A acute treatment. The information obtained contributes to this end and may help to gain insight especially in the case of infection.

From Water to Land: The Structural Construction and Molecular Switches in Lungs during Metamorphosis of Microhyla fissipes

Simple Summary

The functionalization of lungs is a necessity for most anurans to breathe on land. Previous studies have focused on the morphological and physiological functions of amphibian lungs, while the microstructural changes and molecular mechanisms that underpin the functional maturation of lungs remain under-researched. We used integrated histology and transcriptomics to study the critical cytological and molecular events associated with lung maturation in Microhyla fissipes. The results illuminated the molecular processes and their coordination in lung development, providing an insight into the transition of amphibians from aquatic to terrestrial life stages.

Abstract

Most anurans must undergo metamorphosis to adapt to terrestrial life. This process enhances the air-breathing ability of the lungs to cope with the change in oxygen medium from water to air. Revealing the structural construction and molecular switches of lung organogenesis is essential to understanding the realization of the air-breathing function. In this study, histology and transcriptomics were conducted in combination to explore these issues in Microhyla fissipes’ lungs during metamorphosis. During the pro-metamorphic phase, histological structural improvement of the alveolar wall is accompanied by robust substrate metabolism and protein turnover. The lungs, at the metamorphic climax phase, are characterized by an increased number of cilia in the alveolar epithelial cells and collagenous fibers in the connective tissues, corresponding to the transcriptional upregulation of cilia and extracellular matrix-related genes. Post-metamorphic lungs strengthen their contracting function, as suggested by the thickened muscle layer and the upregulated expression of genes involved in muscle contraction. The blood–gas barrier is fully developed in adult lungs, the transcriptional features of which are tissue growth and regulation of differentiation and immunity. Importantly, significant transcriptional switches of pulmonary surfactant protein and hemoglobin facilitate air breathing. Our results illuminated four key steps of lung development for amphibians to transition from water to land.

The alveolar macrophage toponome of female SP-A knockout mice differs from that of males before and after SP-A1 rescue

Using the Toponome Imaging System (TIS), a serial immunostainer, we studied the patterns of expression of multiple markers in alveolar macrophages (AM) from female mice lacking surfactant protein A (SP-A knockouts; KO) after "rescue" with exogenous SP-A1. We also used a 7-marker subset to compare with AM from males. AM were harvested 18 h after intrapharyngeal SP-A1 or vehicle, attached to slides, and subjected to serial immunostaining for 12 markers. Expression of the markers in each pixel of the image was analyzed both in the whole image and in individual selected cells. The marker combination in each pixel is referred to as a combinatorial molecular phenotype (CMP). A subset of antibodies was used to compare AM from male mice to the females. We found: (a) extensive AM heterogeneity in females by CMP analysis and by clustering analysis of CMPs in single cells; (b) AM from female KO mice respond to exogenous SP-A1 by increasing CMP phenotypic diversity and perhaps enhancing their potential innate immune capabilities; and (c) comparison of male and female AM responses to SP-A1 revealed that males respond more vigorously than females and clustering analysis was more effective in distinguishing males from females rather than treated from control.

Human Surfactant Protein SP-A1 and SP-A2 Variants Differentially Affect the Alveolar Microenvironment, Surfactant Structure, Regulation and Function of the Alveolar Macrophage, and Animal and Human Survival Under Various Conditions

The human innate host defense molecules, SP-A1 and SP-A2 variants, differentially affect survival after infection in mice and in lung transplant patients. SP-A interacts with the sentinel innate immune cell in the alveolus, the alveolar macrophage (AM), and modulates its function and regulation. SP-A also plays a role in pulmonary surfactant-related aspects, including surfactant structure and reorganization. For most (if not all) pulmonary diseases there is a dysregulation of host defense and inflammatory processes and/or surfactant dysfunction or deficiency. Because SP-A plays a role in both of these general processes where one or both may become aberrant in pulmonary disease, SP-A stands to be an important molecule in health and disease. In humans (unlike in rodents) SP-A is encoded by two genes (SFTPA1 and SFTPA2) and each has been identified with extensive genetic and epigenetic complexity. In this review, we focus on functional, structural, and regulatory differences between the two SP-A gene-specific products, SP-A1 and SP-A2, and among their corresponding variants. We discuss the differential impact of these variants on the surfactant structure, the alveolar microenvironment, the regulation of epithelial type II miRNome, the regulation and function of the AM, the overall survival of the organism after infection, and others. Although there have been a number of reviews on SP-A, this is the first review that provides such a comprehensive account of the differences between human SP-A1 and SP-A2.

Can Prophylactic High Flow of Humidified and Warmed Filtered Air Improve Survival from Bacterial Pneumonia and SARS-CoV-2 in Elderly Individuals? The Role of Surfactant Protein A

In this opinion article, we discuss a serendipitous observation we made in a study investigating survival in aged mice after bacterial infection. This observation involved a non-invasive ventilation approach that led to variable and higher survival in male and female mice with different genetic backgrounds for the innate immune molecule, surfactant protein A (SP-A). We suggest that employing the best ventilatory modality, whether that be HFNC or another method, may augment the role of other factors such as SP-A genetics and sex in a personalized approach, and may ultimately improve the outcome.

SNP and Haplotype Interaction Models Reveal Association of Surfactant Protein Gene Polymorphisms With Hypersensitivity Pneumonitis of Mexican Population

Background: Hypersensitivity pneumonitis (HP) is an interstitial lung disease caused by inhalation of common environmental organic particles. Surfactant proteins (SPs) play a role in innate immunity and surfactant function. We hypothesized that single nucleotide polymorphisms (SNPs) or haplotypes of the SP genes associate with HP. Methods: Seventy-five HP patients caused by avian antigen and 258 controls, asymptomatic antigen exposed and non-exposed were enrolled. SNP association was performed using logistic regression analysis and SNP-SNP interaction models. Results: Based on odds ratio, regression analyses showed association of (a) rs7316_G, 1A3 (protective) compared to antigen exposed; (b) male sex, smoking, rs721917_T and rs1130866_T (protective) compared to non-exposed controls with HP; (c) compared to antigen exposed, 25 interactions associated with HP in a three-SNP model; (d) compared to non-exposed, (i) rs1136451 associated with increased, whereas rs1136450 and rs1130866 associated with lower HP risk, (ii) 97 interactions associated with HP in a three-SNP model. The majority of SNP-SNP interactions associated with increased HP risk involved SNPs of the hydrophilic SPs, whereas, the majority of interactions associated with lower HP risk involved SNPs of both hydrophilic and hydrophobic SPs; (e) haplotypes of SP genes associated with HP risk. Conclusions: The complexity of SNPs interactions of the SFTP genes observed indicate that the lung inflammatory response to avian antigens is modulated by a complex gene interplay rather than by single SNPs.

Single Nucleotide Polymorphisms Interactions of the Surfactant Protein Genes Associated With Respiratory Distress Syndrome Susceptibility in Preterm Infants

Background: Neonatal respiratory distress syndrome (RDS), due to surfactant deficiency in preterm infants, is the most common cause of respiratory morbidity. The surfactant proteins (SFTP) genetic variants have been well-studied in association with RDS; however, the impact of SNP-SNP (single nucleotide polymorphism) interactions on RDS has not been addressed. Therefore, this study utilizes a newer statistical model to determine the association of SFTP single SNP model and SNP-SNP interactions in a two and a three SNP interaction model with RDS susceptibility. Methods: This study used available genotype and clinical data in the Floros biobank at Penn State University. The patients consisted of 848 preterm infants, born <36 weeks of gestation, with 477 infants with RDS and 458 infants without RDS. Seventeen well-studied SFTPA1, SFTPA2, SFTPB, SFTPC, and SFTPD SNPs were investigated. Wang's statistical model was employed to test and identify significant associations in a case-control study. Results: Only the rs17886395 (C allele) of the SFTPA2 was associated with protection for RDS in a single-SNP model (Odd's Ratio 0.16, 95% CI 0.06-0.43, adjusted p = 0.03). The highest number of interactions (n = 27) in the three SNP interactions were among SFTPA1 and SFTPA2. The three SNP models showed intergenic and intragenic interactions among all SFTP SNPs except SFTPC. Conclusion: The single SNP model and SNP interactions using the two and three SNP interactions models identified SFTP-SNP associations with RDS. However, the large number of significant associations containing SFTPA1 and/or SFTPA2 SNPs point to the importance of SFTPA1 and SFTPA2 in RDS susceptibility.

