Interactions between an M. tuberculosis strain overexpressing mtrA and mononuclear phagocytes

Area of Science:

• Microbiology
• Immunology
• Cell Biology

Background:

• The bacterial two-component regulatory signal transduction (2CR) system MtrAB is implicated in Mycobacterium tuberculosis (Mtb) survival within host macrophages.
• Understanding MtrAB's role is key to deciphering Mtb's pathogenesis and developing novel therapeutic strategies.

Purpose of the Study:

• To investigate the influence of the MtrAB system on the interaction between Mtb and human monocytes.
• To analyze the impact of MtrA overexpression and phosphorylation-defective MtrA mutants on Mtb's intracellular survival.

Main Methods:

• Flow cytometry assessed MHC class II molecule expression on monocytes.
• RT-PCR quantified inducible nitric oxide synthase (iNOS) and cathepsin G gene expression.
• Confocal microscopy tracked Mtb association with Rab5 and Rab7 positive phagosomes.
• Investigated IL-10 and IL-12 secretion by monocytes and Mtb susceptibility to cathepsin G.

Main Results:

• Mtb strains, both wild type and mutant, similarly inhibited MHC class II expression on monocytes.
• Monocyte stimulation induced IL-10 production but not IL-12 or nitric oxide (NO).
• iNOS gene expression was undetectable, while cathepsin G expression was observed but not linked to MtrA mutation.
• Mtb mutant strains exhibited enhanced enclosure within Rab7-positive phagosomes (late endosomes) compared to wild-type.

Conclusions:

• The MtrAB system appears vital for Mtb's survival within phagocytic cells.
• The enhanced colocalization of Mtb Rv-78 mutant with mature phagosomes underscores the MtrAB system's significance in intracellular persistence.