Adh enhances Actinobacillus pleuropneumoniae pathogenicity by binding to OR5M11 and activating p38 which induces apoptosis of PAMs and IL-8 release.

Liancheng Lei,Lei Wang,Hu Zhang,Chuntong Bao,Jingmin Gu,Yanyi Che,Xin Feng,Changjiang Sun,Paul Langford Richard,Jing Zhang,Wenyu Han,Wanhai Qin,Chongtao Du

doi:10.1038/srep24058

Abstract

Members of the Trimeric Autotransporter Adhesin (TAA) family play a crucial role in the adhesion of Gram-negative pathogens to host cells, but the immunopathogenesis of TAAs remains unknown. Our previous studies demonstrated that Adh from Actinobacillus pleuropneumoniae (A. pleuropneumoniae) is required for full bacterial pathogenicity. Alveolar macrophages are the first line of defense against respiratory infections. This study compared the interactions between porcine alveolar macrophages (PAMs) and wild-type A. pleuropneumoniae (5b WT) or an Adh-deletion strain (5b ΔAdh) via gene microarray, immunoprecipitation and other technologies. We found that Adh was shown to interact with the PAMs membrane protein OR5M11, an olfactory receptor, resulting in the high-level secretion of IL-8 by activation of p38 MAPK signaling pathway. Subsequently, PAMs apoptosis via the activation of the Fax and Bax signaling pathways was observed, followed by activation of caspases 8, 9, and 3. The immunological pathogenic roles of Adh were also confirmed in both murine and piglets infectious models in vivo. These results identify a novel immunological strategy for TAAs to boost the pathogenicity of A. pleuropneumoniae. Together, these datas reveal the high versatility of the Adh protein as a virulence factor and provide novel insight into the immunological pathogenic role of TAAs.

Highlights

Adhesion is a key factor in the colonization and pathogenesis of A. pleuropneumoniae
From a comparison of the different outcomes of Adh-knockout (5bΔAdh) and wild-type (5b WT) strains in the infection of piglet porcine primary alveolar macrophages, mice and piglets, we found that Adh mediates bacterial adhesion to host cells and induces porcine alveolar macrophages (PAMs) to undergo apoptosis and release IL-8, which results in the recruitment of excessive inflammatory cells to the lungs
This study confirmed that Adh contributes to the pathogenicity of A. pleuropneumoniae by interacting with OR5M11 to activate the p38 Mitogen activated protein kinases (MAPKs) signaling pathway, resulting in PAM apoptosis and IL-8 release

Summary

Introduction

Adhesion is a key factor in the colonization and pathogenesis of A. pleuropneumoniae. Primary alveolar macrophages (PAMs) are the earliest immune cells that interact with pathogenic microbes during lung infection, and they are an important indicator of the host’s innate and specific immunity. Recent results suggest that an excessive inflammatory immune response is important in the pathogenesis of pneumonia; we speculated that Adh is likely to induce an excessive immune response that contributes to the pathogenesis of APP, rather than just mediating bacterial adhesion. This study focused on Adh, the functional domain of Apa. From a comparison of the different outcomes of Adh-knockout (5bΔAdh) and wild-type (5b WT) strains in the infection of piglet porcine primary alveolar macrophages, mice and piglets, we found that Adh mediates bacterial adhesion to host cells and induces PAMs to undergo apoptosis and release IL-8, which results in the recruitment of excessive inflammatory cells to the lungs. This study is the first to confirm that Adh mediates bacterial virulence by interacting with OR5M11, illuminating a new pathogenic mechanism for TAA and providing novel targets for bacterial vaccine development and drug treatment

Methods

Results

Conclusion