Antibodies to cell envelope proteins of Pseudomonas aeruginosa in cystic fibrosis patients

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.

Pseudomonas aeruginosa and the host pulmonary immune response

Pseudomonas aeruginosa is a highly adaptable, opportunistic pathogen that is commonly found in the environment. It can infect a number of sites in the body and disseminate. It can cause both acute and chronic pulmonary infection and the acuity of infection and accompanying inflammatory phenotype is determined, for the most part, by the host. Although P. aeruginosa has been a successful opportunist in the context of a number of different disease states, it has been best studied in the context of cystic fibrosis (CF). The adaptability of P. aeruginosa has enabled it to adjust quickly to the CF airway, transitioning from initial colonization to chronic infection. The organism quickly expresses virulence factors that allow it to circumvent some elements of the host immune response and, even more importantly, quickly develops antimicrobial resistance. In the case of CF, chronic infection resulting in progressive lung damage, coupled with antimicrobial resistance, becomes an increasingly important issue as individuals with CF live longer. It is for these reasons that both organism- and host-targeted immunotherapies are being increasingly explored.

Pseudomonas aeruginosa: the potential to immunise against infection

Pseudomonas aeruginosa remains a serious pathogen for specific cohorts of patients where chronic infection is a poor prognostic indicator, such as those with cystic fibrosis, burn wounds or those who are immunocompromised. Significant disease burden is associated with a diverse spectrum of both nosocomial and community-acquired infections. To date, vaccines against P. aeruginosa have shown limited and often conflicting efficacy data, especially against heterologous strains, which are increasingly identified as co-colonisers of biofilms. While few studies have gone beyond Phase II clinical trials, a particular concern is the ability of P. aeruginosa to evade the immune system while provoking an immune response that contributes to the destructive nature of infection. Therefore, vaccine development needs to focus on preventing attachment and colonisation, as well as preventing conversion to a mucoid phenotype that is characteristic of the chronic condition that promotes pathology.

Seroprevalence of Helicobacter pylori infection in cystic fibrosis and its cross-reactivity with anti-pseudomonas antibodies

BACKGROUND

The prevalence of Helicobacter pylori infection and its role in gastroduodenal disease in cystic fibrosis (CF) are controversial. Additionally, serologic determination of infection in this population may be inaccurate because of cross-reactivity with other bacterial species. The seroprevalence of H. pylori in a cohort of patients with CF and its cross-reactivity with Pseudomonas antibodies were investigated.

METHODS

A research enzyme-linked immunosorbent assay (ELISA), and three commercial serologic assays (PyloriStat; BioWhittaker, Walkersville, MD, U.S.A.; Flexsure; SmithKline Diagnostics, Inc., San Jose, CA, U.S.A.; and HM-CAP; EPI, Stony Brook, NY, U.S.A.) at three independent laboratories determined the seroprevalence of anti-H. pylori IgG antibodies in 70 patients with CF. Cross-reactivity between solid-phase H. pylori antigens and Pseudomonas antibodies was ascertained by a competitive inhibition assay, preadsorbing sera of patients with CF with whole cell proteins from different Pseudomonas species, and serum reanalysis by each assay. Western blot analysis before and after adsorption was performed to identify potential cross-reactive antigens.

RESULTS

The research ELISA, Flexsure, Pyloristat, and HM-CAP initially showed H. pylori seropositivity of 47%, 28%, 24%, and 37%, respectively. Postadsorption seropositivity declined to 8%, 0%, 0%, and 15%, respectively. All patients with research ELISA true-positive results were confirmed endoscopically to have H. pylori infection. Western blot analysis showed a 31-kDa H. pylori protein with antigenic epitopes common to both bacterial species.

CONCLUSIONS

Cross-reactivity between solid-phase H. pylori antigens and anti-Pseudomonas antibodies occurs in patients with CF. A high index of suspicion should be assumed in evaluating results of serologic H. pylori tests in this population. Preadsorption of CF sera with Pseudomonas proteins should be used in serologic testing.

