Mycobacteria Counteract a TLR-Mediated Nitrosative Defense Mechanism in a Zebrafish Infection Model

Pulmonary tuberculosis (TB), caused by the intracellular bacterial pathogen Mycobacterium tuberculosis (Mtb), is a major world health problem. The production of reactive nitrogen species (RNS) is a potent cytostatic and cytotoxic defense mechanism against intracellular pathogens. Nevertheless, the protective role of RNS during Mtb infection remains controversial. Here we use an anti-nitrotyrosine antibody as a readout to study nitration output by the zebrafish host during early mycobacterial pathogenesis. We found that recognition of Mycobacterium marinum, a close relative of Mtb, was sufficient to induce a nitrosative defense mechanism in a manner dependent on MyD88, the central adaptor protein in Toll like receptor (TLR) mediated pathogen recognition. However, this host response was attenuated by mycobacteria via a virulence mechanism independent of the well-characterized RD1 virulence locus. Our results indicate a mechanism of pathogenic mycobacteria to circumvent host defense in vivo. Shifting the balance of host-pathogen interactions in favor of the host by targeting this virulence mechanism may help to alleviate the problem of infection with Mtb strains that are resistant to multiple drug treatments.

由胞内细菌病原体结核分枝杆菌（Mycobacterium tuberculosis, Mtb）引发的肺结核（Pulmonary tuberculosis, TB）是全球重大公共卫生问题。活性氮类物质（reactive nitrogen species, RNS）的产生是对抗胞内病原体的强效细胞生长抑制与细胞毒性防御机制。然而，RNS在Mtb感染过程中的保护作用仍存在争议。本研究以抗硝基酪氨酸抗体作为检测指标，探究斑马鱼宿主在分枝杆菌感染早期致病过程中的硝基化产物生成情况。研究发现，识别结核分枝杆菌的近缘菌种海分枝杆菌（Mycobacterium marinum），即可诱导依赖于MyD88的亚硝化防御机制——MyD88是Toll样受体（Toll-like receptor, TLR）介导的病原体识别通路中的核心适配蛋白。不过，分枝杆菌可通过一种独立于已被充分表征的RD1毒力基因座的毒力机制，削弱该宿主防御反应。本研究结果揭示了致病性分枝杆菌在体内规避宿主防御的机制。通过靶向该毒力机制以调整宿主与病原体互作的平衡，使其偏向宿主，或可有助于缓解多重耐药Mtb菌株感染的问题。