Exhaled particles as markers of small airway inflammation in subjects with asthma.

Exhaled breath contains suspended particles of respiratory tract lining fluid from the small airways. The particles are formed when closed airways open during inhalation. We have developed a method called Particles in Exhaled air (PExA® ) to measure and sample these particles in the exhaled aerosol. Here, we use the PExA® method to study the effects of birch pollen exposure on the small airways of individuals with asthma and birch pollen allergy. We hypothesized that birch pollen-induced inflammation could change the concentrations of surfactant protein A and albumin in the respiratory tract lining fluid of the small airways and influence the amount of exhaled particles. The amount of exhaled particles was reduced after birch pollen exposure in subjects with asthma and birch pollen allergy, but no significant effect on the concentrations of surfactant protein A and albumin in exhaled particles was found. The reduction in the number of exhaled particles may be due to inflammation in the small airways, which would reduce their diameter and potentially reduce the number of small airways that open and close during inhalation and exhalation.

[Repair effect of Qinbai Qingfei concentrated pellets to AEC-â ¡ of rats infected by Mycoplasmal pneumonia].

To discuss the repair mechanism of Qinbai Qingfei concentrated pellets to AEC-Ⅱ of rats infected by mycoplasma through the observation of the changes and distribution of TGF-ß and SP-A in lungs, totally 60 Wistar rats that weighing 80-100 g were collected, with male and female in half. The rats were divided into six groups randomly, with 10 rats each group, namely blank group, model group, positive group and Qinbai Qingfei concentrated pellets high, middle and low dose groups. Rats were infected through nasal intubation drip of MP. After 10 days of administration, serum and bronchoalveolar lavage fluid (BALF) were collected to detect the concentration of surface activity related protein A (SP-A) by ELISA, left pulmonary tissues of rats were collected to observe the expression and distribution of transforming growth factor-beta (TGF-ß) and SP-A by immunohistochemistry, and right pulmonary tissues were taken to detect TGF-ß and SP-A mRNA expression level by real-time quantitative PCR (RT-PCR). Qinbai Qingfei concentrated pellets can reduce the expression of TGF-ß and increase the expression of SP-A in the lung tissues of rats infected by mycoplasma. Specifically, TGF-ß was mainly distributed among the lung interstitium, while SPAs were mainly distributed in AEC-II and parts of alveolar macrophage. The level of SP-A was reduced in serum and increased in BALF in rats in Qinbai Qingfei concentrated pellets groups. It was proved that Qinbai Qingfei concentrated pellets can restore the normal morphology and function of the lung by reducing the content of TGF-ß to inhibit epithelial-mesenchymal transition (EMT) of alveolar type II epithelial cells and increasing the expression of SP-A. Qinbai Qingfei concentrated pellets have the repairing ability to capillary vessel damage caused by MP in lung tissues of rats.

Surfactant protein (SP)-A suppresses preterm delivery and inflammation via TLR2.

Toll like receptors (TLRs) are pattern-recognition molecules that initiate the innate immune response to pathogens. Pulmonary surfactant protein (SP)-A is an endogenously produced ligand for TLR2 and TLR4. SP-A has been proposed as a fetally produced signal for the onset of parturition in the mouse. We examined the effect of interactions between SP-A and the pathogenic TLR agonists lipopolysaccharide (LPS), peptidoglycan (PGN) and polyinosinic:cytidylic acid (poly(I:C)) (ligands for TLR4, TLR2 and TLR3, respectively) on the expression of inflammatory mediators and preterm delivery. Three types of mouse macrophages (the cell line RAW 264.7, and fresh amniotic fluid and peritoneal macrophages, including macrophages from TLR4 and TLR2 knockout mice) were treated for up to 7 hours with pathogenic TLR agonists with or without SP-A. SP-A alone had no effect upon inflammatory mediators in mouse macrophages and did not independently induce preterm labor. SP-A significantly suppressed TLR ligand-induced expression of inflammatory mediators (interleukin (IL)-1ß, tumor necrosis factor (TNF)-α and the chemokine CCL5) via a TLR2 dependent mechanism. In a mouse inflammation-induced preterm delivery model, intrauterine administration of SP-A significantly inhibited preterm delivery, suppressed the expression of proinflammatory mediators and enhanced the expression of the CXCL1 and anti-inflammatory mediator IL-10. We conclude that SP-A acts via TLR2 to suppress TLR ligand-induced preterm delivery and inflammatory responses.