Differences in the alveolar macrophage toponome in humanized SP-A1 and SP-A2 transgenic mice

Alveolar macrophages (AMs) are differentially regulated by human surfactant protein-A1 (SP-A1) or SP-A2. However, AMs are very heterogeneous and differences are difficult to characterize in intact cells. Using the Toponome Imaging System (TIS), an imaging technique that uses sequential immunostaining to identify patterns of biomarker expression or combinatorial molecular phenotypes (CMPs), we studied individual single cells and identified subgroups of AMs (n = 168) from SP-A–KO mice and mice expressing either SP-A1 or SP-A2. The effects, as shown by CMPs, of SP-A1 and SP-A2 on AMs were significant and differed. SP-A1 AMs were the most diverse and shared the fewest CMPs with KO and SP-A2. Clustering analysis of each group showed 3 clusters where the CMP-based phenotype was distinct in each cluster. Moreover, a clustering analysis of all 168 AMs revealed 10 clusters, many dominated by 1 group. Some CMP overlap among groups was observed with SP-A2 AMs sharing the most CMPs and SP-A1 AMs the fewest. The CMP-based patterns identified here provide a basis for understanding not only AMs’ diversity, but also most importantly, the molecular basis for the diversity of functional differences in mouse models where the impact of genetics of innate immune molecules on AMs has been studied.

Differential Sex-Dependent Regulation of the Alveolar Macrophage miRNome of SP-A2 and co-ex (SP-A1/SP-A2) and Sex Differences Attenuation after 18 h of Ozone Exposure

Background: Human SP-A1 and SP-A2, encoded by SFTPA1 and SFTPA2, and their genetic variants differentially impact alveolar macrophage (AM) functions and regulation, including the miRNome. We investigated whether miRNome differences previously observed between AM from SP-A2 and SP-A1/SP-A2 mice are due to continued qualitative differences or a delayed response of mice carrying a single gene. Methods: Human transgenic (hTG) mice, carrying SP-A2 or both SP-A genes, and SP-A-KO mice were exposed to filtered air (FA) or ozone (O₃)_. AM miRNA levels, target gene expression, and pathways determined 18 h after O₃ exposure. RESULTS: We found (a) differences in miRNome due to sex, SP-A genotype, and exposure; (b) miRNome of both sexes was largely downregulated by O₃, and co-ex had fewer changed (≥2-fold) miRNAs than either group; (c) the number and direction of the expression of genes with significant changes in males and females in co-ex are almost the opposite of those in SP-A2; (d) the same pathways were found in the studied groups; and (e) O₃ exposure attenuated sex differences with a higher number of genotype-dependent and genotype-independent miRNAs common in both sexes after O₃ exposure. Conclusion: Qualitative differences between SP-A2 and co-ex persist 18 h post-O₃, and O₃ attenuates sex differences.

Impact of Ozone, Sex, and Gonadal Hormones on Bronchoalveolar Lavage Characteristics and Survival in SP-A KO Mice Infected with Klebsiella pneumoniae

Surfactant protein A (SP-A) plays an important role in innate immunity. The sex-dependent survival of infected SP-A knockout (KO) mice has been observed. Our goal was to study the impact of ozone (O₃) and sex, as well as gonadal hormones, on the bronchoalveolar lavage (BAL) readouts and survival, respectively, of Klebsiella pneumoniae-infected SP-A KO mice. Male and female SP-A KO mice were exposed to O₃ or filtered air and infected with K. pneumoniae. We studied markers of inflammation and tissue damage at 4, 24, and 48 h, as well as the survival over 14 days, of gonadectomized (Gx) mice implanted with control pellets (CoP) or hormone (5α-dihydrotestosterone (DHT) in female gonadectomized mice (GxF) or 17β-estradiol (E₂) in male gonadectomized mice (GxM)). We observed: (1) an increase in neutrophil and macrophage inflammatory protein-2 levels as time progressed post-infection, and O₃ exposure appeared to increase this response; (2) an increase in lactate dehydrogenase, total protein, oxidized protein, and phospholipids in response to O₃ with no consistent sex differences in studied parameters; and (3) a reduction in survival of the GxM and CoP mice, the GxM and E₂ mice, and the GxF and DHT mice but not for the GxF and CoP mice after O₃. Without SP-A, (a) sex was found to have a minimal impact on BAL cellular composition and tissue damage markers, and (b) the impact of gonadal hormones on survival was found to involve different mechanisms than in the presence of SP-A.

The Importance of Redox Status in the Frame of Lifestyle Approaches and the Genetics of the Lung Innate Immune Molecules, SP-A1 and SP-A2, on Differential Outcomes of COVID-19 Infection

The pandemic of COVID-19 is of great concern to the scientific community. This mainly affects the elderly and people with underlying diseases. People with obesity are more likely to experience unpleasant disease symptoms and increased mortality. The severe oxidative environment that occurs in obesity due to chronic inflammation permits viral activation of further inflammation leading to severe lung disease. Lifestyle affects the levels of inflammation and oxidative stress. It has been shown that a careful diet rich in antioxidants, regular exercise, and fasting regimens, each and/or together, can reduce the levels of inflammation and oxidative stress and strengthen the immune system as they lead to weight loss and activate cellular antioxidant mechanisms and reduce oxidative damage. Thus, a lifestyle change based on the three pillars: antioxidants, exercise, and fasting could act as a proactive preventative measure against the adverse effects of COVID-19 by maintaining redox balance and well-functioning immunity. Moreover, because of the observed diversity in the expression of COVID-19 inflammation, the role of genetics of innate immune molecules, surfactant protein A (SP-A)1 and SP-A2, and their differential impact on the local lung microenvironment and host defense is reviewed as genetics may play a major role in the diverse expression of the disease.

Phelps D, Kala P, Ravi R, Floros Phelps A, M. Umstead T, Zhang X, Floros J. Impact of Surfactant Protein-A Variants on Survival in Aged Mice in Response to Klebsiella pneumoniae Infection and Ozone: Serendipity in Action

Innate immune molecules, SP-A1 (6A², 6A⁴) and SP-A2 (1A⁰, 1A³), differentially affect young mouse survival after infection. Here, we investigated the impact of SP-A variants on the survival of aged mice. hTG mice carried a different SP-A1 or SP-A2 variant and SP-A-KO were either infected with Klebsiella pneumoniae or exposed to filtered air (FA) or ozone (O₃) prior to infection, and their survival monitored over 14 days. In response to infection alone, no gene- or sex-specific (except for 6A²) differences were observed; variant-specific survival was observed (1A⁰ > 6A⁴). In response to O₃, gene-, sex-, and variant-specific survival was observed with SP-A2 variants showing better survival in males than females, and 1A⁰ females > 1A³ females. A serendipitous, and perhaps clinically important observation was made; mice exposed to FA prior to infection exhibited significantly better survival than infected alone mice. 1A⁰ provided an overall better survival in males and/or females indicating a differential role for SP-A genetics. Improved ventilation, as provided by FA, resulted in a survival of significant magnitude in aged mice and perhaps to a lesser extent in young mice. This may have clinical application especially within the context of the current pandemic.

Ozone-derived oxysterols impair lung macrophage phagocytosis via adduction of some phagocytosis receptors

Inhalation of the ambient air pollutant ozone causes lung inflammation and can suppress host defense mechanisms, including impairing macrophage phagocytosis. Ozone reacts with cholesterol in the lung to form oxysterols, like secosterol A and secosterol B (SecoA and SecoB), which can form covalent adducts on cellular proteins. How oxysterol-protein adduction modifies the function of lung macrophages is unknown. Herein, we used a proteomic screen to identify lung macrophage proteins that form adducts with ozone-derived oxysterols. Functional ontology analysis of the adductome indicated that protein binding was a major function of adducted proteins. Further analysis of specific proteins forming adducts with SecoA identified the phagocytic receptors CD206 and CD64. Adduction of these receptors with ozone-derived oxysterols impaired ligand binding and corresponded with reduced macrophage phagocytosis. This work suggests a novel mechanism for the suppression of macrophage phagocytosis following ozone exposure through the generation of oxysterols and the formation of oxysterol-protein adducts on phagocytic receptors.

