insufficient generation of mycobactericidal mediators and inadequate level of phagosomal maturation are related with susceptibility to virulent mycobacterium tuberculosis infection in mouse macrophages

insufficient generation of mycobactericidal mediators and inadequate level of phagosomal maturation are related with susceptibility to virulent mycobacterium tuberculosis infection in mouse macrophages

;Hyo-Ji eLee;Hyun-Jeong eKo;Yu-Jin eJung
journal of magnetic resonance (san diego, calif : 1997) 2016 Vol. 7 pp. -
217
elee2016frontiersinsufficient

Abstract

Tuberculosis is caused by Mycobacterium tuberculosis (M. tuberculosis, Mtb) infection, and it remains major life-threatening infectious diseases worldwide. Although Mtb has infected one-third of the present human population, only 5-10% of immunocompetent individuals are genetically susceptible to tuberculosis. All inbred strains of mice are susceptible to tuberculosis; however, some mouse strains are much more susceptible than others. In a previous report, we showed that Th1-mediated immunity was not responsible for the differential susceptibility between mouse models. To examine whether these susceptibility differences between inbred mouse strains are due to the insufficient production of effector molecules in the early stage of innate immunity, we investigated mycobacteriostatic function of bone marrow-derived macrophages (BMDMs) in resistant (BALB/c and C57BL/6) and susceptible strains (DBA/2) that were infected with virulent Mtb (H37Rv) or attenuated Mtb (H37Ra). The growth rate of virulent Mtb in infected cells was significantly higher in DBA/2 BMDMs, whereas the growth of the attenuated strain was similar in the three inbred mouse BMDM strains. In addition, the death rate of Mtb-infected cells increased with the infectious dose when DBA/2 BMDMs were infected with H37Rv. The intracellular reactive oxygen species (ROS) level was lower in DBA/2 BMDMs that were infected with virulent Mtb at an early post-infection time point. The expression levels of phagosomal maturation markers, including early endosomal antigen-1 (EEA1) and lysosome-associated membrane protein-1 (LAMP-1), were significantly decreased in DBA/2 BMDM that were infected with virulent Mtb, whereas IFNγ-treatment restored the phagosomal maturation activity. The nitric oxide (NO) production levels were also significantly lower in DBA/2 BMDMs that were infected with virulent H37Rv at late post infection points; however, this was not observed with the attenuated H37Ra strain. Furthermore, IFNγ-treatment rescued the low NO production level and insufficient Mtb growth control of DBA/2 BMDMs to the same level as of both resistant strains. The secreted TNF-α and IL-10 level were not significantly different between strains. Therefore, our findings suggest that DBA/2 BMDMs may have defects in the phagosomal maturation process and in inflammatory mediator production, as they showed innate immune defects when infected with the virulent, but not attenuated Mtb strain.

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