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.

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.