Pulmonary surfactant proteins A and D directly suppress CD3+/CD4+ cell function: evidence for two shared mechanisms

Changes in surfactant protein A and D in ovine ovaries related to follicle development

Surfactant protein A (SP-A) and Surfactant protein D (SP-D) glycoproteins play a crucial role in maintaining lung homeostasis and lung host defense. Interestingly, these proteins are also expressed in extra-pulmonary tissues, including the female genital tract. The ovarian tissue, where SP-A and SP-D expression increases with follicular development, may serve as the primary site of defense for this tissue. However, their functions in these tissues are not well understood and are currently an active area of research. Therefore, the objective of this study is to investigate the expression of SP-A and SP-D in the ovine ovary throughout the ovarian cycle using immunohistochemistry by semiquantitative intensity classification and Western blotting techniques. These findings revealed the presence of SP-A and SP-D in various compartments of the ovary, such as the follicular epithelium, granulosa cells, cumulus cells, theca cells, oocyte I, follicular fluid, and luteal cells of Graafian follicles, excluding the corpus albicans. SP-A and SP-D likely act as a first line of defense against potential pathogens that infiltrate the ovaries. Further investigation of the differential expression of SP-A and SP-D proteins in ovarian follicles will provide a basis for understanding their interactions with key proteins involved in oogenesis.

Immunoregulatory function of SP-A

Surfactant protein A (SP-A), a natural immune molecule, plays an important role in lung health. SP-A recognizes and binds microbial surface glycogroups through the C-type carbohydrate recognition domain, and then binds corresponding cell surface receptors (such as C1qRp, CRT-CD91 complex, CD14, SP-R210, Toll-like receptor, SIRP-α, CR3, etc.) through collagen-like region, and subsequently mediates biological effects. SP-A regulates lung innate immunity by promoting surfactant absorption by alveolar type II epithelial cells and phagocytosis of pathogenic microorganisms by alveolar macrophages. SP-A also regulates lung adaptive immunity by inhibiting DC maturation, and T cell proliferation and differentiation. This article reviews latest relationships between SP-A and adaptive and intrinsic immunity.

Bioaerosol-induced in vitro activation of toll-like receptors and inflammatory biomarker expression in waste workers

PURPOSE

Occupational exposure to bioaerosols during waste handling remains a health concern for exposed workers. However, exposure-related health effects and underlying immunological mechanisms are still poorly described.

METHODS

The present study assessed the inflammatory potential of work-air samples (n = 56) in vitro and investigated biomarker expression in exposed workers (n = 69) compared to unexposed controls (n = 25). These quantitative results were compared to self-reported health conditions.

RESULTS

Personal air samples provoked an activation of TLR2 and TLR4 HEK reporter cells in one-third of all samples, indicating that the work environment contained ligands capable of inducing an immune response in vitro. Monocyte levels, as well as plasma biomarker levels, such as IL-1Ra, IL-18 and TNFα were significantly higher in exposed workers, compared to the control group when confounding factors such as BMI, sex, age and smoking habits were accounted for. Furthermore, a significant exposure-related increase in midweek IL-8 levels was measured among exposed workers. Tendencies of increased prevalence of health effects of the respiratory tract were identified in exposed workers.

CONCLUSION

Inhalable dust provoked TLR activation in vitro, indicating that an exposure-related immune response may be expected in susceptible workers. However, despite significant differences in inflammatory plasma biomarker levels between exposed and unexposed workers, prevalence of self-reported health effects did not differ between the groups. This may be due to the healthy worker effect, or other factors such as adequate use of personal protective respiratory devices or adaptation to the work environment with reduced activation of the immune system.

Dysregulated serum and seminal plasma levels of surfactant protein D and MCP-1 in men with genital tract infection/inflammation

PROBLEM

Surfactant protein D (SP-D), a multimeric collectin expressed by testicular mucosal epithelia and is positively regulated by testosterone. It exerts antimicrobial effects, modulates inflammation and rescued spermatogenesis in a murine model. Various cytokines and chemokines, including MCP-1, play a key role in regulating the inflammation in rat and human testis. The study aimed to investigate the role of SP-D and involvement of chemokines and cytokines in the male infertility associated with urogenital infections or inflammation.

METHOD OF STUDY

The cross-sectional study evaluated levels of SP-D, testosterone, estradiol and the cytokines/chemokines including MCP-1 in the serum and semen samples of fertile and infertile Indian men with and without urogenital infections/inflammation (n = 76).

RESULTS

Both fertile and infertile males with urogenital infection/inflammation had significantly lower levels of SP-D and higher levels of the chemokine, Monocyte chemoattractant protein 1 (MCP-1) in the serum and seminal plasma. Seminal plasma of these males exhibited significantly higher proportion of proteolytically degraded forms of SP-D. The serum SP-D levels positively correlated with testosterone/estradiol (TE) ratio. There was no significant correlation between the SP-D levels in seminal plasma and sperm count/motility. With a significant area under the Receiver Operating Characteristic curves, the serum and seminal plasma SP-D levels exhibited significant potential to predict infertility with high sensitivity and specificity in men with genital infections/inflammation.

CONCLUSIONS

The circulating and seminal plasma SP-D levels were decreased in men with urogenital infection and inflammation. This could be due to their engagement at the site of infection, dysregulated expression owing to the altered hormonal profile and increased proteolytic degradation.

Surfactant protein-A inhibits thymic stromal lymphopoietin-mediated T follicular helper cell differentiation and IgE production in asthma

Lung surfactant protein A (SP-A) is critical for immunomodulation. Thymic stromal lymphopoietin (TSLP)-activated dendritic cells (DCs) drive T follicular helper (Tfh) cells differentiation in allergic asthma. We employed wild-type (WT) and SP-A^-/- mice injected with TSLP and ovalbumin (OVA)-activated DCs and challenged with OVA. Compared with WT mice, we showed that allergic inflammation was dramatically increased in SP-A^-/- mice. In parallel, both IL-4-producing CD45RA^-CXCR5⁺PD-1⁺CD4⁺ cells (Tfh2) and IgE were markedly increased in SP-A^-/- mice. Further study showed that SP-A prohibited TSLP activated-DCs from expressing OX40L. When we blocked OX40L-OX40 and IL-4R signaling, the differentiation of Tfh2 and IgE responses in SP-A^-/- mice was significantly inhibited. In severe asthma patients, SP-A is dysfunctional in modulating the TSLP-DCs-mediated differentiation of Tfh cells. This study suggests that SP-A acts as a modulator of Tfh differentiation and IgE generation in asthma.

