Christiane Brohm 26.01.2009

(1) M. tuberculosis profile

(2) Infection route

(3) Survival strategies of M. tuberculosis

Mycobacterium Tuberculosis Profile

Family: Mycobacteriaceae

Genus: Mycobacterium

Feature: waxy coating gram-positive obligate aerobe

Disease: Tuberculosis

Prevalence: 2 billion worldwide 10% casuality

Therapy: antimycobacterial therapy (e.g. isoniazid, rifampicin)

Infection Route of M. tuberculosis

(1) Inhalation of aerosols containing bacilli

(2) Phagocytosis in lung by resident macrophages

(3) Lysosomal degradation or survival within macrophage

Infection Route of M. tuberculosis- Phagosomal Way -

Nature Reviews Immunology 1, 20-30 (October 2001) | doi:10.1038/35095558

(1) Internalization into phagosome→ delivery to antigen processing/presentation pathway

(2) Activation of T-cells by peptide-loaded MHC class II molecules; mycobacterial lipids presented to γδ T cells→ adaptive immune response

But:

Escape of immune defense mechanisms

Survival Strategies of M. tuberculosis

(1) Phagocytosis into macrophage→ receptor dependent macrophage activation

(6) Subversion of macrophage activation→ reaction on oxygen/nitrogen

(5) Hijacking cellular calcineurin pathway→ preventing fusion/degradation

(4) Mimicking of host signaling molecules→ preventing fusion/degradation

(3) Prevention of phagosome-lysosome fusion→ no degradation but persistence

(2) Establishment of a balance: the granuloma→ persistence for long time

Bacteria – Host Balance : The Granuloma

- T cell activation following presentation of mycobacterial antigens

- actively dividing bacilli or „dormant“ state

- attenuated immune system can lead to development of tuberculosis

Mycobacterial Prevention of Phagosome-Lysosome-Fusion

Non-infected cells: Generation of PI3P regulates delivery of phagocytosed cargo to lysosomes

PI3P: phosphatidylinositol 3-phosphateLAM: mycobacterial cell-wall component lipoarabinomannanSapM: eukaryotic-like acid phosphatase secreted by M.t.

Infected cells: Interference with phagosome-lysosome fusion

M. tuberculosis

(1) prevents PI3P generation by mycobacterial LAM

(2) hydrolizes PI3P on phagosomal membranes by SapM

Production of Host-like Signaling Molecules

Nature Medicine 13, 282 - 284 (2007) doi:10.1038/nm0307-282

Mycobacterial production of eukaryotic-like serine/threonine kinases- two kinases are soluble and thereby released into the cytoplasm

PknGPrevention of phagosome-lysosome fusion

Drug targetSpecific kinase inhibitor interacting with the unique domain of PknG

Inhibitors do not need to aquire accessto impermeable mycobacterial cell wall

Interfering with Host Cell SignalingHijacking the Calcineurin Pathway

TACO, P57, Coronin 1Host factor that specifically prevents lysosomal delivery.Exclusively presence on phagosomes harboring mycobacteria.

Regulation of calcium-dependent signaling processes:

Infected macrophages respond with sustained calcium flux dependent on Coronin 1.

Activation of calcineurin blocks fusion.

Calcineurin blockers (cyclosporin A, FK506)fully block mycobacterial proliferation.

Macrophage Activation and Its Subversion by M. tuberculosis

Block of fusion only in non-activated macrophages.What happens in activated macrophages?

(1) Mycobacterial production of KatG: Inactivation of reactive oxygen

(2) Mycobacterial proteasome copes with nitric-oxid stress

KatG: mycobacterial catalase-peroxidase

Macrophage Activation and Its Subversion by M. tuberculosis

Cathelicidin

TLR-ligands can cause macrophage activation

Phagosome maturation through TLR adaptor MyD88 and p38MAPK

Upregulation of vitamin D receptor

Induction of cathelicidin (antimicrobial peptide)

MyD88: myeloid differentiation factor 88p38MAPK: mitogen-associated protein kinase p38 protein

Macrophage Activation and Its Subversion by M. tuberculosis

LAM interferes with macrophage by modulating signaling pathways

IFN-γ-mediated gene expressionTLR activationMAPK activationPhagosome-lysosome fusion

Modulation of bacterial metabolic pathways

fatty acids as carbon source within macrophagesSec-dependent secretion pathway (signal-sequence dependent transport)Tat-system (transport of folded molecules)ESX-1 secretion system (transport of virulence factors, escape of bacilli into cytoplasm)

LAM: cell-wall component lipoarabinomannanTat-system: twin-arginine transporter systemESX-1: early secretory antigenic target of 6kD (ESAT-6) system 1

Conclusions

M. tuberculosis

plays hide-and-seek in phagosomes within macrophages and granulomas within the lung.

prevents phagosome-lysosome fusion by mimicking and hijacking host signaling pathways.

actively reacts and persists in activated macrophages.

Prolonged coevolution of M. tuberculosis with its human host resulted in a number of survival strategies.

Thank you for your attention!Thank you for your attention!