Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/14/2007
Publication Date: 11/30/2007
Citation: Stabel, J.R., Robbe-Austerman, S., Davis, W.C. 2008. Immunologic Responses to Mycobacterium avium subsp. paratuberculosis in Neonatal Calves after Oral or Intraperitoneal Experimental Infection. In: Proceedings of the 9th International Colloquium on Paratuberculosis, October 28th-November 2, 2007, Tsukuba, Japan. p.54-57. Interpretive Summary: Johne's disease is a chronic, debilitating intestinal disorder in cattle,sheep and wild ruminants, characterized by diarrhea, reduced feed intake, weight loss and death. Animals usually become infected when they are young 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 production by these animals through reduced milk production, they also present a potential infective threat to the rest of the herd. Johne’s disease is difficult to diagnose and therefore to control. Animal infection models are necessary for the study of host responses to infection under controlled conditions. In this paper, we present results from a study designed to evaluate different methods of experimental infection in a calf model. Further, we discuss results of measures of the host immune response to infection. Results of this study suggest that experimental infection of calves results in the secretion of proteins associated with an early response to infection. Being able to accurately detect infected animals will help allay the spread of this disease in wildlife and domesticated animals.
Technical Abstract: The current study was designed to compare experimental oral and intraperitoneal inoculation on early host immune responses to MAP infection. Blood samples were obtained on d -5 and -4, 7, 14, 21, 28, and monthly thereafter for the 12 month term of the study. Isolation of peripheral blood mononuclear cells (PBMC) was performed, followed by incubation with medium only (nonstimulated), concanavalin A (ConA), a whole cell sonicate of MAP (MpS), and johnin purified protein derivative (JPPD) for 24, 48, 72, or 144 hr for determination of cytokine secretion, lymphocyte proliferation, and flow cytometric analyses. Results demonstrated that oral inoculation of calves significantly increased lymphocyte proliferative responses to MpS at 12 months. Secretion of MPS-stimulated iNOS by PBMC was higher for oral infection groups at both 6 and 12 months post-infection compared to control calves. IP calves had the earliest antigen-specific IFN-' responses at 7 d post-infection, preceding responses noted for other infection groups that followed between 90 and 120 d. Average IL-10 responses to ConA and MPS were higher at 1 and 6 months and declined significantly by 12 months post-infection. At 1 month, Oral and Oral/M calves had higher MPS-stimulated IL-10 than other treatment groups. By 12 months only the Oral/M calves had higher IL-10 secretion than control calves. Intracellular IFN-gamma and IL-10 levels were measured for CD4+, CD8+, and gamma delta T cell subpopulations. At 3 months post-infection, there was significantly higher IFN-gamma in CD4+ cells stimulated with MPS in the Oral treatment. Intracellular IL-10 was higher in CD4+ and CD8+ T cells in Oral and IP calves compared to the other treatments. Results demonstrated that oral inoculation of calves increased lymphocyte proliferative responses and iNOS secretion by PBMC stimulated with MpS. Antigen-specific IFN-gamma responses were apparent for all infected calves by 90 d post-inoculation and remained elevated throughout the study. At 1 month, Oral and Oral/M calves had higher MPS-stimulated IL-10 than other treatment groups but IL-10 secretion declined by 12 months for all calves. Intracellular IFN-gamma and IL-10 in T cell subpopulations stimulated with MPS was higher for calves in the Oral infection groups. T cell activation markers such as CD25, CD26, CD5, and CD45RO were upregulated in infected calves compared to noninfected controls. These results demonstrate that exposure and infection to MAP will invoke early immunologic responses characterized by IFN-gamma, IL-10, and iNOS secretion.