Immunization of mice after airborne infection with various strains of BCG.

The growth of 6 strains of bacillus Calmette-Guérin (BCG) in the lungs of mice was compared after direct implantation into those organs. Bacilli of the Connaught, Pasteur, Phipps, and Tice strains multiplied appreciably in the lungs and disseminated into the spleen In contrast, BCG Birkhaug and Glaxo strains did not replicate in the lungs or spread to the spleen. The immunizing ability of 3 of these strains was examined in more detail. Aerosol infection with BCG Glaxo, Pasteur, or Phipps strains produced resistance to subsequent pulmonary challenge with Mycobacterium tuberculosis RIRv. Such immunity was significantly greater in mice immunized with the Pasteur and Phipps strains and was not attributable to nonspecific resistance. Spleen cells from mice immunized with these 3 strains of BCG conferred similar degrees of immunity to intravenous challenge with M. tuberculosis on syngenic recipients. It was concluded that growth of BCG in the lungs influenced the degree of local immunity but not the degree of systemic immunity.