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.

Surfactant protein B inhibits secretory phospholipase A2 hydrolysis of surfactant phospholipids.

Hydrolysis of surfactant phospholipids (PL) by secretory phospholipases A(2) (sPLA(2)) contributes to surfactant damage in inflammatory airway diseases such as acute lung injury/acute respiratory distress syndrome. We and others have reported that each sPLA(2) exhibits specificity in hydrolyzing different PLs in pulmonary surfactant and that the presence of hydrophilic surfactant protein A (SP-A) alters sPLA(2)-mediated hydrolysis. This report tests the hypothesis that hydrophobic SP-B also inhibits sPLA(2)-mediated surfactant hydrolysis. Three surfactant preparations were used containing varied amounts of SP-B and radiolabeled tracers of phosphatidylcholine (PC) or phosphatidylglycerol (PG): 1) washed ovine surfactant (OS) (pre- and postorganic extraction) compared with Survanta (protein poor), 2) Survanta supplemented with purified bovine SP-B (1-5%, wt/wt), and 3) a mixture of dipalmitoylphosphatidylcholine (DPPC), 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC), and 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG) (DPPC:POPC:POPG, 40:40:20) prepared as vesicles and monomolecular films in the presence or absence of SP-B. Hydrolysis of PG and PC by Group IB sPLA(2) (PLA2G1A) was significantly lower in the extracted OS, which contains SP-B, compared with Survanta (P = 0.005), which is SP-B poor. Hydrolysis of PG and PC in nonextracted OS, which contains all SPs, was lower than both Survanta and extracted OS. When Survanta was supplemented with 1% SP-B, PG and PC hydrolysis by PLA2G1B was significantly lower (P < 0.001) than in Survanta alone. When supplemented into pure lipid vesicles and monomolecular films composed of PG and PC mixtures, SP-B also inhibited hydrolysis by both PLA2G1B and Group IIA sPLA2 (PLA2G2A). In films, PLA2G1B hydrolyzed surfactant PL monolayers at surface pressures ≤30 mN/m (P < 0.01), and SP-B lowered the surface pressure range at which hydrolysis can occur. These results suggest the hydrophobic SP, SP-B, protects alveolar surfactant PL from hydrolysis mediated by multiple sPLA(2) in both vesicles (alveolar subphase) and monomolecular films (air-liquid interface).

[Effect of acupuncture on SP-A expression in bronchoalveolar lavage fluid of asthmatic rats].

OBJECTIVE: To explore the mechanism of acupuncture for treatment of asthma. METHODS: Forty SD rats were randomly divided into 5 groups: blank control group, normal saline control group (NS control group), asthma model group, asthma model with acupuncture group (asthma acupuncture group) and asthma model with binding group (asthma binding group). The asthma acupuncture group was treated with acupuncture at "Dazhui" (GV 14), "Feishu" (BL 13) and "Fengmen" (BL 12); the asthma binding group was only binding without acupuncture and no intervention was given in the other groups. Surfactant protein-A (SP-A) expression was examined by Western-Blot. RESULTS: Airway resistance in asthma model group was significantly higher than that in blank control group and NS control group from 3 to 6 min after asthma provocation (all P<0.01). Western-Blot detection showed that SP-A expression in bronchoalveolar lavage fluid (BALF) of the rats in asthma model group was significantly lower than that in blank control group and NS control group (both P<0.05), and which in asthma acupuncture group was significantly higher than that in asthma model group (P<0.05). CONCLUSION: The mechanism of prevention and treatment of acupuncture for allergic asthma is related to regulating SP-A expression of airway in asthmatic rats.

