Preparation of recombinant ESAT-6 and CFP10. Plasmids containing inserts encoding histidine-tagged ESAT-6 or CFP10 were expressed in E. coli, and proteins were purified, as described in Materials and Methods. Purity of the recombinant proteins was analyzed by 15% SDS- PAGE, and visualized by staining with Coomassie Blue, followed by destaining the gel (A), or by Western blot (B), after electroblotting to a nitrocellulose membrane and blotting with Abs as indicated (bottom). M: m.w. markers. Standards are recombinant proteins from the TB Vaccine Testing and Research Materials Contract, the two far right lanes show the recombinant proteins we prepared. A representative result from three independent preparations is shown.