Use of Monoclonal Antibodies for Analyses of Coxiella burnetii Major Antigens

Genome-wide epitope mapping across multiple host species reveals significant diversity in antibody responses to Coxiella burnetii vaccination and infection

Coxiella burnetii is an important zoonotic bacterial pathogen of global importance, causing the disease Q fever in a wide range of animal hosts. Ruminant livestock, in particular sheep and goats, are considered the main reservoir of human infection. Vaccination is a key control measure, and two commercial vaccines based on formalin-inactivated C. burnetii bacterins are currently available for use in livestock and humans. However, their deployment is limited due to significant reactogenicity in individuals previously sensitized to C. burnetii antigens. Furthermore, these vaccines interfere with available serodiagnostic tests which are also based on C. burnetii bacterin antigens. Defined subunit antigen vaccines offer significant advantages, as they can be engineered to reduce reactogenicity and co-designed with serodiagnostic tests to allow discrimination between vaccinated and infected individuals. This study aimed to investigate the diversity of antibody responses to C. burnetii vaccination and/or infection in cattle, goats, humans, and sheep through genome-wide linear epitope mapping to identify candidate vaccine and diagnostic antigens within the predicted bacterial proteome. Using high-density peptide microarrays, we analyzed the seroreactivity in 156 serum samples from vaccinated and infected individuals to peptides derived from 2,092 open-reading frames in the C. burnetii genome. We found significant diversity in the antibody responses within and between species and across different types of C. burnetii exposure. Through the implementation of three different vaccine candidate selection methods, we identified 493 candidate protein antigens for protein subunit vaccine design or serodiagnostic evaluation, of which 65 have been previously described. This is the first study to investigate multi-species seroreactivity against the entire C. burnetii proteome presented as overlapping linear peptides and provides the basis for the selection of antigen targets for next-generation Q fever vaccines and diagnostic tests.

Development of a lipopolysaccharide-targeted peptide mimic vaccine against Q fever

Coxiella burnetii is a Gram-negative bacterium that causes acute and chronic Q fever in humans. Creation of a safe and effective new generation vaccine to prevent Q fever remains an important public health goal. Previous studies suggested that Ab-mediated immunity to C. burnetii phase I LPS (PI-LPS) is protective. To identify the potential peptides that can mimic the protective epitopes on PI-LPS, a PI-LPS-specific mAb 1E4 was generated, characterized, and used to screen a phage display library. Interestingly, our results indicate that 1E4 was able to inhibit C. burnetii infection in vivo, suggesting that 1E4 is a protective mAb. After three rounds of biopanning by 1E4 from the phage display library, a mimetic peptide, m1E41920, was identified, chemically synthesized, and conjugated to keyhole limpet hemocyanin (KLH) for examining its immunogenicity. The results indicate that the synthetic peptide m1E41920 was able to inhibit the binding of 1E4 to PI Ag, suggesting m1E41920 shares the same binding site of 1E4 with the epitopes of PI Ag. In addition, m1E41920-KLH elicited a specific IgG response to PI Ag, and immune sera from m1E41920-KLH-immunized mice was able to inhibit C. burnetii infection in vivo, suggesting that m1E41920 may specifically mimic the protective epitope of PI-LPS. Furthermore, m1E41920-KLH was able to confer significant protection against C. burnetii challenge. Thus, m1E41920-KLH is a protective Ag and may be useful for developing a safe and effective vaccine against Q fever. This study demonstrates the feasibility of developing a peptide mimic vaccine against Q fever.

Preparation of monoclonal antibodies for detection and identification of Francisella tularensis

Monoclonal antibodies (MAbs) against Francisella tularensis were obtained. Three MAbs specifically reacted with F. tularensis, while four MAbs reacted with other members of the genus Francisella as well. Fluorescent isothiocyanate-conjugated MAbs unequivocally stained bacterial cells in specimens from experimentally infected mice. Two MAbs agglutinated F. tularensis antigen in the agglutination tests. These MAbs should improve methods for detection and identification of F. tularensis.

Identification and Characterization of Coxiella burnetii Strains and Isolates Using Monoclonal Antibodies

We evaluated 6 monoclonal antibodies (MAbs) for their usefulness in identifying and characterizing recognized laboratory strains as well as field isolates of Coxiella burnetii. Five had been generated in response to strain Nine Mile (3 IgM class, 1 IgG class, 1 light chain producers only) and were polypeptide-specific, and 1 was anti-Priscilla (IgG class) and was lipopolysaccharide (LPS)-specific. Initially, the MAbs were used in conjunction with a dot blot assay with which we could differentiate C. burnetii from rickettsiae or chlamydiae. Confirmation of the specificity of these MAbs was provided by demonstrating that only C. burnetii antigens were recognized by certain combinations of antibodies used for immunoblotting proteins of various C. burnetii strains. Subsequently, we characterized antigens of 11 C. burnetii field isolates and 3 reference strains by Western blotting with individual MAbs. MAb 921 and 922 (IgG class), MAb 241, 242, 384, 386, 614 (IgM class), and 7A5, 7A1 (light chain) consistently recognized a protein. Staining intensity differed, depending on the strain tested, and there was variability in the size of the antigen immunoreactive with MAb 14H (IgG class, LPS-specific). The most reactive region was at about 249 kD. Variability of reactivities with field isolates was seen in both the distribution of individual bands and their intensities. We conclude that an extensive immunoblotting technique may be useful for C. burnetii strain differentiation and routine identification of C. burnetii can be accomplished using this MAb-based dot blot assay.