Catalase immunization from Pseudomonas aeruginosa enhances bacterial clearance in the rat lung

Evaluation of Pseudomonas aeruginosa pathogenesis and therapeutics in military-relevant animal infection models

Modern combat-related injuries are often associated with acute polytrauma. As a consequence of severe combat-related injuries, a dysregulated immune response results in serious infectious complications. The gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that often causes life-threatening bloodstream, lung, bone, urinary tract, and wound infections following combat-related injuries. The rise in the number of multidrug-resistant P. aeruginosa strains has elevated its importance to civilian clinicians and military medicine. Development of novel therapeutics and treatment options for P. aeruginosa infections is urgently needed. During the process of drug discovery and therapeutic testing, in vivo testing in animal models is a critical step in the bench-to-bedside approach, and required for Food and Drug Administration approval. Here, we review current and past literature with a focus on combat injury-relevant animal models often used to understand infection development, the interplay between P. aeruginosa and the host, and evaluation of novel treatments. Specifically, this review focuses on the following animal infection models: wound, burn, bone, lung, urinary tract, foreign body, and sepsis.

Hematological Picture of Rabbits Immunized with Pseudomonas aeruginosa

The current study was established to find out the role of immunization of Pseudomonas aeruginosa-whole sonicated antigen in adult white fur domestic rabbits. To achieve this goal, fifteen rabbits were allocated into 3 groups, the first group was immunized with P. aeruginosa–whole sonicated antigen and challenged with viable pathogenic P. aeruginosa; the second group (control negative) was treated with phosphate buffer saline and the third group was injected with viable pathogenic P. aeruginosa (control positive). The results demonstrated increasing levels of the measured parameters blood picture (total WBCs, lymphocytes, and granulocytes, RBCs and hemoglobin concentrations) in the first group compared with control negative group (T test was used). In contrast, a sharp fall was noted in total thrombocytes (platelets) count in the first group compared with control negative group. It can be concluded that immunization with P. aeruginosa– whole sonicated antigen may consider as a potent reproducible effective immunogen model for experimental immunological studies in rabbits.

Understanding Pseudomonas aeruginosa-Host Interactions: The Ongoing Quest for an Efficacious Vaccine

Pseudomonas aeruginosa is a leading cause of chronic respiratory infections in people with cystic fibrosis (CF), bronchiectasis or chronic obstructive pulmonary disease (COPD), and acute infections in immunocompromised individuals. The adaptability of this opportunistic pathogen has hampered the development of antimicrobial therapies, and consequently, it remains a major threat to public health. Due to its antimicrobial resistance, vaccines represent an alternative strategy to tackle the pathogen, yet despite over 50 years of research on anti-Pseudomonas vaccines, no vaccine has been licensed. Nevertheless, there have been many advances in this field, including a better understanding of the host immune response and the biology of P. aeruginosa. Multiple antigens and adjuvants have been investigated with varying results. Although the most effective protective response remains to be established, it is clear that a polarised Th2 response is sub-optimal, and a mixed Th1/Th2 or Th1/Th17 response appears beneficial. This comprehensive review collates the current understanding of the complexities of P. aeruginosa-host interactions and its implication in vaccine design, with a view to understanding the current state of Pseudomonal vaccine development and the direction of future efforts. It highlights the importance of the incorporation of appropriate adjuvants to the protective antigen to yield optimal protection.

Cystic Fibrosis and Pseudomonas aeruginosa: the Host-Microbe Interface

In human pathophysiology, the clash between microbial infection and host immunity contributes to multiple diseases. Cystic fibrosis (CF) is a classical example of this phenomenon, wherein a dysfunctional, hyperinflammatory immune response combined with chronic pulmonary infections wreak havoc upon the airway, leading to a disease course of substantial morbidity and shortened life span. Pseudomonas aeruginosa is an opportunistic pathogen that commonly infects the CF lung, promoting an accelerated decline of pulmonary function. Importantly, P. aeruginosa exhibits significant resistance to innate immune effectors and to antibiotics, in part, by expressing specific virulence factors (e.g., antioxidants and exopolysaccharides) and by acquiring adaptive mutations during chronic infection. In an effort to review our current understanding of the host-pathogen interface driving CF pulmonary disease, we discuss (i) the progression of disease within the primitive CF lung, specifically focusing on the role of host versus bacterial factors; (ii) critical, neutrophil-derived innate immune effectors that are implicated in CF pulmonary disease, including reactive oxygen species (ROS) and antimicrobial peptides (e.g., LL-37); (iii) P. aeruginosa virulence factors and adaptive mutations that enable evasion of the host response; and (iv) ongoing work examining the distribution and colocalization of host and bacterial factors within distinct anatomical niches of the CF lung.

