Submitted to: ARS Immunology Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2003
Publication Date: 3/1/2005
Citation: Stabel, J.R., Khalifeh, M.S. 2005. Modulatory Effects of IFN-g, IL-10 and TGF-b in cattle Infected with Mycobacterium paratuberculosis [abstract]. ARS Immunology Workshop. p. 51.
Technical Abstract: Johne's disease is an important disease that results in great economic losses for both dairy and beef production in the United States and worldwide. The disease progresses through distinct stages, a subclinical stage where there are no clinical signs and a clinical stage that is characterized by progressive symptoms associated with chronic shedding of high levels of bacteria in the feces along with severe diarrhea and concomitant weight loss. The host immune response to M. paratuberculosis is paradoxical, with strong cell-mediated immune responses during subclinical stages and strong humoral responses during clinical stages of the disease. It is possible that immune modulation of an effective cell-mediated immune response may play an important role in disease progression. We hypothesized that the clinical stage of Johne's disease is mediated by production of cytokines such as TGF-b and IL-10 that downregulate IFN-g production and interfere with an effective cell-mediated immune response. Therefore, ileum, ileal cecal junction, ilealcecal lymph node and mesenteric lymph node tissues from the healthy, subclinical or clinical animals were collected and analyzed for the presence of TGF-b, IL-10 and IFN-g mRNA by quantitative RT-cPCR. The results show that TGF-b and IL-10 mRNA levels in animals that have progressed to the clinical stage of the disease is higher than that found in subclincal and healthy animals, whereas IFN-g is higher in subclinical animals. Interferon-g plays a significant role in the control of mycobacterial infections, including Mycobacterium paratuberculosis. However, the contribution of other immunoregulatory cytokines such as IL-10 and TGF-b in Johne's disease has not been investigated as yet. In the present study, we examined the effects of in vivo and in vitro infection with M. paratuberculosis on the production of IFN-g, IL-10 and TGF-b by peripheral blood mononuclear cells (PBMC). We also examined the effects of exogenous IFN-g, IL-10 and TGF-b on M. paratuberculosis survival in the cell cultures. PBMC obtained from naturally infected cows, regardless of their disease status, specifically upregulated IL-10 and TGF-b in culture supernatants in response to stimulation with live M. paratuberculosis. Non-stimulated PBMC recovered from subclinically infected animals secreted the lowest levels of TGF-b but after stimulation with live M. paratuberculosis TGF-b levels in the culture supernatants increased to levels similar to that produced by PBMC from healthy animals. Compared to healthy cows, naturally infected animals had higher numbers of viable M. paratuberculosis recovered from their cultures after in vitro infection with M. paratuberculosis. The addition of exogenous IL-10 and TGF-b to PBMC isolated from healthy cows inhibited the bactericidal activity of these cells as evidenced by the increased number of viable M. paratuberculosis recovered from those cultures compared to cell cultures containing medium alone. These data suggest an important immune regulatory role of IL-10 and TGF-b during infection with M. paratuberculosis that may be directly related to their effects on macrophage activation and killing of M. paratuberculosis.