SP-A and SP-D: Dual Functioning Immune Molecules With Antiviral and Immunomodulatory Properties

Surfactant proteins A (SP-A) and D (SP-D) are soluble innate immune molecules which maintain lung homeostasis through their dual roles as anti-infectious and immunomodulatory agents. SP-A and SP-D bind numerous viruses including influenza A virus, respiratory syncytial virus (RSV) and human immunodeficiency virus (HIV), enhancing their clearance from mucosal points of entry and modulating the inflammatory response. They also have diverse roles in mediating innate and adaptive cell functions and in clearing apoptotic cells, allergens and other noxious particles. Here, we review how the properties of these first line defense molecules modulate inflammatory responses, as well as host-mediated immunopathology in response to viral infections. Since SP-A and SP-D are known to offer protection from viral and other infections, if their levels are decreased in some disease states as they are in severe asthma and chronic obstructive pulmonary disease (COPD), this may confer an increased risk of viral infection and exacerbations of disease. Recombinant molecules of SP-A and SP-D could be useful in both blocking respiratory viral infection while also modulating the immune system to prevent excessive inflammatory responses seen in, for example, RSV or coronavirus disease 2019 (COVID-19). Recombinant SP-A and SP-D could have therapeutic potential in neutralizing both current and future strains of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus as well as modulating the inflammation-mediated pathology associated with COVID-19. A recombinant fragment of human (rfh)SP-D has recently been shown to neutralize SARS-CoV-2. Further work investigating the potential therapeutic role of SP-A and SP-D in COVID-19 and other infectious and inflammatory diseases is indicated.

The Dual Role of Surfactant Protein-D in Vascular Inflammation and Development of Cardiovascular Disease

Cardiovascular disease (CVD) is responsible for 31% of all global deaths. Atherosclerosis is the major cause of cardiovascular disease and is a chronic inflammatory disorder in the arteries. Atherosclerosis is characterized by the accumulation of cholesterol, extracellular matrix, and immune cells in the vascular wall. Recently, the collectin surfactant protein-D (SP-D), an important regulator of the pulmonary immune response, was found to be expressed in the vasculature. Several in vitro studies have examined the role of SP-D in the vascular inflammation leading to atherosclerosis. These studies show that SP-D plays a dual role in the development of atherosclerosis. In general, SP-D shows anti-inflammatory properties, and dampens local inflammation in the vessel, as well as systemic inflammation. However, SP-D can also exert a pro-inflammatory role, as it stimulates C-C chemokine receptor 2 inflammatory blood monocytes to secrete tumor necrosis-factor α and increases secretion of interferon-γ from natural killer cells. In vivo studies examining the role of SP-D in the development of atherosclerosis agree that SP-D plays a proatherogenic role, with SP-D knockout mice having smaller atherosclerotic plaque areas, which might be caused by a decreased systemic inflammation. Clinical studies examining the association between SP-D and cardiovascular disease have reported a positive association between circulatory SP-D level, carotid intima-media thickness, and coronary artery calcification. Other studies have found that circulatory SP-D is correlated with increased risk of both total and cardiovascular disease mortality. Both in vitro, in vivo, and clinical studies examining the relationship between SP-D and CVDs will be discussed in this review.

Airway Epithelium Dysfunction in Cystic Fibrosis and COPD

Cystic fibrosis is a genetic disease caused by mutations in the CFTR gene, whereas chronic obstructive pulmonary disease (COPD) is mainly caused by environmental factors (mostly cigarette smoking) on a genetically susceptible background. Although the etiology and pathogenesis of these diseases are different, both are associated with progressive airflow obstruction, airway neutrophilic inflammation, and recurrent exacerbations, suggesting common mechanisms. The airway epithelium plays a crucial role in maintaining normal airway functions. Major molecular and morphologic changes occur in the airway epithelium in both CF and COPD, and growing evidence suggests that airway epithelial dysfunction is involved in disease initiation and progression in both diseases. Structural and functional abnormalities in both airway and alveolar epithelium have a relevant impact on alteration of host defences, immune/inflammatory response, and the repair process leading to progressive lung damage and impaired lung function. In this review, we address the evidence for a critical role of dysfunctional airway epithelial cells in chronic airway inflammation and remodelling in CF and COPD, highlighting the common mechanisms involved in the epithelial dysfunction as well as the similarities and differences of the two diseases.

Surfactant protein D delays Fas- and TRAIL-mediated extrinsic pathway of apoptosis in T cells

Only a few extracellular soluble proteins are known to modulate apoptosis. We considered that surfactant-associated protein D (SP-D), an innate immune collectin present on many mucosal surfaces, could regulate apoptosis. Although SP-D is known to be important for immune cell homeostasis, whether SP-D affects apoptosis is unknown. In this study we aimed to determine the effects of SP-D on Jurkat T cells and human T cells dying by apoptosis. Here we show that SP-D binds to Jurkat T cells and delays the progression of Fas (CD95)-Fas ligand and TRAIL-TRAIL receptor induced, but not TNF-TNF receptor-mediated apoptosis. SP-D exerts its effects by reducing the activation of initiator caspase-8 and executioner caspase-3. SP-D also delays the surface exposure of phosphatidylserine. The effect of SP-D was ablated by the presence of caspase-8 inhibitor, but not by intrinsic pathway inhibitors. The binding ability of SP-D to dying cells decreases during the early stages of apoptosis, suggesting the release of apoptotic cell surface targets during apoptosis. SP-D also delays FasL-induced death of primary human T cells. SP-D delaying the progression of the extrinsic pathway of apoptosis could have important implications in regulating immune cell homeostasis at mucosal surfaces.

Surfactant Protein D in Respiratory and Non-Respiratory Diseases

Surfactant protein D (SP-D) is a multimeric collectin that is involved in innate immune defense and expressed in pulmonary, as well as non-pulmonary, epithelia. SP-D exerts antimicrobial effects and dampens inflammation through direct microbial interactions and modulation of host cell responses via a series of cellular receptors. However, low protein concentrations, genetic variation, biochemical modification, and proteolytic breakdown can induce decomposition of multimeric SP-D into low-molecular weight forms, which may induce pro-inflammatory SP-D signaling. Multimeric SP-D can decompose into trimeric SP-D, and this process, and total SP-D levels, are partly determined by variation within the SP-D gene, SFTPD. SP-D has been implicated in the development of respiratory diseases including respiratory distress syndrome, bronchopulmonary dysplasia, allergic asthma, and chronic obstructive pulmonary disease. Disease-induced breakdown or modifications of SP-D facilitate its systemic leakage from the lung, and circulatory SP-D is a promising biomarker for lung injury. Moreover, studies in preclinical animal models have demonstrated that local pulmonary treatment with recombinant SP-D is beneficial in these diseases. In recent years, SP-D has been shown to exert antimicrobial and anti-inflammatory effects in various non-pulmonary organs and to have effects on lipid metabolism and pro-inflammatory effects in vessel walls, which enhance the risk of atherosclerosis. A common SFTPD polymorphism is associated with atherosclerosis and diabetes, and SP-D has been associated with metabolic disorders because of its effects in the endothelium and adipocytes and its obesity-dampening properties. This review summarizes and discusses the reported genetic associations of SP-D with disease and the clinical utility of circulating SP-D for respiratory disease prognosis. Moreover, basic research on the mechanistic links between SP-D and respiratory, cardiovascular, and metabolic diseases is summarized. Perspectives on the development of SP-D therapy are addressed.

Surfactant protein D regulates murine testicular immune milieu and sperm functions

PROBLEM

Surfactant protein D (SP-D), a pattern recognition protein that regulates inflammation and immune homoeostasis, is expressed by testicular germ cells under the influence of testosterone. This study investigates the role of SP-D in testicular immune privilege and sperm functions.