Sex-Specific Regulation of Gene Expression Networks by Surfactant Protein A (SP-A) Variants in Alveolar Macrophages in Response to Klebsiella pneumoniae

Surfactant protein A (SP-A) in addition to its surfactant-related functions interacts with alveolar macrophages (AM), the guardian cells of innate immunity in the lungs, and regulates many of its functions under basal condition and in response to various pressures, such as infection and oxidative stress. The human SP-A locus consists of two functional genes, SFTPA1 and SFTPA2, and one pseudogene. The functional genes encode human SP-A1 and SP-A2 proteins, respectively, and each has been identified with several genetic variants. SP-A variants differ in their ability to regulate lung function mechanics and survival in response to bacterial infection. Here, we investigated the effect of hSP-A variants on the AM gene expression profile in response to Klebsiella pneumoniae infection. We used four humanized transgenic (hTG) mice that each carried SP-A1 (6A², 6A⁴) or SP-A2 (1A⁰, 1A³), and KO. AM gene expression profiling was performed after 6 h post-infection. We found: (a) significant sex differences in the expression of AM genes; (b) in response to infection, 858 (KO), 196 (6A²), 494 (6A⁴), 276 (1A⁰), and 397 (1A³) genes were identified (P < 0.05) and some of these were differentially expressed with ≥2 fold, specific to either males or females; (c) significant SP-A1 and SP-A2 variant-specific differences in AM gene expression; (d) via Ingenuity Pathway Analysis (IPA), key pathways and molecules were identified that had direct interaction with TP53, TNF, and cell cycle signaling nodes; (e) of the three pathways (TNF, TP-53, and cell cycle signaling nodes) studied here, all variants except SP-A2 (1A³) female, showed significance for at least 2 of these pathways, and KO male showed significance for all three pathways; (f) validation of key molecules exhibited variant-specific significant differences in the expression between sexes and a similarity in gene expression profile was observed between KO and SP-A1. These results reveal for the first time a large number of biologically relevant functional pathways influenced in a sex-specific manner by SP-A variants in response to infection. These data may assist in studying molecular mechanisms of SP-A-mediated AM gene regulation and potentially identify novel therapeutic targets for K. pneumoniae infection.

Association of SNP-SNP Interactions of Surfactant Protein Genes with Pediatric Acute Respiratory Failure

The hallmarks of pediatric acute respiratory failure (ARF) are dysregulated inflammation and surfactant dysfunction. The objective is to study association of surfactant protein (SP) genes’ single nucleotide polymorphisms (SNPs) with ARF and its morbidity: pulmonary dysfunction at discharge (PDAD), employing a single-, two-, and three-SNP interaction model. We enrolled 468 newborn controls and 248 children aged ≤ 24 months with ARF; 86 developed PDAD. Using quantitative genetic principles, we tested the association of SP genes SNPs with ARF and PDAD. We observed a dominant effect of rs4715 of the SFTPC on ARF risk. In a three-SNP model, we found (a) 34 significant interactions among SNPs of SFTPA1, SFTPA2, and SFTPC associated with ARF (p = 0.000000002–0.05); 15 and 19 of those interactions were associated with increased and decreased risk for ARF, respectively; (b) intergenic SNP–SNP interactions of both hydrophobic and hydrophilic SP genes associated with PDAD (p = 0.00002–0.03). The majority of intra- and intergenic interactions associated with ARF involve the SFTPA2 SNPs, whereas most of the intra- and intergenic interactions associated with PDAD are of SFTPA1 SNPs. We also observed a dominant effect of haplotypes GG of SFTPA1 associated with increased and AA of SFTPC associated with decreased ARF risk (p = 0.02). To the best of our knowledge, this is the first study showing an association of complex interactions of SP genes with ARF and PDAD. Our data indicate that SP genes polymorphisms may contribute to ARF pathogenesis and subsequent PDAD and/or may serve as markers for disease susceptibility in healthy children.

Donor surfactant protein A2 polymorphism and lung transplant survival

PURPOSE

Gene polymorphisms of surfactant proteins, key players in lung innate immunity, have been associated with various lung diseases. The aim of this study was to investigate the potential association between variations within the surfactant protein (SP)-A gene of the donor lung allograft and recipient post-transplant outcome.

METHODS

Lung-transplant patients (n=192) were prospectively followed-up with pulmonary function tests, bronchoscopies with bronchoalveolar lavage and biopsies. Donor lungs were assayed for SP-A1 (6Aⁿ) and SP-A2 (1Aⁿ) gene polymorphism using the pyrosequencing method. Unadjusted and adjusted stratified Cox survival models are reported.

RESULTS

SP-A1 and SP-A2 genotype frequency and lung transplant recipient and donor characteristics as well as cause of death are noted. Recipients were grouped per donor SP-A2 variants. Individuals that received lungs from donors with the SP-A2 1A⁰ (n=102) versus 1A¹ variant (n=68) or SP-A2 genotype 1A⁰1A⁰ (n=54) versus 1A⁰A¹ (n=38) had greater survival at 1 year (log-rank p<0.025). No significant association was noted for SP-A1 variants. Stratified adjusted survival models for 1-year survival and diagnosis showed a reduced survival for 1A¹ variant and the 1A⁰1A¹ genotype. Furthermore, when survival was conditional on 1-year survival no significance was observed, indicating that the survival difference was due to the first year's outcome associated with the 1A¹ variant.

CONCLUSION

Donor lung SP-A gene polymorphisms are associated with post-transplant clinical outcome. Lungs from donors with the SP-A2 variant 1A¹ had a reduced survival at 1 year. The observed donor genetic differences, via innate immunity relate to the post-transplant clinical outcome.

Using toponomics to characterize phenotypic diversity in alveolar macrophages from male mice treated with exogenous SP-A1

Background

We used the Toponome Imaging System (TIS) to identify “patterns of marker expression”, referred to here as combinatorial molecular phenotypes (CMPs) in alveolar macrophages (AM) in response to the innate immune molecule, SP-A1.

Methods

We compared 114 AM from male SP-A deficient mice. One group (n = 3) was treated with exogenous human surfactant protein A1 (hSP-A1) and the other with vehicle (n = 3). AM obtained by bronchoalveolar lavage were plated onto slides and analyzed using TIS to study the AM toponome, the spatial network of proteins within intact cells. With TIS, each slide is sequentially immunostained with multiple FITC-conjugated antibodies. Images are analyzed pixel-by-pixel identifying all of the proteins within each pixel, which are then designated as CMPs. CMPs represent organized protein clusters postulated to contribute to specific functions.

Results

1) We compared identical CMPs in KO and SP-A1 cells and found them to differ significantly (p = 0.0007). Similarities between pairs of markers in the two populations also differed significantly (p < 0.0001). 2) Focusing on the 20 most abundant CMPs for each cell, we developed a method to generate CMP “signatures” that characterized various groups of cells. Phenotypes were defined as cells exhibiting similar signatures of CMPs. i) AM were extremely diverse and each group contained cells with multiple phenotypes. ii) Among the 114 AM analyzed, no two cells were identical. iii) However, CMP signatures could distinguish among cell subpopulations within and between groups. iv) Some cell populations were enriched with SP-A1 treatment, some were more common without SP-A1, and some seemed not to be influenced by the presence of SP-A1. v) We also found that AM were more diverse in mice treated with SP-A1 compared to those treated with vehicle.

Conclusions

AM diversity is far more extensive than originally thought. The increased diversity of SP-A1-treated mice points to the possibility that SP-A1 enhances or activates several pathways in the AM to better prepare it for its innate immune functions and other functions shown previously to be affected by SP-A treatment. Future studies may identify key protein(s) responsible for CMP integrity and consequently for a given function, and target it for therapeutic purposes.

Structural and Functional Determinants of Rodent and Human Surfactant Protein A: A Synthesis of Binding and Computational Data

Surfactant protein A (SP-A) provides surfactant stability, first line host defense, and lung homeostasis by binding surfactant phospholipids, pathogens, alveolar macrophages (AMs), and epithelial cells. Non-primates express one SP-A protein whereas humans express two: SP-A1 and SP-A2 with core intra- and inter-species differences in the collagen-like domain. Here, we used macrophages and solid phase binding assays to discern structural correlates of rat (r) and human (h) SP-A function. Binding assays using recombinant rSP-A expressed in insect cells showed that lack of proline hydroxylation, truncations of amino-terminal oligomerization domains, and site-directed serine (S) or alanine (A) mutagenesis of cysteine 6 (C6S), glutamate 195 (E195A), and glutamate 171 (E171A) in the carbohydrate recognition domain (CRD) all impaired SP-A binding. Replacement of arginine 197 with alanine found in hSP-A (R197A), however, restored the binding of hydroxyproline-deficient rSP-A to the SP-A receptor SP-R210 similar to native rat and human SP-A. In silico calculation of Ca⁺⁺ coordination bond length and solvent accessibility surface area revealed that the “humanized” R197A substitution alters topology and solvent accessibility of the Ca⁺⁺ coordination residues of the CRD domain. Binding assays in mouse AMs that were exposed to either endogenous SP-A or hSP-A1 (6A²) and hSP-A2 (1A⁰) isoforms in vivo revealed that mouse SP-A is a functional hybrid of hSP-A1 and hSP-A2 in regulating SP-A receptor occupancy and binding affinity. Binding assays using neonatal and adult human AMs indicates that the interaction of SP-A1 and SP-A2 with AMs is developmentally regulated. Furthermore, our data indicate that the auxiliary ion coordination loop encompassing the conserved E171 residue may comprise a conserved site of interaction with macrophages, and SP-R210 specifically, that merits further investigation to discern conserved and divergent SP-A functions between species. In summary, our findings support the notion that complex structural adaptation of SP-A regulate conserved and species specific AM functions in vertebrates.

