Avidity of anti-P aeruginosa antibodies during chronic infection in patients with cystic fibrosis

Recombinant Pseudomonas bio-nanoparticles induce protection against pneumonic Pseudomonas aeruginosa infection

To develop an effective Pseudomonas aeruginosa (PA) outer-membrane-vesicles (OMVs) vaccine, we eliminated multiple virulence factors from a wild-type P. aeruginosa PA103 strain (PA103) to generate a recombinant strain, PA-m14. The PA-m14 strain was tailored with a pSMV83 plasmid encoding the pcrV-hitA_T fusion gene to produce OMVs. The recombinant OMVs enclosed increased amounts of PcrV-HitA_T bivalent antigen (PH) (termed OMV-PH) and exhibited reduced toxicity compared to the OMVs from PA103. Intramuscular vaccination with OMV-PH from PA-m14(pSMV83) afforded 70% protection against intranasal challenge with 6.5 × 10⁶ CFU (∼30 LD₅₀) of PA103, while immunization using OMVs without the PH antigen (termed OMV-NA) or the PH antigen alone failed to offer effective protection against the same challenge. Further immune analysis showed that the OMV-PH immunization significantly stimulated potent antigen-specific humoral and T-cell (Th1/Th17) responses in comparison to the PH or OMV-NA immunization in mice, which can effectively hinder PA infection. Undiluted anti-sera from OMV-PH-immunized mice displayed significant opsonophagocytic killing of WT PA103 compared to antisera from PH antigen- or OMV-NA-immunized mice. Moreover, the OMV-PH immunization afforded significant antibody-indentpednet cross-protection to mice against PAO1 and a clinical isolate AMC-PA10 strains. Collectively, the recombinant PA OMV delivering the PH bivalent antigen exhibits high immunogenicity and would be a promising next-generation vaccine candidate against PA infection.

Pseudomonas aeruginosa Biofilms: Host Response and Clinical Implications in Lung Infections

Pseudomonas aeruginosa is a major health challenge that causes recalcitrant multidrug-resistant infections, especially in immunocompromised and hospitalized patients. P. aeruginosa is an important cause of nosocomial and ventilator-associated pneumonia characterized by high prevalence and fatality rates. P. aeruginosa also causes chronic lung infections in individuals with cystic fibrosis. Multidrug- and totally drug-resistant strains of P. aeruginosa are increasing threats that contribute to high mortality in these patients. The pathogenesis of many P. aeruginosa infections depends on its ability to form biofilms, structured bacterial communities that can coat mucosal surfaces or invasive devices. These biofilms make conditions more favorable for bacterial persistence, as embedded bacteria are inherently more difficult to eradicate than planktonic bacteria. The molecular mechanisms that underlie P. aeruginosa biofilm pathogenesis and the host response to P. aeruginosa biofilms remain to be fully defined. However, it is known that biofilms offer protection from the host immune response and are also extremely recalcitrant to antimicrobial therapy. Therefore, development of novel therapeutic strategies specifically aimed at biofilms is urgently needed. Here, we review the host response, key clinical implications of P. aeruginosa biofilms, and novel therapeutic approaches to treat biofilms relevant to lung infections. Greater understanding of P. aeruginosa biofilms will elucidate novel avenues to improve outcomes for P. aeruginosa pulmonary infections.

Mechanisms of humoral immune response against Pseudomonas aeruginosa biofilm infection in cystic fibrosis

P. aeruginosa chronic lung infection is the major cause of morbidity and mortality in patients with cystic fibrosis (CF), and is characterized by a biofilm mode of growth, increased levels of specific IgG antibodies and immune complex formation. However, despite being designed to combat this infection, such elevated humoral response is not associated with clinical improvement, pointing to a lack of anti-pseudomonas effectiveness. The mode of action of specific antibodies, as well as their structural features, and even the background involving B-cell production, stimulation and differentiation into antibody-producing cells in the CF airways are poorly understood. Thus, the aim of this review is to discuss studies that have addressed the intrinsic features of the humoral immune response and provide new insights regarding its insufficiency in the CF context.

IgG avidity to Pseudomonas aeruginosa over the course of chronic lung biofilm infection in cystic fibrosis

BACKGROUND AND OBJECTIVES

The mechanisms leading to low effectiveness of the humoral immune response against P. aeruginosa in cystic fibrosis (CF) are poorly understood. The aim of the present study was to assess the avidity maturation of specific antipseudomonal IgG before and during the development of chronic lung infection in a cohort of Danish CF patients.