METHOD OF STUDY

Testicular levels of cytokines and immunoregulatory molecules were evaluated in lipopolysaccharide (LPS)-challenged SP-D gene knockout mice (SP-D^-/- ). Further, sperm functions were assessed by computer-assisted sperm analyser (CASA) and in vitro capacitation. The effect of a recombinant fragment of human SP-D (rhSP-D) on LPS-induced testicular inflammation and sperm motility was assessed in wild-type (WT) mice.

RESULT

Endogenous absence of SP-D led to significantly increased testicular levels of immunosuppressive molecules, viz. serpina3, TGF-β1 and IL-10, and reduced levels of immune cell activation markers, CD86, IL-2 and ITGAX. These compensatory mechanisms resulted in markedly blunted levels of TNF-α, IL-12p40, MIP-1α, G-CSF and IL-6 in response to LPS challenge. Notably, exogenous supplementation of rhSP-D salvaged the WT mice from LPS-induced pro-inflammatory immune response and impairment of sperm motility by upregulating the levels of TGF-β1 and IL-10.

CONCLUSION

The study highlights the involvement of SP-D in maintenance of testicular immune privilege and its indirect contribution to male fertility.

Novel expression of a functional trimeric fragment of human SP-A with efficacy in neutralisation of RSV

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and hospitalisation of infants in developed countries. Surfactant protein A (SP-A) is an important innate immune molecule, localized in pulmonary surfactant. SP-A binds to carbohydrates on the surface of pathogens in a calcium-dependent manner to enable neutralisation, agglutination and clearance of pathogens including RSV.

SP-A forms trimeric units and further oligomerises through interactions between its N-terminal domains. Whilst a recombinant trimeric fragment of the closely related molecule (surfactant protein D) has been shown to retain many of the native protein’s functions, the importance of the SP-A oligomeric structure in its interaction with RSV has not been determined.

The aim of this study was to produce a functional trimeric recombinant fragment of human (rfh)SP-A, which lacks the N-terminal domain (and the capacity to oligomerise) and test its ability to neutralise RSV in an in vitro model of human bronchial epithelial infection.

We used a novel expression tag derived from spider silk proteins (‘NT’) to produce rfhSP-A in Escherichia coli, which we found to be trimeric and to bind to mannan in a calcium-dependent manner. Trimeric rfhSP-A reduced infection levels of human bronchial epithelial (AALEB) cells by RSV by up to a mean (±SD) of 96.4 (±1.9) % at 5 μg/ml, which was significantly more effective than dimeric rfhSP-A (34.3 (±20.5) %) (p < 0.0001). Comparatively, native human SP-A reduced RSV infection by up to 38.5 (±28.4) %.

For the first time we report the development of a functional trimeric rfhSP-A molecule which is highly efficacious in neutralising RSV, despite lacking the N-terminal domain and capacity to oligomerise.

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.

Surfactant Proteins SP-A and SP-D Modulate Uterine Contractile Events in ULTR Myometrial Cell Line

Pulmonary surfactant proteins SP-A and SP-D are pattern recognition innate immune molecules. However, there is extrapulmonary existence, especially in the amniotic fluid and at the feto-maternal interface. There is sufficient evidence to suggest that SP-A and SP-D are involved in the initiation of labour. This is of great importance given that preterm birth is associated with increased mortality and morbidity. In this study, we investigated the effects of recombinant forms of SP-A and SP-D (rhSP-A and rhSP-D, the comprising of trimeric lectin domain) on contractile events in vitro, using a human myometrial cell line (ULTR) as an experimental model. Treatment with rhSP-A or rhSP-D increased the cell velocity, distance travelled and displacement by ULTR cells. rhSP-A and rhSP-D also affected the contractile response of ULTRs when grown on collagen matrices showing reduced surface area. We investigated this effect further by measuring contractility-associated protein (CAP) genes. Treatment with rhSP-A and rhSP-D induced expression of oxytocin receptor (OXTR) and connexin 43 (CX43). In addition, rhSP-A and rhSP-D were able to induce secretion of GROα and IL-8. rhSP-D also induced the expression of IL-6 and IL-6 Ra. We provide evidence that SP-A and SP-D play a key role in modulating events prior to labour by reconditioning the human myometrium and in inducing CAP genes and pro-inflammatory cytokines thus shifting the uterus from a quiescent state to a contractile one.

Surfactant protein D inhibits HIV-1 infection of target cells via interference with gp120-CD4 interaction and modulates pro-inflammatory cytokine production

Surfactant Protein SP-D, a member of the collectin family, is a pattern recognition protein, secreted by mucosal epithelial cells and has an important role in innate immunity against various pathogens. In this study, we confirm that native human SP-D and a recombinant fragment of human SP-D (rhSP-D) bind to gp120 of HIV-1 and significantly inhibit viral replication in vitro in a calcium and dose-dependent manner. We show, for the first time, that SP-D and rhSP-D act as potent inhibitors of HIV-1 entry in to target cells and block the interaction between CD4 and gp120 in a dose-dependent manner. The rhSP-D-mediated inhibition of viral replication was examined using three clinical isolates of HIV-1 and three target cells: Jurkat T cells, U937 monocytic cells and PBMCs. HIV-1 induced cytokine storm in the three target cells was significantly suppressed by rhSP-D. Phosphorylation of key kinases p38, Erk1/2 and AKT, which contribute to HIV-1 induced immune activation, was significantly reduced in vitro in the presence of rhSP-D. Notably, anti-HIV-1 activity of rhSP-D was retained in the presence of biological fluids such as cervico-vaginal lavage and seminal plasma. Our study illustrates the multi-faceted role of human SP-D against HIV-1 and potential of rhSP-D for immunotherapy to inhibit viral entry and immune activation in acute HIV infection.

Leukocyte-associated Ig-like receptor-1 is a novel inhibitory receptor for surfactant protein D

The collagenous C-type lectin, SP-D, is a multitrimeric glycoprotein present at mucosal surfaces and is involved in host defense against infections in mammals. SP-D has immunomodulatory properties, but the underlying mechanisms are incompletely understood. SP-D contains collagen domains. LAIR-1 is an inhibitory immune receptor at the cell surface of various immune-competent cells that binds collagen. We hypothesized that the immunomodulatory functions of SP-D can be mediated via interactions between its collagen domain and LAIR-1. Binding assays show that SP-D interacts via its collagenous domain with LAIR-1 and the related LAIR-2. This does not affect the mannan-binding capacities of SP-D, which induces cross-linking of LAIR-1 in a cellular reporter assay. Functional assays show that SP-D inhibits the production of FcαR-mediated reactive oxygen via LAIR-1. Our studies indicate that SP-D is a functional ligand of the immune inhibitory receptor LAIR-1. Thus, we have identified a novel pathway for the immunomodulatory functions of SP-D mediated via binding of its collagenous domains to LAIR-1. This may provide a mechanism for the unexplained immunomodulatory function of the collagenous domains of SP-D.

