One third of the human population is estimated to be latently infected with M. tuberculosis and each year about 9 million new cases of active tuberculosis (TB) are reported. However, only about 30% of healthy people closely exposed to TB will get infected and of those only 5%-10% will go on to develop active disease - an indicative that a competent immune system is able to fight of the infection in the majority of cases. TB incidence is especially high in areas of poverty in low income countries, where infections with helminths also are common, and it has been proposed that immunological changes induced by a helminths infection leads to increased susceptibility to TB. It is generally accepted that cell mediated immunity play a pivotal role in controlling the initial TB infection, wth macrophages being key players with a somewhat ambiguous dual role. The macrophage can act both as a first-line effector cell, but also serve as a nutritious host cell for the mycobacterum to thrive in. Part of the explanation to this paradox may be found in the activation of the macrophage. A macrophage can be classically activated (CAM) or alternatively activated (AAM). The CAMs are pro-inflammatory and protects the host against various pathogens, whereas the AAMs are anti-inflammatory and are important for dampening inflammation and in the healing of tissue damage from inflammation. A problem may arise if one macrophage type is induced at an inappropriate time. It is thought that helminth infection give rise to alternatively activated macrophages. We suggest that helminths induced macrophages have low levels of intracellular glutathione and that this is a factor for the increased susceptibility to TB in helminths infected persons.
We aim to investigate the presence of such a macrophage polarization and glutathione depletion and the effect on macrophage killing of TB. Macrophages will be isolated from patients with TB with and without helminths co-infection, helminths infected and healthy controls. Macrophage activation profile will be assessed using luminex for cytokines;FACS for AAM and CAM markers, and colorimetric assays for iNOS and agrinase activity. Glutathione levels will be measured using a fluorophoric method. The effect of glutathione depletion on mycobacterial killing will be evaluated using an infection assay with a luciferase tagged Mycobacterial tuberculosis strain.
Over two billion persons are estimated to be infected with helminths and it is becoming clear that helminths infection may be a factor behind the high tuberculosis burden seen in poor communities. The proposed project aims to elevate if helminths infection leads to reduced levels of a substance called glutathione in an immune cell involved in the protection against tuberculosis infection, and if so, if this impairs the cells abiity to eradicate the infecting bacterium.