Preparation of tuberculin antigen L

Summary The preparation of antigen L using culture filtrates of live BCG isdescribed. The procedure consisted essentially of precipitating this filtrate with 10% trichloroacetic acid in the presence of N-butyl alcohol 4% final concetration. The precipitate was chromatographed on carboxymethyl-trisacryl-M and then on DEAE-trisacryl-M; in both cases, maximal biological activity (delayed-type hypersensitivity) was found in the void volume. The product thus obtained was chromatographed on a molecular sieve so as to eliminate poorly active fractions. The final product was 30-fold more active on guinea-pigs sensitized with live BCG than on those sensitized with inactivated BCG.