Expression analysis of 13 ovine immune response candidate genes in Visna/Maedi disease progression

Visna/Maedi virus (VMV) is a lentivirus that infects cells of the monocyte/macrophage lineage in sheep. Infection with VMV may lead to Visna/Maedi (VM) disease, which causes a multisystemic inflammatory disorder causing pneumonia, encephalitis, mastitis and arthritis. The role of ovine immune response genes in the development of VM disease is not fully understood. In this work, sheep of the Rasa Aragonesa breed were divided into two groups depending on the presence/absence of VM-characteristic clinical lesions in the aforementioned organs and the relative levels of candidate gene expression, including cytokines and innate immunity loci were measured by qPCR in the lung and udder. Sheep with lung lesions showed differential expression in five target genes: CCR5, TLR7, and TLR8 were up regulated and IL2 and TNFα down regulated. TNFα up regulation was detected in the udder.

Perinatal exposure to alcohol: implications for lung development and disease

In utero alcohol exposure dramatically increases the risk of premature delivery. However, the majority of premature and term newborns exposed to alcohol remain undetected by medical caregivers. There is a desperate need for reliable and accurate biomarkers of alcohol exposure for the term and premature newborn population. The inability to identify the exposed newborn severely limits our understanding of alcohol's pathophysiological effects on developing organs such as the lung. This chapter will review potential advancements in future biomarkers of alcohol exposure for the newborn population. We will discuss alcohol's effects on redox homeostasis and cellular development of the neonatal lung. Finally, we will present the evidence describing in utero alcohol's derangement of innate and adaptive immunity and risk for infectious complications in the lung. Continued investigations into the identification and understanding of the mechanisms of alcohol-induced alterations in the premature lung will advance the care of this vulnerable patient population.

Linking surfactant protein SP-D and IL-13: implications in asthma and allergy

Surfactant protein D (SP-D) is an innate immune molecule that plays a protective role against lung infection, allergy, asthma and inflammation. In vivo experiments with murine models have shown that SP-D can protect against allergic challenge via a range of mechanisms including inhibition of allergen-IgE interaction, histamine release by sensitised mast cells, downregulation of specific IgE production, suppression of pulmonary and peripheral eosinophilia, inhibition of mechanisms that cause airway remodelling, and induction of apoptosis in sensitised eosinophils. SP-D can also shift helper T cell polarisation following in vivo allergenic challenge, from pathogenic Th2 to a protective Th1 cytokine response. Interestingly, SP-D gene deficient (-/-) mice show an IL-13 over-expressing phenotype. IL-13 has been shown to be involved in the development of asthma. Transgenic mice over-expressing IL-13 in the lung develop several characteristics of asthma such as pulmonary eosinophilia, airway epithelial hyperplasia, mucus cell metaplasia, sub-epithelial fibrosis, charcot-Leyden-Like crystals, airways obstruction, and non-specific airways hyper-responsiveness to cholinergic stimulation. Although both IL-4 and IL-13 are capable of inducing asthma like phenotype, the effector activity of IL-13 appears to be greater than that of IL-4. SP-D -/- mice seem to express considerably higher levels of IL-13, which is consistent with increased sensitivity and exaggerated immune response of the mice to allergenic challenge. Allergenic exposure also induces elevation in SP-D protein levels in an IL-4/IL-13-dependent manner, which prevents further activation of sensitised T cells. This negative feedback loop seems essential in protecting the airways from inflammatory damage after allergen inhalation. Here, we examine this link between IL-13 and SP-D, and its implications in the progression/regulation of asthma and allergy.

Immunohistochemical staining of surfactant proteins A and B in skin of psoriatic patients before and after narrow-band UVB phototherapy

BACKGROUND

Psoriasis is a chronic inflammatory disorder that is mediated by elements of the innate and adaptive immune systems. Surfactant proteins (SPs) play an important role in host defense mechanisms. They are thought to have a potential role in some inflammatory skin diseases including psoriasis.

OBJECTIVE

The aim of the study was to evaluate SP-A and SP-B immunohistochemical staining in skin of psoriatic patients before and after narrow-band UV radiation type B (NB-UVB) phototherapy.

STUDY DESIGN

Immunohistochemical staining for SP-A and SP-B was performed on tissues from 20 psoriatic patients before and after NB-UVB. Results were compared with the degree of improvement assessed by the Psoriasis Area and Severity Index (PASI) and duration of treatment.

RESULTS

In unaffected skin, SP-A and SP-B were restricted to the basal layer; however, in psoriatic skin, they appeared in suprabasal layers in 80% and 85% of cases, respectively. Dermal inflammatory cells showed SP-A in 11 cases (55%) and SP-B in only one case (5%). After treatment by NB-UVB, SP-A and SP-B staining showed predilection to the basal layer. Absence of SP-A staining in suprabasal layers after NB-UVB therapy was correlated to better response to therapy (p=0.003) and shorter duration of treatment (p<0.0001).

CONCLUSIONS

SP-A and SP-B positivity is increased in psoriatic skin and reduced after NB-UVB therapy. Absence of SP-A in suprabasal layers after NB-UVB therapy is associated with better response and shorter duration of treatment.

CD8(+) T cells responding to alveolar self-antigen lack CD25 expression and fail to precipitate autoimmunity

Although the contribution of CD8(+) T cells to the pathogenesis of noncommunicable lung diseases has become increasingly appreciated, our knowledge about the mechanisms controlling self-reactive CD8(+) T cells in the respiratory tract remains largely elusive. The outcome of the encounter between pulmonary self-antigen and naive CD8(+) T cells, in the presence or absence of inflammation, was traced after adoptive transfer of fluorescence-labeled CD8(+) T cells specific for the neo-self-antigen influenza A hemagglutinin into transgenic mice expressing hemagglutinin specifically in alveolar type II epithelial cells in order: to study the outcome of alveolar antigen encounter in the steady state and under inflammatory conditions; to define the phenotype and fate of CD8(+) T cells primed in the respiratory tract; and, finally, to correlate these findings with the onset of autoimmunity in the lung. We found that CD8(+) T cells remain ignorant in the steady state, whereas transient proliferation of self-reactive CD8(+) T cells is induced by forced maturation or licensing of dendritic cells, increases in the antigenic threshold, and targeted release of alveolar self-antigen by epithelial injury. However, these cells fail to acquire effector functions, lack the expression of the high-affinity IL-2 receptor CD25, and do not precipitate autoimmunity in the lung. We conclude that inadvertent activation of CD8(+) T cells in the lung is prevented in the absence of "danger signals," whereas tissue damage after infection or noninfectious inflammation creates an environment that allows the priming of previously ignorant T cells. Failure in effector cell differentiation after abortive priming, however, precludes the establishment of self-perpetuating autoimmunity in the lung.

Surfactant protein D (SP-D) alters cellular uptake of particles and nanoparticles

Surfactant protein D (SP-D) is primarily expressed in the lungs and modulates pro- and anti-inflammatory processes to toxic challenge, maintaining lung homeostasis. We investigated the interaction between NPs and SP-D and subsequent uptake by cells involved in lung immunity. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) measured NP aggregation, particle size and charge in native human SP-D (NhSP-D) and recombinant fragment SP-D (rfhSP-D). SP-D aggregated NPs, especially following the addition of calcium. Immunohistochemical analysis of A549 epithelial cells investigated the co-localization of NPs and rfhSP-D. rfhSP-D enhanced the co-localisation of NPs to epithelial A549 cells in vitro. NP uptake by alveolar macrophages (AMs) and lung dendritic cells (LDCs) from C57BL/6 and SP-D knock-out mice were compared. AMs and LDCs showed decreased uptake of NPs in SP-D deficient mice compared to wild-type mice. These data confirmed an interaction between SP-D and NPs, and subsequent enhanced NP uptake.

