Skin test response-inducing capacity of individual protein antigens. Skin test responses induced by the ESAT-6, CFP-10, MPB83, and Rv3615c proteins were determined either individually (10 μg) or in combination (10 μg per protein) for cattle naturally exposed to M. bovis (n = 12). Additionally, responses to a cocktail of 25 peptides (10 μg per peptide) derived from ESAT-6, CFP-10, MPB83, and Rv3615c were measured in these cattle, along with SICCT skin test responses. Reactions measured at 72 h for each animal are represented by open circles, and the horizontal line provides the mean (± SEM), with results expressed as the difference in skin thicknesses (mm) between the pre- and post-skin test readings.