Gamma interferon responses to proteome-determined specific recombinant proteins in cattle experimentally- and naturally-infected with paratuberculosis

Individual ranked IFN-γ responses of experimentally infected calves to PPDJ showed a high, statistically significant association with ranked responses of recombinant Map antigens. Responses of infected animals were higher than the control group. Threshold values determined using data from an experimental infection were applied to naturally infected animals. Some animals exhibited responses above these threshold values. Responses to MAP_3651c on a farm categorised as high-risk for JD showed strong evidence (P < 0.001) that responses were significantly different to lower-risk farms. The IGRA test may prove to be an additional tool for the diagnosis of JD, and inclusion of specific antigens a refinement however, understanding and interpretation of IGRA results remain challenging and further investigation will be required to determine whether the IGRA test can detect exposure and hence predict clinical JD.