METHODS

Avidity maturation was assessed against a pooled P. aeruginosa antigen (St-Ag) and against P. aeruginosa alginate in 10 CF patients who developed chronic lung infection and 10 patients who developed intermittent lung colonization, using an ELISA technique with the thiocyanate elution method. Avidity was quantitatively determined by calculating the avidity Constant (Kav).

RESULTS

IgG avidity to St-Ag significantly increased at the onset (Median Kav=2.47) and one year after the onset of chronic infection (Median Kav=3.27), but did not significantly changed in patients who developed intermittent colonization. IgG avidity against alginate did not significantly change over the years neither in patients who developed chronic lung infection (Median Kav=3.84 at the onset of chronic infection), nor in patients who developed intermittent colonization.

CONCLUSION

IgG avidity to P. aeruginosa alginate does not significantly enhance as chronic lung infection progresses. This probably plays a role in the difficulty to mount an effective opsonophagocytic killing to clear mucoid P. aeruginosa infection in CF.

X-ray Irradiated Vaccine Confers protection against Pneumonia caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa is a gram-negative bacterium and one of the leading causes of nosocomial infection worldwide, however, no effective vaccine is currently available in the market. Here, we demonstrate that inactivation of the bacteria by X-ray irradiation inhibits its replication capability but retained antigenic expression functionally thus allowing its use as a potential vaccine. Mice immunized by this vaccine were challenged by the parental strain, the O-antigen-homologous strain PAO-1 (O2/O5) and heterologous strain PAO-6 (O6) in an acute pneumonia model. We further measured the protective effect of the vaccine, as well as host innate and cellular immunity responses. We found immunized mice could protect against both strains. Notably, the antiserum only had significant protective role against similar bacteria, while adoptive transfer of lymphocytes significantly controlled the spread of the virulent heterologous serogroup PAO-6 infection, and the protective role could be reversed by CD4 rather than CD8 antibody. We further revealed that vaccinated mice could rapidly recruit neutrophils to the airways early after intranasal challenge by PAO-6, and the irradiated vaccine was proved to be protective by the generated CD4(+) IL-17(+) Th17 cells. In conclusion, the generation of inactivated but metabolically active microbes is a promising strategy for safely vaccinating against Pseudomonas aeruginosa.

Host response to Staphylococcus aureus cytotoxins in children with cystic fibrosis

BACKGROUND

Staphylococcus aureus is one of the earliest bacterial pathogens to colonize the lungs of children with cystic fibrosis and is an important contributor to pulmonary exacerbations. The adaptive host response to S. aureus in cystic fibrosis remains inadequately defined and has important implications for pathogenesis and potential interventions. The objectives of this study were to determine the functional antibody response to select staphylococcal exotoxins (LukAB, alpha-hemolysin, and PVL) in children with cystic fibrosis and to evaluate the relationship of this response with pulmonary exacerbations.

METHODS

Fifty children with cystic fibrosis were enrolled and followed prospectively for 12months. Clinical characteristics and serologic profiles were assessed at routine visits and during pulmonary exacerbations, and functional antibody assessments were performed to measure neutralization of LukAB-mediated cytotoxicity.

RESULTS

For each antigen, geometric mean titers were significantly higher if S. aureus was detected at the time of exacerbation. For LukAB, geometric mean titers were significantly higher at exacerbation follow-up compared to titers during the exacerbation, consistent with expression during human disease, and the humoral response capably neutralized LukAB-mediated cytotoxicity. Moreover, the presence of a positive S. aureus culture during a pulmonary exacerbation was associated with 31-fold higher odds of having a LukA titer ≥1:160, suggesting potential diagnostic capability of this assay.

CONCLUSIONS

The leukotoxin LukAB is expressed by S. aureus and recognized by the human adaptive immune response in the setting of pulmonary infection in cystic fibrosis. Anti-LukAB antibodies were not only predictive of positive staphylococcal culture during exacerbation, but also functional in the neutralization of this toxin.

