IFN-γ ELISPOT responses to mycobacterial proteins at various times prior to death (B662) or euthanasia (B369). Three mycobacterial antigen preparations (bovine PPD, ESAT-6 and CFP-10) were used in IFN-γ ELISPOT assay using cryo-preserved PBMC from baboon B662 (infected with M. tuberculosis) and B369 (infected with M. intracellulare). The IFN-γ response to each protein was determined by subtracting the background (response to PBMC in the culture medium only) from the antigen response. Data points are the magnitudes of response to each antigen preparation at various time points. The dotted lines indicate the cut-off value for ESAT-6 (70 IFN-γ SFC/106 PBMC).