A bovine alveolus model to replace cattle in the study of host-pathogen interactions in bovine tuberculosis

Lead Research Organisation: University of Surrey
Department Name: Veterinary Medicine & Science

Abstract

Mycobacterium bovis (M. bovis) is the causative agent of bovine tuberculosis (BTB) and infects livestock with severe socio-economic consequences and an impact on animal health. As well as the financial and emotional impact BTB has on the cattle farming community and government, the disease is a major risk to human and livestock health in developing countries. The control of BTB has proved problematic in Great Britain and Ireland. In the absence of improved control the projected economic burden to GB over the next decade is predicted to be £1 billion.

Tackling BTB requires deeper insights into host-pathogen interactions otherwise it is unlikely any major breakthroughs in developing effective tools for disease intervention will occur. The principle route of infection with M. bovis is via inhalation of infectious aerosols. On inhalation, M. bovis reaches the lung tissues, especially the alveolus. What happens next determines whether the host goes on to acquire TB, or whether the host deals with the threat. Research in human TB shows that epithelial cells lining the alveolus are far more than a simple physical barrier to pathogens. Indeed, M. tuberculosis is able to penetrate these cells and gain access to the deeper tissues whilst evading elimination by the immune system. In turn, the epithelium detects the presence of mycobacteria, responding by producing molecules involved in antimicrobial activity, inflammation, and pathology. As the lung epithelium is central to early response to TB, better understanding of the early events and interactions that occur when virulent mycobacteria arrive in the bovine alveolus are needed. No model currently exists with which to conduct these studies and the crucial events in the earlier stages of infection are intractable for study in the live animal. Understanding early events that are played out within the alveolus is critical if we are to gain new insights in how to enhance host resistance to infection, e.g. through vaccination.

In response to this need, we shall develop a tissue culture model of the bovine alveolus with which to study the interaction of M. bovis with the bovine host. The model represents a non-animal alternative with which to study of the pathogenesis of BTB by removing the need to infect cattle with mycobacteria to answer fundamental questions in TB pathogenesis and provide a valid substitute for cattle that can be used by researchers without access to animal facilities. The simplicity of the model make it preferable over the use of the whole animal, and for answering questions that require data to be gathered within minutes of infection or where time course studies are required. This will be a new tool available to the scientific community. Its use is not confined to BTB, but would be applicable to the study of respiratory infections of cattle in general, many of global importance, such as bovine respiratory disease (BRD).

Vaccines against BTB developed to generate a specific host response would be a significant advance on the current state of affairs where vaccines must be tested empirically in cattle to evaluate their efficacy. A specific objective of this project will determine whether the behaviour of BCG / M. bovis and host cells in the model correlates with protective efficacy seen in cattle challenge studies from which we have stored blood cells to evaluate. Identifying a read-out in our model that is related to vaccine efficacy in the whole animal could be a basis of screening vaccine candidates without the need to challenge cattle with M. bovis. This would reduce the severity and duration of animal experiments, as well as significantly reduce their cost.

We hypothesise that a significant aspect of vaccine-mediated protection against BTB is expressed at the level of host-pathogen interactions within the alveolus.

Technical Summary

Tackling BTB requires deeper insights into host-pathogen interactions otherwise it is unlikely any major breakthroughs in developing effective tools for disease intervention will occur. In keeping with the aim of this call, we shall develop a tissue culture model of the bovine alveolus as a surrogate with which to study the interaction of M. bovis with the host.

We shall work with Professor William Hope, University of Liverpool who through previous NCR3Rs funding (Project Grant G0700599) refined a culture model of the human alveolus containing an air-liquid interface. This model consists of a cellular bilayer constructed of human pulmonary artery endothelial cells and human alveolar epithelial cells on opposing sides of a Transwell insert. The Hope group use this model to study invasive pulmonary aspergillosis. Professor Hope will provide direct training in his model at Liverpool. This will ensure successful transfer of the methodology. We shall modify the Hope model to produce a functional bovine model. We shall replace the human cells of their model with immortalised bovine cells. The PDRA undertaking the work will visit the Hope laboratory to learn the techniques involved.

The functional utility of the model will be demonstrated by using it to address our hypothesis that a significant aspect of vaccine-mediated protection is expressed at the level of host-pathogen interactions within the alveolus. We reason that the phenotype of successful vaccination in cattle is expressed in the speed and activity of the host response and the behaviour of the pathogen within the alveolus. We shall test this by introducing into our model stored PBMCs from cattle that expressed either strong or weak levels of vaccine protection. Initially we shall introduce mycobacteria into the model using BCG. This is for safety reasons: the methodology can be established safely under CL2 laboratory conditions before being transferred to the CL3 laboratory in order to use M. bovis.

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