Pulmonary immunity to Pseudomonas aeruginosa

Pseudomonas aeruginosa, an opportunistic bacterial pathogen, is a major course of morbidity and mortality in subjects with compromised respiratory function despite the significant advances in therapeutic practices. The bacteria produces an armoury of products which modify its infective niche to ensure bacterial survival. The role of antibody in protection against pulmonary infection remains poorly defined. Protection appears to be associated with opsonizing antibody whilst some other antibody responses may be deleterious and promote further lung damage. Cell mediated responses are clearly important in protection against infection. This review proposes a vaccine strategy aimed at enhancing specific T cell responses in the lung which, though T cell-derived cytokines, drive the recruitment of neutrophils to the lung and the subsequent activation of these cells results in the clearance of bacteria from the lung.

Serum antibodies to outer membrane proteins (OMPs) of Moraxella (Branhamella) catarrhalis in patients with bronchiectasis: identification of OMP B1 as an important antigen

Moraxella (Branhamella) catarrhalis is a common cause of lower respiratory tract infections in adults and of otitis media in children. Little is known about the human immune response to this bacterium. In this study, immunoblot assays were performed to detect serum immunoglobulin G antibodies directed at purified outer membrane of M. catarrhalis. Twelve serum samples, two each from six patients with bronchiectasis who were persistently colonized with this organism, were tested with their homologous M. catarrhalis sputum isolates. In all the sera, the most prominent and consistent antibody response was to a minor 84-kDa outer membrane protein, OMP B1. Immunoblot adsorption assays show that these antibodies recognize surface exposed epitopes on OMP B1. Further analysis of human serum antibodies eluted from the surface of intact bacterial cells shows that these surface-exposed epitopes on OMP B1 are heterogeneous among strains of M. catarrhalis. OMP B1 is therefore an important OMP antigen on the surface of M. catarrhalis for the human immune response to infection by this bacterium.

Cross-reactive antigens shared by Pseudomonas aeruginosa, Helicobacter pylori, Campylobacter jejuni, and Haemophilus influenzae may cause false-positive titers of antibody to H. pylori

Cystic fibrosis (CF) patients suffer from many of the gastrointestinal conditions which occur in non-CF individuals, e.g., dyspepsia and peptic ulceration. These symptoms may be caused by Helicobacter pylori but could also be due to either pancreatic insufficiency or the intensive antibiotic treatment used in CF patients. Since CF patients chronically infected with Pseudomonas aeruginosa produce antibodies against a wide range of antigens, including antigens common to many other bacteria, e.g., GroEL and lipopolysaccharide, we studied, by the Western blot (immunoblot) technique, the specificity of immunoglobulin G antibodies to H. pylori in Danish CF patients chronically infected with P. aeruginosa, CF patients without P. aeruginosa infection but with Haemophilus influenzae infection, patients with dyspeptic ulcers associated with H. pylori, and patients recovering from acute Campylobacter jejuni or Campylobacter coli infection. Sera from CF patients with chronic P. aeruginosa or H. influenzae infection and patients recovering from acute C. jejuni infection cross-reacted with H. pylori antigens. A strong cross-reacting protein antigen at approximately 14 kDa and minor cross-reactive antigens at approximately 27, 30, and 60 kDa (the heat shock protein GroEL is equivalent to the common antigen of P. aeruginosa) could be demonstrated. The results of this study show that high immunoglobulin G antibody titers against H. pylori in CF patients cannot be regarded as indicating present or past H. pylori infection unless their specificity is proven by absorption studies.

