Mycobacterium tuberculosis (MTB), the causative agent of tuberculosis (TB), infects and kills millions each year. Actively infected patients exhibit a heterogeneity of disease lesions in the lungs, which make it difficult for current treatment regimens to effectively cure. Efforts are underway to develop novel pre-clinical drugs, and this requires a thorough re-evaluation of the current animal models used to test these formulations. A new mouse model using C3HeB/FeJ mice, deficient at the sst-1 locus develops a similar heterogeneity of pulmonary lesions to human disease when aerosol infected with MTB.
The studies presented here have found the C3HeB/FeJ mice develop 3 types of lesions: type I) necrotic granulomas delineated with a collagen rim, type II) necrotic alveolitis, and type III) cellular inflammation. Type I lesions, consist of an accumulation of amphophilic cellular debris admixed with numerous extracellular bacilli. At the periphery of the necrotic core on the inside of the collagen rim is a cuff with foamy macrophages of variable size, which contain very large numbers of intracellular bacilli. Type II lesions, the alveolar septal walls remain mostly intact, while the alveolar spaces are filled with high numbers of dying neutrophils, intact cells, extracellular bacteria and debris, creating a honeycomb-like necrosis, which is only seen at very late stage in immunocompetent mouse models. Type III lesions, are disorganized and have a mix of lymphocytes, macrophages (epitheloid and foamy), and a small number of neutrophils with low numbers of intracellular bacilli.
The necrotic encapsulated type I granuloma creates an environment that promotes hypoxia, creates a physical barrier, and causes physiological changes to the various bacterial populations. The Kramnik mouse model has higher populations of resistant bacteria when drug treated, such as isoniazid (INH), rifampin (RIF), and pyrazinamide (PZA). These drugs are less effective when administered as monotherapies in C3HeB/FeJ mice. The adaptations the MTB undertake in the core of the type I granuloma while under stress not only make drug treatment less effective, but also make standard acid-fast staining techniques, such as auramine-rhodamine less efficient at detecting bacilli. While, Sybr Gold, a novel acid-fast stain that binds to nucleic acid, is capable of staining bacilli throughout infection and in all lesion types. The discrepancy in staining ability of the two acid-fast stains is indicative of the physical target for auramine-rhodamine no longer being present or available for staining in the bacilli in the core of the necrotic granuloma.
The knowledge on histopathology then leads us further to modify the granuloma in the Kramnik mouse model. Firstly, using collagen disrupters we aimed to improve treatment efficacy. Secondly, by using clinical TB strains the goal was to advance disease to potentiate cavitary disease and gain a greater understanding of strain relevance to treatment. Thirdly, by taking advantage of the structural similarity of the necrotic granuloma and solid cancerous tumors allow for the translation of therapy technologies, such as liposomal nanoparticles to be exploited for treatment of MTB. Preliminary findings suggest that the use nanomedicines in TB therapy may be an effective method of drastically reducing treatment as well as potential issues.
The C3HeB/FeJ mouse strain is a highly relevant disease model that can be used for determining the efficacy of novel pre-clinical drugs and drug regimens, to gain a better understanding of disease pathogenesis, to understand the specific immunological events of disease, and to explore alternatives to standard therapy.
|Commitee:||Basaraba, Randall, Crick, Dean, Gustafson, Daniel|
|School:||Colorado State University|
|Department:||Microbiology, Immunology, & Pathology|
|School Location:||United States -- Colorado|
|Source:||DAI-B 75/10(E), Dissertation Abstracts International|
|Subjects:||Microbiology, Pathology, Pharmacy sciences|
|Keywords:||Drug treatment, Granuloma, Mycobacterium tuberculosis, Pathogenesis, Preclinical drugs|
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