Table 2.

IFN-γ responses to tuberculin and the ESAT-6–CFP-10 peptide cocktail in tuberculin skin test-positive field reactors, BCG-vaccinated cattle, and cattle from herds free of TBa

Antigen testCattle with confirmed TBTB-free cattleBCG-vaccinated cattle
Responder frequency (%)bResponsecResponder frequency (%)ResponseResponder frequency (%)Response
Comparison of PPD-B and PPD-A88.2 (60/68)0.735 (−0.381 to 3.287)8 (2/25)−0.03 (−2.417 to 0.516)75 (12/16)0.258 (−0.294 to 0.552)
Peptide cocktail77.9 (53/68)5.01 (1.1 to 66.04)0 (0/25)1.18 (0.81 to 2.6)0 (0/16)1.24 (0.65 to 1.98)
  • a Heparinized whole-blood cultures were initiated within 24 h of sampling, and IFN-γ in plasma supernatants was determined using the BOVIGAM ELISA kit. For tuberculins, a positive response was defined as a value for the OD450 with PPD-B minus the OD450 with PPD-A of ≥0.1 and a value for the OD450 with PPD-B minus the OD450 without stimulation of ≥0.1. For the ESAT-6–CFP-10 peptide cocktail, a positive response was defined as an interferon stimulation index (OD450 with antigen/OD450 for medium control) of ≥3.

  • b Values in parentheses are number of responders/total number of animals tested.

  • c Tuberculin-specific responses are expressed as median OD differences between PPD-B and PPD-A (medians of OD450 with PPD-B minus OD450 with PPD-A, with ranges in parentheses. Peptide-induced responses are expressed as median interferon stimulation indices, with ranges in parentheses.