Defining potential targets for immunotherapy in Burkholderia cepacia infection

Burkholderia cepacia has become a serious source of infection in patients with cystic fibrosis. Antibiotic therapy is difficult as the bacteria are intrinsically resistant to most antibiotics. The present study compared the antibody response by immunoblot of 50 negative control sera, 22 patients with cystic fibrosis and no evidence of B. cepacia, 9 clinically well patients with cystic fibrosis colonised by B. cepacia and 5 patients with cystic fibrosis and deteriorating or fatal B. cepacia infection. Nineteen antigenic bands varying in apparent molecular weights from 19 to 170 kDa were identified. Two bands at 19 and 21 kDa were only present when the organism was grown in an iron-deficient medium. The band at 30 kDa was identified as a porin and the possession of IgG antibody carried a statistically significant (P = 0.00003) better prognosis. This antigen was thus a potential target for immunotherapy.

Determination of IgG subclass antibodies to Pseudomonas aeruginosa outer membrane proteins in cystic fibrosis lung infection using immunoblotting and enzyme-linked immunosorbent assay

IgG subclass antibodies to Pseudomonas aeruginosa outer membrane proteins (OMP) were investigated in serum from cystic fibrosis (CF) patients by immunoblotting and enzyme-linked immunosorbent assay (ELISA). Fifteen patients (eight in good and seven in poor clinical condition) have been followed for an average of 13 years with multiple serum samples covering the preinfection, and early and late stages of chronic infection. Laser-scanning densitometry of photographs taken from immunoblots was used to quantify antibody level and compare with ELISA titres. The earliest anti-OMP antibodies to appear were of the IgG1 subclass. There was no significant difference in IgG subclass antibody levels to OMPs between patients in relatively good and poor clinical condition. Data presented indicate a high positive correlation among measurements of IgG subclass antibodies to P. aeruginosa OMPs using ELISA and immunoblotting.

Comparative studies of the outer membranes of Bacteroides gingivalis, strains ATCC 33277, W50, W83, 381

Outer membrane fractions from Bacteroides gingivalis strains ATCC 33277, 381, W50, and W83 were isolated by French pressure cell disruption and the distribution of major and minor proteins was determined by SDS-PAGE electrophoresis after treatment with 2% Sarkosyl and 2% Triton X-100. Heat-modifiability of the outer membrane proteins (OMPs) from these B. gingivalis strains was also determined after treatment at 100 degrees C and analysis by both 1- and 2-dimensional SDS-PAGE. The distribution of the OMPs on the surface of these B. gingivalis strains was determined by 125I labelling. For the most part of the OMPs of B. gingivalis presented a complex distribution, with OMPs observed between 123 kD and 13 kD. While the distribution of the OMPs was strain specific, OMPs common to all of the strains were observed. Two percent Sarkosyl treatment of the OMs at room temperature resulted in the solubilization of approximately 60% of the OMP. The Sarkosyl-insoluble MOMPs had relative molecular weights between 110 kD and 20 kD. Many of the OMPs which were separated at room temperature were heat-modified at either 65 degrees C or 100 degrees C. Heating of the OMs at 100 degrees C resulted in the heat modification of the majority of those OMPs observed at room temperature. Sarkosyl-100 degrees C OMs displayed MOMPs at apparent molecular weights between 90 kD and 15 kD. Radioiodination of the B. gingivalis strains ATCC 33277, 381, W83 and W50 revealed between 7 and 14 MOMPs at the cell surface depending upon the strain. The complexity of the OM of these B. gingivalis strains indicated the possibility of identifying and separating those OMPs involved in a variety of biological functions, including virulence, transport, and cell interaction.

