Antigenic characteristics of polypeptides of Coxiella burnetii isolates

Engineering Protein Nanoparticles Functionalized with an Immunodominant Coxiella burnetii Antigen to Generate a Q Fever Vaccine

Coxiella burnetii is the causative agent of Q fever, for which there is yet to be an FDA-approved vaccine. This bacterial pathogen has both extra- and intracellular stages in its life cycle, and therefore both a cell-mediated (i.e., T lymphocyte) and humoral (i.e., antibody) immune response are necessary for effective eradication of this pathogen. However, most proposed vaccines elicit strong responses to only one mechanism of adaptive immunity, and some can either cause reactogenicity or lack sufficient immunogenicity. In this work, we aim to apply a nanoparticle-based platform toward producing both antibody and T cell immune responses against C. burnetii. We investigated three approaches for conjugation of the immunodominant outer membrane protein antigen (CBU1910) to the E2 nanoparticle to obtain a consistent antigen orientation: direct genetic fusion, high affinity tris-NTA-Ni conjugation to polyhistidine-tagged CBU1910, and the SpyTag/SpyCatcher (ST/SC) system. Overall, we found that the ST/SC approach yielded nanoparticles loaded with the highest number of antigens while maintaining stability, enabling formulations that could simultaneously co-deliver the protein antigen (CBU1910) and adjuvant (CpG1826) on one nanoparticle (CBU1910-CpG-E2). Using protein microarray analyses, we found that after immunization, antigen-bound nanoparticle formulations elicited significantly higher antigen-specific IgG responses than soluble CBU1910 alone and produced more balanced IgG1/IgG2c ratios. Although T cell recall assays from these protein antigen formulations did not show significant increases in antigen-specific IFN-γ production compared to soluble CBU1910 alone, nanoparticles conjugated with a CD4 peptide epitope from CBU1910 generated elevated T cell responses in mice to both the CBU1910 peptide epitope and whole CBU1910 protein. These investigations highlight the feasibility of conjugating antigens to nanoparticles for tuning and improving both humoral- and cell-mediated adaptive immunity against C. burnetii.

Coxiella burnetii in wild mammals: A systematic review

Coxiella burnetii is a multi-host bacterium that causes Q fever in humans, a zoonosis that is emerging worldwide. The ecology of C. burnetii in wildlife is still poorly understood and the influence of host, environmental and pathogen factors is almost unknown. This study gathers current published information on different aspects of C. burnetii infection in wildlife, even in species with high reservoir potential and a high rate of interaction with livestock and humans, in order to partially fill the existing gap and highlight future needs. Exposure and/or infection by C. burnetii has, to date, been reported in 109 wild mammal species. The limited sample size of most of the existing studies could suggest an undervalued prevalence of C. burnetii infection. Knowledge on the clinical outcome of C. burnetii infection in wildlife is also very limited, but currently includes reproductive failure in waterbuck (Kobus ellipsiprymnus), roan antelope (Hippotragus niger), dama gazelle (Nanger dama) and water buffalo (Bubalus bubalis) and placentitis in the Pacific harbor seal (Phoca vitulina richardsi), Steller sea lion (Eumetopias jubatus) and red deer (Cervus elaphus). The currently available serological tests need to be optimised and validated for each wildlife species. Finally, there is a huge gap in the research on C. burnetii control in wildlife, despite of the increasing evidence that wildlife is a source of C. burnetii for both livestock and humans.

Genotypes of Coxiella burnetii in wildlife: disentangling the molecular epidemiology of a multi-host pathogen

Evidences point to a relevant role of wildlife in the ecology of Coxiella burnetii worldwide. The lack of information on C. burnetii genotypes in wildlife prevents tracing-back clinical animal and human Q fever cases with potential wildlife origin. To compare C. burnetii genotypes circulating in wildlife, livestock and humans, 107 samples from red deer, European wild rabbit, racoon, small mammals, goat and sheep were genotyped by polymerase chain reaction and reverse line blot hybridization. Genomic groups I, II, VI and VII were found in wildlife and groups I, II, III and IV in domestic ruminants. Livestock genotypes clustered mainly with genotypes reported previously in livestock. Genotyping confirmed previous findings that suggest that C. burnetii may display host specificity since most genotypes of sympatric deer and rabbits clustered in separate groups. Wildlife genotypes clustered with genotypes from ticks and from acute hepatitis human Q fever cases, suggesting that particular C. burnetii genotypes circulating in a wildlife-tick cycle may occasionally jump into humans through tick bites or exposure to wildlife. This finding could be behind the reported geographic variation in the clinical presentation of acute Q fever in humans in Spain: atypical pneumonia in the north and hepatitis in the south.

