Medical Microbiology, Department of Clinical and Experimental Medicine, Faculty of Health Sciences, Linköping University, Linköping, Sweden. Mail amanda.welin @ liu.se
J Innate Immun. 2011;3(5):508-18. doi: 10.1159/000325297. Epub 2011 May 11.
The best characterized survival mechanism of Mycobacterium tuberculosis inside the macrophage is the inhibition of phagosomal maturation. Phagosomal maturation involves several steps including fusion with lysosomes and acidification. However, it has not been elucidated which components of phagosomal maturation correlate with growth restriction of virulent mycobacteria in human macrophages, and we aimed to study this. We infected human monocyte-derived macrophages with M. tuberculosis and assessed bacterial replication, translocation of CD63 to the phagosome, and phagosomal acidification. We found that unstimulated human macrophages were able to control infection with M. tuberculosis upon inoculation at a low multiplicity of infection (MOI) of 1, but not at a high MOI of 10. The low MOI resulted in a macrophage-controlled balance between host cells and bacteria. Both H37Rv and H37Ra infection, at high and low MOI, led to equally ineffective translocation of CD63 to the phagosome. On the other hand, acidification of mycobacterial phagosomes was more efficient at MOI 1 than 10 with both mycobacterial strains, consistent with a direct or indirect role for phagosomal acidification in restricting M. tuberculosis growth. Furthermore, inhibition of the vacuolar H(+)-ATPase as well as of cathepsin D led to enhanced mycobacterial replication inside the macrophage. This again shows the importance of phagosomal acidification for control of mycobacterial growth, through the activation of lysosomal hydrolases. We conclude that acidification and related functional aspects of the mature phagosome are important factors for restriction of M. tuberculosis replication in human macrophages.
分枝杆菌在巨噬细胞内的最佳特征生存机制是抑制吞噬体成熟。吞噬体成熟涉及几个步骤，包括与溶酶体融合和酸化。然而，尚未阐明与人类巨噬细胞中毒力分枝杆菌生长受限相关的吞噬体成熟的哪些成分，我们旨在对此进行研究。我们用结核分枝杆菌感染人单核细胞衍生的巨噬细胞，并评估细菌复制、CD63 向吞噬体的易位以及吞噬体酸化。我们发现，未受刺激的人巨噬细胞能够在接种低感染复数（MOI）为 1 的情况下控制结核分枝杆菌的感染，但在高 MOI 为 10 的情况下则不能。低 MOI 导致宿主细胞和细菌之间的平衡处于巨噬细胞控制之下。高 MOI 和低 MOI 下的 H37Rv 和 H37Ra 感染均导致 CD63 向吞噬体的易位同样无效。另一方面，两种分枝杆菌菌株在 MOI 为 1 时，其吞噬体酸化的效率均高于 MOI 为 10 时，这与吞噬体酸化在限制结核分枝杆菌生长中的直接或间接作用一致。此外，抑制液泡 H(+)-ATP 酶和组织蛋白酶 D 导致巨噬细胞内分枝杆菌的复制增强。这再次表明吞噬体酸化通过激活溶酶体水解酶对于控制分枝杆菌生长非常重要。我们得出结论，酸化和成熟吞噬体的相关功能方面是限制人巨噬细胞中结核分枝杆菌复制的重要因素。