Immunoblot detection of class-specific humoral immune response to outer membrane proteins isolated from Salmonella typhi in humans with typhoid fever

The studies reported here were undertaken to assess the ability of the outer membrane proteins (OMPs) of Salmonella typhi to induce a humoral immune response in humans with typhoid fever. OMPs were isolated with the nonionic detergent Triton X-100 and were found to be contaminated with approximately 4% lipopolysaccharide. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns showed protein bands with molecular size ranges from 17 to 70 kilodaltons; the major groups of proteins were those that correspond to the porins and OmpA of gram-negative bacteria. Rabbit antiserum to OMPs or to S. typhi recognized OMPs after absorption with lipopolysaccharide. Sera from patients with typhoid fever contained immunoglobulin M antibodies which reacted with a protein of 28 kilodaltons and immunoglobulin G antibodies which reacted mainly with the porins, as determined by immunoblotting. These results indicate that the porins are the major immunogenic OMPs from S. typhi and that the immune response induced in the infection could be related to the protective status.

Immune response in cystic fibrosis to outer membrane proteins of Pseudomonas aeruginosa

The systemic humoral immune response in cystic fibrosis (CF) to outer membrane (OM) proteins of Pseudomonas aeruginosa was investigated as a function of the time of colonization by immunoblotting. OM proteins were prepared from bacteria grown in ion-sufficient, magnesium-depleted, and iron-deficient media. The location of proteins F, H, and I on the blots was verified by monoclonal antibodies. Proteins H2 and H1 were differentiated by the overexpression of H1 under magnesium depletion. Iron-regulated membrane proteins (IRMPs) were recognized by their overproduction under iron limitation. Plasma samples from 43 CF patients and ten healthy adults were analyzed after preadsorption with lipopolysaccharide (LPS). Within the first year of colonization, only two to six specific plasma antibodies to OM proteins were produced. After a strong increase during the second year, long-lasting levels were seen in the majority of patients. Large variations of the immune response were noted among the patients. The number of specific antibodies to different OM proteins correlated with the severity of the course of lung disease. At maximum 38 immunostained bands were observed. Proteins H and I were the earliest antigens amongst the major OM proteins. During the second year, antibodies directed to protein F became detectable. IRMPs which indicate the growth of P. aeruginosa under iron deprivation were only recognized by plasma samples from chronically colonized CF patients with advanced lung disease.

Isolation and antigenic reactivity of Brucella ovis outer membrane proteins

Brucella ovis cell membranes were isolated from fractured and lysozyme-treated cells by ultracentrifugation. These preparations appeared to consist largely of outer membranes, as judged from the results of ultracentrifugation experiments in sucrose density gradients under conditions that are widely used to separate inner and outer membranes of gram-negative bacteria. The sequential detergent extraction of cell membranes yielded mainly lipopolysaccharide and three groups of outer membrane proteins. In immunoblotting, lipopolysaccharide had good antigenic reactivity with all sera from rams exposed to B. ovis (vaccination or natural infection), but some outer membrane proteins reacted strongly only with sera from immune (vaccinated) rams, not from infected rams, suggesting a possible diagnostic role for such proteins in predicting immunity or infection.

Diagnosis of chronic Pseudomonas aeruginosa infection in cystic fibrosis by enzyme-linked immunosorbent assay

An easily applicable test for diagnosis of chronic Pseudomonas aeruginosa infection in cystic fibrosis by enzyme-linked immunosorbent assay (ELISA) for determination of serum immunoglobulin G to P. aeruginosa was developed. Soluble antigens obtained by ultrasonication of P. aeruginosa, serotypes O:1 to O:17, were used as antigens immobilized to polystyrene microtiter plates. The intraplate, plate-to-plate, and day-to-day variations were 14, 19, and 20%, respectively. Plates coated with the antigens could be stored for at least 64 days at +4 and +22 degrees C without any significant change in activity. Normal values were determined in sera from 164 controls (100 children and 64 adults). The sensitivity and specificity of the ELISA was determined by using serum samples from 243 cystic fibrosis patients and were compared to results with crossed immunoelectrophoresis (CIE). The ELISA could diagnose chronic P. aeruginosa infection with a diagnostic sensitivity of 93% and specificity of 92%. The sensitivity and specificity for the diagnosis of the early stages of chronic P. aeruginosa infection by a single sample were 90 and 100%, respectively, and by using an increased antibody response in paired samples, the sensitivity was 93% and specificity was 87%. There was a statistically significant correlation between antibody levels obtained by ELISA and those obtained by CIE. The sensitivity and specificity of the ELISA were equal to those of CIE, and because of its simplicity, the ELISA is recommended as a routine test in patients with cystic fibrosis.

