FIG. 2.

Whole-blood IFN-γ release assay with single antigens. Blood collected from skin test reactors (○) or TB-free animals (×) was incubated with different mycobacterial antigens, and the amount of IFN-γ released was measured by ELISA after 20 h of incubation in a humidified incubator at 37°C with 5% CO₂. Samples were collected from animals from Northern Ireland (A), Argentina (B), and Mexico (C). The results are given as ODI units. Horizontal bars represent median values. The numbers of animals were 49, 39, and 36 for reactors in Northern Ireland, Argentina and México, respectively, and 20, 18, and 9 for TB-free animals from the three countries, respectively. The data for the PPDB-PPDA group are calculated by subtraction of the value for PPDA from the value for PPDB for a given animal.