Quality controls and in vitro diagnostic efficiency of bovine PPD tuberculins

Wide heterogeneity was shown among different batches of bovine protein purified derivative (PPD) tuberculin, as regards protein content and antigenic profile. These features were also investigated in pilot preparations of Mycobacterium bovis secreted antigens and PPD tuberculins. Under controlled conditions, widely different compositions were revealed as a function of the M. bovis strain and also of the time in culture, due to the transient expression of seemingly important clusters of antigens. Furthermore, these parameters could dramatically affect the efficacy of the above preparations in in vitro assays of cell-mediated immunity on M. bovis-infected cattle. The field exposure to mycobacteria of the avium/intracellular group could also influence the readout of such assays, results being in agreement with a bystander suppression model of the response to M. bovis antigens. Due to the above, practical suggestions are put forward to improve the composition of bovine PPD tuberculins and the relevant control procedures.