Submitted to: American Dairy Science Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/8/1996
Publication Date: N/A
Technical Abstract: This paper describes an assay to measure antigen-specific cell-mediated immune function as a means of detecting subclinical (subC) Johne's disease in infected animals. Peripheral blood mononuclear cells were isolated from noninfected control cows and from cows with either subC or clinical paratuberculosis (Ptb). Cells were incubated for 6, 12, 24, and 48 hours in ncomplete medium with the following mitogens: concanavalin A (ConA), phytohemagglutinin-P (PHAP), pokeweed mitogen (PWM), and E. coli lipopolysaccharide. In addition, cells were incubated for the same time periods with a Mycobacterium paratuberculosis (MPtb) sonicate (MpS) and live and heat-killed MPtb at 10:1 bacteria to cell ratio. After incubation, cell-free supernatants were analyzed for gamma-interferon (IFN) activity. Cells from subC cows produced significantly greater levels of gamma-IFN than did cells from clinical animals after stimulation with mitogens, ConA, ,PHAP, and PWM. Levels of gamma-IFN produced by noninfected control animals generally followed the pattern of subC animals. After incubation with MpS, significantly greater quantities of gamma-IFN were produced by cells isolated from subC animals compared to cells from clinical cows and noninfected controls. Stimulation of cells with heat-killed or live MPtb evoked a similar response. This study indicates that gamma-IFN production by peripheral blood mononuclear cells in response to MPtb antigen may be an important diagnostic tool for detection of Ptb in subC animals.