FIG 4.

Effects of PPD administration for skin tests on avidity indices for proteinase K-digested whole-cell sonicate of M. bovis (WCS-PK) antigens (A) or MPB83/MPB70 antigens (B) measured by ELISA. Sample collection time points were as follows: post CFT, 14 days after the CFT and 103 days after the M. bovis challenge; pre CCT, 28 days prior to the CCT and 173 days after the M. bovis challenge; post CCT, 14 days after the CCT and 215 days after the challenge. Avidity indices were calculated by dividing the ΔV_max for samples that received NH₄SCN (i.e., 0.3125 to 7.0 M) by the ΔV_max for samples that received diluent buffer alone (i.e., 0 M NH₄SCN) and multiplying that value by 100. Data were analyzed by ANOVA followed by Tukey's multiple-comparison test. a to c, different letters indicate that responses (mean ± SEM, n = 8) differ (P < 0.05) within the NH₄SCN concentration.