Porcine ISG15 exacerbates Actinobacillus pleuropneumoniae infection by promoting inflammatory cytokine release and macrophage death

Abstract:

[Background] Porcine transmissible pleuropneumonia is a respiratory disease caused by Actinobacillus pleuropneumoniae infection, and the mortality rate of the disease can reach 80%–100%. The ISG15 protein inhibits viral replication, but its study in Actinobacillus pleuropneumoniae is unknown. [Objective] To build a prokaryotic expression vector for porcine ISG15, purify the protein, and study its effect on Actinobacillus pleuropneumoniae (APP) infection. [Methods] A prokaryotic expression vector pET-28a-ISG15 was constructed for the expression of ISG15. Flow cytometry and fluorescence quantitative PCR were used to detect the death of alveolar macrophages and the expression of inflammatory cytokines after ISG15 treatment. A mouse model of APP infection was established. After intranasal administration of ISG15, the body weight, clinical symptoms, and survival of the mice were measured to analyze the influence of ISG15 on the pathogenicity of APP. [Results] ISG15 was obtained successfully after prokaryotic expression and purification. The death of alveolar macrophages and the expression levels of inflammatory cytokines interleukin-6 (IL-6) and interferon-gamma (IFN-γ) were increased after ISG15 treatment (P<0.05). Compared with the APP challenge group, the mice treated with medium- and high-dose ISG15 post-infection showed severe clinical symptoms, increased mortality, and up-regulated expression levels of IL-6, IFN-γ, and IL-1β in the lung tissue. [Conclusion] ISG15 aggravates the APP infection by promoting the death of alveolar macrophages and the expression of inflammatory cytokines. The findings provide a theoretical basis for developing methods for the prevention and treatment of APP.

Key words:Actinobacillus pleuropneumoniae;ISG15;inflammatory cytokine;macrophage