Detection of Q Fever Specific Antibodies Using Recombinant Antigen in ELISA with Peroxidase Based Signal Amplification

Currently, the accepted method for Q fever serodiagnosis is indirect immunofluorescent antibody assay (IFA) using the whole cell antigen. In this study, we prepared the recombinant antigen of the 27-kDa outer membrane protein (Com1) which has been shown to be recognized by Q fever patient sera. The performance of recombinant Com1 was evaluated in ELISA by IFA confirmed serum samples. Due to the low titers of IgG and IgM in Q fever patients, the standard ELISA signals were further amplified by using biotinylated anti-human IgG or IgM plus streptavidin-HRP polymer. The modified ELISA can detect 88% (29 out of 33) of Q fever patient sera collected from Marines deployed to Iraq. Less than 5% (5 out of 156) of the sera from patients with other febrile diseases reacted with the Com1. These results suggest that the modified ELISA using Com1 may have the potential to improve the detection of Q fever specific antibodies.

Comparison of Japanese Isolates ofCoxiella burnetiiby PCR-RFLP and Sequence Analysis

The genetic variation of Japanese isolates of Coxiella burnetii, the agent of Q fever, was found for the first time. Forty-nine out of 72 isolates had the chronic pattern of the isocitrate hydrogenase gene. Sequence analysis revealed that the isolates have a specific nucleotide sequence. The putative amino acid sequence was the same as that of chronic reference strains. These results suggest the variation of C. burnetii isolates in Japan.

Microevolution of the chromosomal region of acute disease antigen A (adaA) in the query (Q) fever agent Coxiella burnetii

The acute disease antigen A (adaA) gene is believed to be associated with Coxiella burnetii strains causing acute Q fever. The detailed analysis of the adaA genomic region of 23 human- and 86 animal-derived C. burnetii isolates presented in this study reveals a much more polymorphic appearance and distribution of the adaA gene, resulting in a classification of C. burnetii strains of better differentiation than previously anticipated. Three different genomic variants of the adaA gene were identified which could be detected in isolates from acute and chronic patients, rendering the association of adaA positive strains with acute Q fever disease disputable. In addition, all adaA positive strains in humans and animals showed the occurrence of the QpH1 plasmid. All adaA positive isolates of acute human patients except one showed a distinct SNP variation at position 431, also predominant in sheep strains, which correlates well with the observation that sheep are a major source of human infection. Furthermore, the phylogenetic analysis of the adaA gene revealed three deletion events and supported the hypothesis that strain Dugway 5J108-111 might be the ancestor of all known C. burnetii strains. Based on our findings, we could confirm the QpDV group and we were able to define a new genotypic cluster. The adaA gene polymorphisms shown here improve molecular typing of Q fever, and give new insights into microevolutionary adaption processes in C. burnetii.

Antigenic analysis for vaccines and diagnostics

Coxiella burnetii infection is frequently unrecognized or misdiagnosed, as symptoms generally mimic an influenza-like illness. However, the disease (Q fever) may result in chronic infection, usually manifesting as potentially fatal endocarditis. The development of a chronic fatigue-like sequela may also occur. Infected ruminants are the major reservoir for infection in humans, primarily through exposure to birth products or aerosols that transmit the bacterium over wide regions. A vaccine against C. burnetii infection has been in use in Australia for abattoir and agricultural workers for many years. The possibility of adverse reactions in those with previous exposure to the agent has prevented its use elsewhere. Subunit vaccines, utilizing chemical extraction of components thought to cause adverse reactions, are in development, but none are yet licensed. Others have sought to combine immunogenic peptides with or without selected lipopolysaccharide components to produce a vaccine without the possibility of adverse reactions. Selected immunogenic proteins have been shown to induce both humoral and cellular immune responses. Although current diagnosis of infection relies on serological testing, the presentation of specific antibody occurs 7-15 days following the onset of symptoms, delaying treatment that may result in prolonged morbidity. PCR detection of DNA to specific C. burnetii antigens in the blood is possible early in infection, but PCR may become negative when PII IgG antibodies appear. PCR is useful for early diagnosis when Q fever is suspected, as in large epidemics, and shortens the delay in the identification of Q fever endocarditis. Others have combined PCR with ELISA or other methods to increase the ability to detect infection at any stage. The search for new diagnostic reagents and vaccines has utilized new methods for discovery of immunoreactive proteins. DNA analysis of the heterogeneity of C. burnetii isolates has led to a greater understanding of the diversity of isolates and a means to determine whether there is a correlation between strain and disease severity. 2-D SDS PAGE of immunogenic proteins reactive with human or animal infection sera and mass spectrometric analysis of specific secreted or outer membrane proteins have identified candidate antigens. Microarrays have allowed the analysis of peptide libraries of open reading frames to evaluate the immunogenicity of complete genomes.

