Human and murine paraoxonase 1 are host modulators of Pseudomonas aeruginosa quorum-sensing

The pathogenic bacterium Pseudomonas aeruginosa uses acyl-HSL quorum-sensing signals to regulate genes controlling virulence and biofilm formation. We found that paraoxonase 1 (PON1), a mammalian lactonase with an unknown natural substrate, hydrolyzed the P. aeruginosa acyl-HSL 3OC12-HSL. In in vitro assays, mouse serum-PON1 was required and sufficient to degrade 3OC12-HSL. Furthermore, PON2 and PON3 also degraded 3OC12-HSL effectively. Serum-PON1 prevented P. aeruginosa quorum-sensing and biofilm formation in vitro by inactivating the quorum-sensing signal. Although 3OC12-HSL production by P. aeruginosa was important for virulence in a mouse sepsis model, Pon1-knock-out mice were paradoxically protected. These mice showed increased levels of PON2 and PON3 mRNA in epithelial tissues suggesting a possible compensatory mechanism. Thus, paraoxonase interruption of bacterial communication represents a novel mechanism to modulate quorum-sensing by bacteria. The consequences for host immunity are yet to be determined.     

甘蓝型油菜下胚轴原生质体培养的研究

从甘蓝型油菜下胚轴分离纯化原生质体。种子萌发时进行光照处理对原生质体产率影响不大,但可提高其活力。对液体浅层、固体平板和“琼脂岛”3种培养方法进行比较,结果“琼脂岛”法效果最好,不但细胞分裂速度快,而且克隆形成频率高。再生的愈伤组织转到分化培养基上后迅速分化出芽。诱导生根后进行移栽,生长状况良好。     

DNA vaccines against chronic lung infections by Pseudomonas aeruginosa

Vaccines containing outer membrane protein F (OprF) of Pseudomonas aeruginosa are effective in reducing lesion severity in a mouse pulmonary chronic infection model. One OprF-based vaccine, called F/I, contains carboxy oprF sequences fused to oprI in an expression vector. When delivered three times biolistically by gene gun, the F/I vaccine induces protection that is antibody-mediated in outbred mice. To demonstrate the role of F/I-induced antibody-mediated immunity, B-cell-deficient [B(-)] and B-cell-intact [B(+)] mice were immunized with F/I, challenged with Pseudomonas, and examined for lesion severity. As expected, F/I-immunized B(+) mice had fewer and less severe lesions than vector-immunized B(+) mice. However, surprisingly, F/I- and vector-immunized B(-) mice were equally protected to levels similar to F/I-immunized B(+) mice. Examination of immune cell populations and cytokine levels indicated a relative increase in the quantity of CD3+ T-lymphocytes in vector- or F/I-immunized and challenged B(-) mice compared to B(+) mice. These data indicate the protective role played by cell-mediated immunity in B(-) mice, which supports our hypothesis that cell-mediated immunity can play an important role in protection against P. aeruginosa.     

Interaction between granulocytes and antibodies in the enhancement of lung defenses against Staphylococcus aureus after intranasal immunization of mice with live-attenuated bacteria

Abstract Immunization with live-attenuated Staphylococcus aureus induced measurable levels of specific IgG and IgA in the lungs, but the pulmonary clearance of S. aureus in immunized mice did not differ from that of control mice. Aerosol exposure of mice to Pseudomonas aeruginosa induced a significant recruitment of polymorphonuclear leukocytes (PMNL) to the lungs in both immunized and control mice, whereas S. aureus challenge did not. However, challenge with a mixture of P. aeruginosa-S. aureus or exposure to an aerosol of Escherichia coli lipopolysaccharide (LPS) before S. aureus challenge induced PMNL migration and a significant enhancement of pulmonary clearance of S. aureus in immunized mice. The presence of both antibodies and PMNL was required for enhancement of S. aureus pulmonary clearance.     

Pseudomonas M162 confers protection against rainbow trout fry syndrome by stimulating immunity

Aims: To evaluate the antagonistic effect of Pseudomonas M162 against Flavobacterium psychrophilum. Methods and Results: The antagonistic activity of M162 was tested in vivo and in vitro, and its mode of action examined by siderophore production and immunological responses of rainbow trout (Oncorhynchus mykiss) fry. Pseudomonas M162 inhibited the growth of Fl. psychrophilum in vitro and increased the resistance of the fish against the pathogen, resulting in a relative per cent survival (RPS) of 39·2%. However, the siderophores produced by M162 did not have an inhibitory effect on Fl. psychrophilum. In fish fed with M162, the probiotic colonized the gastrointestinal tract and stimulated peripheral blood leucocyte counts, serum lysozyme activity and total serum immunoglobulin levels after 3 weeks from the start of feeding. Conclusions: This study showed the potential of Pseudomonas M162 as a probiotic by reducing the mortalities that occurred during an experimental Fl. psychrophilum infection, resulting mainly through the immunostimulatory effects of the bacterium. Significance and Impact of the Study: Rainbow trout fry syndrome (RTFS) causes high mortalities during the early life stages of the fish’s life cycle, partly because their adaptive immunity has not yet fully developed. Thus, immunomodulation by probiotics could be an effective prophylactic method against RTFS.     