Novel role for surfactant protein A in gastrointestinal graft-versus-host disease

Graft-versus-host disease (GVHD) is a severe and frequent complication of allogeneic bone marrow transplantation (BMT) that involves the gastrointestinal (GI) tract and lungs. The pathobiology of GVHD is complex and involves immune cell recognition of host Ags as foreign. We hypothesize a central role for the collectin surfactant protein A (SP-A) in regulating the development of GVHD after allogeneic BMT. C57BL/6 (H2b; WT) and SP-A-deficient mice on a C57BL/6 background (H2b; SP-A(-/-)) mice underwent allogeneic or syngeneic BMT with cells from either C3HeB/FeJ (H2k; SP-A-deficient recipient mice that have undergone an allogeneic BMT [SP-A(-/-)alloBMT] or SP-A-sufficient recipient mice that have undergone an allogeneic BMT) or C57BL/6 (H2b; SP-A-deficient recipient mice that have undergone a syngeneic BMT or SP-A-sufficient recipient mice that have undergone a syngeneic BMT) mice. Five weeks post-BMT, mice were necropsied, and lung and GI tissue were analyzed. SP-A(-/-) alloBMT or SP-A-sufficient recipient mice that have undergone an allogeneic BMT had no significant differences in lung pathology; however, SP-A(-/-)alloBMT mice developed marked features of GI GVHD, including decreased body weight, increased tissue inflammation, and lymphocytic infiltration. SP-A(-/-)alloBMT mice also had increased colon expression of IL-1β, IL-6, TNF-α, and IFN-γ and as well as increased Th17 cells and diminished regulatory T cells. Our results demonstrate the first evidence, to our knowledge, of a critical role for SP-A in modulating GI GVHD. In these studies, we demonstrate that mice deficient in SP-A that have undergone an allogeneic BMT have a greater incidence of GI GVHD that is associated with increased Th17 cells and decreased regulatory T cells. The results of these studies demonstrate that SP-A protects against the development of GI GVHD and establishes a role for SP-A in regulating the immune response in the GI tract.

The distribution of immune cells in the lungs of classical and atypical ovine pulmonary adenocarcinoma

Ovine pulmonary adenocarcinoma (OPA) is a contagious tumour caused by infection of sheep with Jaagsiekte sheep retrovirus. Two forms of OPA have been identified, classical and atypical, which can be distinguished clinically and pathologically. Most notably classical OPA is progressive until death, while atypical OPA remains subclinical. In the present study the local immune responses in the lungs of cases of atypical OPA were compared with those from classical cases by immunohistochemistry using a panel of mouse anti-sheep mAbs. Distinct differences in the distribution of immune cell subsets in the two forms of OPA were observed. In particular there was an intratumoural influx of T cell subsets and MHC Class II expression on the tumour cells in atypical OPA, neither of which was seen in classical OPA. It is possible that these differences may contribute, at least in part, to determining the progressive course of classical OPA compared with the subclinical nature of atypical OPA.

Surfactant protein A integrates activation signal strength to differentially modulate T cell proliferation

Pulmonary surfactant lipoproteins lower the surface tension at the alveolar-airway interface of the lung and participate in host defense. Previous studies reported that surfactant protein A (SP-A) inhibits lymphocyte proliferation. We hypothesized that SP-A-mediated modulation of T cell activation depends upon the strength, duration, and type of lymphocyte activating signals. Modulation of T cell signal strength imparted by different activating agents ex vivo and in vivo in different mouse models and in vitro with human T cells shows a strong correlation between strength of signal (SoS) and functional effects of SP-A interactions. T cell proliferation is enhanced in the presence of SP-A at low SoS imparted by exogenous mitogens, specific Abs, APCs, or in homeostatic proliferation. Proliferation is inhibited at higher SoS imparted by different doses of the same T cell mitogens or indirect stimuli such as LPS. Importantly, reconstitution with exogenous SP-A into the lungs of SP-A(-/-) mice stimulated with a strong signal also resulted in suppression of T cell proliferation while elevating baseline proliferation in unstimulated T cells. These signal strength and SP-A-dependent effects are mediated by changes in intracellular Ca(2+) levels over time, involving extrinsic Ca(2+)-activated channels late during activation. These effects are intrinsic to the global T cell population and are manifested in vivo in naive as well as memory phenotype T cells. Thus, SP-A appears to integrate signal thresholds to control T cell proliferation.

An official American Thoracic Society research statement: noninfectious lung injury after hematopoietic stem cell transplantation: idiopathic pneumonia syndrome

RATIONALE

Acute lung dysfunction of noninfectious etiology, known as idiopathic pneumonia syndrome (IPS), is a severe complication following hematopoietic stem cell transplantation (HSCT). Several mouse models have been recently developed to determine the underlying causes of IPS. A cohesive interpretation of experimental data and their relationship to the findings of clinical research studies in humans is needed to better understand the basis for current and future clinical trials for the prevention/treatment of IPS.

OBJECTIVES

Our goal was to perform a comprehensive review of the preclinical (i.e., murine models) and clinical research on IPS.

METHODS

An ATS committee performed PubMed and OVID searches for published, peer-reviewed articles using the keywords "idiopathic pneumonia syndrome" or "lung injury" or "pulmonary complications" AND "bone marrow transplant" or "hematopoietic stem cell transplant." No specific inclusion or exclusion criteria were determined a priori for this review.

MEASUREMENTS AND MAIN RESULTS

Experimental models that reproduce the various patterns of lung injury observed after HSCT have identified that both soluble and cellular inflammatory mediators contribute to the inflammation engendered during the development of IPS. To date, 10 preclinical murine models of the IPS spectrum have been established using various donor and host strain combinations used to study graft-versus-host disease (GVHD). This, as well as the demonstrated T cell dependency of IPS development in these models, supports the concept that the lung is a target of immune-mediated attack after HSCT. The most developed therapeutic strategy for IPS involves blocking TNF signaling with etanercept, which is currently being evaluated in clinical trials.

CONCLUSIONS

IPS remains a frequently fatal complication that limits the broader use of allogeneic HSCT as a successful treatment modality. Faced with the clinical syndrome of IPS, one can categorize the disease entity with the appropriate tools, although cases of unclassifiable IPS will remain. Significant research efforts have resulted in a paradigm shift away from identifying noninfectious lung injury after HSCT solely as an idiopathic clinical syndrome and toward understanding IPS as a process involving aspects of both the adaptive and the innate immune response. Importantly, new laboratory insights are currently being translated to the clinic and will likely prove important to the development of future strategies to prevent or treat this serious disorder.

