Studies with the light microscope and electron microscope of lung macrophages in rabbits inoculated with an attenuated stain of Mycobacterium microti.

One of the main difficulties in trying to standardize BCG vaccine or to develop a new antituberculosis vaccine with no allergenic properties is the lack of a suitable protection test. The virulence of the challenge strain, the dosage, and the period of observation of the animals are factors that complicate the standardization and reproducibility of any protection test involving animals. On the other hand an ultramorphological test based on the macrophages obtained from immunized animals would eliminate many of the variable factors.With this in mind, pulmonary macrophages of rabbits immunized with attenuated "MP" strain of Mycobacterium microti were examined in ultrathin sections prepared from lung specimens taken from rabbits under general anaesthesia. In comparison with normal rabbits, increased numbers of immune macrophages were found and they contained larger numbers of lysosomal bodies, mitochondria, and Golgi bodies. Quantitative assessment of these differences in ultrastructure by the application of gradient centrifugation may lead to the elaboration of a simpler test for assaying the protective values of antituberculosis vaccines.