Tuberculosis - Clinical Value of Initial Host Molecular Signalling and Molecular Fingerprinting

Mycobacterium tuberculosis (Mtb) is principally a pulmonary pathogen infecting one-third of the world's population and causing two million deaths annually. The only approved tuberculosis vaccine today is the Mycobacterium bovis bacilli Calmette-Guérin (BCG). BCG vaccine is used as a benchmark to compare the immunogenicity of new vaccines, but not much is known about its mechanisms to induce protection. We investigated the initial events of mycobacterial activation of airway epithelial cells (AECs) through the signalling pathways of toll like receptors (TLRs) and the G- protein coupled receptors (GPCR; CXCR1, CXCR2). Our data indicate that mycobacteria attenuate epithelial pro-inflammatory production by supressing NF-B activation, thereby supporting the production of the anti-inflammatory cytokines IL-22 and IL-10. BCG infection of AECs also resulted in epithelial actin redistribution that involved the MAPK signalling pathway. This study demonstrated that BCG infection of AECs manipulated the GPCRs to suppress epithelial signalling pathways. Future vaccine strategies could thus be improved by targeting GPCRs.

In a second part of the thesis, we investigated the expression and function of GPCRs in a simple whole blood model from patients with pulmonary TB and in subjects with latent TB infection (LTBI). We found variations in GPCRs as pulmonary TB patients had significantly increased CXCR1 expression on blood cells compared to LTBI subjects and controls. These variations in receptor expression were linked to disease progression and affected the immune response against Mycobacterium tuberculosis (Mtb). As an airborne infection, tuberculosis (TB) has no boundaries and easily spreads by migration from one region to another. In this study, 93 patient Mtb-isolates, previously genotypically analysed by standard techniques, were re-analysed by whole genome sequencing (WGS). Compared to the standard genotyping, WGS had an overall high match in identifying cluster transmissions in this patient population. When comparing the different techniques individually, WGS and epidemiological data had the highest cluster similarity, while MIRU-VNTR had less cluster resolution. We can conclude that WGS is well suited for identifying transmission clusters in settings with low TB incidence.