Lung effector memory and activated CD4+ T cells display enhanced proliferation in surfactant protein A-deficient mice during allergen-mediated inflammation

Although many studies have shown that pulmonary surfactant protein (SP)-A functions in innate immunity, fewer studies have addressed its role in adaptive immunity and allergic hypersensitivity. We hypothesized that SP-A modulates the phenotype and prevalence of dendritic cells (DCs) and CD4(+) T cells to inhibit Th2-associated inflammatory indices associated with allergen-induced inflammation. In an OVA model of allergic hypersensitivity, SP-A(-/-) mice had greater eosinophilia, Th2-associated cytokine levels, and IgE levels compared with wild-type counterparts. Although both OVA-exposed groups had similar proportions of CD86(+) DCs and Foxp3(+) T regulatory cells, the SP-A(-/-) mice had elevated proportions of CD4(+) activated and effector memory T cells in their lungs compared with wild-type mice. Ex vivo recall stimulation of CD4(+) T cell pools demonstrated that cells from the SP-A(-/-) OVA mice had the greatest proliferative and IL-4-producing capacity, and this capability was attenuated with exogenous SP-A treatment. Additionally, tracking proliferation in vivo demonstrated that CD4(+) activated and effector memory T cells expanded to the greatest extent in the lungs of SP-A(-/-) OVA mice. Taken together, our data suggested that SP-A influences the prevalence, types, and functions of CD4(+) T cells in the lungs during allergic inflammation and that SP deficiency modifies the severity of inflammation in allergic hypersensitivity conditions like asthma.

Collectin 11 (CL-11, CL-K1) is a MASP-1/3-associated plasma collectin with microbial-binding activity

Collectins play important roles in the innate immune defense against microorganisms. Recently, a new collectin, collectin 11 (CL-11 or CL-K1), was identified via database searches. In present work, we characterize the structural and functional properties of CL-11. Under nonreducing conditions, in gel permeation chromatography recombinant CL-11 forms disulfide-linked oligomers of 100 and 200 kDa. A mAb-based ELISA estimates the concentration of CL-11 in plasma to be 2.1 μg/ml, and the presence of CL-11 in plasma was further verified by Western blotting and mass spectrometry. Mannan-binding lectin-associated serine protease 1 (MASP-1) copurified with CL-11 and the interaction in plasma with MASP-1 and/or MASP-3 was further demonstrated using ELISA. We identified the adrenal glands, the kidneys, and the liver as primary sites of expression. CL-11 lectin activity was demonstrated by ELISA and showed that CL-11 has preference for l-fucose and d-mannose. We finally show that CL-11 binds to intact bacteria, fungi, and viruses and that CL-11 decreases influenza A virus infectivity and forms complexes with DNA. On the basis of the significant concentration of CL-11 in circulation and CL-11's interaction with various microorganisms and MASP-1 and/or MASP-3, it is conceivable that CL-11 plays a role in activation of the complement system and in the defense against invading microorganisms.

Innate immunity

Innate immunity is an exciting area of research in rhinology because emerging evidence suggests that abnormal local immune responses, rather than pathogen-specific adaptive immunity, may play a more important role in the pathogenesis of chronic rhinosinusitis (CRS). This article reviews important recent research regarding the innate immune system and CRS, with particular focus on the role of pattern recognition receptors, antimicrobial peptides and biofilms, epithelial ciliary function, cystic fibrosis, and cigarette smoking, and on areas for future research and therapy.

Surfactant protein D-mediated decrease of allergen-induced inflammation is dependent upon CTLA4

Pulmonary surfactant protein D (SP-D), a member of the collectin family, is an innate immune molecule critical for defense that can also modulate adaptive immune responses. We previously showed that SP-D-deficient mice exhibit enhanced allergic responses and that SP-D induction requires lymphocytes. Thus, we postulated that SP-D may decrease adaptive allergic responses through interaction with T cells. In this study, we used two forms of SP-D, a dodecamer and a shorter fragment containing the trimeric neck and carbohydrate recognition domains (SP-D NCRD). Both forms decreased immune responses in vitro and in a murine model of pulmonary inflammation. SP-D NCRD increased transcription of CTLA4, a negative regulator of T cell activation, in T cells. SP-D NCRD no longer decreased lymphoproliferation and IL-2 cytokine production when CTLA4 signals were abrogated. Administration of SP-D NCRD in vivo no longer decreased allergen induced responses when CTLA4 was inhibited. Our results indicate that SP-D decreases allergen responses, an effect that may be mediated by increase of CTLA4 in T cells.

The presence of CD14 overcomes evasion of innate immune responses by virulent Francisella tularensis in human dendritic cells in vitro and pulmonary cells in vivo

Francisella tularensis is a Gram-negative bacterium that causes acute, lethal disease following inhalation. We have previously shown that viable F. tularensis fails to stimulate secretion of proinflammatory cytokines following infection of human dendritic cells (hDC) in vitro and pulmonary cells in vivo. Here we demonstrate that the presence of the CD14 receptor is critical for detection of virulent F. tularensis strain SchuS4 by dendritic cells, monocytes, and pulmonary cells. Addition of soluble CD14 (sCD14) to hDC restored cytokine production following infection with strain SchuS4. In contrast, addition of anti-CD14 to monocyte cultures inhibited the ability of these cells to respond to strain SchuS4. Addition of CD14 or blocking CD14 following SchuS4 infection in dendritic cells and monocytes, respectively, was not due to alterations in phagocytosis or replication of the bacterium in these cells. Administration of sCD14 in vivo also restored cytokine production following infection with strain SchuS4, as assessed by increased concentrations of tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-12p70, and IL-6 in the lungs of mice receiving sCD14 compared to mock-treated controls. In contrast to homogenous cultures of monocytes or dendritic cells infected in vitro, mice treated with sCD14 in vivo also exhibited controlled bacterial replication and dissemination compared to mock-treated controls. Interestingly, animals that lacked CD14 were not more susceptible or resistant to pulmonary infection with SchuS4. Together, these data support the hypothesis that the absence or low abundance of CD14 on hDC and in the lung contributes to evasion of innate immunity by virulent F. tularensis. However, CD14 is not required for development of inflammation during the last 24 to 48 h of SchuS4 infection. Thus, the presence of this receptor may aid in control of virulent F. tularensis infections at early, but not late, stages of infection.

Mannose binding lectin and lung collectins interact with Toll-like receptor 4 and MD-2 by different mechanisms

BACKGROUND

We have previously shown that lung collectins, surfactant protein A (SP-A) and surfactant protein D, interact with Toll-like receptor (TLR) 2, TLR4, or MD-2. Bindings of lung collectins to TLR2 and TLR4/MD-2 result in the alterations of signaling through these receptors, suggesting the immunomodulatory functions of lung collectins. Mannose binding lectin (MBL) is another collectin molecule which has structural homology to SP-A. The interaction between MBL and TLRs has not yet been determined.

METHODS

We prepared recombinant MBL, and analyzed its bindings to recombinant soluble forms of TLR4 (sTLR4) and MD-2.

RESULTS

MBL bound to sTLR4 and MD-2. The interactions were Ca2+-dependent and inhibited by mannose or monoclonal antibody against the carbohydrate-recognition domain of MBL. Treatment of sTLR4 or MD-2 by peptide N-glycosidase F significantly decreased the binding of MBL. SP-A bound to deglycosylated sTLR4, and this property did not change in chimeric molecules of SP-A/MBL in which Glu195-Phe228 or Thr174-Gly194 of SP-A were replaced with the corresponding MBL sequences.

