Submitted to: Animal Health Research Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 29, 2006
Publication Date: December 31, 2006
Citation: Stabel, J.R. 2006. Host Responses to Mycobacterium avium subsp. paratuberculosis: A Complex Arsenal. Animal Health Research Reviews. 7(1):61-70. 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 paper reviews the current information on host immunity to Mycobacterium avium subsp. paratuberculosis in domestic animals. Further work on host immunity will lead to better understanding of the pathogenesis of disease and aid in new preventative and therapeutic regimes.
Technical Abstract: The immune system is not always successful in recognizing and destroying pathogens it may encounter. Host immunity to mycobacteria is characterized by a very complex series of events, designed to clear the infection. The first line of defense is uptake and processing of the pathogen by macrophages, followed by the initiation of cell-mediated immunity. The secretion of pro-inflammatory cytokines such as IFN-' is credited with containment of mycobacterial infections. Yet it is clear that activated T cells may contain but fail to clear the infection in some hosts. Further it is recognized that if infection progresses to a more clinical state, the production of pro-inflammatory cytokines is suppressed and expression of anti-inflammatory cytokines is increased. It is unclear what defines a host that can successfully contain the infection versus one that succumbs to severe immunopathologic disease. This review will address some of the key elements in host immunity to mycobacterial pathogens, with an emphasis on Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis), in an attempt to understand the dialogue between immune cells and their mediators during infection and what causes this discourse to go awry.