Surfactant protein A inhibits lipopolysaccharide-induced in vivo production of interleukin-10 by mononuclear phagocytes during lung inflammation

We previously demonstrated that resident alveolar macrophages from naive mice do not synthesize interleukin (IL)-10, whereas mononuclear phagocytes (MP) recruited during the lung inflammatory process are transiently competent for IL-10 production when exposed to lipopolysaccharide (LPS) in vitro. As surfactant protein A (SP-A), a member of the collectin family, inhibits LPS-induced in vitro IL-10 formation by bone marrow-derived macrophages, we studied its effect on MP under in vivo inflammatory conditions. When mice with LPS-induced inflamed lungs were given a second intranasal LPS administration, IL-10 concentration recovered in the bronchoalveolar lavage fluids varied as a function of the time interval between the two LPS doses. Thus, IL-10 concentration increased with the number of MP up to Day 3, and then decreased to undetectable values within 24 h, despite a continued increase in the number of MP. Analysis of IL-10 mRNA from purified MP indicated that gene expression correlated with the IL-10 level in the bronchoalveolar lavage fluid. In contrast to IL-10 production, SP-A concentrations during LPS-induced inflammation decreased with a nadir at Day 3, and then increased significantly within 24 h. Furthermore, intranasal administration of exogenous SP-A to mice with LPS-induced inflamed lungs led to a repression of the IL-10 production. In summary, this study demonstrates for the first time an in vivo inhibitory role of SP-A on the anti-inflammatory activity of MP, through inhibition of IL-10 production.     

IL-12 inhibits endotoxin-induced inflammation in the eye

Interleukin-12 (IL-12) is a heterodimeric cytokine that induces interferon (IFN)-γ production and an increased generation of Th1 cells. Both IL-12 and IL-12 antagonists are being studied for the treatment of allergic reactions, autoimmune disease and malignancy. The goal of the present experiments was to examine the importance of IL-12 in endotoxin-induced ocular inflammation. The number of inflammatory cells infiltrating eyes with endotoxin-induced uveitis (EIU) was significantly increased in animals treated with intraperitoneal anti-IL-12 antibody when compared to control animals, but there was no difference in infiltrating inflammatory cells in the eyes of animals treated with IL-12 when compared to controls. In contrast, intraocular injection of IL-12 significantly inhibited the development of endotoxin-induced intraocular inflammation. The infiltrating inflammatory cells were reduced in the eyes of animals receiving intraocular IL-12 when compared to controls. Cytokine analysis of the aqueous humor obtained from eyes with EIU showed increased levels of IFN-γ and decreased levels of IL-6 in eyes receiving intraocular IL-12. These data show that IL-12 has an inhibitory effect on endotoxin-induced inflammation in the eye and suggest that IL-12 can have an immunoregulatory function in some forms of inflammatory disease.     

Surfactant protein B and C analogues

Mammalian lung surfactant is a mixture of phospholipids and four surfactant-associated proteins (SP-A, SP-B, SP-C, and SP-D). Its major function is to reduce surface tension at the air-water interface in the terminal airways by the formation of a surface-active film highly enriched in dipalmitoyl phosphatidylcholine (DPPC), thereby preventing alveolar collapse during expiration. SP-A and SP-D are large hydrophilic proteins, which play an important role in host defense, whereas the small hydrophobic peptides SP-B and SP-C interact with DPPC to generate and maintain a surface-active film. Surfactant replacement therapy with bovine and porcine lung surfactant extracts, which contain only polar lipids and SP-B and SP-C, has revolutionized the clinical management of premature infants with respiratory distress syndrome. Newer surfactant preparations will probably be based on SP-B and SP-C, produced by recombinant technology or peptide synthesis, and reconstituted with selected synthetic lipids. The development of peptide analogues of SP-B and SP-C offers the possibility to study their molecular mechanism of action and will allow the design of surfactant formulations for specific pulmonary diseases and better quality control. This review describes the hydrophobic peptide analogues developed thus far and their potential for use in a new generation of synthetic surfactant preparations.     

Surfactant protein D--endogenous regulator of inflammation and immune defense

Surfactant protein D (SP-D) is a component of lung surfactant, the representative of collagen-like lectines (collectines) family. It plays one of the significant roles in innate antibody-independent immune response. Structural features of SP-D, the possibility of its influence on pathogenetic componentes of inflammatory reaction, expression of inflammatory mediators and attainment of necessary balance between control of inflammatory reaction intensity and formation of the proper response to pathogens allow to consider SP-D as a part of innate immune system of the lung and endogenous regulator of inflammatory reactions in the organism.     

