Response of vaccinated and nonvaccinated syngeneic C57B1-6 mice to infection with Mycobacterium tuberculosis.

Data are presented which show that the syngeneic C57B1/6 mouse strain is far more susceptible to infection with Mycobacterium tuberculosis strain H37Rv than are the other allogeneic mouse strains used in this laboratory, particularly the Strong A and the CF-1 strains. Not only are the C57B1/6 mice more susceptible to tuberculous infection, but also they respond to infection more uniformly than do the allogeneic strains. C57B1/6 mice develop immunity to challenge with small infecting doses of the virulent H37Rv strain when they are vaccinated with viable cells of the attenuated H37Ra strain and with ribonucleic acid (RNA) preparations isolated from the H37Ra strain. Mice vaccinated with viable cells of the H37Ra strain, however, may die more rapidly than nonvaccinated mice when given a large infecting dose (1.0 mg). This accelerated type of disease is not seen in mice vaccinated with mycobacterial RNA. Since C57B1/6 mice are known to develop tuberculin hypersensitivity more readily than many other mouse strains, the possibility is discussed that the increased susceptibility to tuberculous infection of mice vaccinated with viable cells of the H37Ra strain may be due to a superimposition of a pronounced acute inflammatory response due to tuberculin hypersensitivity upon the infectious process. The several advantages that may be gained in the study of certain host-parasite interactions in tuberculosis by the use of a highly susceptible syngeneic mouse strain such as the C57B1/6 are discussed.