Differential Impact of Co-expressed SP-A1/SP-A2 Protein on AM miRNome; Sex Differences

In humans there are two surfactant protein A (SP-A) functional genes SFTPA1 and SFTPA2 encoding innate immune molecules, SP-A1 and SP-A2, respectively, with numerous genetic variants each. SP-A interacts and regulates many of the functions of alveolar macrophages (AM). It is shown that SP-A variants differ in their ability to regulate the AM miRNome in response to oxidative stress (OxS). Because humans have both SP-A gene products, we were interested to determine the combined effect of co-expressed SP-A1/SP-A2 (co-ex) in response to ozone (O₃) induced OxS on AM miRNome. Human transgenic (hTG) mice, carrying both SP-A1/SP-A2 (6A²/1A⁰, co-ex) and SP-A- KO were utilized. The hTG and KO mice were exposed to filtered air (FA) or O₃ and miRNA levels were measured after AM isolation with or without normalization to KO. We found: (i) The AM miRNome of co-ex males and females in response to OxS to be largely downregulated after normalization to KO, but after Bonferroni multiple comparison analysis only in females the AM miRNome remained significantly different compared to control (FA); (ii) The targets of the significantly changed miRNAs were downregulated in females and upregulated in males; (iii) Several of the validated mRNA targets were involved in pro-inflammatory response, anti-apoptosis, cell cycle, cellular growth and proliferation; (iv) The AM of SP-A2 male, shown, previously to have major effect on the male AM miRNome in response to OxS, shared similarities with the co-ex, namely in pathways involved in the pro-inflammatory response and anti-apoptosis but also exhibited differences with the cell-cycle, growth, and proliferation pathway being involved in co-ex and ROS homeostasis in SP-A2 male. We speculate that the presence of both gene products vs. single gene products differentially impact the AM responses in males and females in response to OxS.

Major Effect of Oxidative Stress on the Male, but Not Female, SP-A1 Type II Cell miRNome

Pulmonary surfactant protein A (SP-A) plays an important role in surfactant metabolism and lung innate immunity. In humans there are two proteins, SP-A1 and SP-A2, encoded by SFTPA1 and SFTPA2, respectively, which are produced by the alveolar type II cells (T2C). We sought to investigate the differential influence of SP-A1 and SP-A2 in T2C miRNome under oxidative stress (OxS). SP-A knock out (KO) and hTG male and female mice expressing SP-A1 or SP-A2 as well as gonadectomized (Gx) mice were exposed to O₃-induced oxidative stress (OxS) or filtered air (FA). Expression of miRNAs and mRNAs was measured in the T2C of experimental animals. (a) In SP-A1 males after normalizing to KO males, significant changes were observed in the miRNome in terms of sex-OxS effects, with 24 miRNAs being differentially expressed under OxS. (b) The mRNA targets of the dysregulated miRNAs included Ago2, Ddx20, Plcg2, Irs1, Elf2, Jak2, Map2k4, Bcl2, Ccnd1, and Vhl. We validated the expression levels of these transcripts, and observed that the mRNA levels of all of these targets were unaffected in SP-A1 T2C but six of these were significantly upregulated in the KO (except Bcl2 that was downregulated). (c) Gondadectomy had a major effect on the expression of miRNAs and in three of the mRNA targets (Irs1, Bcl2, and Vhl). Ccnd1 was upregulated in KO regardless of Gx. (d) The targets of the significantly changed miRNAs are involved in several pathways including MAPK signaling pathway, cell cycle, anti-apoptosis, and other. In conclusion, in response to OxS, SP-A1 and male hormones appear to have a major effect in the T2C miRNome.

Differential Effects of Human SP-A1 and SP-A2 on the BAL Proteome and Signaling Pathways in Response to Klebsiella pneumoniae and Ozone Exposure

Surfactant protein A (SP-A) plays critical roles in host defense, regulation of inflammation and surfactant metabolism in the lung. The human SP-A locus consists of two functional genes, SFTPA1 and SFTPA2 encoding surfactant proteins SP-A1 and SP-A2, respectively. Structural and functional differences exist between SP-A1 and SP-A2 in vitro and in vivo. Ozone is a major air pollutant with a negative impact on many biological processes. In this study we used humanized transgenic (hTG) SP-A1 and SP-A2 mice, and SP-A KO mice to study in vivo effects of SP-A1 and SP-A2 on the bronchoalveolar lavage (BAL) proteomic profile and associated signaling pathways in response to ozone or filtered air (FA) exposure and Klebsiella pneumoniae infection. The BAL samples were harvested 24 h after ozone (2 ppm for 3 h) or FA exposure and infection and analyzed by two-dimensional difference gel electrophoresis (2D-DIGE) and MALDI-ToF/ToF. We found: that (1) Ozone exposure, but not infection, is a major factor for increases in total BAL protein content. (2) A total of 36 proteins were identified, accounting for 89.62% of the BAL proteins resolved by the 2D-DIGE system. (3) The number of proteins in which levels were altered more than 25% following infection and FA exposure was: SP-A2 > SP-A1 > KO for male mice, and SP-A2 ≈ SP-A1 > KO for female mice. (4) The number of proteins with more than 25% increase/decrease after ozone exposure and infection was: SP-A2 > SP-A1 ≈ KO, with the majority being increases in male mice and decreases in female mice. (5) Eleven out of the 36 proteins, including annexin A5, glutathione S-transferase A4, SP-A1/SP-A2, and 14-3-3 zeta protein, exhibited significant differences among SP-A genotypes. The acute phase response (APR) that includes the NF-kB signaling pathway plays a critical role, followed by Nrf2-mediated oxidative response, and others. These associated with SP-A genotype, sex, and ozone-induced oxidative stress in response to infection. We concluded that human SP-A2 and SP-A1 exhibit differential genotype-and sex-dependent innate immune responses to microbial pathogens and/or ozone-induced oxidative stress by modulating proteomic patterns and signaling pathways in the lung.

Survival of Surfactant Protein-A1 and SP-A2 Transgenic Mice After Klebsiella pneumoniae Infection, Exhibits Sex-, Gene-, and Variant Specific Differences; Treatment With Surfactant Protein Improves Survival

Surfactant protein A (SP-A) is involved in lung innate host defense and surfactant-related functions. The human SFTPA1 and SFTPA2 genes encode SP-A1 and SP-2 proteins, and each gene has been identified with numerous genetic variants. SP-A1 and SP-A2 differentially enhance bacterial phagocytosis. Sex differences have been observed in pulmonary disease and in survival of wild type and SP-A knockout (KO) mice. The impact of human SP-A variants on survival after infection is unknown. In this study, we determined whether SP-A variants differentially affect survival of male and female mice infected with Klebsiella pneumoniae. Transgenic (TG) mice, where each carries a different human (h) SP-A1 (6A², 6A⁴), SP-A2 (1A⁰, 1A³) variant or both variants SP-A1/SP-A2 (6A²/1A⁰, co-ex), and SP-A- KO, were utilized. The hTG and KO mice were infected intratracheally with K. pneumoniae bacteria, and groups of KO mice were treated with SP-A1 or SP-A2 either prior to and/or at the time of infection and survival for both experimental groups was monitored over 14 days. The binding of purified SP-A1 and SP-A2 proteins to phagocytic and non-phagocytic cells and expression of cell surface proteins in alveolar macrophages (AM) from SP-A1 and SP-A2 mice was examined. We observed gene-, variant-, and sex-specific (except for co-ex) differences with females showing better survival: (a) Gene-specific differences: co-ex = SP-A2 > SP-A1 > KO (both sexes); (b) Variant-specific survival co-ex (6A²/1A⁰) = 1A⁰ > 1A³ = 6A² > 6A⁴ (both sexes); (c) KO mice treated with SPs (SP-A1 or SP-A2) proteins exhibit significantly (p < 0.05) better survival; (d) SP-A1 and SP-A2 differentially bind to phagocytic, but not to non-phagocytic cells, and AM from SP-A1 and SP-A2 hTG mice exhibit differential expression of cell surface proteins. Our results indicate that sex and SP-A genetics differentially affect survival after infection and that exogenous SP-A1/SP-A2 treatment significantly improves survival. We postulate that the differential SP-A1/SP-A2 binding to the phagocytic cells and the differential expression of cell surface proteins that bind SP-A by AM from SP-A1 and SP-A2 mice play a role in this process. These findings provide insight into the importance of sex and innate immunity genetics in survival following infection.