Recent developments for Pseudomonas vaccines

Infections with Pseudomonas aeruginosa are a major health problem for immune-compromised patients and individuals with cystic fibrosis. A vaccine against: P. aeruginosa has long been sought after, but is so far not available. Several vaccine candidates have been assessed in experimental animals and humans, which include sub-cellular fractions, capsule components, purified and recombinant proteins. Unique characteristics of the host and the pathogen have complicated the vaccine development. This review summarizes the current state of vaccine development for this ubiquitous pathogen, in particular to provide mucosal immunity against infections of the respiratory tract in susceptible individuals with cystic fibrosis.

Pseudomonas aeruginosa biofilms in cystic fibrosis

The persistence of chronic Pseudomonas aeruginosa lung infections in cystic fibrosis (CF) patients is due to biofilm-growing mucoid (alginate-producing) strains. A biofilm is a structured consortium of bacteria, embedded in a self-produced polymer matrix consisting of polysaccharide, protein and DNA. In CF lungs, the polysaccharide alginate is the major part of the P. aeruginosa biofilm matrix. Bacterial biofilms cause chronic infections because they show increased tolerance to antibiotics and resist phagocytosis, as well as other components of the innate and the adaptive immune system. As a consequence, a pronounced antibody response develops, leading to immune complex-mediated chronic inflammation, dominated by polymorphonuclear leukocytes. The chronic inflammation is the major cause of the lung tissue damage in CF. Biofilm growth in CF lungs is associated with an increased frequency of mutations, slow growth and adaptation of the bacteria to the conditions in the lungs, and to antibiotic therapy. Low bacterial metabolic activity and increase of doubling times of the bacterial cells in CF lungs are responsible for some of the tolerance to antibiotics. Conventional resistance mechanisms, such as chromosomal β-lactamase, upregulated efflux pumps, and mutations of antibiotic target molecules in the bacteria, also contribute to the survival of P. aeruginosa biofilms. Biofilms can be prevented by early aggressive antibiotic prophylaxis or therapy, and they can be treated by chronic suppressive therapy.

The immune system vs. Pseudomonas aeruginosa biofilms

Ilya Metchnikoff and Paul Ehrlich were awarded the Nobel price in 1908. Since then, numerous studies have unraveled a multitude of mechanistically different immune responses to intruding microorganisms. However, in the vast majority of these studies, the underlying infectious agents have appeared in the planktonic state. Accordingly, much less is known about the immune responses to the presence of biofilm-based infections (which is probably also due to the relatively short period of time in which the immune response to biofilms has been studied). Nevertheless, more recent in vivo and in vitro studies have revealed both innate as well as adaptive immune responses to biofilms. On the other hand, measures launched by biofilm bacteria to achieve protection against the various immune responses have also been demonstrated. Whether particular immune responses to biofilm infections exist remains to be firmly established. However, because biofilm infections are often persistent (or chronic), an odd situation appears with the simultaneous activation of both arms of the host immune response, neither of which can eliminate the biofilm pathogen, but instead, in synergy, causes collateral tissue damage. Although the present review on the immune system vs. biofilm bacteria is focused on Pseudomonas aeruginosa (mainly because this is the most thoroughly studied), many of the same mechanisms are also seen with biofilm infections generated by other microorganisms.

Usefulness of serum IgG4 in the diagnosis and follow up of autoimmune pancreatitis: A systematic literature review and meta-analysis

High circulating serum immunoglobulin G4 (IgG4) levels have been proposed as a marker of autoimmune pancreatitis (AIP). The aim of the present study was to review the data existing in the English literature on the usefulness of the IgG4 serum levels in the diagnosis and follow up of patients with AIP. A total of 159 patients with AIP and 1099 controls were described in seven selected papers reporting the usefulness of serum IgG4 in diagnosing AIP. In total, 304 controls had pancreatic cancer, 96 had autoimmune diseases, and the remaining 699 had other conditions. The summary receiver-operating characteristic curve analysis was carried out by means of Meta-DiSc open-access software. Serum IgG4 showed good accuracy in distinguishing between AIP and the overall controls, pancreatic cancer and other autoimmune diseases (area under the curve [+/- SE]: 0.920 +/- 0.073, 0.914 +/- 0.191, and 0.949 +/- 0.024, respectively). The studies analyzed showed significantly heterogeneous specificity values in each of the three analyses performed. The analysis of the four studies comparing AIP and pancreatic cancers also showed significantly heterogeneous values of sensitivities and odds ratios. Regarding the usefulness of IgG4 as a marker of efficacy of steroid treatment, a decrease in the serum concentrations of IgG4 was found in the four available studies. The serum IgG4 subclass is a good marker of AIP, and its determination should be included in the diagnostic workup of this disease. However, the heterogeneity of the studies published until now means that more studies are necessary in order to better evaluate the true accuracy of IgG4 in discriminating AIP versus other autoimmune diseases.