Strain and phase identification of the U.S. category B agent Coxiella burnetii by matrix assisted laser desorption/ionization time-of-flight mass spectrometry and multivariate pattern recognition

Accurate bacterial identification is important in diagnosing disease and in microbial forensics. Coxiella burnetii, a highly infective microorganism causative of the human disease Q fever, is now considered a U.S. category B potential bioterrorism agent. We report here an approach for the confirmatory identification of C. burnetii at the strain level which involves the combined use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and supervised pattern recognition via Partial Least Squares-Discriminant Analysis (PLS-DA). C. burnetii isolates investigated in this study included the following prototype strains from different geographical and/or historical origins and with different antigenic properties: Nine Mile I, Australian QD, M44, KAV, PAV, Henzerling, and Ohio. After culture and purification following standard protocols, linear MALDI-TOF mass spectra of pure bacterial cultures were acquired in positive ion mode. Mass spectral data were normalized, baseline-corrected, denoised, binarized and modeled by PLS-DA under crossvalidation conditions. Robustness with respect to uncontrolled variations in the sample preparation and MALDI analysis protocol was assessed by repeating the experiment on five different days spanning a period of 6 months. The method was validated by the prediction of unknown C. burnetii samples in an independent test set with 100% sensitivity and specificity for five out of six strain classes.

Vaccines against Coxiella infection

Coxiella burnetii is an obligate intracellular bacterium that causes a worldwide zoonotic disease, Q fever. Since C. burnetii infection is an occupational hazard and could develop into severe chronic disease in humans, vaccination should be considered to protect individuals at-risk of contact with naturally infected animals or exposure to the agents. Although several vaccines produced from Phase I whole-cell C. burnetii are effective in protecting against the infection in humans, vaccination of previously sensitized people can induce severe local and occasional systemic reactions. Safe use of these vaccines requires screening of potential vaccinees by skin tests, serological tests, or in vitro lymphocyte proliferation assay. Since these procedures are time-consuming and costly, they limit the use of whole-cell vaccines in a mass vaccination program. Efforts have been underway to develop a safer, more effective new-generation vaccine that will not cause adverse reactions when given to someone with pre-existing immunity. This article describes new information relating to the characterization of acquired immunity to C. burnetii infection that will provide a fundamental understanding of the development of protective immunity against Q fever. Recent works focused on development of recombinant vaccines against this pathogen offers promise in the pursuit of a new Q fever vaccine.

New criteria for immunofluorescence assay for Q fever diagnosis in Japan

A study was made to evaluate the cutoff value of indirect immunofluorescent-antibody (IFA) test for Q fever diagnosis in Japan. We used 346 sera, including 16 from confirmed Q fever cases, 304 from Japanese pneumonia patients, and 26 from negative cases. Thirteen sera from the confirmed Q fever cases with an immunoglobulin M (IgM) titer of > or =1:128 and/or IgG titer of > or =1:256 by the IFA test were positive by both enzyme-linked immunosorbent assay (ELISA) and Western blotting assay (WBA), whereas 298 sera from pneumonia patients and 26 negative sera with an IgM titer of < or =1:16 and an IgG titer of < or =1:32 by the IFA test were negative by both ELISA and WBA. In the proposed "equivocal area," with an IgM titer of > or =1:32 and < or =1:64 and/or an IgG titer of > or =1:64 and < or =1:128, we found 9 sera, 3 from confirmed Q fever cases and 6 from Japanese pneumonia patients, by the IFA test. Three sera from the confirmed Q fever cases and one of the sera from pneumonia patients were IgM and/or IgG positive by both ELISA and WBA. These results suggest that a single cutoff value for the IFA test may cause false-positive and false-negative results. In conclusion, this study showed that an "equivocal area" should be used for the IFA test rather than a single cutoff value and that sera in the equivocal area should be tested by additional serological assays for confirmation.