Automation in clinical microbiology: a new approach to identifying micro-organisms by automated pattern matching of proteins labelled with 35S-methionine

A new rapid automated method for the identification and classification of microorganisms is described. It is based on the incorporation of 35S-methionine into cellular proteins and subsequent separation of the radiolabelled proteins by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The protein patterns produced were species specific and reproducible, permitting discrimination between the species. A large number of Gram negative and Gram positive aerobic and anaerobic organisms were successfully tested. Furthermore, there were sufficient differences within species between the protein profiles to permit subdivision of the species. New typing schemes for Clostridium difficile, coagulase negative staphylococci, and Staphylococcus aureus, including the methicillin resistant strains, could thus be introduced; this has provided the basis for useful epidemiological studies. To standardise and automate the procedure an automated electrophoresis system and a two dimensional scanner were developed to scan the dried gels directly. The scanner is operated by a computer which also stores and analyses the scan data. Specific histograms are produced for each bacterial species. Pattern recognition software is used to construct databases and to compare data obtained from different gels: in this way duplicate "unknowns" can be identified. Specific small areas showing differences between various histograms can also be isolated and expanded to maximise the differences, thus providing differentiation between closely related bacterial species and the identification of differences within the species to provide new typing schemes. This system should be widely applied in clinical microbiology laboratories in the near future.

Antibodies to porin antigens of Salmonella typhi induced during typhoid infection in humans

Immunoglobulin G (IgG)- and IgM-specific antibody titers against Salmonella typhi Ty2 porins have been measured in 30 paired typhoid sera by enzyme-linked immunosorbent assay. These studies have found that IgG serum titers of acute and convalescent sera were 625 and 5,000 times higher, respectively than the control serum titers. The same typhoid sera were titrated with S. typhi Ty2 flagellin and S. typhi lipopolysaccharide. The titers against these antigens were considerably lower than those against the porins. The highest IgM-specific titer has also been found against porins in convalescent-phase sera. However, the largest increase in IgM-specific titer compared with the control group titer was obtained against flagellin during the acute phase of typhoid. The lowest increases in antibody titer were obtained with the IgM-specific anti-lipopolysaccharide in both types of sera. This may be because many normal individuals in endemic areas already have IgM titers against lipopolysaccharide. This study has provided good evidence that porins are excellent antigens and that IgG-specific antiporin titers may be of diagnostic value in typhoid infections in endemic areas.

Characterization of antibody to the ferripyochelin-binding protein of Pseudomonas aeruginosa

An outer membrane protein of Pseudomonas aeruginosa was previously shown to bind 59Fe-labeled pyochelin. Antibodies to the purified ferripyochelin-binding protein (FBP) were characterized by using a variety of assays. Anti-FBP cross-reacted with several P. aeruginosa isolates in an enzyme-linked immunosorbent assay. Anti-FBP significantly enhanced phagocytosis of P. aeruginosa by human polymorphonuclear leukocytes. In a serum bactericidal assay we observed no difference in viability between cells incubated with antiserum to FBP and cells incubated with preimmune serum. Anti-FBP immunoglobulin G inhibited both binding and uptake of 59Fe-labeled pyochelin by whole cells. Passive protection by anti-FBP was examined in experimental P. aeruginosa burn infections in mice. The protection provided by this antibody was strain dependent but lipopolysaccharide serotype independent.

