Publicação
Impact of differential TLR recognition of Mycobacterium tuberculosis strains for the production of nitric oxide by macrophages
| Resumo: | Tuberculosis (TB) remains one of the major worldwide threats, with approximately one third of the world population infected with the causative agent of this disease, Mycobacterium tuberculosis (Mtb). Recently developed genetic tools have showed the presence of a variety of Mtb lineages associated to the geographic distribution of the population. In our laboratory, we have been interested in the study of the immune response to Mtb strains from the Beijing family, associated to the East-Asian lineage, considered one of the most virulent Mtb lineages. The recognition of the mycobacteria soon after infection is important to promote efficient immune responses. Macrophages are one of the first innate immune cells to recognize Mtb. The capacity to eliminate the pathogen depends on the macrophage ability to recognize and develop the correct immune signaling through, for instance, the production of cytokines and of bactericidal compounds such as nitric oxide (NO). We previously found that particular Beijing Mtb strains were preferentially recognized through toll-like receptor 4 (TLR4) in addition to TLR2, and that this differential recognition had an impact in the pro- and anti-inflammatory responses of infected macrophages. In this work, we observed that a TLR4-activating Mtb strain 02-171, induced high expression of nitric oxide synthase 2 gene ( Nos2) and subsequent production of NO by infected macrophages comparatively to various TLR2-actvating Mtb strains. Our results demonstrated that this differential induction of Nos2 in Mtb strain 02-171-infected macrophages depended on the production of type I interferon (IFN) by these cells. Results from in vivo experiments showed that Mtb strain 02-171 also induced earlier and higher Nos2 expression in the lung of infected animals, as compared to TLR2-activating Mtb strains. Furthermore, our findings suggest a protective function for the early expression of Nos2 possibly to control the bacterial burden in mice infected with the TLR4-activating Mtb strain. As observed in macrophages, the regulation of Nos2 in infected mice was also dependent on type I IFN. Therefore, our results point to a protective function of early Nos2 expression and type I IFN production during infection with TLR4- activating Mtb strain and to the existence of an IFN-γ-independent regulation pathway of Nos2 expression in the context of infection by certain Mtb strains. Finally, we performed initial tests to determine the TLR4 ligand present in Mtb strain 02-171. We demonstrated that this ligand is most likely structurally different from lipopolysaccharide (LPS), thermosensitive and possibly dependent of live bacteria. This initial characterization of TLR4 ligand present in Mtb strain 02-171 will contribute to establish the experimental conditions required for an effective isolation of this molecule. |
|---|---|
| Autores principais: | Sousa, Jeremy Nicolas Carvalho |
| Ano: | 2013 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso restrito |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Tuberculosis (TB) remains one of the major worldwide threats, with approximately one third of the world population infected with the causative agent of this disease, Mycobacterium tuberculosis (Mtb). Recently developed genetic tools have showed the presence of a variety of Mtb lineages associated to the geographic distribution of the population. In our laboratory, we have been interested in the study of the immune response to Mtb strains from the Beijing family, associated to the East-Asian lineage, considered one of the most virulent Mtb lineages. The recognition of the mycobacteria soon after infection is important to promote efficient immune responses. Macrophages are one of the first innate immune cells to recognize Mtb. The capacity to eliminate the pathogen depends on the macrophage ability to recognize and develop the correct immune signaling through, for instance, the production of cytokines and of bactericidal compounds such as nitric oxide (NO). We previously found that particular Beijing Mtb strains were preferentially recognized through toll-like receptor 4 (TLR4) in addition to TLR2, and that this differential recognition had an impact in the pro- and anti-inflammatory responses of infected macrophages. In this work, we observed that a TLR4-activating Mtb strain 02-171, induced high expression of nitric oxide synthase 2 gene ( Nos2) and subsequent production of NO by infected macrophages comparatively to various TLR2-actvating Mtb strains. Our results demonstrated that this differential induction of Nos2 in Mtb strain 02-171-infected macrophages depended on the production of type I interferon (IFN) by these cells. Results from in vivo experiments showed that Mtb strain 02-171 also induced earlier and higher Nos2 expression in the lung of infected animals, as compared to TLR2-activating Mtb strains. Furthermore, our findings suggest a protective function for the early expression of Nos2 possibly to control the bacterial burden in mice infected with the TLR4-activating Mtb strain. As observed in macrophages, the regulation of Nos2 in infected mice was also dependent on type I IFN. Therefore, our results point to a protective function of early Nos2 expression and type I IFN production during infection with TLR4- activating Mtb strain and to the existence of an IFN-γ-independent regulation pathway of Nos2 expression in the context of infection by certain Mtb strains. Finally, we performed initial tests to determine the TLR4 ligand present in Mtb strain 02-171. We demonstrated that this ligand is most likely structurally different from lipopolysaccharide (LPS), thermosensitive and possibly dependent of live bacteria. This initial characterization of TLR4 ligand present in Mtb strain 02-171 will contribute to establish the experimental conditions required for an effective isolation of this molecule. |
|---|