Identification of novel Haemophilus parasuis serovar 5 vaccine candidates using an immunoproteomic approach

Haemophilus parasuis is the aetiological agent of Glässer's disease, which is responsible for cases of fibrinous polyserositis, polyarthritis and meningitis. No vaccine is known that provides cross-protection against all serovars. The identification of novel immunoprotective antigens would undoubtedly contribute to the development of efficient subunit vaccines. In the present study, an immunoproteomic approach was used to analyze secreted proteins of H. parasuis and six proteins with high immunogenicity were identified. Five of them were successfully expressed, and their immunogenicity and protective efficacy were assessed in a mouse challenge model. All five proteins elicited strong humoral antibody and cellular immune responses in mice. They all effectively reduced the growth of H. parasuis in mouse organs and conferred different levels of protection (40-80%) against challenge. IgG subtype analysis revealed that the five proteins induce a bias toward a Th1-type immune response, and a significant increase was observed in the cytokine levels of IL-2, IFN-γ and Th2-specific IL-4 in the culture supernatants of splenocytes isolated from immunized mice. The results suggest that both Th1 and Th2 responses are involved in mediating protection. These data suggest that the five proteins could be potential subunit vaccine candidates for use to prevent H. parasuis infection.

BIOLOGICAL SIGNIFICANCE

Haemophilus parasuis can cause huge financial loss in the swine industry worldwide. There are still no vaccines which can provide cross-protection against all serovars. To address this need, we applied an immunoproteomic approach involving 2-DE, MALDI-TOF/TOF MS and Western-blot to identify the secreted proteins which may be able to provide immunoprotection to this disease. We identified six immunogenic proteins, and the immunogenicity and protective efficacy were validated. This result provides a foundation for developing novel subunit vaccines against Haemophilus parasuis.

Vaccination against respiratory Pseudomonas aeruginosa infection

Respiratory infections caused by Pseudomonas aeruginosa are a major clinical problem globally, particularly for patients with chronic pulmonary disorders, such as those with cystic fibrosis (CF), non-CF bronchiectasis (nCFB) and severe chronic obstructive pulmonary disease (COPD). In addition, critically ill and immunocompromised patients are also at significant risk of P. aeruginosa infection. For almost half a century, research efforts have focused toward development of a vaccine against infections caused by P. aeruginosa, but a licensed vaccine is not yet available. Significant advances in identifying potential vaccine antigens have been made. Immunisations via both the mucosal and systemic routes have been trialled in animal models and their effectiveness in clearing acute infections demonstrated. The challenge for translation of this research to human applications remains, since P. aeruginosa infections in the human respiratory tract can present both as an acute or chronic infection. In addition, immunisation prior to infection may not be possible for many patients with CF, nCFB or COPD. Therefore, development of a therapeutic vaccine provides an alternative approach for treatment of chronic infection. Preliminary animal and human studies suggest that mucosal immunisation may be effective as a therapeutic vaccine against P. aeruginosa respiratory infections. Nevertheless, more research is needed to improve our understanding of the basic biology of P. aeruginosa and the mechanisms needed to upregulate the induction of host immune pathways to prevent infection. Recognition of variability in the host immune responses for a range of patient health conditions at risk from P. aeruginosa infection is also required to support development of a successful vaccine delivery strategy and vaccine. Activation of mucosal immune responses may provide improved efficacy of vaccination for P. aeruginosa during both acute exacerbations and chronic infection.

Mucosal and systemic antibody responses to potential Pseudomonas aeruginosa vaccine protein antigens in young children with cystic fibrosis following colonization and infection

Pseudomonas aeruginosa is an important prognostic determinant in cystic fibrosis (CF). Little is known however, about P. aeruginosa induced local mucosal and systemic immune responses. Twenty CF children were categorized according to their P. aeruginosa status: (1) chronic lower respiratory tract infection (LRTI), (2) prior successfully treated initial LRTI, (3) isolated upper respiratory tract (URT) colonization, and (4) no known URT colonization or previous LRTI. Their antibody responses, and those of six non-CF disease controls, in serum and bronchoalveolar lavage (BAL) fluid to potential P. aeruginosa vaccine antigens outer membrane protein F (OprF), outer membrane protein H (OprH), catalase A (KatA) and a whole killed cell (WKC) extract were evaluated. Outer membrane protein G (OprG) responses were also measured in blood. Natural exposure, colonization and infection resulted in detectable antibody levels in BAL and serum in all CF groups. Both chronically infected and URT colonized CF children had substantially elevated immunoglobulin A antibody levels in the BAL fluid and sera toward the WKC extract and OprF antigen compared with the other groups of CF children and non-CF controls. The serum levels of specific P. aeruginosa antibodies involving immunoglobulin G and M isotypes increased with chronic LRTI, especially antibody levels to KatA, OprH and WKC extract, which were substantially greater in chronically infected children compared with all other groups. In conclusion, natural exposure, URT colonization and LRTI with P. aeruginosa all induce substantial mucosal and systemic antibody responses to potential vaccine antigens with chronically infected CF children having the highest levels.

