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.

MAPK Activation Is Essential for Waddlia chondrophila Induced CXCL8 Expression in Human Epithelial Cells.

BACKGROUND: Waddlia chondrophila (W. chondrophila) is an emerging agent of respiratory and reproductive disease in humans and cattle. The organism is a member of the order Chlamydiales, and shares many similarities at the genome level and in growth studies with other well-characterised zoonotic chlamydial agents, such as Chlamydia abortus (C. abortus). The current study investigated the growth characteristics and innate immune responses of human and ruminant epithelial cells in response to infection with W. chondrophila. METHODS: Human epithelial cells (HEp2) were infected with W. chondrophila for 24h. CXCL8 release was significantly elevated in each of the cell lines by active-infection with live W. chondrophila, but not by exposure to UV-killed organisms. Inhibition of either p38 or p42/44 MAPK significantly inhibited the stimulation of CXCL8 release in each of the cell lines. To determine the pattern recognition receptor through which CXCL8 release was stimulated, wild-type HEK293 cells which express no TLR2, TLR4, NOD2 and only negligible NOD1 were infected with live organisms. A significant increase in CXCL8 was observed. CONCLUSIONS/SIGNIFICANCE: W. chondrophila actively infects and replicates within both human and ruminant epithelial cells stimulating CXCL8 release. Release of CXCL8 is significantly inhibited by inhibition of either p38 or p42/44 MAPK indicating a role for this pathway in the innate immune response to W. chondrophila infection. W. chondrophila stimulation of CXCL8 secretion in HEK293 cells indicates that TLR2, TLR4, NOD2 and NOD1 receptors are not essential to the innate immune response to infection.

Waddlia chondrophila infects and multiplies in ovine trophoblast cells stimulating an inflammatory immune response.

BACKGROUND: Waddlia chondrophila (W. chondrophila) is an emerging abortifacient organism which has been identified in the placentae of humans and cattle. The organism is a member of the order Chlamydiales, and shares many similarities at the genome level and in growth studies with other well-characterised zoonotic chlamydial abortifacients, such as Chlamydia abortus (C. abortus). This study investigates the growth of the organism and its effects upon pro-inflammatory cytokine expression in a ruminant placental cell line which we have previously utilised in a model of C. abortus pathogenicity. METHODOLOGY/PRINCIPAL FINDINGS: Using qPCR, fluorescent immunocytochemistry and electron microscopy, we characterised the infection and growth of W. chondrophila within the ovine trophoblast AH-1 cell line. Inclusions were visible from 6 h post-infection (p.i.) and exponential growth of the organism could be observed over a 60 h time-course, with significant levels of host cell lysis being observed only after 36 h p.i. Expression of CXCL8, TNF-α, IL-1α and IL-1ß were determined 24 h p.i. A statistically significant response in the expression of CXCL8, TNF-α and IL-1ß could be observed following active infection with W. chondrophila. However a significant increase in IL-1ß expression was also observed following the exposure of cells to UV-killed organisms, indicating the stimulation of multiple innate recognition pathways. CONCLUSIONS/SIGNIFICANCE: W. chondrophila infects and grows in the ruminant trophoblast AH-1 cell line exhibiting a complete chlamydial replicative cycle. Infection of the trophoblasts resulted in the expression of pro-inflammatory cytokines in a dose-dependent manner similar to that observed with C. abortus in previous studies, suggesting similarities in the pathogenesis of infection between the two organisms.

Profiling antibody responses to infections by Chlamydia abortus enables identification of potential virulence factors and candidates for serodiagnosis.

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.

Inflammatory cytokine responses in a pregnant mouse model of Chlamydophila abortus infection.

Chlamydophila abortus (C. abortus) is the aetiological agent of ovine enzootic abortion (OEA). The highly elevated expression of the pro-inflammatory cytokine tumour necrosis factor-alpha (TNFalpha) and low-level expression of interferon-gamma (IFNgamma) that are detected in C. abortus-infected placentas have been implicated in the pathogenesis of OEA. Late-term abortions similar to those occurring in sheep have also been observed in mouse models of C. abortus infection. Since mouse studies have contributed significantly to our understanding of the immunological responses to chlamydial infections and serve as a good model for rapidly assessing candidate vaccines for OEA, we investigated local expression of TNFalpha and IFNgamma in infected mice. At various time points over the course of infection mice were sacrificed, serum samples obtained for serum antibody and cytokine analyses, and livers and placental tissues were removed and fixed to determine C. abortus colonisation and cytokine expression. Immunostaining for C. abortus was significantly greater in placenta compared to liver (P<0.001), whereas local IFNgamma expression was lower and TNFalpha expression was absent in the placenta compared with the liver across all time points. Serum concentrations of both IFNgamma and TNFalpha increased throughout pregnancy in infected mice. These data suggest that a protective systemic inflammatory immune response controls maternal C. abortus infection but not placental/fetal infection in mice. In contrast to sheep, murine placental TNFalpha expression does not correlate with C. abortus infection, suggesting that the immunopathogenesis of chlamydial abortion differs in these species.

Ovine trophoblast is a primary source of TNFalpha during Chlamydophila abortus infection.

Chlamydophila abortus is a Gram-negative obligate intracellular bacterium that causes infectious abortion in sheep (ovine enzootic abortion, OEA) and humans. Infected placentas recovered from sheep that experience OEA have thickened membranes, contain dense inflammatory cellular infiltrates and show evidence of intravascular thrombosis. Despite widespread inflammation, chlamydial multiplication is restricted to the chorionic trophoblast cells. To investigate the potential role of trophoblast in the initiation and propagation of placental inflammation during OEA, the AH-1 ovine trophoblast cell line was experimentally infected with C. abortus and analysed for the release of pro-inflammatory mediators. C. abortus was found to induce the release of both tumour necrosis factor-alpha (TNFalpha) and CXCL8 (interleukin-8) from AH-1 cells in a dose- and time-dependent manner. Ultra-violet (UV)-killed organisms did not elicit this profile, indicating that intracellular multiplication of C. abortus was required for release of these pro-inflammatory mediators. Exposure of AH-1 cells to recombinant ovine TNFalpha alone resulted in the release of CXCL8, suggestive of a self-propagating inflammatory cytokine and chemokine cascade. These data indicate a primary role for trophoblast in the initiation and propagation of placental inflammation during chlamydial abortion.