Resistance of high and low antibody responder lines of mice to the growth of avirulent (BCG) and virulent (H37Rv) strains of mycobacteria

The resistance to Mycobacterium bovis (BCG) of lines of mice selected for high (H) or low (L) antibody responsiveness was estimated from the rate of BCG multiplication in the organs. During the first 2 weeks after i.v. infection with 5 X 10(6) CFU, BCG multiplied faster in the spleens of H than of L mice. Afterwards there was a more drastic reduction of viable BCG counts in H mice than in L mice so that the residual BCG counts were significantly lower in H mice than in L mice, not only in the spleen but also in the liver and lungs. On the 14th day of infection, the spleen and liver enlargement and the increase of phagocytic activity were similar in the two lines, suggesting an identical T lymphokine release. In contrast with BCG, during the first 2 weeks after infection with 7 X 10(5) CFU, M. tuberculosis (H37Rv) multiplied in the spleens of L mice at a similar or a slightly faster rate than in the spleens of H mice. On the 4th week, the viable H37Rv counts were reduced in H mice whereas L mice did not survive the infection. In mice vaccinated with BCG 5 months before virulent challenge, the multiplication of H37Rv was inhibited in the H and L lines. The protective effect of BCG is therefore stronger in L mice taking into account their higher innate susceptibility to H37Rv. This might be due to the higher level of living BCG found in L mice at the time of challenge.