Effect of acupuncture on SP-A expression in bronchoalveolar lavage fluid of asthmatic rats / 中国针灸

<p><b>OBJECTIVE</b>To explore the mechanism of acupuncture for treatment of asthma.</p><p><b>METHODS</b>Forty SD rats were randomly divided into 5 groups: blank control group, normal saline control group (NS control group), asthma model group, asthma model with acupuncture group (asthma acupuncture group) and asthma model with binding group (asthma binding group). The asthma acupuncture group was treated with acupuncture at "Dazhui" (GV 14), "Feishu" (BL 13) and "Fengmen" (BL 12); the asthma binding group was only binding without acupuncture and no intervention was given in the other groups. Surfactant protein-A (SP-A) expression was examined by Western-Blot.</p><p><b>RESULTS</b>Airway resistance in asthma model group was significantly higher than that in blank control group and NS control group from 3 to 6 min after asthma provocation (all P<0.01). Western-Blot detection showed that SP-A expression in bronchoalveolar lavage fluid (BALF) of the rats in asthma model group was significantly lower than that in blank control group and NS control group (both P<0.05), and which in asthma acupuncture group was significantly higher than that in asthma model group (P<0.05).</p><p><b>CONCLUSION</b>The mechanism of prevention and treatment of acupuncture for allergic asthma is related to regulating SP-A expression of airway in asthmatic rats.</p>

Effects of maternal retinoic acid administration in a congenital diaphragmatic hernia rabbit model.

Maternal retinoid administration has beneficial effects on lung development in the nitrofen rodent toxic model of congenital diaphragmatic hernia (DH). We wanted to investigate the effects in a surgical model, where the retinoid signaling pathway is not primarily disrupted by the toxic agent. We created DH in fetal rabbits at day 23 of gestation, administrated to the does all trans-retinoic acid (ATRA) or vehicle (VHC) intramuscularly for 8 consecutive days and harvested normal and operated (DH) fetuses at 31 d (n = 7 in each group). Normal lungs exposed to ATRA had increased surfactant protein mRNA levels without change in type II pneumocyte density. There was no measurable effect on lung-to-body weight ratio and airway morphometry by ATRA. In DH lungs (DH/VHC) surfactant protein mRNA levels were increased, as well as the density of type II pneumocytes. When supplemented with ATRA (DH/ATRA) these parameters returned to normal (VHC). Cell proliferation or apoptosis were not influenced by ATRA supplementation. In conclusion, maternal ATRA supplementation does not affect gross anatomic, morphologic or proliferation indices in hypoplastic lungs related to surgically induced DH in rabbit. However, ATRA lowers surfactant protein expression and normalizes type I/II pneumocyte ratio to what is observed in normal lungs.

Surfactant protein D decreases pollen-induced IgE-dependent mast cell degranulation.

Mast cells play a key role in allergy and asthma. They reside at the host-environment interface and are among the first cells to make contact with inhaled microorganisms and particulate antigens. Pulmonary surfactant proteins A and D (SP-A and SP-D) function in lung host defense by enhancing microbe phagocytosis and mediating other immune cell functions, but little is known about their effects on mast cells. We hypothesized that SP-A and/or SP-D modulate IgE-dependent mast cell functions. Pollen starch granules (PSG) extracted from Dactylis glomerata and coated with trinitrophenol (TNP) were used as a model of an inhaled organic particulate allergen. Our data revealed that SP-D inhibited by 50% the release of beta-hexosaminidase by peritoneal mast cells sensitized with IgE anti-TNP and stimulated with TNP-PSG. In contrast, SP-A had no effect. Furthermore, SP-D aggregated PSG in a dose-dependent manner, and this aggregation was mediated by SP-D's carbohydrate recognition domain. A single arm SP-D mutant (RrSP-Dser15,20) neither aggregated PSG nor inhibited degranulation, suggesting that multimerization of SP-D is required for maximal PSG aggregation and inhibition of PSG-induced mast cell degranulation. This study is the first to demonstrate that SP-D modulates IgE-mediated mast cell functions, which are important in asthma and allergic inflammation.

Surfactant protein D increases phagocytosis and aggregation of pollen-allergen starch granules.