Monoclonal antibodies to outer membrane antigens of Vibrio cholerae

Hybridoma-derived monoclonal antibodies were prepared against outer membrane antigens of four strains of Vibrio cholerae that were cultivated under iron-limited conditions, and these antibodies were partially characterized. We established a library of 66 hybridomas which produced monoclonal antibodies defining 16 different V. cholerae antigens. Two antigens (molecular weights, 18,000 and 112,000) were heat modifiable, whereas the reacting epitope of a third antigen (40,000-dalton-18,000-dalton doublet) was completely destroyed when it was heated at 100 degrees C. The 112,000-dalton heat-modifiable protein was an iron-regulated outer membrane protein. This protein bound 59Fe in vitro when it was combined with the V. cholerae siderophore-iron complex 59Fe-vibriobactin; it was also found in in vivo grown V. cholerae, as were three other antigens. A total of 26 hybridomas produced antibody to V. cholerae lipopolysaccharide. Of these, 12 were cross-reactive with lipopolysaccharides of other gram-negative bacteria, including 2 which recognized lipid A. Several of these anti-lipopolysaccharide monoclonal antibodies appeared to be lipopolysaccharide region specific. Some membrane antigens were strain specific, whereas others were common to both O group 1 and non-O group 1 vibrios.

[Infections of the respiratory tract with Pseudomonas aeruginosa in cystic fibrosis]

The main cause of death in cystic fibrosis (CF) patients is progressive pulmonary insufficiency frequently associated with chronic infections of the respiratory tract by Pseudomonas aeruginosa. Bacteria of this species synthesize numerous extracellular products contributing to its pathogenicity. An alginate-like exopolysaccharide is characteristic for mucoid mutants predominating among P. aeruginosa isolates from CF patients. It interferes with immune defense mechanisms of the host and probably protects the bacteria against certain antibiotics. Furthermore, it is involved in the formation of bacterial microcolonies that resist mucociliary clearance, opsonisation, and phagocytosis. Exotoxin A and elastase are regarded as the most important among various extracellular enzymes involved in pulmonary injury in CF patients. Exotoxin A inhibits eukaryotic protein synthesis leading to necrosis; elastase, together with other Pseudomonas-proteases, induces hemorrhagic lesions and necrosis and seems to inactivate immunoglobulins and complement factors. Phospholipase C and glycolipid represent two hemolysins of P. aeruginosa that may contribute to cytopathogenic effects in infected lungs. No primary defect in the immunological defense mechanisms of CF patients has been described so far. Antibodies against various P. aeruginosa antigens including those mentioned above have been demonstrated, but a complete elimination of the bacteria from infected lungs has not been observed. Therapy of pulmonary P. aeruginosa infections in CF patients usually includes combinations of antibiotics of the beta-lactam and aminoglycoside type. Difficulties arise from an unusually high intrinsic resistance of P. aeruginosa as well as from poor penetration of many antibiotics into the sputum of CF patients. Therefore, future efforts to manage the Pseudomonas problem in CF will probably concentrate on prophylactic therapy, e.g. childhood vaccination of CF patients in order to prevent bacterial colonization of the respiratory tract.

Comparison of sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles and antigenic relatedness among outer membrane proteins of 49 Brucella abortus strains

Outer membrane proteins were solubilized from 49 strains of Brucella abortus by sequential extraction of physically disrupted cells with N-lauroylsarcosinate and a dipolar ionic detergent (Verstreate et al., Infect. Immun. 35:979-989, 1982). The strains tested included standard agglutination test strain 1119, virulent strain 2308, and eight reference strains representing each of the biotypes; the remainder were isolates from cattle in North America with natural infections and included biotypes 1, 2, and 4. Three principal protein groups with apparent molecular weights of 88,000 to 94,000 (group 1), 35,000 to 40,000 (group 2, now established as porins [Douglas et al., Infect. Immun. 44:16-21, 1984]), and 25,000 to 30,000 (group 3) were observed in every strain. Some variability in banding patterns occurred among strains, but intrastrain variation was sufficient to preclude the use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of outer membrane proteins for differentiating among strains of B. abortus. One antigen ([b]) was shared among the porin proteins, and three others ([c], ([d], and ([ e]) were shared among the group 3 proteins of all of the strains tested, indicating that these relationships are probably species wide. These results suggest that it may be possible to use outer membrane proteins from a representative strain of B. abortus in a vaccine for species-wide immunization.

