Duration of Immunity to Tuberculosis in Mice Vaccinated Intravenously with Oil-Treated Cell Walls of Mycobacterium Bovis Strain Bcg

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Abstract
Summary: Resistance of mice to aerosol infection by Mycobacterium tuberculosis H37Rv engendered by intravenous (i.v.) administration of BCG cell walls treated with Drakeol 6-VR or viable BCG has been studied by determining the number of virulent organisms and the presence of tuberculous lesions in 1) lungs of vaccinated and uninoculated control mice 1 month after challenge infection at various intervals up to 28 weeks after immunization and in 2) lungs of mice challenged 1 month after immunization and sacrificed at various intervals up to 231 days after challenge. Mice inoculated with the cell wall vaccine and challenged at various intervals consistently had fewer and smaller tuberculous lung lesions than did the BCG-vaccinated and control mice at all intervals tested, fewer organisms in the lungs than did the control mice at all intervals tested, and fewer organisms in the lungs than did the BCG-vaccinated mice at all times except at the longer intervals (21 to 28 weeks) when the numbers for both were about equal. Mice inoculated with the cell wall vaccine, challenged 1 month later and sacrificed at various intervals after challenge, had fewer and smaller lung lesions than did the BCG-vaccinated and control mice at all intervals up to 231 days after challenge, fewer virulent organisms in the lungs than did the control mice at all times, and fewer organisms in the lungs than did the BCG-vaccinated mice at all times except at the later intervals (180 to 231 days) when the numbers were nearly the same. Lung weights of mice inoculated with the cell wall vaccine were greater than those of the BCG-vaccinated and control mice at the time of challenge; resistance of the mice to challenge was correlated with lung weight, but it is not known whether this lung enlargement was directly related to immunity. These results indicate that the BCG cell wall vaccine, when administered i.v., confers to mice, for an extended period of time, resistance to aerosol infection superior or equal to that afforded by viable BCG.