Cystic Fibrosis and Formes Frustes of CFTR-Related Disease

Cystic fibrosis (CF) is the commonest genetic cause of bronchiectasis in the Caucasian population. Since identification of the putative gene in 1989, the molecular basis of the condition has become clearer with characterisation of the unique pathophysiology. The small airways are the primary site of lung disease, with an intense but localised inflammatory picture, dominated by neutrophils. The clinical heterogeneity is explained to some degree by the distinct molecular consequences of the many mutations that have been recognised to affect the CF transmembrane conductance regulator (CFTR) gene; however other genes appear to modify the phenotype as well as environmental exposure. It has become increasingly apparent that certain conditions may result from CFTR dysfunction without fulfilling diagnostic criteria for CF. In some cases this may result in single organ disease for which the term CF (or CFTR)-related disease has been advocated. Congenital bilateral absence of the vas deferens is the most clearly characterised of these. In other cases where a mild CF phenotype is apparent, atypical CF is probably a better term. It remains unclear whether carrier status predisposes to certain conditions such as chronic rhinosinusitis or pancreatitis.

Low avidity and level of serum anti-Abeta antibodies in Alzheimer disease

Some studies have indicated that low level of anti-Abeta antibodies may play an important role in the pathogenesis of Alzheimer disease (AD), but little is known about the avidity of these antibodies. We investigated the avidity and levels of anti-Abeta antibodies in 20 AD patients and 40 healthy controls by an enzyme-linked immunosorbent assay with thiocyanate elution. Our data revealed that both the levels and the avidity of anti-Abeta antibodies were statistically lower in AD patients than in healthy controls. However, there was no correlation between both of them, suggesting that the levels and the avidity of anti-Abeta antibodies might be regulated by different mechanisms. We hypothesize that incomplete B cell immune tolerance may be the major reason for low antibody avidity in AD patients. Avidity declination in AD patients should have immunopathologic implications as antigen-antibody complexes containing low avidity antibodies are not readily cleared by the immune system.

Antibody responses induced by long-term vaccination with an octovalent conjugate Pseudomonas aeruginosa vaccine in children with cystic fibrosis

We assessed the serological responses over 10 years to repeated immunization of cystic fibrosis (CF) patients with an O-polysaccharide (OPS)-toxin A conjugate vaccine against Pseudomonas aeruginosa. A retrospective analysis was performed with sera from 25 vaccinated and 25 unvaccinated children treated at the same CF centre and matched for clinical management, age and gender. Yearly immunization led to sustained elevations of serum immunoglobulin G (IgG) antibody levels to all vaccine components. Eighteen unvaccinated patients but only eight vaccinated ones developed chronic pseudomonal lung infections. Infection rapidly caused further marked elevations of polysaccharide- but not toxin A-specific serum IgG in both immunized and nonimmunized patients, indicating that protection did not depend on the quantity of IgG present. However, qualitative analyses revealed that the protective capacity of specific serum IgG antibodies was linked to high affinity and to specificity for OPS serotypes rather than for lipopolysaccharide core epitopes.

Longevity of the Immune Response and Memory to Blood-Stage Malaria Infection

Immunity to malaria develops slowly with protection against the parasite lagging behind protection against disease symptoms. The data on the longevity of protective immune responses are sparse. However, studies of antibody responses associated with protection reveal that they consist of a short- and a long-lived component. Compared with the antibody levels observed in other infection and immunization systems, the levels of the short-lived antibody compartment drop below the detectable threshold with unusual rapidity. The prevalence of long-lived antibodies is comparable to that seen after bacterial and protozoan infections. There is even less available data concerning T cell longevity in malaria infection, but what there is seems to indicate that T cell memory is short in the absence of persistent antigen. In general, the degree and duration of parasite persistence represent a major factor determining how immune response longevity and protection correlate. The predilection for short-lived immune responses in malaria infection could be caused by a number of mechanisms resulting from the interplay of normal regulatory mechanisms of the immune system and immune evasion by the parasite. In conclusion, it appears that the parasite-host relationship has developed to favor some short-lived responses, which allow the host to survive while allowing the parasite to persist. Anti-malarial immune responses present a complex picture, and many aspects of regulation and longevity of the response require further research.

