Actinobacillus pleuropneumoniae Possesses an Antiviral Activity against Porcine Reproductive and Respiratory Syndrome Virus
Article [Accepted Manuscript]
Abstract(s)
Pigs are often colonized by more than one bacterial and/or viral species during respiratory tract infections. This
phenomenon is known as the porcine respiratory disease complex (PRDC). Actinobacillus pleuropneumoniae (App) and
porcine reproductive and respiratory syndrome virus (PRRSV) are pathogens that are frequently involved in PRDC. The main
objective of this project was to study the in vitro interactions between these two pathogens and the host cells in the
context of mixed infections. To fulfill this objective, PRRSV permissive cell lines such as MARC-145, SJPL, and porcine alveolar
macrophages (PAM) were used. A pre-infection with PRRSV was performed at 0.5 multiplicity of infection (MOI) followed by
an infection with App at 10 MOI. Bacterial adherence and cell death were compared. Results showed that PRRSV preinfection
did not affect bacterial adherence to the cells. PRRSV and App co-infection produced an additive cytotoxicity
effect. Interestingly, a pre-infection of SJPL and PAM cells with App blocked completely PRRSV infection. Incubation of SJPL
and PAM cells with an App cell-free culture supernatant is also sufficient to significantly block PRRSV infection. This antiviral
activity is not due to LPS but rather by small molecular weight, heat-resistant App metabolites (,1 kDa). The antiviral
activity was also observed in SJPL cells infected with swine influenza virus but to a much lower extent compared to PRRSV.
More importantly, the PRRSV antiviral activity of App was also seen with PAM, the cells targeted by the virus in vivo during
infection in pigs. The antiviral activity might be due, at least in part, to the production of interferon c. The use of in vitro
experimental models to study viral and bacterial co-infections will lead to a better understanding of the interactions
between pathogens and their host cells, and could allow the development of novel prophylactic and therapeutic tools.
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