Badger macrophages fail to produce nitric oxide, a key anti-mycobacterial effector molecule

Kirstin Bilham,Stephen G. Preston,Chris Newman,David W. Macdonald,Adrian L. Smith,Amy C. Boyd,Christina D. Buesching

doi:10.1038/srep45470

Kirstin Bilham, Stephen G. Preston + Show 5 more

Open Access

https://doi.org/10.1038/srep45470

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Journal: Scientific Reports	Publication Date: Apr 6, 2017
Citations: 13	License type: open-access

Affiliation: University of Oxford

Abstract

The European badger is recognised as a wildlife reservoir for bovine tuberculosis (bTB); the control of which is complex, costly and controversial. Despite the importance of badgers in bTB and the well-documented role for macrophages as anti-mycobacterial effector cells, badger macrophage (bdMφ) responses remain uncharacterised. Here, we demonstrate that bdMφ fail to produce nitric oxide (NO) or upregulate inducible nitric oxide synthase (iNOS) mRNA following Toll-like receptor (TLR) agonist treatment. BdMφ also failed to make NO after stimulation with recombinant badger interferon gamma (bdIFNγ) or a combination of bdIFNγ and lipopolysaccharide. Exposure of bdMφ to TLR agonists and/or bdIFNγ resulted in upregulated cytokine (IL1β, IL6, IL12 and TNFα) mRNA levels indicating that these critical pathways were otherwise intact. Although stimulation with most TLR agonists resulted in strong cytokine mRNA responses, weaker responses were evident after exposure to TLR9 agonists, potentially due to very low expression of TLR9 in bdMφ. Both NO and TLR9 are important elements of innate immunity to mycobacteria, and these features of bdMφ biology would impair their capacity to resist bTB infection. These findings have significant implications for the development of bTB management strategies, and support the use of vaccination to reduce bTB infection in badgers.

Highlights

European badgers (Meles meles) are implicated as a major wildlife reservoir for bovine tuberculosis, the control of which poses substantial practical and political challenges[1,2,3]
Badger macrophages did not produce nitric oxide (NO) detectable by Griess assay following 48 hours exposure to lipopolysaccharide (LPS, Fig. 1a)
Similar treatment of murine and chicken macrophages resulted in substantial NO production (Fig. 1a)

Summary

Introduction

European badgers (Meles meles) are implicated as a major wildlife reservoir for bovine tuberculosis (bTB), the control of which poses substantial practical and political challenges[1,2,3]. Understanding of badger immune responses to bTB challenge is limited despite the potential for this research to better inform bTB control efforts as well as enhancing vaccine development and deployment strategies. Macrophages produce NO by upregulation of the iNOS gene in response to stimulation by Toll-like receptor (TLR) agonists and/or cytokines such as interferon gamma (IFNγ)[13]. Mammals typically express 10–12 TLRs that recognise different pathogen-associated molecular patterns (PAMPs)[14] and initiate a signalling cascade, triggering macrophages to produce cytokines (including IL1β,IL6, IL12 and TNFα)and enter an enhanced antimicrobial state We investigated NO production and cytokine mRNA upregulation in bdMφfollowing activation of TLR and IFNγpathways revealing two aspects of macrophage function in badgers relevant to bTB susceptibility and vaccination strategies

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