Pathophysiology and management of pulmonary infections in cystic fibrosis

This comprehensive State of the Art review summarizes the current published knowledge base regarding the pathophysiology and microbiology of pulmonary disease in cystic fibrosis (CF). The molecular basis of CF lung disease including the impact of defective cystic fibrosis transmembrane regulator (CFTR) protein function on airway physiology, mucociliary clearance, and establishment of Pseudomonas aeruginosa infection is described. An extensive review of the microbiology of CF lung disease with particular reference to infection with P. aeruginosa is provided. Other pathogens commonly associated with CF lung disease including Staphylococcal aureus, Burkholderia cepacia, Stenotrophomonas maltophilia, Achromobacter xylosoxidans and atypical mycobacteria are also described. Clinical presentation and assessment of CF lung disease including diagnostic microbiology and other measures of pulmonary health are reviewed. Current recommendations for management of CF lung disease are provided. An extensive review of antipseudomonal therapies in the settings of treatment for early P. aeruginosa infection, maintenance for patients with chronic P. aeruginosa infection, and treatment of exacerbation in pulmonary symptoms, as well as antibiotic therapies for other CF respiratory pathogens, are included. In addition, the article discusses infection control policies, therapies to optimize airway clearance and reduce inflammation, and potential future therapies.

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.

Antibodies against beta-lactamase can improve ceftazidime treatment of lung infection with beta-lactam-resistant Pseudomonas aeruginosa in a rat model of chronic lung infection

To test the hypothesis that antibodies against the chromosomal beta-lactamase of Pseudomonas aeruginosa (a beta ab) might act as beta-lactamase inhibitors in patients with cystic fibrosis and chronic lung infection with P. aeruginosa, we compared in a rat model of chronic lung infection the efficacy of treatment with ceftazidime in beta-lactamase-immunized (group I) and non-immunized (group II) rats. Chronic lung infection was established with alginate-embedded P. aeruginosa producing high amounts of beta-lactamase in 133 Lewis rats. Prior to infection, group I (66 rats) was immunized three times at 2-week intervals with purified beta-lactamase in incomplete Freund's adjuvant (IFA) and group II (67 rats) received IFA. Ceftazidime treatment was initiated after challenge and continued for 10 days, after which the rats were sacrificed and the lung bacteriology and pathology were analysed. Rat serum was analysed for the beta-lactamase inhibitory activity and a beta ab-specific IgG and IgG subclasses titres. Beta-lactamase inhibitory activity was found only in sera of rats belonging to group I and it was used to divide these rats into two subgroups: rats whose sera inhibited > or = 75% of beta-lactamase activity (responders) and rats whose sera inhibited < or = 25% of beta-lactamase activity (non-responders). The responder subgroup had significantly smaller pathological areas in the lungs and lower cfu/ml lung homogenate compared to the non-immunized group (p=0.02 and p=0.01, respectively) and compared to the non-responder subgroup (p=0.008 and p=0.0001, respectively). On the day of challenge, significantly higher titres of a beta ab-specific IgG and IgG subclasses antibodies were found in the responders compared to the non-responders (p<0.0001). In the responder subgroup the avidity of IgG a beta ab was significantly higher than in the non-responder subgroup (p=0.0003). Our study showed that a beta ab with beta-lactamase inhibitory activity raised by immunization with beta-lactamase can improve the outcome of treatment with ceftazidime of resistant P. aeruginosa in a rat model of chronic lung infection.

Pseudomonas aeruginosa and the in vitro and in vivo biofilm mode of growth

The biofilm mode of growth is the survival strategy of environmental bacteria like Pseudomonas aeruginosa. Such P. aeruginosa biofilms also occur in the lungs of chronically infected cystic fibrosis patients, where they protect the bacteria against antibiotics and the immune response. The lung tissue damage is due to immune complex mediated chronic inflammation dominated by polymorphonuclear leukocytes releasing proteases and oxygen radicals.