Genetic Association of Pulmonary Surfactant Protein Genes, SFTPA1, SFTPA2, SFTPB, SFTPC, and SFTPD With Cystic Fibrosis

Surfactant proteins (SP) are involved in surfactant function and innate immunity in the human lung. Both lung function and innate immunity are altered in CF, and altered SP levels and genetic association are observed in Cystic Fibrosis (CF). We hypothesized that single nucleotide polymorphisms (SNPs) within the SP genes associate with CF or severity subgroups, either through single SNP or via SNP-SNP interactions between two SNPs of a given gene (intragenic) and/or between two genes (intergenic). We genotyped a total of 17 SP SNPs from 72 case-trio pedigree (SFTPA1 (5), SFTPA2 (4), SFTPB (4), SFTPC (2), and SFTPD (2)), and identified SP SNP associations by applying quantitative genetic principles. The results showed (a) Two SNPs, SFTPB rs7316 (p = 0.0083) and SFTPC rs1124 (p = 0.0154), each associated with CF. (b) Three intragenic SNP-SNP interactions, SFTPB (rs2077079, rs3024798), and SFTPA1 (rs1136451, rs1059057 and rs4253527), associated with CF. (c) A total of 34 intergenic SNP-SNP interactions among the 4 SP genes to be associated with CF. (d) No SNP-SNP interaction was observed between SFTPA1 or SFTPA2 and SFTPD. (e) Equal number of SNP-SNP interactions were observed between SFTPB and SFTPA1/SFTPA2 (n = 7) and SP-B and SFTPD (n = 7). (f) SFTPC exhibited significant SNP-SNP interactions with SFTPA1/SFTPA2 (n = 11), SFTPB (n = 4) and SFTPD (n = 3). (g) A single SFTPB SNP was associated with mild CF after Bonferroni correction, and several intergenic interactions that are associated (p < 0.01) with either mild or moderate/severe CF were observed. These collectively indicate that complex SNP-SNP interactions of the SP genes may contribute to the pulmonary disease in CF patients. We speculate that SPs may serve as modifiers for the varied progression of pulmonary disease in CF and/or its severity.

Differential effects of innate immune variants of surfactant protein-A1 (SFTPA1) and SP-A2 (SFTPA2) in airway function after Klebsiella pneumoniae infection and sex differences

Background

Surfactant Protein-A (SP-A) is a major protein component of surfactant and plays a role in surfactant-related functions and innate immunity. Human SP-A consists of two functional genes, SFTPA1 and SFTPA2, encoding SP-A1 and SP-A2 proteins, respectively and each is identified with numerous genetic variants. These differentially enhance bacterial phagocytosis, with SP-A2 variants being more effective than SP-A1.

Methods

Lung functions of humanized transgenic (hTG) mice that carry different SP-A1 and SP-A2 variants or both variants SP-A1/SP-A2 (6A²/1A⁰, co-ex), as well as SP-A knockout (KO), were studied. The animals were connected to a flexiVent system to obtain forced oscillation technique (FOT) measurements and the data were analyzed using various models. Lung function was assessed after infection (baseline) and following inhaled methacholine concentrations (0–50 mg/mL).

Results

Here, we investigated the role of SP-A variants on airway function after Klebsiella pneumoniae (Kp) infection (baseline) and following inhaled methacholine. We found that: 1) in the absence of methacholine no significant differences were observed between SP-A1 and SP-A2 variants and/or SP-A knockout (KO) except for sex differences in most of the parameters studied. 2) In response to methacholine, i) sex differences were observed that were reverse of those observed in the absence of methacholine; ii) SP-A2 (1A³) gene variant in males exhibited increased total and central airway resistance (Rrs and Rn) versus all other variants; iii) In females, SP-A2 (1A³) and SP-A1 (6A²) variants had similar increases in total and central airway resistance (Rrs and Rn) versus all other variants; iv) Allele-specific differences were observed, a) with SP-A2 (1A³) exhibiting significantly higher lung functions versus SP-A2 (1A⁰) in both sexes, except for Crs, and b) SP-A1 (6A², 6A⁴) had more diverse changes in lung function in both sexes.

Conclusion

We conclude that, in response to infection and methacholine, SP-A variants differentially affect lung function and exhibit sex-specific differences consistent with previously reported findings of functional differences of SP-A variants. Thus, the observed changes in respiratory function mechanics provide insight into the role and importance of genetic variation of innate immune molecules, such as SP-A, on mechanical consequences of lung function after infection and inhaled substances.

SP-A2 contributes to miRNA-mediated sex differences in response to oxidative stress: pro-inflammatory, anti-apoptotic, and anti-oxidant pathways are involved

BACKGROUND

Human innate host defense molecules, surfactant protein A1 (SP-A1), and SP-A2 differentially affect the function and proteome of the alveolar macrophage (AM). We hypothesized that SP-A genes differentially regulate the AM miRNome.

METHODS

Humanized transgenic mice expressing SP-A1 and SP-A2 were subjected to O3-induced oxidative stress (OxS) or filtered air (FA), AMs were isolated, and miRNA levels were measured.

RESULTS

In SP-A2 males, we found significant changes in miRNome in terms of sex and sex-OxS effects, with 11 miRNAs differentially expressed under OxS. Their mRNA targets included BCL2, CAT, FOXO1, IL6, NF-kB, SOD2, and STAT3. We followed the expression of these transcripts as well as key cytokines, and we found that (a) the STAT3 mRNA significantly increased at 4 h post OxS and returned to baseline at 18 h post OxS. (b) The anti-oxidant protein SOD2 level significantly increased, but the CAT level did not change after 4 h post OxS compared to control. (c) The anti-apoptotic BCL2 mRNA increased significantly (18 h post OxS), but the levels of the other transcripts were decreased. The presence of the SP-A2 gene had a protective role in apoptosis of AMs under OxS compared to mice lacking SP-A (knockout, KO). (d) Pro-inflammatory cytokine IL-6 protein levels were significantly increased in SP-A2 mice compared to KO (4 and 18 h post OxS), which signifies the role of SP-A2 in pro-inflammatory protein expression. (e) SOD2 and CAT mRNAs changed significantly in OxS indicating a plausible role of SP-A2 in the homeostasis of reactive oxygen species. (f) Gonadectomy of transgenic mice showed that sex hormones contribute to significant changes of the miRNome expression.

CONCLUSIONS

We conclude that SP-A2 influences the miRNA-mediated sex-specific differences in response to OxS. In males, these differences pertain to inflammatory, anti-apoptotic, and anti-oxidant pathways.

Human Pulmonary Surfactant Protein SP-A1 Provides Maximal Efficiency of Lung Interfacial Films

Pulmonary surfactant is a lipoprotein complex that reduces surface tension to prevent alveolar collapse and contributes to the protection of the respiratory surface from the entry of pathogens. Surfactant protein A (SP-A) is a hydrophilic glycoprotein of the collectin family, and its main function is related to host defense. However, previous studies have shown that SP-A also aids in the formation and biophysical properties of pulmonary surfactant films at the air-water interface. Humans, unlike rodents, have two genes, SFTPA1 and SFTPA2. The encoded proteins, SP-A1 and SP-A2, differ quantitatively or qualitatively in function. It has been shown that both gene products are necessary for tubular myelin formation, an extracellular structural form of lung surfactant. The goal of this study was to investigate potential differences in the biophysical properties of surfactants containing human SP-A1, SP-A2, or both. For this purpose, we have studied for the first time, to our knowledge, the biophysical properties of pulmonary surfactant from individual humanized transgenic mice expressing human SP-A1, SP-A2, or both SP-A1 and SP-A2, in the captive bubble surfactometer. We observed that pulmonary surfactant containing SP-A1 reaches lower surface tension after postexpansion interfacial adsorption than surfactants containing no SP-A or only SP-A2. Under interfacial compression-expansion cycling conditions, surfactant films containing SP-A1 also performed better, particularly with respect to the reorganization of the films that takes place during compression. On the other hand, addition of recombinant SP-A1 to a surfactant preparation reconstituted from the hydrophobic fraction of a porcine surfactant made it more resistant to inhibition by serum than the addition of equivalent amounts of SP-A2. We conclude that the presence of SP-A1 allows pulmonary surfactant to adopt a particularly favorable structure with optimal biophysical properties.

