|Robbe Austerman, Suelee|
Submitted to: International Colloquium on Paratuberculosis
Publication Type: Proceedings
Publication Acceptance Date: 9/1/2005
Publication Date: 6/1/2006
Citation: Stabel, J.R., Kimura, K., Robbe Austerman, S. 2006. Sensitization with johnin purified protein derivative augments secreted and intracellular interferon-gamma in cows infected with Mycobacterium avium subsp. paratuberculosis. In: Proceedings of the 8th International Colloquium on Paratuberculosis, August 13-17, 2005, Copenhagen, Denmark. p. 135-145. Interpretive Summary: Johne's disease is a chronic, debilitating intestinal disorder in cattle characterized by diarrhea, reduced feed intake, weight loss and death. Cattle usually become infected as young calves by ingesting feces containing the causative bacteria. However, symptoms of disease do not usually present themselves until the animals reach 3 to 5 years of age or even older. During this time the animal is infected and may be shedding the organism in its feces without showing any clinical signs of disease. In addition to reduced milk production by these animals, they also present a potential infective threat to the rest of the herd. Johne's disease is difficult to diagnose and therefore to control. Development of accurate and sensitive diagnostic tests is dependent upon understanding the immune responses of the host animal during infection. This study demonstrated that animals in different stages of infection with the same microorganism have very different immune responses with high levels of interferon-gamma in subclinical infection that can be increased after exposure to a purified protein derivative from the bacteria. The interferon-gamma test is being evaluated for use as a diagnostic tool for paratuberculosis and it may be helpful in detection of early infection.
Technical Abstract: Measurement of secreted IFN-gamma''has proven to be a valuable tool for the detection of animals infected with mycobacterial pathogens,including Mycobacterium avium subsp. paratuberculosis. Previous reports have suggested that tuberculin skin testing can influence the performance of the IFN-gamma assay. In the present study, healthy noninfected cows, and cows subclinically and clinically infected with M. paratuberculosis were administered an intradermal injection of johnin purified protein derivative and effects on secreted and intracellular IFN-gamma were observed. Significant increases in secreted IFN-gamma were noted in antigen-stimulated PBMC isolated from subclinically infected cows within 2 days of the skin test. An increase in intracellular IFN-gamma expression was noted after the intradermal injection for all treatment groups after in vitro stimulation of cells with medium only (nonstimulated), or pokeweed mitogen. Intracellular IFN-gamma was higher within CD4+ and CD8+ subpopulations for infected cows compared to healthy controls throughout the study. When T cell populations were further defined by CD45RO expression, intracellular IFN-gamma was higher for CD8+/CD45RO+ lymphocytes compared to CD4+/CD45RO+ cells. These results indicate that intradermal sensitization of cows in the early stage of infection with antigen will enhance the sensitivity of detection by the IFN-' assay. In addition, CD8+ lymphocytes appear to play an important role as a mediator of M. paratuberculosis infection in naturally exposed cattle. Keywords: interferon-g, Mycobacterium avium subsp. paratuberculosis, skin test, cattle.