The effect of two distinct forms of cell-mediated response to mycobacteria on the protective efficacy of BCG.

The previous paper presents evidence that prior exposure to some environmental mycobacteria enhances the protective efficacy of BCG, whereas exposure to other species opposes it, and suggests that these different species act by evoking one of two types of cell-mediated response of different protective efficacy. This paper reviews past evidence for the existence of these two types of response, and suggests that both can be demonstrated in mice. The type of response evoked in mice by environmental species correlates with their effect on the efficacy of BCG in man, and with the type of proliferative response evoked in human peripheral blood lymphocytes by their soluble antigens in vitro. Preimmunisation of mice to give one type of response can block subsequent induction of the other. We therefore present a model, based on this principle, for the interaction of contact with environmental mycobacteria with subsequent BCG vaccination.