Submitted to: Journal of Comparative Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2015
Publication Date: 8/5/2015
Citation: Palmer, M.V., Thacker, T.C., Waters, W.R. 2015. Analysis of cytokine mRNA expression using a novel chromogenic in situ hybridization method in pulmonary granulomas of cattle experimentally infected by aerosolized Mycobacterium bovis. Journal of Comparative Pathology. 153(2-3):150-159.
Interpretive Summary: The bacterium Mycobacterium bovis is the cause of tuberculosis in most animal species and humans. In humans, M. bovis infection can result in disease clinically indistinguishable from that caused by Mycobacterium tuberculosis, the cause of most tuberculosis in humans. Insights into the disease processes associated with infection of cattle with M. bovis may reveal findings leading to improved diagnostic tests or vaccines. Various inflammatory mediators were examined in tissues from cattle experimentally infected with M. bovis. Each mediator was visualized within the tissue using a novel assay and the amount of mediator present was measured. The types of mediators and their relative amounts were characteristic of a protective immune response to M. bovis. The novel assay is a useful means of visualizing various inflammatory mediators in tissue.
Technical Abstract: Mycobacterium bovis is the cause of tuberculosis in most animal species, including cattle and is a serious zoonotic pathogen. In humans, M. bovis infection can result in disease clinically indistinguishable from that caused by Mycobacterium tuberculosis, the cause of most tuberculosis in humans. Regardless of host, the typical lesion induced by M. bovis or M. tuberculosis is the tuberculoid granuloma. Tuberculoid granulomas are dynamic structures reflecting the interface of host and pathogen and; therefore, pass through various morphological stages, categorized as stages I through IV. Using a novel in situ hybridization assay, mRNA expression of various cytokines and chemokines were examined qualitatively and quantitatively using image analysis. In experimentally infected cattle, pulmonary granulomas were examined approximately 150 days after aerosol exposure to M. bovis. Expression of mRNA for IFN-gammma, IL-17A, TNF-alpha, IL-10, CXCL9 and CXCL10 did not differ between granulomas of different stages. However, relative expression of the various cytokines was characteristic of a Th1 response with high TNF-alpha, intermediate IFN-gamma and low IL-10 expression. Expression of the chemokines CXCL9 and CXCL10 was high, suggestive of granulomas actively involved in T-cell chemotaxis.