The DAF-2 insulin-like signaling pathway independently regulates aging and immunity in C. elegans

The Caenorhabditis elegans DAF-2 insulin-like signaling pathway, which regulates lifespan and stress resistance, has also been implicated in resistance to bacterial pathogens. Loss-of-function daf-2 and age-1 mutants have increased lifespans and are resistant to a variety of bacterial pathogens. This raises the possibility that the increased longevity and the pathogen resistance of insulin-like signaling pathway mutants are reflections of the same underlying mechanism. Here we report that regulation of lifespan and resistance to the bacterial pathogen Pseudomonas aeruginosa is mediated by both shared and genetically distinguishable mechanisms. We find that loss of germline proliferation enhances pathogen resistance and this effect requires daf-16, similar to the regulation of lifespan. In contrast, the regulation of pathogen resistance and lifespan is decoupled within the DAF-2 pathway. Long-lived mutants of genes downstream of daf-2, such as pdk-1 and sgk-1, show wildtype resistance to pathogens. However, mutants of akt-1 and akt-2, which we find to individually have modest effects on lifespan, show enhanced resistance to pathogens. We also demonstrate that pathogen resistance of daf-2, akt-1, and akt-2 mutants is associated with restricted bacterial colonization, and that daf-2 mutants are better able to clear an infection after challenge with P. aeruginosa. Moreover, we find that pathogen resistance among insulin-like signaling mutants is associated with increased expression of immunity genes during infection. Other processes that affect organismal longevity, including Jun kinase signaling and caloric restriction, do not affect resistance to bacterial pathogens, further establishing that aging and innate immunity are regulated by genetically distinct mechanisms.     

病原菌保守性特征分子及其介导的植物抗病性

每种病原菌都有一些保守的特征性分子,也称病原菌相关分子模式(PAMPs)。植物细胞表面的模式识别受体PRRs通过识别病原菌的PAMPs而激发免疫反应(PTI)。目前,已发现多种PRRs/PAMPs的识别模式,如拟南芥FLS2识别细菌鞭毛蛋白、拟南芥EFR识别细菌延长因子Tu(EF-Tu)、水稻CEBiP/CERK1识别真菌几丁质、水稻抗病蛋白XA21识别白叶枯病菌的硫化蛋白Ax21等。这些识别模式都能激发植物的基础免疫反应以抵抗病原菌的侵染。但是病原菌为了成功侵染寄主植物,也进化出一些致病机制,例如向植物细胞中注入毒性效应蛋白阻断PTI途径,或者产生一种\"自我伪装\"机制以逃避PRRs的识别。因此,研究者们根据PAMPs的结构特性对PRRs重新改造,以期使植物获得持久、广谱和高效的抗性。综述目前已知的PAMPs分子类型、PRRs/PAMPs的识别机制及改造后的新型PRRs,并分析PTI研究中存在的问题及其发展前景。     

Specific and non-specific mouse protection induced by different chemotypes of the Pseudomonas aeruginosa lipopolysaccharides

Abstract Lipopolysaccharides (LPS) of Pseudomonas aeruginosa were studied by the mouse active, cross-protection test. The primary structure of O-specific polysaccharides (O-repeating units) of different chemotypes was determined and their cross-protective activity demonstrated. Low doses of LPS (0.1–1 μg) stimulated chemotype-specific protection against P. aeruginosa in mice. This immunity was associated with the primary structure of the LPS and it lasted for 14 days after the first or second immunization. High doses of LPS (10–100 μg) induced cross-protection against P. aeruginosa in mice. The cross-protective capacity was caused evidently by the secondary structure or conformation of LPS molecule, i.e. by the common conformational protective determinant. This cross-protection lasted for only 5 days after the first or second immunization.     

Saccharides of seven Pseudomonas aeruginosa immunotypes

Abstract The structures of O-specific polysaccharides obtained by mild acid degredation of lipopolysaccharides (LPS) from seven Pseudomonas aeruginosa Fisher's immunotypes have been studied. The polysaccharides consist mainly of monoamino and diamino sugars, frequently also carrying acidic functions. Some of the sugars were detected in nature for the O-specific polysaccharides of the immunotypes 2, 3, 4, 5 and 6 are identical to those of the polysaccharides of the 011; 0(2a)2c; 01; 010a, 10b and 07a, 7d Lányi-Bergan serological subgroups respectively, whereas no analogues have been found for the immunotypes 1 and 7. Some cross-reactions between the LPS of different immunotypes were observed in passive haemagglutination tests; the results of inhibition of passive haemagglutination and agar gel immunoprecipitation point, however, to a specificity of the LPS. Many of the LPS of the seven Pseudomonas aeruginosa immunotypes manifest rather a high cross-protective activity in active immunization tests in mice. The nature of the cross-protective activity of the LPS is discussed.