Badger macrophages fail to produce nitric oxide, a key antimycobacterial effector molecule

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 welldocumented role for macrophages as anti- mycobacterial effector cells, badger macrophage (bdM.) responses remain uncharacterised. Here, we demonstrate that bdM. fail to produce nitric oxide (NO) or upregulate inducible nitric oxide synthase (iNOS) mRNA following Toll- like receptor (TLR) agonist treatment. BdM. also failed to make NO after stimulation with recombinant badger interferon gamma (bdIFN phi) or a combination of bdIFN phi and lipopolysaccharide. Exposure of bdM. to TLR agonists and/ or bdIFN phi resulted in upregulated cytokine (IL1 beta, IL6, IL12 and TNF alpha) 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 bdM phi. Both NO and TLR9 are important elements of innate immunity to mycobacteria, and these features of bdM. 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.