Recent studies have shown that surfactant components, in particular the collectins surfactant protein (SP)-A and -D, modulate the phagocytosis of various pathogens by alveolar macrophages. This interaction might be important not only for the elimination of pathogens but also for the elimination of inhaled allergens and might explain anti-inflammatory effects of SP-A and SP-D in allergic airway inflammation. We investigated the effect of surfactant components on the phagocytosis of allergen-containing pollen starch granules (PSG) by alveolar macrophages. PSG were isolated from Dactylis glomerata or Phleum pratense, two common grass pollen allergens, and incubated with either rat or human alveolar macrophages in the presence of recombinant human SP-A, SP-A purified from patients suffering from alveolar proteinosis, a recombinant fragment of human SP-D, dodecameric recombinant rat SP-D, or the commercially available surfactant preparations Curosurf and Alveofact. Dodecameric rat recombinant SP-D enhanced binding and phagocytosis of the PSG by alveolar macrophages, whereas the recombinant fragment of human SP-D, SP-A, or the surfactant lipid preparations had no effect. In addition, recombinant rat SP-D bound to the surface of the PSG and induced aggregation. Binding, aggregation, and enhancement of phagocytosis by recombinant rat SP-D was completely blocked by EDTA and inhibited by d-maltose and to a lesser extent by d-galactose, indicating the involvement of the carbohydrate recognition domain of SP-D in these functions. The modulation of allergen phagocytosis by SP-D might play an important role in allergen clearance from the lung and thereby modulate the allergic inflammation of asthma.

[Sivelestat sodium hydrate was effective for ARDS in a patient suffering from chronic rheumatoid arthritis with acute exacerbation after failing to respond to high dose steroid pulse therapy].

Sivelestat sodium hydrate (ELASPOL) was effective for ARDS in a fifty-year-old female patient suffering from chronic rheumatoid arthritis with acute exacerbation, after failing to respond to high dose steroid pulse therapy. In ICU, the patient had bilateral lung opacities, especially of the upper lobes, respiratory acidosis, hypercapnea (PaCO2 89 mmHg), and poor oxygenation (P/F ratio 193). High dose steroid pulse therapy had been performed, but oxygenation was not improved, and a low level of oxygenation (P/F ratio 155) persisted. Sivelestat was started two days after finishing the steroid pulse therapy. The butterfly shadow on chest X ray and impaired oxygenation were markedly improved from the third day of sivelestat administration. Respiratory support was terminated with P/F ratio 300. Plasma concentrations of SP-A and SP-D decreased after sivelestat administration, but concentration of KL-6 was still elevated. In this case, sivelestat was effective for ARDS in the patient not responding to steroid pulse therapy, and clinical finding and plasma concentrations of SP-A and SP-D were correlated well.

Regularity of distribution of immunoreactive pulmonary surfactant protein A in rat tissues.

Existing data has shown that SP-A-like protein or mRNA is widely distributed in lamellar bodies such as tissues and mucosal surfaces. Using immunohistochemistry method with a polyclonal antibody against human SP-A, in this study we investigated distribution of immunoreactive pulmonary surfactant protein A (IR-SP-A) in a number of rat tissues. The SP-A-like immunoreactivity was found in alveolar, parenchyma, pleura of lung; myelin sheath of brain; epithelia of Bowman's capsule, glomerulus and renal tubules of kidney; epithelia of colon, stomach, duct of salivary gland, pharynx; and blood vessel wall and connective tissue of extracellular matrix. The positive signal was blocked by pre-absorbed SP-A antigen from recombinant or bronchoalveolar lavage (BAL). SP-A has long been considered as an important frontier host defense molecule which participates in immune and inflammatory regulation of lung. With every inhalation, small particles, viruses, bacteria, and antigens from environment are continuously deposited onto the vast pulmonary epithelial surface. While a proper host defense is required to protect the lung, an over-exuberant response can disrupt the appropriate balance between pro- and anti-inflammatory. Traditional Chinese medicine believes that body is an open system relevant to the external environment. The physical, chemical and biological environmental factors constantly affect the open system, and the body properly reacts to maintain homeostasis of body machinery. The Chinese traditional medicine scholars have thus hypothesized that 'Qi' (meaning air) is the communication way between the body and external environment. What is 'Qi'? The results from our study suggest that IR-SP-A is a candidate of 'Qi'. It is compatible with the sites, theoretically containing collagenous and lectin domain molecules, also compatible with the primary injury sites of some autoimmune diseases. SP-A may be as one of 'Qi' molecules mentioned in traditional Chinese medicine that trigger some of autoimmune diseases.

Foetal rat lung epithelial (FRLE) cells: partial characterisation and response to pneumotoxins.