Differential anti-inflammatory and anti-oxidative effects of dexamethasone and N-acetylcysteine in endotoxin-induced lung inflammation

Inhalation of bacterial endotoxin induces an acute inflammation in the lower respiratory tract. In this study, the anti-inflammatory effects of the anti-oxidant N-acetylcysteine (NAC) and the glucocorticoid dexamethasone were investigated in mice exposed to aerosolized endotoxin (lipopolysaccharide (LPS)). Powerful reduction of neutrophils in bronchoalveolar lavage fluid (BALF) was obtained by a single i.p. injection of dexamethasone (10 mg/kg), whereas treatment with NAC only resulted in reduction of neutrophils when administered at a high dose (500 mg/kg). Measurement of cytokine and chemokine expression in lung tissue revealed a significant decrease of tumour necrosis factor-alpha, IL-1alpha, IL-1beta IL-6, IL- 12p40, and MIP-1alpha mRNA when mice where treated with dexamethasone but not when treated with NAC. Analysis of oxidative burst demonstrated a remarkable reduction of oxygen radicals in BALF neutrophils after treatment with dexamethasone, whereas the effect of NAC was not significantly different from that in untreated animals. In conclusion, dexamethasone exerted both anti-inflammatory and anti-oxidative effects in acute airway inflammation, probably by blocking early events in the inflammatory cascade. In contrast, treatment with NAC resulted in a weak reduction of the inflammatory response but no inhibition of proinflammatory cytokines or reduction of oxidative burst in neutrophils. These results demonstrate dramatic differences in efficiency and also indicate that the two drugs have different actions. Combined treatment with NAC and dexamethasone revealed an additive action but no synergy was observed.     

Resident alveolar macrophages are replaced by recruited monocytes in response to endotoxin-induced lung inflammation

In the acute respiratory distress syndrome, recruitment of peripheral blood monocytes results in expansion of the total pool of resident alveolar macrophages. The fate of resident macrophages, or whether recruited monocytes are selectively eliminated from the alveolar airspace or differentiate into resident alveolar macrophages during the resolving phase of inflammation, has not been determined. Here, we analyzed the kinetics of resident and recruited macrophage turnover within the alveolar airspace of untreated and LPS-challenged mice. Using bone marrow chimeric CD45.2 mice that were generated by lethal irradiation of CD45.2 alloantigen-expressing recipient mice and bone marrow transplantation from CD45.1 alloantigen-expressing donor mice, we employed a flow cytometric approach to distinguish recipient from donor-type macrophages in bronchoalveolar lavage fluids. Our data show that resident alveolar macrophages of untreated chimeric CD45.2 mice are very slowly replaced by constitutively immigrating CD45.1 positive monocytes, resulting in a replacement rate of approximately 40% by 1 yr. In contrast, more than 85% of the resident CD45.2 positive alveolar and lung homogenate macrophages were exchanged by donor CD45.1-expressing macrophages within 2 mo after treatment with Escherichia coli endotoxin (LPS). Importantly, fluorescence-activated cell sorter analysis of increased annexin V binding to both recipient and donor-type macrophages revealed increased apoptotic events to underlie this endotoxin-driven inflammatory macrophage turnover. Collectively, the data show that under baseline conditions the alveolar macrophage turnover exhibits very slow kinetics, whereas acute lung inflammation in response to treatment with LPS triggers a brisk acceleration of recruitment of monocytes that replace the resident alveolar macrophage population.     

Surfactant protein D inhibits early airway response in Aspergillus fumigatus-sensitized mice

BACKGROUND: The surfactant protein SP-D has been reported to reduce bronchial hyper-responsiveness, blood eosinophilia, and T-helper type 2 cytokines in models of allergic asthma. However, little is known about the functional effect of SP-D on the early airway response upon allergen inhalation, which is an important feature of this disease. OBJECTIVE: We investigated whether SP-D is able to reduce the immediate allergen-induced mediator release and the early bronchial obstruction in addition to its effects on airway inflammation and bronchial hyperresponsiveness in an Aspergillus fumigatus mouse asthma model. METHODS: A. fumigatus-sensitized mice were treated with a recombinant fragment of human SP-D or placebo. Lung functions were measured in orotracheally intubated, spontaneously breathing animals using body plethysmography. In addition, passively sensitized precision-cut lung slices (PCLS) were used to determine the effect of SP-D on allergen-induced histamine release. RESULTS: SP-D inhibited the allergen-induced early airway response and reduced airway hyperresponsiveness compared with placebo. Eosinophilia in bronchoalveolar lavage and lung tissue was reduced after SP-D treatment, possibly by reducing eotaxin levels in the lung. Furthermore, SP-D treatment reduced the allergen-induced histamine release from PCLS. CONCLUSION: These data suggest that SP-D not only reduces allergen-induced eosinophilic inflammation and airway hyperresponsiveness but also provides protection against early airway obstruction by inhibition of early mediator release.     