Identification and characterization of an immunodominant 28-kilodalton Coxiella burnetii outer membrane protein specific to isolates associated with acute disease

Coxiella burnetii causes acute Q fever in humans and occasional chronic infections that typically manifest as endocarditis or hepatitis. Isolates associated with acute disease were found to be distinct from a group of chronic disease isolates by a variety of biochemical parameters and in a guinea pig fever model of acute disease, suggesting a difference in virulence potential. We compared antigenic polypeptides among C. burnetii isolates and found an immunodominant 28-kDa protein in acute group isolates but not in chronic group isolates (T. Ho, A. Hotta, G. Q. Zhang, S. V. Nguyen, M. Ogawa, T. Yamaguchi, H. Fukushi, and K. Hirai, Microbiol. Immunol. 42:81-85, 1998). In order to clone the adaA gene, the N-terminal amino acid sequence of adaA was determined and a 59-bp fragment was amplified from Nine Mile phase I DNA by PCR. The putative gene fragment was used to screen a lambda ZAP II genomic DNA library, and an open reading frame expressing a 28-kDa immunoreactive protein was identified. Sequence analysis predicted a gene encoding an approximately 28-kDa mature protein with a typical signal sequence. The adaA (acute disease antigen A) gene was detected in acute group C. burnetii isolates but not identified in chronic group isolates by PCR and Southern blotting. A typical signal peptide was predicted in adaA, and specific antibody to adaA reacted with the purified membrane fraction of acute group isolates by Western blotting, suggesting that adaA is exposed on the outer surface of C. burnetii. adaA was overexpressed in pET23a as a fusion protein in Escherichia coli to develop anti-recombinant adaA (anti-radaA) specific antibody, which recognized a approximately 28-kDa band in acute group isolates but not in chronic group isolates. In addition, immunoblotting indicates that radaA reacted with sera derived from animals infected with acute group isolates but did not react with sera from animals infected with chronic group isolates. These results support the idea that an adaA gene-targeted PCR assay and an radaA antigen-based serodiagnostic test may be useful for differential diagnosis of acute and chronic Q fever.

Identification and cloning of immunodominant antigens of Coxiella burnetii

A sublethal-challenge model was established in BALB/c mice by using protection from the development of severe splenomegaly as an indicator of vaccinogenic activity for evaluation of the protective efficacies of vaccine candidates. To determine the immunodominant antigens as defined by reaction to an infection-derived antibody, mouse sera from different stages of experimental infection with various doses of Coxiella burnetii were tested by immunoblotting. Proteins with molecular masses of 14, 16, 21, 28, 32, 45 to 50, 57, and 60 kDa were recognized as immunodominant antigens. Antibody responses in whole-cell antigen (WCA)-vaccinated mice were compared with those in unvaccinated mice by immunoblotting using two-dimensional gel-separated C. burnetii antigens. The results indicated that there were significantly different antibody responses during different stages of vaccination and challenge, suggesting that several specific immunogenic antigens may play critical roles in the protection of mice against challenge. To clone these immunogenic antigens, a genomic DNA library of Nine Mile phase I was screened with convalescent-phase antisera from mice. Eighteen novel immunoreactive proteins with molecular masses ranging from approximately 14 to 67 kDa were cloned and identified. Interestingly, several recombinant proteins reacted with sera from both early-stage infected and WCA-vaccinated prechallenged mice. These results suggest that these proteins may play critical roles in the development of protective immunity and that they are logical candidates for vaccine and serodiagnostic reagents.

Use of Monoclonal Antibodies for Analyses of Coxiella burnetii Major Antigens

Monoclonal antibodies (MAbs) to major antigens of Coxiella burnetii were produced. Some of the MAbs to a 62-kDa protein antigen, peptidoglycan protein complex and lipopolysaccharide (LPS) O-chains reacted with other bacteria whereas none of the MAbs to outer membrane proteins and LPS outer-core did. The LPS outer-core and OMPs may be useful antigens for specifically detecting antibodies to C. burnetii.

Use of monoclonal antibodies to lipopolysaccharide for antigenic analysis of Coxiella burnetii

Antigenic differences among Coxiella burnetii strains were analyzed. The monoclonal antibodies against the lipopolysaccharide outer core did not react with the strains containing a QpRS plasmid or with plasmidless strains, whereas they reacted with strains containing a QpH1 or QpDV plasmid. C. burnetii isolates could be divided into two groups immunologically.

[Q fever in Gran Canaria: 40 new cases]

INTRODUCTION

The aim of this study was to describe the clinical and epidemiologic features of Q fever in the southern area of the island of Gran Canaria (Spain).

