The effect of oral Mycobacterium vaccae on subsequent responses of mice to BCG sensitization.

It has been postulated that previous exposure to mycobacteria in the environment may be a contributing factor to the variable efficacy of BCG vaccination in protecting against human tuberculosis or leprosy, in different geographical regions. To test this hypothesis mice were given Mycobacterium vaccae in their drinking water for 3 weeks immediately, 27 days, or 54 days before they were injected subcutaneously with BCG. Spleen cells were examined, 50 days after injection of the mice, for ability to proliferate in vitro in response to killed mycobacteria added to the cultures. The results show that, depending on the timing of the exposure of the mice in vivo to M. vaccae before BCG injection and the dose of the mycobacterial challenge in vitro, oral administration of this species of environmental mycobacteria can either enhance, mask or interfere with the expression of sensitization by BCG. Thus, our data from mice support the hypothesis that the results of BCG vaccination for a particular human population are influenced by exposure to indigenous mycobacteria.

BCG, Corynebacterium parvum or Mycobacterium leprae added to cultures of BCG-primed mouse spleen cells cause an enhanced primary antibody response in vitro.

A few weeks after mice were injected i.v. with 10(8) live Mycobacterium bovis, BCG, the antibody response of their spleen cells to SRBC in vitro was comparable with the response of cells from untreated mice. Addition of BCG organisms to the culture vessels resulted in enhanced antibody-forming cell (AFC) responses by the primed cells but not by the cells from the untreated mice. No evidence was found for a direct stimulation of B cells and cell depletion experiments suggested macrophages were directly involved. BCG added to the cultures up to 68 h after they were set up, but not later, still caused enhancement. No enhancement was found when DNP-Ficoll was used as antigen. The ability to stimulate the anti-SRBC response was not restricted to the organism used for priming. Enhancement was also found if C. parvum or M. leprae were added to BCG-primed cells and if BCG was added to C. parvum-primed cells. The relevance of the results to the search for a leprosy vaccine is discussed.

Phagosome/lysosome fusion: a possible prerequisite for the enhancement of antibody responses in vitro by BCG, Mycobacterium leprae and Corynebacterium parvum.

Primary in vitro antibody responses to SRBC were suppressed in cultures prepared from the spleens of CBA mice injected i.v. 20 days previously with 10(8) liver BCG. In contrast, cultures prepared from mice injected with dead BCG showed enhanced responses. In vitro spleen cell responses of the mice had returned to normal levels 4--6 weeks after their injection, but if dead BCG, M. leprae or C. parvum was added to the cultures, responses were enhanced. The enhancing effect of the added bacteria could be removed by adding also suramin, a drug known to inhibit in vitro fusion of lysosomes with phagosomes. It is suggested that the different in vivo effects of live and dead BCG may relate to differences in their handling by macrophages and more especially that the enhanced antibody forming cell response seen in the restimulated cultures of spleen cells from BCG primed mice, depends upon efficient intracellular fusion of lysosomes with the phagosomes containing the added dead bacteria.