IL-10 is one of the major immune regulatory cytokines, inhibiting synthesis of a number of cytokines including IFN-gamma. IL-10 producing T cells have been reported to be specific immune suppressors in progression of anergy in tuberculosis (Boussiotis et al., 2000). The shifting immune response from an early cellular mediated type to a humoral response in development of paratuberculosis warrants comparison between specific IFN-gamma and IL-10 production over time in this disease.

Materials and Methods.

Twenty-five cattle, aged 3 to 54 months, were selected from 2 herds infected with M. avium subsp. paratuberculosis and 3-10 blood samples from each were collected over a 2-year period. On the day of collection, heparinized whole blood was cultured overnight with johnin PPD (PPDj) and PBS (Jungersen et al., 2002). Culture supernatants were analysed for IFN-gamma by the BOVIGAM(r) ELISA and for IL-10 by a chemiluminescent monoclonal sandwich ELISA (Kwong et al., 2002). IFN-gamma contents were calibrated against the kit positive and negative controls, while IL-10 levels were calculated from a recombinant bovine IL-10 standard curve. PPDj specific IFN-gamma and IL-10 responses were calculated by subtracting values in nil (PBS) stimulated wells from PPDj stimulated wells.

Results and discussion.

PPDj specific IL-10 levels were correlated (P<0.0001, r = 0.33) with specific IFN-gamma production. However, in contrast to IFN-gamma, a strong (P<0.0001, r = 0.75) correlation was also observed between IL-10 levels in nil and PPDj stimulated samples, indicating some IL-10 production in cultures ""ex vivo"", presumably cells having been stimulated in vivo and synthesis continuing in culture wells. IL-10 levels in the nil cultures were, however, not correlated with specific IFN-gamma production. Although paratuberculosis specific IFN-gamma and IL-10 thus was produced in PPDj stimulated cultures, no clear role in the relation between individual animals' IFN-gamma and IL-10 responses over time could be deduced.