Cultured cell lines are routinely used for in vitro toxicity screens, reducing the requirement for animal studies during the development of new pharmaceutical, agrochemical and cosmetic products. The foetal rat lung epithelial (FRLE) cell line was originally derived from alveolar type II cells (ATII) of the lung. The aims of this study were to further characterise FRLE cells and investigate their potential for screening for pneumotoxins. The cells were found to have retained some of the features of their progenitor cells, namely the expression of cytokeratin proteins, specifically cytokeratin 18, and the ability to actively accumulate the non-selective contact herbicide paraquat. However, the cells have lost the ability to synthesise surfactant protein mRNA and no longer contain multiple lamellar bodies. Toxins that damage ATII cells in vivo (cadmium chloride, cobalt chloride and paraquat) were found to induce cytotoxicity in FRLE cells, as did the non-specific pneumotoxin nitrofurantoin, and hydrogen peroxide. However, the cells were less sensitive to the effects of compounds that require metabolic activation (1-nitronaphthalene, coumarin and butylated hydroxytoluene) and the hepatotoxin bromobenzene. Thus, FRLE cells appear to be a good in vitro model for monitoring the potential toxicity to ATII cells and could be used as an initial screen for pneumotoxicity.

Effects of baicalin on the gene expression of surfactant protein A (SP-A) in lung adenocarcinoma cell line H441.

Pulmonary surfactant, a complex lipoprotein, is secreted by alveolar type II cells. It lies at the alveolar air-fluid interface and prevents alveolar collapse by reducing surface tension. The high incidence of respiratory distress syndrome (RDS) in premature infants results principally from a deficiency of pulmonary surfactant. Surfactant protein A (SP-A) is the most abundant surfactant protein and reduces surface tension at the alveolar air-liquid interface in lung cells. In this study, RT-PCR and Western blot analyses of SP-A were performed to evaluate the biological activity of baicalin, a Chinese medicine prescribed extensively for preventing miscarriage. In in vitro experiments, lung adenocarcinoma cell line H441 was cultured with baicalin in varying concentrations and for varying lengths of time. The results show that the expression of SP-A gene was positively affected by baicalin in dose-dependent and time-course manners. The maximal expression of the SP-A gene, 1.7-fold greater than control, is induced at 150 nM of baicalin treated for 48 h.

Hericium erinaceum (yamabushitake) extract-induced acute respiratory distress syndrome monitored by serum surfactant proteins.

This is the first report suggesting a causal relationship between acute respiratory distress syndrome and Hericium erinaceum extract, which is commercialized as a diet food. A 63-year-old man was admitted to our hospital for intensive care of severe acute respiratory failure with diffuse infiltration in both lungs. Bronchoalveolar lavage fluid revealed a high percentage of lymphocytes. Lymphocyte stimulation test showed a strong reactivity against extract formulation of Hericium erinaceum (Yamabushitake), which he had taken four months before onset. He recovered with successful steroid pulse therapy under mechanical ventilation. Concentrations of surfactant protein (SP)-A and SP-D in sera reflected the clinical features.

Intranasal delivery of a truncated recombinant human SP-D is effective at down-regulating allergic hypersensitivity in mice sensitized to allergens of Aspergillus fumigatus.

C57BL/6 mice were sensitized to Aspergillus fumigatus 1-week culture filtrate, which is rich in the non-glycosylated allergen Asp f1, a major allergen in allergic bronchopulmonary aspergillosis (ABPA). A comparison of the effect of treatment of allergen challenged mice by intranasal administration of a 60-kDa truncated recombinant form of human SP-D (rfhSP-D) or recombinant full length SP-A (rhSP-A) was undertaken. Treatment with rfhSP-D produced significant reduction in IgE, IgG1 and peripheral blood eosinophilia and treatment with rfhSP-D, but not rhSP-A resulted in a significant reduction in airway hyperresponsiveness as measured by whole body plethysmography. Lung histology revealed less peribronchial lymphocytic infiltration in mice treated with rfhSP-D. Intracellular cytokine staining of spleen homogenates showed increases in IL-12 and IFN-gamma and decrease in IL-4. The level of endogenous mouse SP-D was elevated sixfold in the lungs of sensitized mice and was not affected by treatment with rfhSP-D. Taken with our previous studies, with a BALB/c mouse model of ABPA using a 3-week A. fumigatus culture filtrate, the present results show that rfhSP-D can suppress the development of allergic symptoms in sensitized mice independent of genetic background and using a different preparation of A. fumigatus allergens.

Pulmonary surfactant protein A up-regulates activity of the mannose receptor, a pattern recognition receptor expressed on human macrophages.

