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Immune response in persistent bacterial infections : identification of Borrelia burgdorferi sensu lato and Chlamydia pneumoniae antigens

Immune response in persistent bacterial infections : identification of Borrelia burgdorferi sensu lato and Chlamydia pneumoniae antigens

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BUNK, Sebastian, 2007. Immune response in persistent bacterial infections : identification of Borrelia burgdorferi sensu lato and Chlamydia pneumoniae antigens [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Bunk2007Immun-7145, title={Immune response in persistent bacterial infections : identification of Borrelia burgdorferi sensu lato and Chlamydia pneumoniae antigens}, year={2007}, author={Bunk, Sebastian}, address={Konstanz}, school={Universität Konstanz} }

Immunantwort bei persistierenden bakteriellen Infektionen: Identifizierung von Borrelia burgdorferi sensu lato und Chlamydia pneumoniae Antigenen deposit-license eng application/pdf 2007 Bunk, Sebastian Bunk, Sebastian 2011-03-24T17:32:12Z 2011-03-24T17:32:12Z Borrelia burgdorferi sensu lato, the etiological agent of Lyme borreliosis (LB), and Chlamydia pneumoniae, a common cause of respiratory tract infections, are able to establish persistent infections that can be harmful to the host. Both pathogens lack an adequate serology, which appears to be linked to unique host immune responses associated with different immune evasion strategies of these bacteria.<br />Beside the clinical manifestations, the diagnosis of Borrelia infections is commonly based on serological testing, which has major shortcomings concerning sensitivity and specificity. The performance of currently available serological tests might be improved by using more sensitive and more specific Borrelia antigens. In the first part of this thesis, novel Borrelia antigens were indentified by phage display technology and characterized with regard to their diagnostic value.<br />- Genomic phage surface display libraries were generated from B. afzelii, B. burgdorferi and B. garinii. Affinity selection against IgG from LB patients revealed nine different Borrelia proteins, including the well established antigen BBK32. Another identified protein, the ribosomal protein L25, was demonstrated to be antigenic by enzyme linked immunosorbent assay using sera from 80 LB patients and 75 controls. The specificity and sensitivity of the antigen was 99% and 23%, respectively, qualifying L25 as a useful antigen when combined with others.<br />The development of a sensitive and specific C. pneumoniae serodiagnosis remains difficult because of the limited knowledge about appropriate antigens. To date, C. pneumoniae serology cannot distinguish between past and persistent infection, which represents a major shortcoming. In the second part of this thesis, novel C. pneumoniae antigens were identified and characterized using immunoproteomics. Further, it was evaluated whether the identified antigens can be used to discriminate past from persistent infections.<br />- Using a proteomic approach combined with immunoblotting, we identified 31 major C. pneumoniae antigens, including 15 novel Chlamydia antigens that showed reactivity towards IgG antibodies. When analyzing the intensity of immunoreactive spots among 19 donors with and 15 donors without evidence for persistent infection, we identified 8 persistence associated antigens and 4 antigens that were associated with non persistent infections. These data represent a basis for a serodiagnosis allowing the identification of persistently infected individuals.<br />In the third part of this thesis, the value of C. pneumoniae induced T cell responses for discriminating persistent from non-persistent infections was investigated.<br />- C. pneumoniae induced T cell responses in different donors were analyzed by flow cytometric multiparameter analysis. After stimulation of PBMC with whole bacteria or cytosol, up to 0.12% activated CD4+ T cells were detected, while no CD8+ T cell activation was found. The characterization of the activated CD4+ T cells with regard to their cytokine production and their stability, argued for memory CD4+ T cells primed during persistent infections. Indeed, C. pneumoniae induced memory CD4+ T cell responses were detected in 9 out of 17 donors with evidence, but only in 1 out of 10 donors without evidence for persistent infections, which is of potential interest for diagnostic applications.<br />Innate immune recognition of peptidoglycan (PGN) has a key role in the onset of antigen specific T cell responses and subsequent antibody production. Thus, infections with Chlamydia, a pathogen that lack detectable amounts of PGN, might provoke suboptimal adaptive immune responses possibly contributing to chlamydial persistence. Since the synthesis of chlamydial PGN is being debated, in the fourth part of the thesis, the transcription of chlamydial genes associated with PGN synthesis was analyzed.<br />Highly sensitive and specific real time PCRs were developed to analyze the transcript levels of nine chlamydial genes associated with PGN synthesis. All genes were strongly upregulated during the C. pneumoniae infection cycle in HEp 2 cells arguing for an active PGN synthesis pathway. The transcription kinetics of these genes closely coincided with the early replication phase of C. pneumoniae indicating a role for the presence of PGN in dividing chlamydial reticulate bodies (RB). Since the transcription was markedly decreased at a time when the RB differentiated back into elementary bodies (EB), PGN is likely not, or only in low amounts, present in Chlamydia EB.<br />In summary, this thesis contributes to the understanding of acquired immune responses against B. burgdorferi sensu lato and C. pneumoniae with regard to diagnostic applications. The presented data provide not only a platform for the development of new diagnostic tools that possibly overcome the current limitations but also might be of interest for vaccination and treatment strategies. Immune response in persistent bacterial infections : identification of Borrelia burgdorferi sensu lato and Chlamydia pneumoniae antigens

Dateiabrufe seit 01.10.2014 (Informationen über die Zugriffsstatistik)

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