GENERAL SIGNIFICANCE

These results suggested that MBL binds to TLR4 and MD-2 through the carbohydrate-recognition domain, and that oligosaccharide moieties of TLR4 and MD-2 are important for recognition by MBL. Since our previous studies indicated that lung collectins bind to the peptide portions of TLRs, MBL and lung collectins interact with TLRs by different mechanisms. These direct interactions between MBL and TLR4 or MD-2 suggest that MBL may modulate cellular responses by altering signals through TLRs.

Role of Surfactant Protein A in the Innate Host Defense and Autoimmunity

Surfactant protein A (SP-A) is a lung collectin with diverse immunoregulatory activities. SP-A regulates the innate host defense by enhancing phagocytosis of pathogens and modulating the production of nitric oxide and cytokines by immune cells. Additionally, SP-A also modulates the phenotypic and functional properties of the cells of adaptive immune response such as dendritic cells (DCs) and lymphocytes. Bone marrow-derived DCs generated in the presence of SP-A fail to increase lipopolysaccharide-induced upregulation of major histocompatibility complex (MHC) class II and CD86 costimulatory molecule on DCs surface and behaves like "tolerogenic DCs". SP-A may also induce tolerance by suppressing the proliferation of activated T lymphocytes. Thus, based on immunoregulatory properties of SP-A, it may be employed as a therapeutic agent for the treatment of autoimmune disease and organ transplantation.

Protective role of the lung collectins surfactant protein A and surfactant protein D in airway inflammation

The acute inflammatory airway response is characterized by a time-dependent onset followed by active resolution. Emerging evidence suggests that epithelial cells of the proximal and distal air spaces release host defense mediators that can facilitate both the initiation and the resolution part of inflammatory airway changes. These molecules, also known as the hydrophilic surfactant proteins (surfactant protein [SP]-A and SP-D) belong to the class of collagenous lectins (collectins). The collectins are a small family of soluble pattern recognition receptors containing collagenous regions and C-type lectin domains. SP-A and SP-D are most abundant in the lung. Because of their structural uniqueness, specific localization, and functional versatility, lung collectins are important players of the pulmonary immune responses. Recent studies in our laboratory and others indicated significant associations of lung collectin levels with acute and chronic airway inflammation in both animal models and patients, suggesting the usefulness of these molecules as disease biomarkers. Research on wild-type and mutant recombinant molecules in vivo and in vitro showed that SP-A and SP-D bind carbohydrates, lipids, and nucleic acids with a broad-spectrum specificity and initiate phagocytosis of inhaled pathogens as well as apoptotic cells. Investigations on gene-deficient and conditional overexpresser mice indicated that lung collectins also directly modulate innate immune cell function and T-cell-dependent inflammatory events. Thus, these molecules have a unique, dual-function capacity to induce pathogen elimination and control proinflammatory mechanisms, suggesting a potential suitability for therapeutic prevention and treatment of chronic airway inflammation. This article reviews evidence supporting that the lung collectins play an immune-protective role and are essential for maintenance of the immunologic homeostasis in the lung.

Simultaneous absence of surfactant proteins A and D increases lung inflammation and injury after allogeneic HSCT in mice

The relative contributions of the hydrophilic surfactant proteins (SP)-A and -D to early inflammatory responses associated with lung dysfunction after experimental allogeneic hematopoietic stem cell transplantation (HSCT) were investigated. We hypothesized that the absence of SP-A and SP-D would exaggerate allogeneic T cell-dependent inflammation and exacerbate lung injury. Wild-type, SP-D-deficient (SP-D(-/-)), and SP-A and -D double knockout (SP-A/D(-/-)) C57BL/6 mice were lethally conditioned with cyclophosphamide and total body irradiation and given allogeneic bone marrow plus donor spleen T cells, simulating clinical HSCT regimens. On day 7, after HSCT, permeability edema progressively increased in SP-D(-/-) and SP-A/D(-/-) mice. Allogeneic T cell-dependent inflammatory responses were also increased in SP-D(-/-) and SP-A/D(-/-) mice, but the altered mediators of inflammation were not identical. Compared with wild-type, bronchoalveolar lavage fluid (BALF) levels of nitrite plus nitrate, GM-CSF, and MCP-1, but not TNF-alpha and IFN-gamma, were higher in SP-D-deficient mice before and after HSCT. In SP-A/D(-/-) mice, day 7 post-HSCT BALF levels of TNF-alpha and IFN-gamma, in addition to nitrite plus nitrate and MCP-1, were higher compared with mice lacking SP-D alone. After HSCT, both SP-A and SP-D exhibited anti-inflammatory lung-protective functions that were not completely redundant in vivo.

Surfactant protein D protects against acute hyperoxic lung injury

RATIONALE

Surfactant protein D (SP-D) is a member of the collectin family of soluble, innate, host defense molecules with demonstrated immunomodulatory properties in vitro. Constitutive absence of SP-D in mice is associated with lung inflammation, alteration in surfactant lipid homeostasis, and increased oxidative-nitrative stress.

OBJECTIVES

To test the hypothesis that SP-D would protect against acute lung injury from hyperoxia in vivo.

METHODS

Transgenic mice overexpressing rat SP-D constitutively (SP-D OE) or conditionally via regulation with doxycycline (SP-D Dox-on) were subjected to continuous hyperoxic challenge for up to 14 days.

MEASUREMENTS AND MAIN RESULTS

Compared with littermate control mice (wild-type [WT]), SP-D OE mice exposed to 80% O(2) demonstrated substantially increased survival accompanied by significant reductions in wet to dry lung ratios and bronchoalveolar lavage (BAL) protein. Although SP-D OE and WT mice exhibited a twofold increase in total BAL cells and neutrophilia in response to hyperoxia, the SP-D OE group had lower levels of BAL proinflammatory cytokines and chemokines, including IL-6, tumor necrosis factor-alpha, and monocyte chemotactic protein-1; increased mRNA levels of the transcription factor NF-E2 related factor-2 (NRF-2) and phase 2 antioxidants hemoxygenase-1 (HO-1), glutathione peroxidase-2 (GPx-2) and NAD(P)H quinone oxidoreductase-1 (Nqo-1); and decreases in lung tissue thiobarbituric acid-reactive substances. As proof of principle, the protective role of SP-D on hyperoxic injury was confirmed as SP-D Dox-on mice exposed to 85% O(2) demonstrated increased mortality upon withdrawal of doxycycline.

CONCLUSIONS

Local expression of SP-D protects against hyperoxic lung injury through modulation of proinflammatory cytokines and antioxidant enzymatic scavenger systems.