Immunological response to parenteral vaccination with recombinant hepatitis B virus surface antigen virus-like particles expressing Helicobacter pylori KatA epitopes in a murine H. pylori challenge model

Virus-like particles (VLPs) based on the small envelope protein of hepatitis B virus (HBsAg-S) are immunogenic at the B- and T-cell level. In this study, we inserted overlapping sequences encoding the carboxy terminus of the Helicobacter pylori katA gene product into HBsAg-S. The HBsAg-S-KatA fusion proteins were able to assemble into secretion-competent VLPs (VLP-KatA). The VLP-KatA proteins were able to induce KatA-specific antibodies in immunized mice. The mean total IgG antibody titers 41 days post-primary immunization with VLP-KatA (2.3 × 10(3)) were significantly greater (P < 0.05) than those observed for vaccination with VLP alone (5.2 × 10(2)). Measurement of IgG isotypes revealed responses to both IgG1 and IgG2a (mean titers, 9.0 × 10(4) and 2.6 × 10(4), respectively), with the IgG2a response to vaccination with VLP-KatA being significantly higher than that for mice immunized with KatA alone (P < 0.05). Following challenge of mice with H. pylori, a significantly reduced bacterial load in the gastric mucosa was observed (P < 0.05). This is the first report describing the use of VLPs as a delivery vehicle for H. pylori antigens.

Actinobacillus pleuropneumoniaevaccines: from bacterins to new insights into vaccination strategies

With the growing emergence of antibiotic resistance and rising consumer demands concerning food safety, vaccination to prevent bacterial infections is of increasing relevance.Actinobacillus pleuropneumoniaeis the etiological agent of porcine pleuropneumonia, a respiratory disease leading to severe economic losses in the swine industry. Despite all the research and trials that were performed withA. pleuropneumoniaevaccination in the past, a safe vaccine that offers complete protection against all serotypes has yet not reached the market. However, recent advances made in the identification of new potential vaccine candidates and in the targeting of specific immune responses, give encouraging vaccination perspectives. Here, we review past and current knowledge onA. pleuropneumoniaevaccines as well as the newly available genomic tools and vaccination strategies that could be useful in the design of an efficient vaccine againstA. pleuropneumoniaeinfection.

Intratracheal immunization with pili protein protects against mortality associated with Pseudomonas aeruginosa pneumonia in mice

We examined the protective effect of intratracheal immunization with Pseudomonas aeruginosa pili protein against respiratory infection caused by P. aeruginosa. Mice were immunized intratracheally or subcutaneously with purified pili protein or bovine serum albumin as a control. Intratracheally but not subcutaneously pili protein-immunized mice showed significant improvement of survival after intratracheal challenge with the PAO1 strain. Furthermore, bacterial cell counts in pili protein-immunized murine lungs were significantly decreased compared to controls at 18 h after the challenge. Antipili protein antibody titers in bronchoalveolar lavage fluid of intratracheally pili protein-immunized mice were higher than in bovine serum albumin immunized mice. However, antipili antibody titers were not increased in bronchoalveolar lavage fluid of subcutaneously pili protein-immunized mice, despite the high serum antipili antibody titers. Inoculation of P. aeruginosa induced immediate increases in interleukin-12 and interferon-gamma in bronchoalveolar lavage fluid of pili protein-immunized mice, reflecting an adequate and rapid immune response against P. aeruginosa respiratory tract infection. Our findings suggest that intratracheal pili protein immunization is effective against respiratory tract infection caused by P. aeruginosa in mice.

Oral vaccination of BALB/c mice with Salmonella enterica serovar Typhimurium expressing Pseudomonas aeruginosa O antigen promotes increased survival in an acute fatal pneumonia model

