FIG. 2.

IFN-γ (a) and IL-4 (b) responses of 21 naturally infected M. bovis field reactors (SCITT⁺) and 11 uninfected controls (SCITT⁻). Responses to PPD-A, PPD-M, and ESAT-6 are shown. Results are expressed as the ΔOD₄₅₀ for IFN-γ and as SI values of B-cell proliferation for IL-4. A positive IFN-γ result was taken as a mean OD₄₅₀ of the antigen-stimulated supernatant that was greater than twice the mean OD₄₅₀ of the control unstimulated supernatant and also >0.2. A positive IL-4 result was taken as an SI value that was >3.0 (▴, positive responses; ▵, negative responses).