Proinflammatory response of canine trophoblasts to Brucella canis infection.

Andrea G Fernández,Carlos A Fossati,Pablo C Baldi,Mariana C Ferrero,M Soledad Hielpos,Ana Claudia Zenclussen

doi:10.1371/journal.pone.0186561

Abstract

Brucella canis infection is an important cause of late-term abortion in pregnant bitches. The pathophysiological mechanisms leading to B. canis–induced abortion are unknown, but heavily infected trophoblasts are consistently observed. As trophoblasts responses to other pathogens contribute to placental inflammation leading to abortion, the aim of the present study was to characterize the cytokine response of canine trophoblasts to B. canis infection. To achieve this, trophoblasts isolated from term placenta of healthy female dogs were infected with B. canis, culture supernatants were harvested for cytokine determinations, and the load of intracellular viable B. canis was determined at different times post-infection. Additionally, cytokine responses were assessed in non-infected trophoblasts stimulated with conditioned media (CM) from B. canis-infected canine monocytes and neutrophils. Finally, cytokine response and bacteria replication were assessed in canine placental explants infected ex vivo. B. canis successfully infected and replicated in primary canine trophoblasts, eliciting an increase in IL-8 and RANTES (CCL5) secretion. Moreover, the stimulation of trophoblasts with CM from B. canis-infected monocytes and neutrophils induced a significant increase in IL-8, IL-6 and RANTES secretion. B. canis replication was confirmed in infected placental explants and the infection elicited an increased secretion of TNF-α, IL-8, IL-6 and RANTES. This study shows that canine trophoblasts produce proinflammatory cytokines in response to B. canis infection and/or to stimulation with factors produced by infected monocytes and neutrophils. These cytokines may contribute to placental inflammation leading to abortion in B. canis-infected pregnant bitches.

Highlights

Brucellosis is a worldwide distributed zoonosis caused by Gram negative bacteria of the Brucella genus [1]
As B. canis-infected canine trophoblasts secreted chemoattractants for monocytes (RANTES) and neutrophils (IL-8), and as a histiocytic-neutrophilic infiltrate has been described in B. canis-infected placentas, we investigated whether factors produced by B. canis-infected monocytes and neutrophils could influence the production of cytokines and chemokines by trophoblasts
Trophoblast cytokine responses are known to contribute to placental inflammation leading to infectious abortion by other pathogens [12,13,14,15,16] a fact that is especially interesting as heavily infected canine trophoblasts are observed in B. canis abortions

Summary

Introduction

Brucellosis is a worldwide distributed zoonosis caused by Gram negative bacteria of the Brucella genus [1]. Whereas most cases of human brucellosis are related to contact with secretions or tissues from livestock (cows, pigs, goats, sheep), there have been increasing reports of brucellosis acquired from infected dogs [2,3,4]. The vast majority of cases of canine brucellosis are caused by B. canis, occasional infections due to other Brucella species have been. The most prominent clinical consequences of B. canis infection in dogs relate to genital organs, including late-term abortion and fetal resorption in pregnant females, and orchiepididymitis and prostatitis in males [5,6]. The bacterial load of B. canis is extremely high in vaginal secretions of infected bitches during estrus and parturition, and in fetal and placental tissues from abortions [5]. Transmission occurs between dogs in close contact, especially in kennels where a high proportion of dogs is usually affected resulting in important economic losses due to abortions and infertility [7,8,9]

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