METHODS

We conducted a retrospective analysis of the clinical and epidemiological data of the cases of Q fever diagnosed by the Microbiology Laboratory of the Hospital Universitario Insular in Gran Canaria between 1998 and 2000. Antibodies against phase II Coxiella burnetii antigens were detected using an indirect immunofluorescence test. The diagnosis of acute Q fever was established by IgG titers > or = 1:320 and IgM titers > or = 1:80, or by seroconversion.

RESULTS

During the period of study 59 cases of acute Q fever were diagnosed, making an incidence of 5 cases/100,000 inhabitants/year. The seroprevalence (IgG > or = 1:80) in the patients for whom Q fever serology was requested during that period was 23.9%. Clinical and epidemiologic data were available for 40 patients. All were sporadic cases and 57% were hospitalized. The mean age of the patients was 40.6 6 13.3 years (range 20-74 years), 85% were males and 67.5% came from a rural background. The majority of cases (65%) clustered from April to July. The most frequent clinical presentation was an acute febrile process with elevated liver enzymes (87.5%). Pneumonia was infrequent (only three cases).

CONCLUSIONS

In our area Q fever is mainly manifested as an acute febrile illness with subclinical hepatic involvement. This fact and the small number of cases with pneumonia and chronic forms suggest the etiological involvement of C. burnetii strains different from those in other geographic areas.

Phase variation analysis of Coxiella burnetii during serial passage in cell culture by use of monoclonal antibodies

Antigenic changes in Coxiella burnetii Nine Mile strain phase I during serial passages in cell culture were analyzed with three groups of monoclonal antibodies (MAbs) against lipopolysaccharide. The MAbs of group 1 did not react with organisms that were passaged over five times, and the MAbs of group 2 did not react with organisms that were passaged over eight times. The MAbs of group 3 reacted with organisms passaged up to 15 times but did not react with phase II cells. These results suggest that C. burnetii could be differentiated into four phase states during phase variation.

Characterization of the Coxiella burnetti sucB gene encoding an immunogenic dihydrolipoamide succinyltransferase

The Coxiella burnetii sucB gene encoding the dihydrolipoamide succinyltransferase (E2o) enzyme was cloned by immunological screening of a lambda EMBL3 genomic library prepared from strain Nine Mile DNA and sequenced. The homology of the cloned gene product to the counterpart in Escherichia coli was 54.3%, but the homology of the N-terminal region was only 42%. The gene was expressed in E. coli as an independent unit from its own promoter, producing an immunoreactive protein of about 50 kDa on SDS-PAGE which reacted with antisera from laboratory animals and sera from human patients with acute Q fever. The study results suggest that the C. burnetii E2o enzyme may serve as a potential target antigen for diagnostic assays for Q fever.

Evaluation of a recombinant 27-kDa outer membrane protein of Coxiella burnetii as an immunodiagnostic reagent

The 27-kDa outer membrane protein from eight strains of Coxiella burnetii was expressed in the pET-21c protein expression system. Two fusion proteins with molecular masses of 30 and 32 kDa were evident in all eight of the recombinants by SDS-PAGE and immunoblotting. A protein having an approximate size of 30 kDa was purified from the Escherichia coli lysates by one-step affinity purification. The utility of the purified recombinant protein in ELISA was also evaluated by testing its reactivity with human sera and comparing this reactivity with that of Nine Mile phase II antigen. All of the 40 IF-positive serum samples were ELISA-positive for both the Nine Mile phase II and recombinant antigens, and negative serum controls were negative for both antigens. These results suggest that ELISA with the 27-kDa recombinant antigen is a sensitive and specific method for detecting anti-C. burnetii antibodies in human sera.

Advances in the understanding of Coxiella burnetii infection in Japan

Q fever is a zoonotic disease caused by a rickettsia Coxiella burnetii. Since its first description in 1937, the disease has been found to be present in most countries of the world. Serological evidences of Q fever in humans and coxiellosis in animals were reported in Japan in the 1950s, however, systematic studies of the disease did not begin until the report of isolation of C. burnetii from an acute Q fever patient in 1989. In addition to the extensive information about epidemiology of the disease, the understanding of Japanese isolates of C. burnetii is increasing rapidly in recent years. In this review, the epidemiology of the disease along with some characteristics of isolates of C. burnetii in Japan is summarized in five sections, i.e., coxiellosis, Q fever, modes of spread of the infection, laboratory diagnosis of the infection and some characteristics of Japanese isolates. This review includes some recent, unpublished data from our and other groups.