FIG. 1.

Extent of IFN-γ production in an M. bovis-free area. Young cattle between 2 and 18 months of age (n = 54) from three different herds were tested four times for IFN-γ production after stimulation of whole blood with PPD, ESAT-6, and MPB70 for 24 h. The mean response in each animal is shown as dots, while the means for each antigen stimulation are shown as lines. Corrected OD is expressed as [(mean of antigen-stimulated wells − mean control wells)/(test positive control − test negative control)].