|Robbe Austerman, Suelee|
Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 16, 2006
Publication Date: January 1, 2007
Citation: Stabel, J.R., Kimura, K., Robbe Austerman, S. 2007. Augmentation of Secreted and Intracellular Gamma Interferon Following Johnin Purified Protein Derivative Sensitization of Cows Naturally Infected with Mycobacterium avium subsp. paratuberculosis. Journal of Veterinary Diagnostic Investigation. 19:43-51. 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 the sensitivity of a diagnostic test can be improved by prior sensitization of the animal with a protein from the bacteria. It is possible that this information will lead to better detection methods for paratuberculosis, particularly in the early stages of disease.
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 withmedium 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 inthe early stage of infection with antigen will enhance the sensitivity of detection by the IFN-gamma assay. In addition, CD8+ lymphocytes appear to play an important role as a mediator of M. paratuberculosis infection in naturally exposed cattle.