Recombinant surfactant protein-D selectively increases apoptosis in eosinophils of allergic asthmatics and enhances uptake of apoptotic eosinophils by macrophages

Pulmonary surfactant protein-D (SP-D) is a multifunctional, pattern recognition molecule involved in resistance to allergen challenge and pulmonary inflammation. In view of therapeutic effects of exogenous SP-D or recombinant fragment of human surfactant protein-D (rhSP-D) (composed of eight Gly-X-Y collagen repeat sequences, homotrimeric neck and lectin domains) in murine models of lung allergy and hypereosinophilic SP-D gene-deficient mice, we investigated the possibility of a direct interaction of purified rhSP-D with human eosinophils derived from allergic patients and healthy donors. rhSP-D showed a sugar- and calcium-dependent binding to human eosinophils, suggesting involvement of its carbohydrate recognition domain. While eosinophils from allergic patients showed a significant increase in apoptosis, oxidative burst and CD69 expression in presence of rhSP-D, eosinophils from healthy donors showed no significant change. However, these eosinophils from healthy donors when primed with IL-5 exhibited increase in apoptosis on incubation with rhSP-D. Apoptosis mediated by rhSP-D in primed eosinophils was not affected by the antioxidant, N-acetyl-L-cysteine. There was a manifold increase in binding of rhSP-D to apoptotic eosinophils than the normal eosinophils and rhSP-D induced a significant increase in uptake of apoptotic eosinophils by J774A.1 macrophage cells. The study suggests that rhSP-D mediated preferential increase of apoptosis of primed eosinophils while not affecting the normal eosinophils and increased phagocytosis of apoptotic eosinophils may be important mechanisms of rhSP-D and plausibly SP-D-mediated resolution of allergic eosinophilic inflammation in vivo.

An antibody against the surfactant protein A (SP-A)-binding domain of the SP-A receptor inhibits T cell-mediated immune responses to Mycobacterium tuberculosis

Surfactant protein A (SP-A) suppresses lymphocyte proliferation and IL-2 secretion, in part, by binding to its receptor, SP-R210. However, the mechanisms underlying this effect are not well understood. Here, we studied the effect of antibodies against the SP-A-binding (neck) domain (alpha-SP-R210n) or nonbinding C-terminal domain (alpha-SP-R210ct) of SP-R210 on human peripheral blood T cell immune responses against Mycobacterium tuberculosis. We demonstrated that both antibodies bind to more than 90% of monocytes and 5-10% of CD3+ T cells in freshly isolated PBMC. Stimulation of PBMC from healthy tuberculin reactors [purified protein derivative-positive (PPD+)] with heat-killed M. tuberculosis induced increased antibody binding to CD3+ cells. Increased antibody binding suggested enhanced expression of SP-R210, and this was confirmed by Western blotting. The antibodies (alpha-SP-R210n) cross-linking the SP-R210 through the SP-A-binding domain markedly inhibited cell proliferation and IFN-gamma secretion by PBMC from PPD+ donors in response to heat-killed M. tuberculosis, whereas preimmune IgG and antibodies (alpha-SP-R210ct) cross-linking SP-R210 through the non-SP-A-binding, C-terminal domain had no effect. Anti-SP-R210n also decreased M. tuberculosis-induced production of TNF-alpha but increased production of IL-10. Inhibition of IFN-gamma production by alpha-SP-R210n was abrogated by the combination of neutralizing antibodies to IL-10 and TGF-beta1. Together, these findings support the hypothesis that SP-A, via SP-R210, suppresses cell-mediated immunity against M. tuberculosis via a mechanism that up-regulates secretion of IL-10 and TGF-beta1.

Surfactant protein D alters allergic lung responses in mice and human subjects

BACKGROUND

Surfactant protein (SP) D has been proposed to be protective in allergic airway responses.

OBJECTIVE

We aimed to determine the effect of SP-D deficiency on murine and human airway allergy.

METHODS

Immunologic responses of SP-D gene-deficient mice (Sftpd-/-) at baseline and after 4 intranasal Aspergillus fumigatus exposures were assessed. In addition, the significance of a single nucleotide polymorphism (Met(11)Thr) in the human SP-D gene (known to decrease SP-D function) was investigated.

RESULTS

Macrophage and neutrophil bronchoalveolar lavage fluid levels and large airway mucus production were increased in naive Sftpd-/- mice in association with increased lung CCL17 levels and CD4+ T cell numbers. T(H)2-associated antibody levels (IgG1 and IgE) were significantly lower in 4- to 5-week-old Sftpd-/- mice (P < .05). Accordingly, naive Sftpd-/- splenocytes released significantly less IL-4 and IL-13 on anti-CD3/CD28 stimulation (P < .01). After intranasal allergen exposures, a modest decrease in bronchoalveolar lavage fluid eosinophilia and IL-13 levels was observed in Sftpd-/- mice compared with values seen in wild-type mice in association with decreased airway resistance (P < .01). A single nucleotide polymorphism in the SFTPD gene, affecting SP-D levels and pathogen binding, was associated with decreased atopy in black subjects and potentially lower asthma susceptibility in white subjects.

CONCLUSION

Sftpd-/- mice have an impaired systemic T(H)2 response at baseline and reduced inflammation and airway responses after allergen exposure. Translational studies revealed that a polymorphism in the SFTPD gene was associated with lower atopy and possibly asthma susceptibility. Taken together, these results support the hypothesis that SP-D-dependent innate immunity influences atopy and asthma.

Innate immunity in the paranasal sinuses: a review of nasal host defenses

BACKGROUND

Chronic rhinosinusitis (CRS) is a common inflammatory disorder of the paranasal sinuses. An abnormal host response to common bacterial or fungal pathogens is thought to be an important factor in the disease process. Host sinonasal epithelium plays an important role in initially recognizing the presence of microbes and responding by increasing production of antimicrobial peptides and cytokines, with recruitment of phagocytes and lymphocytes of the adaptive immune system, to eliminate the infection. Recently, the innate immune system and its complex interplay with the adaptive immune system are increasingly being recognized as important in the pathogenesis of chronic inflammatory diseases such as asthma and CRS.

METHODS

Review of recent findings on innate immunity in the pathogenesis of CRS.

RESULTS

New areas of research into potentially novel therapies for CRS are highlighted in this review, with emphasis on toll-like receptors, antimicrobial peptides (cathelicidins and defensins), and surfactant proteins.

CONCLUSION

This review provides an overview of innate immunity in the sinonasal tract and discusses potential use of innate immune peptides as treatments against fungi, biofilms, and superantigens in CRS.

Surfactant protein D/anti-Fc receptor bifunctional proteins as a tool to enhance host defence

BACKGROUND

Drug-resistant pathogens are an increasing threat, particularly for hospitalised patients. In search of a new approach in pathogen targeting, we developed bifunctional proteins that combine broad spectrum pathogen recognition with efficient targeting to phagocytes. Pathogen recognition is provided by a recombinant fragment of surfactant protein D (rfSP-D) while targeting to phagocytic cells is accomplished by coupling rfSP-D to F(ab') fragments directed against Fcalpha receptor I (FcalphaRI) or Fcgamma receptor I (FcgammaRI). FcalphaRI and FcgammaRI are expressed on myeloid cells, and induce rapid internalisation of particles after crosslinking.

OBJECTIVE/METHODS

In this review we discuss the roles of SP-D and Fc receptors in host defence as a rationale for rfSP-D/anti-FcR bifunctional proteins. Furthermore we summarise the available data on rfSP-D/anti-FcR proteins as well as opportunities and considerations for future use of such bifunctional proteins.

RESULTS/CONCLUSION

rfSP-D/anti-FcR bifunctional proteins could be of great value for the treatment of a variety of infectious diseases. The focus in the near future should be on proof-of-principle by testing the bifunctional proteins in different mouse models of infectious disease.