Use of a purified outer membrane protein F (porin) preparation of Pseudomonas aeruginosa as a protective vaccine in mice

The outer membrane protein F (porin) from the PAO1 strain of Pseudomonas aeruginosa was purified by two different methods. One procedure involved separation by column chromatography of proteins extracted from isolated outer membranes, whereas the other involved extraction from gels after slab polyacrylamide gel electrophoresis of proteins extracted from cell envelopes. Both procedures yielded protein F preparations which successfully immunized mice from subsequent challenge with the PAO1 strain. The protein F preparations contained small quantities of lipopolysaccharide (LPS). This level of LPS contamination protected immunized mice from challenge with the homologous LPS serotype strain. However, immunization of mice with protein F preparations from the PAO1 strain also afforded protection against challenge with two different LPS serotype strains. This protective ability was lost when the protein F preparation was treated with papain before use as a vaccine. These observations support the conclusion that protein F has protective ability, which is not due to LPS contamination, when given as a vaccine. After immunization with the protein F preparation, mice showed an increase in antibody titer to the purified protein F preparation by enzyme-linked immunosorbent assay. Mice were protected passively by administration of rabbit antisera raised to the protein F preparation. These results indicate that the protein F preparation elicits a specific humoral antibody response in immunized animals. Our results suggest that purified protein F has potential as an effective vaccine for P. aeruginosa.

Antibody response of infected mice to outer membrane proteins of Pseudomonas aeruginosa

The antibody response to outer membrane proteins of Pseudomonas aeruginosa was studied in mice experimentally infected with P. aeruginosa 220. The infection consisted of an abscess established by subcutaneous injection of bacteria. Sera from these mice were analyzed by indirect radioimmunoprecipitation and immunoblot methods for the presence of antibodies to proteins of the isolated outer membrane. Sera from mice 14 days postinfection were shown to contain antibodies directed against proteins that comigrated with the major outer membrane proteins F (porin), H2, and I (lipoprotein). A 16,000-dalton protein that did not appear to be a major outer membrane protein also elicited a significant antibody response in some instances. It is concluded that mice, in response to infection, elicit an immunological response to outer membrane proteins of P. aeruginosa.

New knowledge on pathogenesis of bacterial enteric infections as applied to vaccine development

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Immunogenicity of Pseudomonas aeruginosa outer membrane antigens examined by crossed immunoelectrophoresis

By crossed immunoelectrophoresis 36 different anode-migrating antigens were demonstrated in sonicated antigen preparations of Pseudomonas aeruginosa. We numbered these antigens to establish a reference precipitin pattern. Antigen no. 31 was identified as the lipopolysaccharide (LPS) antigen, because it was found to be responsible for the O-group specificity and because it reacted with anti-LPS monoclonal antibodies and with Limulus amoebocyte lysate. Purified outer membrane proteins F (porin), H2, and I used as antigens formed precipitins with the reference antibodies, thus establishing their antigenicity. LPS that copurified with protein F and slightly contaminated protein H2 was detectable as an extra precipitin (antigen no. 31). The use of monoclonal antibodies specific for smooth LPS and rough LPS revealed different antigenic determinants in the LPS molecule and suggested that antigen no. 5 could be the core region of the LPS which is equivalent to the rough LPS. Antibodies against these outer membrane antigens were detected in patients with chronic P. aeruginosa pneumonia and in patients with acute P. aeruginosa bacteremia. Antibodies with the same specificity were also found in rats chronically infected with P. aeruginosa 7 days postinfection. This demonstrates the surface accessibility and antigenic reactivity of outer membrane antigens.