Virulence and Immunity Orchestrated by the Global Gene Regulator sigL in Mycobacterium avium subsp. paratuberculosis

Abstract

b Mycobacterium avium subsp. paratuberculosis causes Johne's disease in ruminants, a chronic enteric disease responsible for severe economic losses in the dairy industry. Global gene regulators, including sigma factors are important in regulating mycobacterial virulence. However, the biological significance of such regulators in M. avium subsp. paratuberculosis rremains elusive. To better decipher the role of sigma factors in M. avium subsp. paratuberculosis pathogenesis, we targeted a key sigma factor gene, sigL, activated in mycobacterium-infected macrophages. We interrogated an M. avium subsp. paratuberculosis ⌬sigL mutant against a selected list of stressors that mimic the host microenvironments. Our data showed that sigL was important in maintaining bacterial survival under such stress conditions. Survival levels further reflected the inability of the ⌬sigL mutant to persist inside the macrophage microenvironments. Additionally, mouse infection studies suggested a substantial role for sigL in M. avium subsp. paratuberculosis virulence, as indicated by the significant attenuation of the ⌬sigL-deficient mutant compared to the parental strain. More importantly, when the sigL mutant was tested for its vaccine potential, protective immunity was generated in a vaccine/challenge model of murine paratuberculosis. Overall, our study highlights critical role of sigL in the pathogenesis and immunity of M. avium subsp. paratuberculosis infection, a potential role that could be shared by similar proteins in other intracellular pathogens.

Superior Protection from Live-Attenuated Vaccines Directed against Johne's Disease

“…Due to this limitation, alternative forms of vaccine development have been pursued in an effort to increase the use of JD vaccines in control programs. Recent studies suggest LAVs as a strategy for creating more effective JD vaccine candidates (11)(12)(13)(14)(15)24). The primary goal of this study was to examine the performance of live-attenuated vaccines (represented by pgsH and pgsN) as a viable alternative to inactivated vaccines (represented by Mycopar) to control Johne's disease in dairy herds.…”

“…Live-attenuated vaccines (LAV) are considered advantageous because they are easy to produce and manufacture, and they have been shown to stimulate cell-mediated immunity in mice and ruminant models of JD (11)(12)(13)(14)(15). To develop our novel LAV candidates, our group employed a whole-genome expression profile of M. paratuberculosis exposed to different environmental stress conditions, or shed in cow feces, to identify new virulence genes (16).…”

Superior protection elicited by live-attenuated vaccines in the murine model of paratuberculosis

“…paratuberculosis by stimulating innate and adaptive immunity [19,20]. Moreover, manufacture of LAV is cost effective and easy to produce.…”

“…Moreover, manufacture of LAV is cost effective and easy to produce. An earlier study of M. paratuberculosis with a genetic deletion of sigL indicated the ability of this mutant to generate protective immunity in mice associated with the production of robust IFN-γ levels [19]. Others used a similar infection model in mice which showed a significant reduction in organs bacterial load following immunization with transposon-mutants of M. paratuberculosis [21,22].…”

“…We have shown that many global gene regulators such as sigma factors are activated following macrophage infection and are part of a global virulence regulatory system providing resistance to the host bactericidal activities [19,26]. Both M. paratuberculosis ∆sigH and ∆sigL mutant strains had attenuated pathogenicity in mice, suggesting their role as important virulence factors.…”