Comparison of the Brucella-immune and the BCG-immune histiocyte, each of which is resistant to necrotization by either Brucella or mycobacteria, has revealed a number of dissimilarities in their behavior. The Brucella-immune histiocyte was found to be incapable of transferring its resistance to the cells of normal animals; it was also unable to achieve attenuation of virulent tubercle bacilli. In contrast, the BCG-immune histiocyte and certain of its subcellular components (ribosomes and ribosomal RNA) were effective in inducing cellular resistance in normal animals against both Brucella and mycobacteria. When RNA was used, only immune ribosomal RNA was effective; when intact ribosomes were used, both immune and recipient ribosomes proved active.
These investigations have also shown that the resistance of the BCG-immune histiocyte against Brucella and mycobacteria was of long duration and not readily dissociable.