Quantification of macrophages and Mycobacterium avium subsp. paratuberculosis in bovine intestinal tissue during different stages of Johne's disease.

Authors: JENVEY, CAITLIN - US Department Of Agriculture (USDA); HOSTETTER, JESSE - Iowa State University; Shircliff, Adrienne; Bannantine, John; Stabel, Judith

Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2019
Publication Date: 5/6/2019
Citation: Jenvey, C.J., Hostetter, J.M., Shircliff, A.L., Bannantine, J.P., Stabel, J.R. 2019. Quantification of macrophages and Mycobacterium avium subsp. paratuberculosis in bovine intestinal tissue during different stages of Johne's disease. Veterinary Pathology. https://doi.org/10.1177/0300985819844823.
DOI: https://doi.org/10.1177/0300985819844823

Interpretive Summary: Confocal microscopy is a widely used method utilizing fluorescence to identify the presence of cell types within tissues and/or bacterial or viral pathogens. This method has been used successfully to detect the presence of bacterial pathogens such as mycobacteria and to correlate that presence with the pathogenesis of disease. Understanding the pathogenesis of the disease and the host immune response to infection will allow us to develop improved diagnostic tools and vaccines. In the present study, mid-ileal tissue from naturally infected cattle was stained for macrophage and Mycobacterium avium subsp. paratuberculosis (MAP) and visualized by confocal microscopy. The number of macrophages and MAP present, as well as where they were located within the tissue was assessed for naturally infected cows as well as control uninfected cows and compared. The number of macrophages and MAP associated with macrophages increased with progression of disease from subclinical to clinical status. These results provide critical information on the biology of MAP infection within the target tissue and are useful for producers, clinicians and researchers to gauge the involvement of tissue during the different stages of disease.

Technical Abstract: Johne’s disease is an enteric disease caused by the intracellular pathogen Mycobacterium avium subsp. paratuberculosis (MAP). Upon ingestion of MAP, it is translocated across the intestinal epithelium and taken up by intestinal macrophages. Once ingested, MAP may be killed by macrophages, or depending upon the bacterial burden and immunological status of the animal, MAP may thwart innate defense mechanisms and persist within the macrophage. This study aimed to correlate the presence of macrophages and MAP in bovine mid-ileal tissue with stage of infection. Immunofluorescent (IF) labeling was performed on frozen bovine mid-ileal intestinal tissue collected from 28 Holstein dairy cows. The number of macrophages within the mid-ileal tissue sections was higher for clinical cows, followed by subclinical cows and then uninfected control cows. Macrophages were present throughout the intestinal tissue in clinical cows, including the inner muscle layer, submucosa, and the lamina propria around the crypts and in the villus tips, with progressively fewer macrophages in subclinical and control cows. Clinical cows also demonstrated significantly higher numbers of MAP and numbers of macrophages with intracellular MAP, when compared to subclinical cows. The IF labeling was present within the submucosa and lamina propria around the crypts, progressing into the villus tips in some clinical cows. Clinical cows demonstrated significantly higher MAP mean intensity, however, there was no difference in macrophage mean intensity in regards to stage of infection. Our findings indicate that number of macrophages increases with progression of disease, however, a significant number of the macrophages present in the mid-ileum are not associated with MAP. This suggests that although the bovine innate immune system is sufficiently stimulated to recruit macrophages in response to MAP invasion, the macrophages of clinically infected cows are ultimately unable to clear MAP, resulting in disease progression and clinical presentation.