In any control program aimed at eradicating M. avium subsp. paratuberculosis, the detection of infected animals in the preclinical stage is vital, since shedding and therefore transmission of the bacteria occurs before the onset of clinical symptoms. The measurement of the Cell Mediated Immune response by detection of IFN-g following antigen specific stimulation of lymphocytes is one of the most promising approaches to detect subclinical infected animals. Using Enzyme Immune-Assays, 7 cytokines (IL-1ß, IL-2, IL-6, IL-8, TNF-alpha, GM-CSF and IFN-gamma) were measured in whole blood culture supernatants derived from control and infected animals¹. The cultures were stimulated with either M. avium PPD, Johnin PPD or were left unstimulated. Of the cytokines investigated to date in the lambs and kids, IFN-gamma was found to correlate closest to infection status, especially when presented as a 'classical' stimulation index (ratio between cytokine responses of stimulated versus non-stimulated cells). In the calves however, the IFN-gamma responses of the control group were similar to the infected groups1. The IFN-gamma responses in the controls may be due to the calves being sourced from an unknowingly infected farm. In all three species IL-1ß responses of the infected groups were following the same trend as those of IFN-g, albeit hardly distinguishable from the controls. For the TNF-alpha, GM-CSF and IL-8 responses, no difference between the control and infected groups in either species could be found. IL-2 and IL-6 could not be detected, which could be due to having a much higher detection limit than the IFN-gamma assay and using a suboptimal incubation period for cytokine expression respectively. This data suggests that IFN-gamma is to be preferred over the other cytokines as a marker for infection with M. paratuberculosis, but further optimisation of some of the assays may reveal other suitable markers for infection. This work is in progress and continuing.