Bacillus Calmette-Guérin (BCG) decreases resistance to Listeria monocytogenes infection in mice.

Bacillus Calmette-Guérin (BCG) inoculation has been shown to inhibit certain immune functions. To determine whether this inhibition adversely affects host defences against infection, the effect of BCG on Listeria infection in mice was investigated. Mice were injected intravenously (i.v.) with Listeria monocytogenes and 24-96 hr later were inoculated with 8 x 10(6) BCG. Mice given BCG and Listeria had a greater mortality and higher spleen Listeria counts than mice given Listeria alone. An increased number of bacteria in spleens was noted as early as 24 hr after BCG inoculation. Peritoneal macrophages from mice receiving both organisms had a decreased capacity to kill Listeria in vitro. In addition, BCG inoculation suppressed delayed hypersensitivity responses and in vitro spleen cell proliferative responses to Listeria antigen. Suppression of spleen cell proliferative responses was associated with an adherent, non-T lymphocyte subpopulation. The data indicate that BCG administration decreases resistance to intracellular pathogens by abrogating normal cellular defences.