肺泡表面活性蛋白A调控Tfh亚群分化缓解哮喘气道炎症

目的:探究肺泡表面活性蛋白A(surfactant protein A,SP-A)能否通过调控滤泡辅助性T细胞(follicular helper T cell,Tfh)的分化参与调节哮喘病理过程。方法:6～8周的雌性野生型(wild-type,WT)及SP-A基因敲除( Sp- a-/-)型C...     

Kinetics of endotoxin-induced inflammation in ovine mammary gland

The inflammatory response to stimulation with endotoxin of lactating and nonlactating mammary glands of sheep was examined. Similar numbers of neutrophils and mononuclear cells were recovered from nonlactating glands sampled every 2 h for 8 h and in glands sampled once at 8 h. Thus the inflammatory response was initiated by 2 h and repeated sampling did not modify the time course of the response. In contrast, in lactating ewes, fewer cells were recovered from glands sampled every 2 h than from glands sampled once at 8 h. Fewer neutrophils were also recovered when glands were serially sampled from 4 h to 8 h. Thus, removal of milk and inflammatory exudate modified the time course of the leukocyte influx into lactating glands. Significant accumulation of neutrophils occurred by 2 h in dose-response experiments in nonlactating glands. Peak accumulation of neutrophils occurred between 2 and 6 h, and a marked decline occurred after 8 h. In lactating glands, a slower onset and longer duration of neutrophil accumulation occurred. Twenty- to 30-fold more neutrophils were recovered by 8 h in lactating than nonlactating glands. This difference was not due to a lower threshold of sensitivity to endotoxin. Infusion of milk into nonlactating glands did not modify the intensity or time course of the inflammatory response to endotoxin. Thus, the physiological state of resident cells within the lactating gland, rather than the interaction of inflammatory exudate with milk, can account for the different reaction pattern in lactating glands. Inflammation in the nonlactating gland closely resembles inflammatory rsponses in skin and provides a convenient model for investigating the initiation and regulation of inflammatory processes.     

Dose-dependent activation of lymphocytes in endotoxin-induced airway inflammation

Recruitment of neutrophils to lung tissue and airspaces is a hallmark of inflammatory events following inhalation of endotoxins. We studied the role of different lymphocyte subsets in this inflammation, which is assumed to primarily involve the innate immune system. Inhalation of aerosolized Escherichia coli lipopolysaccharide (LPS) in mice induced a dose-dependent increase in neutrophils in bronchoalveolar lavage fluid, reaching a maximum after 12 h at a low dose and after 24 h at a high dose. Profiles of gene expression in lung tissue indicated an early (2 h) and transient onset of proinflammatory cytokines and chemokines by a low dose of LPS, while a high dose caused more delayed and sustained (6 to 12 h) activation. Gamma interferon, interleukin-2 (IL-2), RANTES, and the α chain of the IL-2 receptor were not expressed at a low dose, whereas a high dose of LPS induced a strong expression of these genes, indicating a dose-dependent activation of T cells. A similar pattern was observed for IL-17, supporting a contribution of T cells to the neutrophilic inflammation only at high-dose exposure to LPS. The involvement of lymphocytes in the inflammatory response was further studied using mice with functional deficiencies in defined lymphocyte subsets. Both γδ T-cell- and B-cell-deficient mice displayed a response similar to that of the corresponding wild-type strains. Selective depletion of NK cells by in vivo administration of the pk136 antibody did not significantly affect the recruitment of neutrophils into airspaces. Thus, neither NK cells, B cells, nor γδ T cells appeared to participate in the host response, suggesting that among the lymphocyte subsets, αβ T cells are exclusively involved in endotoxin-induced airway inflammation.     

