The specificity and stability of old tuberculin and tuberculin PPD

The biological activity of purified protein derivative (PPD) of mammalian tuberculin was compared with that of old tuberculin (OT) prepared from the same strains of Mycobacterium tuberculosis . The tests were carried out intradermally in groups of experimentally sensitized guinea-pigs and in naturally sensitized cattle. Tuberculin PPD was found to be more specific than OT. Comparisons against tuberculin PPD of the precipitable and non-precipitable nitrogen fractions of OT showed that there are qualitative differences in the proteins of PPD and OT, apparently the result of the prolonged heating of OT during processing. The proteins of OT were less potent per unit of weight and were also less specific than those of PPD. Concentrated solutions of tuberculin PPD and of OT stored in full containers at 4° C. in the dark retained full potency after 10 years. Adsorption of active material to the walls of glass containers from tuberculins in high dilution resulted in greater losses in potency of OT than of tuberculin PPD. It is concluded that there is no reason for the continued use, under any conditions, of OT instead of tuberculin PPD