Pulmonary surfactant metabolism in the alveolar airspace: Biogenesis, extracellular conversions, recycling

Pulmonary surfactant is a lipid-protein complex that lines and stabilizes the respiratory interface in the alveoli, allowing for gas exchange during the breathing cycle. At the same time, surfactant constitutes the first line of lung defense against pathogens. This review presents an updated view on the processes involved in biogenesis and intracellular processing of newly synthesized and recycled surfactant components, as well as on the extracellular surfactant transformations before and after the formation of the surface active film at the air-water interface. Special attention is paid to the crucial regulation of surfactant homeostasis, because its disruption is associated with several lung pathologies.

Single-cell analysis reveals differential regulation of the alveolar macrophage actin cytoskeleton by surfactant proteins A1 and A2: implications of sex and aging

Background

Surfactant protein A (SP-A) contributes to lung immunity by regulating inflammation and responses to microorganisms invading the lung. The huge genetic variability of SP-A in humans implies that this protein is highly important in tightly regulating the lung immune response. Proteomic studies have demonstrated that there are differential responses of the macrophages to SP-A1 and SP-A2 and that there are sex differences implicated in these responses.

Methods

Purified SP-A variants were used for administration to alveolar macrophages from SP-A knockout (KO) mice for in vitro studies, and alveolar macrophages from humanized SP-A transgenic mice were isolated for ex vivo studies. The actin cytoskeleton was examined by fluorescence and confocal microscopy, and the macrophages were categorized according to the distribution of polymerized actin.

Results

In accordance with previous data, we report that there are sex differences in the response of alveolar macrophages to SP-A1 and SP-A2. The cell size and F-actin content of the alveolar macrophages are sex- and age-dependent. Importantly, there are different subpopulations of cells with differential distribution of polymerized actin. In vitro, SP-A2 destabilizes actin in female, but not male, mice, and the same tendency is observed by SP-A1 in cells from male mice. Similarly, there are differences in the distribution of AM subpopulations isolated from SP-A transgenic mice depending on sex and age.

Conclusions

There are marked sex- and age-related differences in the alveolar macrophage phenotype as illustrated by F-actin staining between SP-A1 and SP-A2. Importantly, the phenotypic switch caused by the different SP-A variants is subtle, and pertains to the frequency of the observed subpopulations, demonstrating the need for single-cell analysis approaches. The differential responses of alveolar macrophages to SP-A1 and SP-A2 highlight the importance of genotype in immune regulation and the susceptibility to lung disease and the need for development of individualized treatment options.

Evolution, Development, and Function of the Pulmonary Surfactant System in Normal and Perturbed Environments

Surfactant lipids and proteins form a surface active film at the air-liquid interface of internal gas exchange organs, including swim bladders and lungs. The system is uniquely positioned to meet both the physical challenges associated with a dynamically changing internal air-liquid interface, and the environmental challenges associated with the foreign pathogens and particles to which the internal surface is exposed. Lungs range from simple, transparent, bag-like units to complex, multilobed, compartmentalized structures. Despite this anatomical variability, the surfactant system is remarkably conserved. Here, we discuss the evolutionary origin of the surfactant system, which likely predates lungs. We describe the evolution of surfactant structure and function in invertebrates and vertebrates. We focus on changes in lipid and protein composition and surfactant function from its antiadhesive and innate immune to its alveolar stability and structural integrity functions. We discuss the biochemical, hormonal, autonomic, and mechanical factors that regulate normal surfactant secretion in mature animals. We present an analysis of the ontogeny of surfactant development among the vertebrates and the contribution of different regulatory mechanisms that control this development. We also discuss environmental (oxygen), hormonal and biochemical (glucocorticoids and glucose) and pollutant (maternal smoking, alcohol, and common "recreational" drugs) effects that impact surfactant development. On the adult surfactant system, we focus on environmental variables including temperature, pressure, and hypoxia that have shaped its evolution and we discuss the resultant biochemical, biophysical, and cellular adaptations. Finally, we discuss the effect of major modern gaseous and particulate pollutants on the lung and surfactant system.

Innate immunity of surfactant proteins A and D in urinary tract infection with uropathogenic Escherichia coli

To investigate the effects of surfactant proteins A and D (SP-A and SP-D, respectively) in urinary tract infection (UTI), SP-A and SP-D double knockout (SP-A/D KO) and wild type (WT) C57BL/6 female mice were infected with uropathogenic Escherichia coli by intravesical inoculation. Compared with WT mice SP-A/D KO mice showed increased susceptibility to UTI, as evidenced by higher bacterial CFU, more infiltrating neutrophils and severe pathological changes. Keratinocyte-derived chemokine increased in the kidney of WT mice but not in SP-A/D KO mice 24 h post-infection. Compared with control, the level of IL-17 was elevated in the kidney of infected WT and SP-A/D KO mice and the level of IL-17 was higher in the infected SP-A/D KO mice than in infected WT mice 24 and 48 h post-infection. The basal level of p38 MAPK phosphorylation in SP-A/D KO mice was higher than in WT mice. The phosphorylated p38 level was elevated in the kidney of WT mice post infection but not in SP-A/D KO mice. Furthermore, in vitro growth of uropathogenic E. coli was inhibited by SP-A and SP-D. We conclude that SP-A and SP-D function as mediators of innate immunity by inhibiting bacterial growth and modulating renal inflammation in part by regulating p38 MAPK-related pathway in murine UTI.

Role of surfactant protein A in non-infectious lung diseases

Surfactant protein A (SP-A) is a large multimeric protein found in the airways and alveoli of the lungs. SP-A is a member of the collectin family of proteins, characterized by NH2-terminal collagen-like regions and COOH-terminal lectin domains. Although other surfactant proteins such as SP-B function to reduce surface tension in the lungs, SP-A as well as SP-D regulates the pulmonary immune response. To date, a number of studies have shown the immunoregulatory function of SP-A, mainly in the field of infectious diseases. By binding to a wide variety of pathogens, SP-A opsonizes and enhances pathogen uptake by phagocytes. In addition to the effect on pathogens, recent studies have shown that SP-A also modulates lung immune system in the area of non-infectious lung diseases. In this review, the potential role of SP-A in the multiple aspects of pulmonary host defense will be discussed, focusing mainly on non-infectious lung diseases such as acute and chronic pulmonary fibrosis and lung cancer. J. Med. Invest. 61: 1-6, February, 2014.

Regulation of translation by upstream translation initiation codons of surfactant protein A1 splice variants

Surfactant protein A (SP-A), a molecule with roles in lung innate immunity and surfactant-related functions, is encoded by two genes in humans: SFTPA1 (SP-A1) and SFTPA2 (SP-A2). The mRNAs from these genes differ in their 5'-untranslated regions (5'-UTR) due to differential splicing. The 5'-UTR variant ACD' is exclusively found in transcripts of SP-A1, but not in those of SP-A2. Its unique exon C contains two upstream AUG codons (uAUGs) that may affect SP-A1 translation efficiency. The first uAUG (u1) is in frame with the primary start codon (p), but the second one (u2) is not. The purpose of this study was to assess the impact of uAUGs on SP-A1 expression. We employed RT-qPCR to determine the presence of exon C-containing SP-A1 transcripts in human RNA samples. We also used in vitro techniques including mutagenesis, reporter assays, and toeprinting analysis, as well as in silico analyses to determine the role of uAUGs. Exon C-containing mRNA is present in most human lung tissue samples and its expression can, under certain conditions, be regulated by factors such as dexamethasone or endotoxin. Mutating uAUGs resulted in increased luciferase activity. The mature protein size was not affected by the uAUGs, as shown by a combination of toeprint and in silico analysis for Kozak sequence, secondary structure, and signal peptide and in vitro translation in the presence of microsomes. In conclusion, alternative splicing may introduce uAUGs in SP-A1 transcripts, which in turn negatively affect SP-A1 translation, possibly affecting SP-A1/SP-A2 ratio, with potential for clinical implication.

