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

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.

Analysis of Humoral Immune Responses to Surface and Virulence-Associated Chlamydiaabortus Proteins in Ovine and Human Abortions by Use of a Newly Developed Line Immunoassay

“…Here, we have demonstrated that virulence-associated antibodies are generated predominantly in animals that have aborted. This report therefore confirms the observation that virulence-associated proteins, including the newly described SINC homolog of C. abortus (CAB063), are immunogenic in ovine abortion (10). Although ewes that have aborted are considered protected from further abortion due to C. abortus, they represent a major reservoir of the pathogen for animals and humans and therefore need to be rapidly identified.…”

“…CPAF was initially described as a chlamydial protease degrading host cell transcription factors; however, its impact on virulence and pathogenicity is currently controversially discussed (20). SINC is a type III secreted protein targeting the nuclear membrane of infected cells, which may modulate the nuclear envelope function (10,11). Here, we have demonstrated that virulence-associated antibodies are generated predominantly in animals that have aborted.…”

“…The human and animal serum samples used in this study were taken from already existing serum collections of previous studies (4,5,7,10,13,14). Human serum samples were anonymized, and their use was approved by the local ethics committee of the University of Ulm (96/09) and the local ethics committee of the University Hospital Jena (2525-04/09).…”

“…Nine immunoreactive C. abortus antigens were selected on the basis of previous work by Forsbach-Birk et al (10) to be recombinantly expressed for the production of a line immunoassay (13). These were CAB048 (MOMP; Gene ID no.…”

“…To extend the spectrum of potential diagnostic marker proteins, we identified 48 immunoreactive proteins by two-dimensional immunoblot analysis and screening of a C. abortus gene expression library in a previous project (10). From these, we have selected nine proteins for recombinant synthesis and further evaluation.…”