Correlation of biological potency of human and bovine tuberculin PPDs in guinea-pigs, cattle and man

Abstract The potency of Weybridge bovine tuberculin PPD relative to Weybridge human PPD was evaluated by biological assay in guinea-pigs artificially sensitized with heat-killed Mycobacterium tuberculosis or Mycobacterium bovis , and correlated with comparisons in cattle naturally infected with M. bovis and in human patients infected with M. tuberculosis or with M. bovis . The potency of the bovine PPD was approximately one and a half times that of the human PPD, weight for weight, in all three M. bovis sensitizations and one half that of the human PPD in the two M. tuberculosis sensitizations. These results demonstrate a specific antigenic difference between human and bovine PPDs, responses to the homologous PPD being significantly greater. The close correlation of relative potencies of human and bovine PPDs in these three host species demonstrates the validity of biological assay in guinea-pigs for the control of potency of mammalian tuberculins. Because of the differences in specificity of the two PPDs of mammalian tuberculin and the fact that bovine PPD is being used to an increasing extent throughout the world in preventive medicine, there is a practical need for separate international standards for PPDs of human and bovine tuberculins.