Pseudomonas aeruginosa is a leading cause of nosocomial pneumonia. We compared the efficacies of oral and intraperitoneal (i.p.) vaccinations of BALB/c mice with attenuated Salmonella enterica serovar Typhimurium SL3261 expressing P. aeruginosa serogroup O11 O antigen to protect against P. aeruginosa infection in an acute fatal pneumonia model. Oral and i.p. vaccines elicited O11-specific serum immunoglobulin G (IgG) antibodies, but IgA was observed only after oral immunization. Challenge of orally vaccinated mice with an O11 strain (9882-80) at 6 and 12 times the 50% lethal dose showed increased survival in mice that received the vaccine compared to phosphate-buffered saline (PBS)- and vector-treated controls; no difference in survival was seen with a heterologous strain, 6294 (serogroup O6). In addition, significant protection against 9882-80 was not observed in i.p. vaccinated animals. Bronchoalveolar lavage fluid taken from immunized mice harbored O11-specific IgA and IgG in orally immunized mice but only modest levels of IgG in i.p. vaccinated mice. To correlate protection, opsonophagocytosis assays were performed with pooled sera from orally immunized animals. Efficient killing of five O11 clinical isolates was observed, while no killing was noted with 6294, indicating that the recombinant SL3261 oral vaccine induces an O11-specific reaction. We next determined the ability of orally vaccinated animals to clear bacteria from their lungs. Following P. aeruginosa challenge, the numbers of viable bacteria were significantly fewer in orally vaccinated animals than in PBS- and vector-treated controls. Our results suggest that oral immunization with recombinant SL3261 is efficacious in protection against pneumonia caused by P. aeruginosa.

Immunisation with non-integral OMPs promotes pulmonary clearance of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that can cause fatal acute lung infections in critically ill individuals. Lung damage due to chronic infections in cystic fibrosis sufferers is the major cause of morbidity and mortality in this group. The bacterium produces various immunomodulatory products that enable it to survive in the lung. Innate and increasing resistance to antibiotic therapy shown by this organism heightens the need for development of a vaccine. This study reports the identification of six non-integral protein antigens; Pa13, azurin, acyl carrier protein (ACP), amidase, aminopeptidase and KatE, purified from a mucoid strain of P. aeruginosa. N-terminal amino acid sequencing was used to identify these proteins and, based on their ascribed functions, determined that their normal cellular location was cytosolic. A rat model of acute pulmonary infection was used to investigate the ability of these protein antigens to enhance pulmonary clearance of a live P. aeruginosa challenge. Mucosal immunisation with four of the six antigens significantly enhanced bacterial clearance from both the lavage fluid and lung tissue. The greatest level of clearance was demonstrated for the antigens; KatE, aminopeptidase and amidase. Enhanced bacterial clearance was maintained when the antigens amidase and aminopeptidase were produced in recombinant form. When delivered parenterally, aminopeptidase demonstrated its continued efficacy as a vaccine candidate. This study has demonstrated that non-integral outer membrane proteins are antigenic and protective and warrant further investigation as potential components of a vaccine.

Protection against pulmonary infection with Pseudomonas aeruginosa following immunization with P. aeruginosa-pulsed dendritic cells

To develop a Pseudomonas aeruginosa vaccine that allows the host immune system to select the antigens, we hypothesized that dendritic cells (DC) pulsed with P. aeruginosa would induce protective immunity against pulmonary infections with P. aeruginosa. Incubation of murine bone marrow-derived DC with P. aeruginosa in vitro led to uptake of P. aeruginosa and activation of the DC. Spleen-derived CD4(+) cells from mice immunized with P. aeruginosa-pulsed DC showed increased proliferation, demonstrating that DC pulsed with P. aeruginosa were capable of eliciting a P. aeruginosa-specific immune response. To evaluate if P. aeruginosa-pulsed DC can induce protective immunity against P. aeruginosa pulmonary infection, DC incubated with P. aeruginosa in vitro were administered systemically to syngeneic mice, and the mice were then challenged by intrapulmonary infection with P. aeruginosa (5 x 10(4) CFU/mouse) 13 days later. Unimmunized control mice and mice who had previously received naive DC or DC stimulated with lipopolysaccharide or Escherichia coli died within 72 h. In contrast, 45% of mice receiving P. aeruginosa-pulsed DC demonstrated prolonged survival (>14 days). Finally, DC-pulsed with heat-inactivated P. aeruginosa protected CD8(-/-) but not CD4(-/-) mice, demonstrating that CD4(+) T cells were required for the DC pulsed with P. aeruginosa to induce protective immunity.

Mucosal immunity in the lung and upper airway

The mucosal surfaces of the lungs and upper airways are common sites for infection. Extensive studies of the mechanisms associated with immune responses in the respiratory tract have found that understanding the system is challenging and involves many complex interactions to prevent and eliminate infection. Immune protection against diseases transmitted through the respiratory tract requires an understanding of the important aspects associated with beneficial, detrimental or ineffective immune responses. Two critical aspects of an immune response against a pathogen are that of the inductive stage, either induced by vaccination or primary infection, and the effector stage, the ability to recognise, respond to and eliminate the infection without detriment to the host. An immunisation strategy must not only have a measure of the induced antigen specific response, but this response must also be protective.