内毒素肺损伤肺淋巴变化的实验研究

本实验应用清醒绵羊内毒素肺损伤模型对内毒素致伤后肺淋巴液的变化作了研究。内毒素致伤后,肺动脉压(Ppa)、肺微血管压(PMV)、肺淋巴流量(QL),淋巴白蛋白/血浆白蛋白比值(LA/PA)、淋巴胶体渗透压(π_(i))和肺微血管滤过系数(Kf)均明显增加。压力和通透性变化对QL的影响之比,在Ⅰ期(0～2h)和Ⅱ期(2～6h)分别为1∶0.53和1∶2.31。提示了PMV增高为Ⅰ期肺水肿形成的主要因素,通透性增加为Ⅱ期的主要因素。     

Surfactant protein a inhibits lipopolysaccharide-induced immune cell activation by preventing the interaction of lipopolysaccharide with lipopolysaccharide-binding protein

Pulmonary surfactant protein (SP)-A, an innate immune molecule, modifies lipopolysaccharide (LPS)-induced cell responses. Because SP-A avidly binds to the deep rough (Re) mutant of LPS, we first investigated the functional consequences of this interaction and found that preincubation of Re-LPS with SP-A significantly and in a dose-dependent manner decreased the sensitivity of rat alveolar macrophages and human mononuclear cells to Re-LPS-induced activation at limited amounts of LPS-binding protein (LBP). At high LBP concentrations, the SP-A-mediated cellular inhibition of Re-LPS-induced activation was abrogated. Because LBP-catalyzed binding of LPS to CD14 is essential for low-dose LPS-induced signaling, we then hypothesized that SP-A inhibits Re-LPS-induced immune cell activation via inhibiting the binding of Re-LPS to LBP. Binding competition experiments employing a surface plasmon resonance technique showed that Re-LPS preincubated with SP-A bound to LBP to a significantly lesser extent than Re-LPS alone. For enhanced cellular association of [(3)H]LPS/SP-A complexes to occur, the expression of membrane-bound CD14 by human embryonic kidney cells 293 was not essential. Therefore, the ability of SP-A to inhibit immune cell activation by Re-LPS may be due to its ability to block the binding of Re-LPS to LBP and prevent the initiation of the LBP/CD14 pathway for inflammatory reactions in the lung.     

Surfactant protein A detection in large cell carcinoma of the lung.

Large cell carcinomas of the lung are undifferentiated malignant epithelial tumors that lack cytologic features of small cell carcinoma, glandular cell carcinoma, or squamous cell differentiation. Lung surfactant protein A (SP-A) is produced by alveolar type II cells and Clara cells. Most bronchioloalveolar carcinomas of the lung react positively for SP-A. Positive SP-A staining of large cell carcinoma of the lung could indicate that at least part of these tumors have the same cellular origin or differentiation as bronchioloalveolar carcinoma. The authors determined the SP-A staining of 63 large cell carcinomas of the lung by IHC. In 20 of the 63 (32%), the tumors stained positive for SP-A. This may imply that about one third of large cell carcinomas of the lung have a similar cellular origin or differentiation as bronchioloalveolar carcinoma. The significance of this finding for prognosis and new forms of treatment remains to be determined.     

Surfactant protein A decreases lung injury and mortality after murine marrow transplantation

Surfactant protein A (SP-A), a collectin associated with surfactant lipids, can have immune modulatory effects. We hypothesized that exogenous and basal endogenous SP-A can function to suppress donor T-cell-dependent inflammation that occurs during the generation of idiopathic pneumonia syndrome after bone marrow transplantation (BMT). Wild-type and SP-A-deficient mice were conditioned with cyclophosphamide and lethal irradiation and then given allogeneic donor bone marrow plus inflammation-inducing spleen T cells. On Day 7 after BMT, bronchoalveolar lavage fluids from SP-A-deficient mice contained increased numbers of inflammatory cells and higher levels of proinflammatory mediators tumor necrosis factor-alpha, interferon-gamma, and nitric oxide than wild-type mice. Exaggerated inflammation in SP-A-deficient mice was associated with decreased dynamic lung compliance and increased donor T-cell-dependent mortality (P = 0.0007, n = 10). Nitrative stress in alveolar macrophages from SP-A(-/-)-conditioned BMT recipients was higher than for SP-A(+/+) mice. Similarly, mice treated with transtracheal human SP-A (50 micro g), instilled on Day 4 after BMT during a time of in vivo donor T cell activation, exhibited decreased inflammation and improved early survival compared with buffer-instilled mice. We concluded that basal endogenous SP-A and enhanced alveolar SP-A level modulate donor T-cell-dependent immune responses and prolong survival after allogeneic BMT.