Profiling Antibody Responses to Infections by Chlamydia abortus Enables Identification of Potential Virulence Factors and Candidates for Serodiagnosis

Corinna Foddis,Martin Ganter,Max Wilkat,Ulrike Simnacher,Vera Forsbach-Birk,Andreas Essig,David Longbottom,Konrad Sachse,Christiane Benesch,Gernot Walder

doi:10.1371/journal.pone.0080310

Abstract

Enzootic abortion of ewes (EAE) due to infection with the obligate intracellular pathogen Chlamydia (C.) abortus is an important zoonosis leading to considerable economic loss to agriculture worldwide. The pathogen can be transmitted to humans and may lead to serious infection in pregnant women. Knowledge about epidemiology, clinical course and transmission to humans is hampered by the lack of reliable diagnostic tools. Immunoreactive proteins, which are expressed in infected animals and humans, may serve as novel candidates for diagnostic marker proteins and represent putative virulence factors. In order to broaden the spectrum of immunogenic C. abortus proteins we applied 2D immunoblot analysis and screening of an expression library using human and animal sera. We have identified 48 immunoreactive proteins representing potential diagnostic markers and also putative virulence factors, such as CAB080 (homologue of the “macrophage infectivity potentiator”, MIP), CAB167 (homologue of the “translocated actin recruitment protein”, TARP), CAB712 (homologue of the “chlamydial protease-like activity factor”, CPAF), CAB776 (homologue of the “Polymorphic membrane protein D”, PmpD), and the “hypothetical proteins” CAB063, CAB408 and CAB821, which are predicted to be type III secreted. We selected two putative virulence factors for further characterization, i.e. CAB080 (cMIP) and CAB063, and studied their expression profiles at transcript and protein levels. Analysis of the subcellular localization of both proteins throughout the developmental cycle revealed CAB063 being the first C. abortus protein shown to be translocated to the host cell nucleus.

Highlights

Chlamydia (C.) abortus is an obligate intracellular bacterium with a biphasic developmental cycle involving infectious, sporelike elementary bodies (EBs) and metabolically active reticulate bodies (RBs), which reside and multiply within a non-fusogenic inclusion
The search for C. abortus proteins that are expressed in the natural host and recognized by the humoral immune response appears relevant as the identified antigens broaden the spectrum of candidates for serodiagnosis and may imply identification of virulence factors, which become targets of the immune defence by interacting with host cell components
Proteins prepared from purified elementary bodies were separated by 2D gel electrophoresis and immunoblot analysis was performed using an assortment of different sera including sheep sera from naturally and experimentally infected sheep as well as two human sera from women with severe C. abortus infection during pregnancy

Summary

Introduction

Chlamydia (C.) abortus is an obligate intracellular bacterium with a biphasic developmental cycle involving infectious, sporelike elementary bodies (EBs) and metabolically active reticulate bodies (RBs), which reside and multiply within a non-fusogenic inclusion. Only a few chlamydial antigens have been used in standardized diagnostic assays so far [4], and serological tests for detection of C. abortus-specific antibodies in humans are not available yet In these circumstances, the search for C. abortus proteins that are expressed in the natural host and recognized by the humoral immune response appears relevant as the identified antigens broaden the spectrum of candidates for serodiagnosis and may imply identification of virulence factors, which become targets of the immune defence by interacting with host cell components. The search for C. abortus proteins that are expressed in the natural host and recognized by the humoral immune response appears relevant as the identified antigens broaden the spectrum of candidates for serodiagnosis and may imply identification of virulence factors, which become targets of the immune defence by interacting with host cell components This is important as tools for targeted genetic manipulation of chlamydiae are not available yet and the number of proven virulence factors of Chlamydia spp. is limited to a few. The PmpD homologue of Chlamydia pneumoniae has been described as an adhesion protein [9]

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Conclusion