Enhancement of the antibody response in vitro by BCG

The addition of heat-killed BCG to mouse spleen cells in Marbrook cultures causes an enhanced in vitro antibody response against sheep red blood cells, the extent depending on BCG concentration and on whether the spleen cells have been previously primed with BCG in vivo. Moreover, a factor is produced by spleen cells incubated in vitro with BCG which enhances the antibody response of spleen cells from normal untreated mice, the extent of enhancement again depending on BCG concentration and the origin of the spleen cells producing the factor. Filtration through a 0.22 mu filter removes the enhancing activity of the bacteria but not of the factor produced by spleen cultures in the presence of the bacteria. The cellular basis of the enhancement of the antibody response will be discussed.