Western blot analysis of HK-PPD and SF-PPD probed with either M. bovis infected or M. bovis sensitized cattle sera. Twelve percent SDS-PAGE were performed followed by electrophoretic transfer of proteins to nitrocellulose. Lanes were cut into strips and individually stained or blotted. (a) Lanes 1, 2 and 3 were loaded with sample buffer, molecular weight standards (Silver Stain SDS-PAGE Standards Low Range, Bio-Rad) and 10 μg of SF-PPD respectively and were stained with Colloidal Gold (Bio-Rad) following transfer. Lanes 4 and 5 were loaded with 10 μg of SF-PPD and lanes 6 and 7 were loaded with 10 Φg of HK-PPD. Lanes 4 and 6 were blotted with M. bovis sensitized bovine sera (animal # 003); lanes 5 and 7 were blotted with M. bovis infected bovine sera (animal # 107). Lane 8 was loaded with 10 μg of HK-PPD and was blotted without sera (1° Ab) to act as a conjugate control.