Growth Of Mycobacterium Tuberculosis In Macrophages Research Articles

Prospective Subunit Nanovaccine against Mycobacterium tuberculosis Infection─Cubosome Lipid Nanocarriers of Cord Factor, Trehalose 6,6' Dimycolate.

An improved vaccine is urgently needed to replace the now more than 100-year-old Bacillus Calmette-Guérin (BCG) vaccine against tuberculosis (TB) disease, which represents a significant burden on global public health. Mycolic acid, or cord factor trehalose 6,6' dimycolate (TDM), a lipid component abundant in the cell wall of the pathogen Mycobacterium tuberculosis (MTB), has been shown to have strong immunostimulatory activity but remains underexplored due to its high toxicity and poor solubility. Herein, we employed a novel strategy to encapsulate TDM within a cubosome lipid nanocarrier as a potential subunit nanovaccine candidate against TB. This strategy not only increased the solubility and reduced the toxicity of TDM but also elicited a protective immune response to control MTB growth in macrophages. Both pre-treatment and concurrent treatment of the TDM encapsulated in lipid monoolein (MO) cubosomes (MO-TDM) (1 mol %) induced a strong proinflammatory cytokine response in MTB-infected macrophages, due to epigenetic changes at the promoters of tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) in comparison to the untreated control. Furthermore, treatment with MO-TDM (1 mol %) cubosomes significantly improved antigen processing and presentation capabilities of MTB-infected macrophages to CD4 T cells. The ability of MO-TDM (1 mol %) cubosomes to induce a robust innate and adaptive response in vitro was further supported by a mathematical modeling study predicting the vaccine efficacy in vivo. Overall, these results indicate a strong immunostimulatory effect of TDM when delivered through the lipid nanocarrier, suggesting its potential as a novel TB vaccine.

Peptide-pulsed dendritic cells’ immunomodulating effect regarding Mycobacterium tuberculosis growth in macrophages

Mycobacterium tuberculosis is one of the most successful pathogens affecting humans, being the main cause of tuberculosis. It accounts for most infectious agent-related deaths worldwide; it has been estimated that a third of the world’s population are bacillus carriers. This pathogen’s evolutionary adaptation is mainly due to its ability to block a host’s immune system by preventing it using an effective immune response in cases of active tuberculosis. Peptide-based synthetic vaccines represent an alternative for counteracting tuberculosis; however, although peptide antigens can be identified, they are not recognised by a host’s immune system. An approach using dendritic cells as immunomodulating agents for increasing synthetic peptides’ antigenic capacity has thus been advanced. Dendritic cells obtained from IL to 4- and GM-CSF-treated peripheral blood mononuclear cells were pulsed with synthetic Mtb protein peptides which have been reported as participating in mycobacteria-host interactions; their amino acid sequences were modified to improve MHC-II coupling and thus increase their recognition by a host’s immune system. pMHC-II/TCR interaction triggered a lymphocyte response which controlled Mtb intracellular growth in infected macrophages. This work has been aimed at contributing to understanding dendritic cells’ role in Mycobacterium tuberculosis protein peptide antigen presentation, thereby increasing individuals’ immune response as a means of controlling the disease.

Protein tyrosine kinase, PtkA, is required for Mycobacterium tuberculosis growth in macrophages

Protein phosphorylation plays a key role in Mycobacterium tuberculosis (Mtb) physiology and pathogenesis. We have previously shown that a secreted protein tyrosine phosphatase, PtpA, is essential for Mtb inhibition of host macrophage acidification and maturation, and is a substrate of the protein tyrosine kinase, PtkA, encoded in the same operon. In this study, we constructed a ∆ptkA deletion mutant in Mtb and found that the mutant exhibited impaired intracellular survival in the THP-1 macrophage infection model, correlated with the strain’s inability to inhibit macrophage phagosome acidification. By contrast, the mutant displayed increased resistance to oxidative stress in vitro. Proteomic and transcriptional analyses revealed upregulation of ptpA, and increased secretion of TrxB2, in the ΔptkA mutant. Kinase and protein-protein interaction studies demonstrated that TrxB2 is a substrate of PtkA phosphorylation. Taken together these studies establish a central role for the ptkA-ptpA operon in Mtb pathogenesis.

Macrophage Activation by Ursolic and Oleanolic Acids during Mycobacterial Infection.

Oleanolic (OA) and ursolic acids (UA) are triterpenes that are abundant in vegetables, fruits and medicinal plants. They have been described as active moieties in medicinal plants used for the treatment of tuberculosis. In this study, we analyzed the effects of these triterpenes on macrophages infected in vitro with Mycobacterium tuberculosis (MTB). We evaluated production of nitric oxide (NO), reactive oxygen species (ROS), and cytokines (TNF-α and TGF-β) as well as expression of cell membrane receptors (TGR5 and CD36) in MTB-infected macrophages following treatment with OA and UA. Triterpenes caused reduced MTB growth in macrophages, stimulated production of NO and ROS in the early phase, stimulated TNF-α, suppressed TGF-β and caused over-expression of CD36and TGR5 receptors. Thus, our data suggest immunomodulatory properties of OA and UA on MTB infected macrophages. In conclusion, antimycobacterial effects induced by these triterpenes may be attributable to the conversion of macrophages from stage M2 (alternatively activated) to M1 (classically activated).

The Effect of the Host’s Iron Status on Tuberculosis

Several lines of evidence have suggested that iron is critical for Mycobacterium tuberculosis growth in macrophages. Macrophage iron loading in patients with African iron overload increases the risk of tuberculosis (TB) and may worsen TB outcome. Likewise, macrophage iron loading may contribute to an increased predisposition toward TB in HIV infection. Human genetic disorders or variations may increase the risk of TB or worsen its outcome through macrophage iron loading, including the haptoglobin 2-2 phenotype, NRAMP1 polymorphisms (at least in Africans and Asians), and possibly ferroportin 1 mutations, but not HFE hemochromatosis. Thus, the host's iron status may be an important yet underevaluated factor in TB prevention and therapy and in TB vaccine design.

Genome-wide requirements for Mycobacterium tuberculosis adaptation and survival in macrophages

Macrophages are central to host defense against microbes, but intracellular pathogens have evolved to evade their antimicrobial functions. Mycobacterium tuberculosis (MTB) has successfully exploited macrophages as its primary niche in vivo, but the bacterial genome-wide requirements that promote its intracellular survival remain undefined. Here we comprehensively identify the MTB genes required for survival by screening for transposon mutants that fail to grow within primary macrophages. We identify mutants showing decreased growth in macrophage environments that model stages of the host immune response. By systematically analyzing several biologically relevant data sets, we have been able to identify putative pathways that could not be predicted by genome organization alone. In one example, phosphate transport, requiring physically unlinked genes, was found to be critical for MTB growth in macrophages and important for establishing persistent infection in lungs. Remarkably, the majority of MTB genes found by this analysis to be required for survival are constitutively expressed rather than regulated by macrophages, revealing the host-adapted lifestyle of an evolutionarily selected intracellular pathogen.