Knockdown of Drosha in human alveolar type II cells alters expression of SP-A in culture: a pilot study

Human surfactant protein A (SP-A) plays an important role in surfactant metabolism and lung innate immunity. SP-A is synthesized and secreted by alveolar type II (ATII) cells, one of the two cell types of the distal lung epithelium (ATII and ATI). We have shown that miRNA interactions with sequence polymorphisms on the SP-A mRNA 3'UTRs mediate differential expression of SP-A1 and SP-A2 gene variants in vitro. In the present study, we describe a physiologically relevant model to study miRNA regulation of SP-A in human ATII. For these studies, we purified and cultured human ATII on an air-liquid interface matrix (A/L) or plastic wells without matrix (P). Gene expression analyses confirmed that cells cultured in A/L maintained the ATII phenotype for over 5 days, whereas P-cultured cells differentiated to ATI. When we transfected ATII with siRNAs to inhibit the expression of Drosha, a critical effector of miRNA maturation, the levels of SP-A mRNA and protein increased in a time dependent manner. We next characterized cultured ATII and ATI by studying expression of 1,066 human miRNAs using miRNA PCR arrays. We detected expression of >300 miRNAs with 24 miRNAs differentially expressed in ATII versus ATI, 12 of which predicted to bind SP-A 3'UTRs, indicating that these may be implicated in SP-A downregulation in ATI. Thus, miRNAs not only affect SP-A expression, but also may contribute to the maintenance of the ATII cell phenotype and/or the trans-differentiation of ATII to ATI cells, and may represent new molecular markers that distinguish ATII and ATI.

Surfactant protein A genetic variants associate with severe respiratory insufficiency in pandemic influenza A virus infection

Introduction

Inherited variability in host immune responses influences susceptibility and outcome of Influenza A virus (IAV) infection, but these factors remain largely unknown. Components of the innate immune response may be crucial in the first days of the infection. The collectins surfactant protein (SP)-A1, -A2, and -D and mannose-binding lectin (MBL) neutralize IAV infectivity, although only SP-A2 can establish an efficient neutralization of poorly glycosylated pandemic IAV strains.

Methods

We studied the role of polymorphic variants at the genes of MBL (MBL2), SP-A1 (SFTPA1), SP-A2 (SFTPA2), and SP-D (SFTPD) in 93 patients with H1N1 pandemic 2009 (H1N1pdm) infection.

Results

Multivariate analysis showed that two frequent SFTPA2 missense alleles (rs1965708-C and rs1059046-A) and the SFTPA2 haplotype 1A⁰ were associated with a need for mechanical ventilation, acute respiratory failure, and acute respiratory distress syndrome. The SFTPA2 haplotype 1A¹ was a protective variant. Kaplan-Meier analysis and Cox regression also showed that diplotypes not containing the 1A¹ haplotype were associated with a significantly shorter time to ICU admission in hospitalized patients. In addition, rs1965708-C (P = 0.0007), rs1059046-A (P = 0.0007), and haplotype 1A⁰ (P = 0.0004) were associated, in a dose-dependent fashion, with lower PaO₂/FiO₂ ratio, whereas haplotype 1A¹ was associated with a higher PaO₂/FiO₂ ratio (P = 0.001).

Conclusions

Our data suggest an effect of genetic variants of SFTPA2 on the severity of H1N1pdm infection and could pave the way for a potential treatment with haplotype-specific (1A¹) SP-A2 for future IAV pandemics.

Sex differences in the acute in vivo effects of different human SP-A variants on the mouse alveolar macrophage proteome

Surfactant protein A (SP-A) is involved in lung innate immunity. Humans have two SP-A genes, SFTPA1 and SFTPA2, each with several variants. We examined the in vivo effects of treatment with specific SP-A variants on the alveolar macrophage (AM) proteome from SP-A knockout (KO) mice. KO mice received either SP-A1, SP-A2, or both. AM were collected and their proteomes examined with 2D-DIGE. We identified 90 proteins and categorized them as related to actin/cytoskeleton, oxidative stress, protease balance/chaperones, regulation of inflammation, and regulatory/developmental processes. SP-A1 and SP-A2 had different effects on the AM proteome and these effects differed between sexes. In males more changes occurred in the oxidative stress, protease/chaperones, and inflammation groups with SP-A2 treatment than with SP-A1. In females most SP-A1-induced changes were in the actin/cytoskeletal and oxidative stress groups. We conclude that after acute SP-A1 and SP-A2 treatment, sex-specific differences were observed in the AM proteomes from KO mice, and that these sex differences differ in response to SP-A1 and SP-A2. Females are more responsive to SP-A1, whereas the gene-specific differences in males were minimal. These observations not only demonstrate the therapeutic potential of exogenous SP-A, but also illustrate sex- and gene-specific differences in the response to it.

BIOLOGICAL SIGNIFICANCE

This study shows that changes occur in the alveolar macrophage proteome in response to a single in vivo treatment with exogenous SP-A1 and/or SP-A2. We demonstrate that SP-A1 and SP-A2 have different effects on the AM proteome and that sex differences exist in the response to each SP-A1 and SP-A2 gene product. This study illustrates the potential of exogenous SP-A1 and SP-A2 treatment for the manipulation of macrophage function and indicates that the specific SP-A variant used for treatment may vary with sex and with the cellular functions being modified. The observed changes may contribute to sex differences in the incidence of some lung diseases.

An 11-nt sequence polymorphism at the 3'UTR of human SFTPA1 and SFTPA2 gene variants differentially affect gene expression levels and miRNA regulation in cell culture

Surfactant protein A (SP-A) plays a vital role in maintaining normal lung function and in host defense. Two genes encode SP-A in humans (SFTPA1, SFTPA2), and several gene variants have been identified for these. We have previously shown that sequence elements of SFTPA1 and SFTPA2 3' untranslated regions (UTRs) differentially affect translation efficiency in vitro. Polymorphisms at the 3'UTRs of mRNA variants may account for differential binding of miRNAs, a class of small noncoding RNAs that regulate gene expression. In this work, we generated 3'UTR reporter constructs of the SFTPA1 and SFTPA2 variants most frequently found in the population, as well as mutants of a previously described 11-nt indel element (refSNP rs368700152). Reporter constructs were transfected in NCI-H441 cells in the presence or absence of miRNA mimics, and reporter gene expression was analyzed. We found that human miRNA mir-767 negatively affected expression of constructs containing SFTPA1 and SFTPA2 variants, whereas mir-4507 affected only constructs with 3'UTRs of SFTPA1 variants 6A, 6A(3), and 6A(4) (not containing the 11-nt element). Three miRNAs (mir-183, mir-449b, and mir-612) inhibited expression of recombinants of SFTPA2 variants and the SFTPA1 variant 6A(2), all containing the 11-nt element. Similar results were obtained for SP-A expression when these miRNAs were transfected in Chinese hamster ovary cells expressing SFTPA1 or SFTPA2 variants or in NCI-H441 cells (genotype 1A(5)/1A(5)-6A(4)/6A(4)). Moreover, transfection with a specific antagomir (antagomir-183) reversed the effects of mir-183 on SP-A mRNA levels. Our results indicate that sequence variability at the 3'UTR of SP-A variants differentially affects miRNA regulation of gene expression.

Effect of ozone exposure and infection on bronchoalveolar lavage: sex differences in response patterns

Female mice exhibit a better survival rate than males after infection, but if infection follows an ozone-induced oxidative stress, male survival exceeds that of females. Our goal was to study bronchoalveolar lavage factors that contribute to these sex differences in outcome. We studied parameters at 4, 24, and 48 h after ozone exposure and infection, including markers of inflammation, oxidative stress, and tissue damage, and surfactant phospholipids and surfactant protein A (SP-A). A multianalyte immunoassay at the 4h time point measured 59 different cytokines, chemokines, and other proteins. We found that: (1) Although some parameters studied revealed sex differences, no sex differences were observed in LDH, total protein, MIP-2, and SP-A. Males showed more intragroup significant differences in SP-A between filtered air- and ozone-exposed mice compared to females. (2) Oxidized dimeric SP-A was higher in FA-exposed female mice. (3) Surfactant phospholipids were typically higher in males. (4) The multianalyte data revealed differences in the exuberance of responses under different conditions - males in response to infection and females in response to oxidative stress. These more exuberant, and presumably less well-controlled responses associate with the poorer survival. We postulate that the collective effects of these sex differences in response patterns of lung immune cells may contribute to the clinical outcomes previously observed.

