FIG. 4.

The antibody response to ESAT-6 peptides in naturally infected animals. (A) Antibody levels against ESAT-6 and ESAT-6-derived peptides were measured by ELISA in serum samples from 20 monkeys naturally infected with M. tuberculosis or with M. bovis. Because of potential differences in the response to M. bovis versus M. tuberculosis infection, raw data are shown for the two groups of infected animals separately. Each data point represents one serum sample tested against the antigen indicated. Open symbols are used for data obtained with peptides spanning to the NH₂-terminal half of ESAT-6; solid symbols correspond to peptides spanning the COOH-terminal half of the protein. (B) Specific antibody levels were not statistically different between the two groups of animals (with the exception of the intergroup analysis of the antibody levels to P8; P = 0.02). Thus, this panel shows the cumulative number of responders to ESAT-6 and ESAT-6-derived peptides in the two groups of naturally infected animals, calculated as described in the legend to Fig. 3.