Dose of BCG does not influence the efficient generation of protective immunity in mice challenged with Mycobacterium tuberculosis.

It is generally agreed that BCG vaccination is relatively ineffective in adults exposed to tuberculosis infection. The reasons for this may well be multiple, and may include the possibility that higher doses of BCG may induce a mixed TH1 and TH2 response, which may lessen the protective effect of the vaccine. To test this hypothesis, mice were vaccinated with a range of doses of BCG and then challenged by the intravenous or aerogenic routes with virulent Mycobacterium tuberculosis. While the data support the hypothesis that a TH2 response is induced by higher doses of BCG, this was found to have no influence whatsoever on the capacity of the vaccinated mouse to express acquired specific resistance to the challenge infection.