Production of γ-Interferon by Peripheral Blood Mononuclear Cells: An Important Diagnostic Tool for Detection of Subclinical Paratuberculosis

Abstract

Peripheral blood mononuclear cells were isolated from noninfected control cows and from cows with either subclinical or clinical paratuberculosis (Johne s disease). Cells were incubated for 6, 12, 24, and 48 hours in complete medium with the following mitogens: concanavalin A (ConA), phytohemagglutinin-P (PHAP), pokeweed mitogen (PWM), and Escherichia coli lipopolysaccharide. In addition, cells were incubated for the same time periods with a Mycobacterium paratuberculosis sonicate (MpS) and live and heat-killed M. paratuberculosis at 10:1 bacteria: cell ratio. After incubation, cell-free supernatants were analyzed for y-interferon (γ-IFN) production. Cells from subclinical cows produced significantly higher levels of γ-IFN than did cells from clinical animals after stimulation with mitogens ConA, PHAP, and PWM. Levels of γ-IFN produced by noninfected control animals generally followed the pattern of those of subclinical animals. After incubation with MpS, significantly greater quantities of γ-IFN were produced by cells isolated from subclinical animals than by cells from clinical cows and noninfected controls. Stimulation of cells with heat-killed or live M. paratuberculosis evoked a similar response. This study indicates that γ-IFN production by peripheral blood mononuclear cells in response to M. paratuberculosis antigen may be an important diagnostic tool for the detection of paratuberculosis in subclinically affected animals.