Suppressed or enhanced antibody responses in vitro after BCG treatment of mice: importance of BCG viability.

Mycobacterium bovis, BCG, is known to be capable of either enhancing or suppressing various immune responses. Using a standard technique and number of organisms, some of the parameters predetermining whether enhancement or supression will occur have been investigated. Dead BCG given intravenously into mice caused an enhancement of the antibody response in vitro to sheep erythrocytes. In contrast, the same number of viable organisms caused suppression if given intravenously but enhancement if given subcutaneously. The inclusion of 25% or more killed organisms in an intravenous inoculum of fully viable organisms changed suppression to enhancement. Treatment of BCG infected mice with streptomycin lessened the suppression but did not change it to enhancement. The possible causes of suppression are discussed.