Distinct Response Kinetics of Gamma Interferon and Interleukin-4 in Bovine Tuberculosis

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Abstract
This study shows that gamma interferon (IFN-γ) and interleukin-4 (IL-4) cytokine responses are produced by peripheral blood cells in cattle infected withMycobacterium bovis. The different kinetics of the IFN-γ and IL-4 responses to bovine tuberculin and to ESAT-6 following experimental intratracheal infection withM. bovisare described. An early increase in IFN-γ was observed that was maintained throughout the period studied. In contrast, the IL-4 response was delayed and confined to a peak of activity lasting 6 to 8 weeks. Interestingly, an experimental challenge of cattle with a lower dose ofM. boviswhich did not result in the development of lesions, positive DTH skin test, or substantial IFN-γ responses nevertheless generated strong specific IL-4 responses. Investigation of naturally infectedM. bovisfield reactors showed increased IFN-γ and IL-4 responses compared to uninfected cattle and that both of these cytokines were equally able to differentiate infected from uninfected animals. The magnitude of theM. bovis-induced IL-4 responses were found to be similar to the antigen-specific IL-4 responses of cattle infected with the parasitic nematodeOnchocerca ochengi, further supporting the presence of this type 2 cytokine in bovine tuberculosis.