Actinobacillus pleuropneumoniae Possesses an Antiviral Activity against Porcine Reproductive and Respiratory Syndrome Virus

摘要

Pigs are often colonized by more than one bacterial and/or viral species during respiratory tract infections. Thisphenomenon is known as the porcine respiratory disease complex (PRDC). Actinobacillus pleuropneumoniae (App) andporcine reproductive and respiratory syndrome virus (PRRSV) are pathogens that are frequently involved in PRDC. The mainobjective of this project was to study the in vitro interactions between these two pathogens and the host cells in thecontext of mixed infections. To fulfill this objective, PRRSV permissive cell lines such as MARC-145, SJPL, and porcine alveolarmacrophages (PAM) were used. A pre-infection with PRRSV was performed at 0.5 multiplicity of infection (MOI) followed byan infection with App at 10 MOI. Bacterial adherence and cell death were compared. Results showed that PRRSV preinfectiondid not affect bacterial adherence to the cells. PRRSV and App co-infection produced an additive cytotoxicityeffect. Interestingly, a pre-infection of SJPL and PAM cells with App blocked completely PRRSV infection. Incubation of SJPLand PAM cells with an App cell-free culture supernatant is also sufficient to significantly block PRRSV infection. This antiviralactivity is not due to LPS but rather by small molecular weight, heat-resistant App metabolites (,1 kDa). The antiviralactivity 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 duringinfection in pigs. The antiviral activity might be due, at least in part, to the production of interferon c. The use of in vitroexperimental models to study viral and bacterial co-infections will lead to a better understanding of the interactionsbetween pathogens and their host cells, and could allow the development of novel prophylactic and therapeutic tools.