Inhaled particulates and microbes are continually cleared by a complex array of lung innate immune determinants, including alveolar macrophages (AMs). AMs are unique cells with an enhanced capacity for phagocytosis that is due, in part, to increased activity of the macrophage mannose receptor (MR), a pattern recognition receptor for various microorganisms. The local factors that "shape" AM function are not well understood. Surfactant protein A (SP-A), a major component of lung surfactant, participates in the innate immune response and can enhance phagocytosis. Here we show that SP-A selectively enhances MR expression on human monocyte-derived macrophages, a process involving both the attached sugars and collagen-like domain of SP-A. The newly expressed MR is functional. Monocyte-derived macrophages on an SP-A substrate demonstrated enhanced pinocytosis of mannose BSA and phagocytosis of Mycobacterium tuberculosis lipoarabinomannan-coated microspheres. The newly expressed MR likely came from intracellular pools because: 1) up-regulation of the MR by SP-A occurred by 1 h, 2) new protein synthesis was not necessary for MR up-regulation, and 3) pinocytosis of mannose BSA via MR recycling was increased. AMs from SP-A(-/-) mice have reduced MR expression relative to SP-A(+/+). SP-A up-regulation of MR activity provides a mechanism for enhanced phagocytosis of microbes by AMs, thereby enhancing lung host defense against extracellular pathogens or, paradoxically, enhancing the potential for intracellular pathogens to enter their intracellular niche. SP-A contributes to the alternative activation state of the AM in the lung.

Surfactant protein A inhibits peptidoglycan-induced tumor necrosis factor-alpha secretion in U937 cells and alveolar macrophages by direct interaction with toll-like receptor 2.

Pulmonary surfactant protein A (SP-A) plays an important role in modulation of the innate immune system of the lung. Peptidoglycan (PGN), a cell wall component of Gram-positive bacteria, is known to elicit excessive proinflammatory cytokine production from immune cells. In this study we investigated whether SP-A interacts with PGN and alters PGN-elicited cellular responses. Binding studies demonstrate that PGN is not a ligand for SP-A. However, SP-A significantly reduced PGN-elicited tumor necrosis factor alpha (TNF-alpha) secretion by U937 cells and rat alveolar macrophages. The inhibitory effect on TNF-alpha secretion was dependent upon SP-A concentrations in physiological range. Coincubation of SP-A and PGN with human embryonic kidney 293 cells that had been transiently transfected with the cDNA of Toll-like receptor 2 (TLR2), a cell signaling receptor for PGN, significantly attenuated PGN-induced nuclear factor-kappaB activity. SP-A directly bound to a soluble form of the recombinant extracellular TLR2 domain (sTLR2). Coincubation of sTLR2 with SP-A significantly reduced the binding of sTLR2 to PGN. These results indicate that the direct interaction of SP-A with TLR2 alters PGN-induced cell signaling. We propose that SP-A modulates inflammatory responses against the bacterial components by interactions with pattern-recognition receptors.

Surfactant protein A regulates complement activation.

Complement proteins aid in the recognition and clearance of pathogens from the body. C1, the first protein of the classical pathway of complement activation, is a calcium-dependent complex of one molecule of C1q and two molecules each of C1r and C1s, the serine proteases that cleave complement proteins. Upon binding of C1q to Ag-bound IgG or IgM, C1r and C1s are sequentially activated and initiate the classical pathway of complement. Because of structural and functional similarities between C1q and members of the collectin family of proteins, including pulmonary surfactant protein A (SP-A), we hypothesized that SP-A may interact with and regulate proteins of the complement system. Previously, SP-A was shown to bind to C1q, but the functional significance of this interaction has not been investigated. Binding studies confirmed that SP-A binds directly to C1q, but only weakly to intact C1. Further investigation revealed that the binding of SP-A to C1q prevents the association of C1q with C1r and C1s, and therefore the formation of the active C1 complex required for classical pathway activation. This finding suggests that SP-A may share a common binding site for C1r and C1s or Clq. SP-A also prevented C1q and C1 from binding to immune complexes. Furthermore, SP-A blocked the ability of C1q to restore classical pathway activity to C1q-depleted serum. SP-A may down-regulate complement activity through its association with C1q. We hypothesize that SP-A may serve a protective role in the lung by preventing C1q-mediated complement activation and inflammation along the delicate alveolar epithelium.