17β-Estradiol alters rat type-II alveolar cell recovery from high levels of ozone

Respiratory health is negatively impacted by exposure to ozone or to estrogens. Increasingly, individuals have simultaneous environmental exposure to both compounds. Characterizing the cellular responses stimulated by the combination of ozone and estrogens, therefore, is crucial to our complete understanding of the compounds' environmental health impacts. Our work introduces an alveolar cell culture model with defined media that provides evidence of ozone damage and determines sex hormones alter the cells' susceptibility to oxidative damage. Specifically, we investigated the individual and combined effects of environmentally relevant levels of ozone and 17β-estradiol on non-cancerous rat, type-II alveolar cells by examining biomarkers of cellular health and redox balance. The data reveal a complex role for 17β-estradiol in cellular recovery from 1 hr exposure to high ozone levels. At 0.5 hr post-ozone necrosis and inflammation markers show 17β-estradiol augments the detrimental effects of 350 ppb ozone, but after 24 hr of recovery, steroid treatment alters glutathione redox ratio and allows cellular proliferation.

Differences in the alveolar macrophage proteome in transgenic mice expressing human SP-A1 and SP-A2

Surfactant protein A (SP-A) plays a number of roles in lung host defense and innate immunity. There are two human genes, SFTPA1 and SFTPA2, and evidence indicates that the function of SP-A1 and SP-A2 proteins differ in several respects. To investigate the impact of SP-A1 and SP-A2 on the alveolar macrophage (AM) phenotype, we generated humanized transgenic (hTG) mice on the SP-A knockout (KO) background, each expressing human SP-A1 or SP-A2. Using two-dimensional difference gel electrophoresis (2D-DIGE) we studied the AM cellular proteome. We compared mouse lines expressing high levels of SPA1, high levels of SP-A2, low levels of SP-A1, and low levels of SP-A2, with wild type (WT) and SP-A KO mice. AM from mice expressing high levels of SP-A2 were the most similar to WT mice, particularly for proteins related to actin and the cytoskeleton, as well as proteins regulated by Nrf2. The expression patterns from mouse lines expressing higher levels of the transgenes were almost the inverse of one another - the most highly expressed proteins in SP-A2 exhibited the lowest levels in the SP-A1 mice and vice versa. The mouse lines where each expressed low levels of SP-A1 or SP-A2 transgene had very similar protein expression patterns suggesting that responses to low levels of SP-A are independent of SP-A genotype, whereas the responses to higher amounts of SP-A are genotype-dependent. Together these observations indicate that in vivo exposure to SP-A1 or SP-A2 differentially affects the proteomic expression of AMs, with SP-A2 being more similar to WT.

Allelic mRNA expression imbalance in C-type lectins reveals a frequent regulatory SNP in the human surfactant protein A (SP-A) gene

Genetic variation in C-type lectins influences infectious disease susceptibility but remains poorly understood. We employed allelic mRNA expression imbalance (AEI) technology for SP-A1, SP-A2, SP-D, DC-SIGN, MRC1, and Dectin-1, expressed in human macrophages and/or lung tissues. Frequent AEI, an indicator of regulatory polymorphisms, was observed in SP-A2, SP-D, and DC-SIGN. AEI was measured for SP-A2 in 38 lung tissues using four marker SNPs and was confirmed by next generation sequencing of one lung RNA sample. Genomic DNA at the SP-A2 DNA locus was sequenced by Ion Torrent technology in 16 samples. Correlation analysis of genotypes with AEI identified a haplotype block, and, specifically, the intronic SNP rs1650232 (30% MAF); the only variant consistently associated with an approximately two-fold change in mRNA allelic expression. Previously shown to alter a NAGNAG splice acceptor site with likely effects on SP-A2 expression, rs1650232 generates an alternative splice variant with three additional bases at the start of exon 3. Validated as a regulatory variant, rs1650232 is in partial LD with known SP-A2 marker SNPs previously associated with risk for respiratory diseases including tuberculosis. Applying functional DNA variants in clinical association studies, rather than marker SNPs, will advance our understanding of genetic susceptibility to infectious diseases.

Genes of innate immunity and the biological response to inhaled ozone

Ambient ozone has a significant impact on human health. We have made considerable progress in understanding the fundamental mechanisms that regulate the biological response to ozone. It is increasingly clear that genes of innate immunity play a central role in both infectious and noninfectious lung disease. The biological response to ambient ozone provides a clinically relevant environmental exposure that allows us to better understand the role of innate immunity in noninfectious airways disease. In this brief review, we focus on (1) specific cell types in the lung modified by ozone, (2) ozone and oxidative stress, (3) the relationship between genes of innate immunity and ozone, (4) the role of extracellular matrix in reactive airways disease, and (5) the effect of ozone on the adaptive immune system. We summarize recent advances in understanding the mechanisms that ozone contributes to environmental airways disease.

Genetic complexity of the human surfactant-associated proteins SP-A1 and SP-A2

Pulmonary surfactant protein A (SP-A) plays a key role in innate lung host defense, in surfactant-related functions, and in parturition. In the course of evolution, the genetic complexity of SP-A has increased, particularly in the regulatory regions (i.e. promoter, untranslated regions). Although most species have a single SP-A gene, two genes encode SP-A in humans and primates (SFTPA1 and SFTPA2). This may account for the multiple functions attributed to human SP-A, as well as the regulatory complexity of its expression by a relatively diverse set of protein and non-protein cellular factors. The interplay between enhancer cis-acting DNA sequences and trans-acting proteins that recognize these DNA elements is essential for gene regulation, primarily at the transcription initiation level. Furthermore, regulation at the mRNA level is essential to ensure proper physiological levels of SP-A under different conditions. To date, numerous studies have shown significant complexity of the regulation of SP-A expression at different levels, including transcription, splicing, mRNA decay, and translation. A number of trans-acting factors have also been described to play a role in the control of SP-A expression. The aim of this report is to describe the genetic complexity of the SFTPA1 and SFTPA2 genes, as well as to review regulatory mechanisms that control SP-A expression in humans and other animal species.

Air pollution and epigenetics: effects on SP-A and innate host defence in the lung

An appropriate immune and inflammatory response is key to defend against harmful agents present in the environment, such as pathogens, allergens and inhaled pollutants, including ozone and particulate matter. Air pollution is a serious public health concern worldwide, and cumulative evidence has revealed that air pollutants contribute to epigenetic variation in several genes, and this in turn can contribute to disease susceptibility. Several groups of experts have recently reviewed findings on epigenetics and air pollution [1-6]. Surfactant proteins play a central role in pulmonary host defence by mediating pathogen clearance, modulating allergic responses and facilitating the resolution of lung inflammation. Recent evidence indicates that surfactant proteins are subject to epigenetic regulation under hypoxia and other conditions. Oxidative stress caused by ozone, and exposure to particulate matter have been shown to affect the expression of surfactant protein A (SP-A), an important lung host defence molecule, as well as alter its functions. In this review, we discuss recent findings in the fields of epigenetics and air pollution effects on innate immunity, with the focus on SP-A, and the human SP-A variants in particular. Their function may be differentially affected by pollutants and specifically by ozone-induced oxidative stress, and this in turn may differentially affect susceptibility to lung disease.

Impact of sex and ozone exposure on the course of pneumonia in wild type and SP-A (-/-) mice

Female mice exhibited higher survival rate than males after pneumonia, with a reversal of this pattern following ozone exposure. Surfactant protein A (SP-A) plays an important role in innate immunity and SP-A (-/-) mice were more susceptible to pneumonia than wild type mice. Here, we investigated underlying mechanisms of the differential susceptibility of mice to pneumonia. Wild type and SP-A (-/-) C57BL/6J male and female mice were exposed to ozone or filtered air (FA) and then infected intratracheally with Klebsiella pneumoniae. Blood, spleen, and lung were analyzed for bacterial counts, lung and spleen weights, and sex hormone and cortisol levels were measured in plasma within two days post-infection. We found: 1) in the absence of ozone-induced oxidative stress, males had higher level of bacterial dissemination compared to females; ozone exposure decreased pulmonary clearance in both sexes and ozone-exposed females were more affected than males; 2) ozone exposure increased lung weight, but decreased spleen weight in both sexes, and in both cases ozone-exposed females were affected the most; 3) plasma cortisol levels in infected mice changed: ozone-exposed>FA-exposed, females>males, and infected>non-infected; 4) no major sex hormone differences were observed in the studied conditions; 5) differences between wild type and SP-A (-/-) mice were observed in some of the studied conditions. We concluded that reduced pulmonary clearance, compromised spleen response to infection, and increased cortisol levels in ozone-exposed females, and the higher level of lung bacterial dissemination in FA-exposed males, contribute to the previously observed survival outcomes.