Commonly administered bacille Calmette-Guerin strains induce comparable immune response

Bacille Calmette-Guerin (BCG) is currently the only available vaccine against tuberculosis (TB), but its protective efficacy in adults is highly variable. This study aimed to compare the immune response induced by two widely used BCG strains: BCG China strain (derivative of BCG Danish strain) in DU2-III group and BCG Pasteur in DU2 -IV group. Healthy BALB/c mice were immunized with BCG China strain or BCG Pasteur strain. Specific IgG, IgG1, and IgG2a antibodies titers, the proliferation of splenocytes, the percentages of splenocyte subsets and the concentrations of induced IFN-gamma and IL-4 at 6th, 8th, 10th, and 12th weeks after the immunization were detected. We found that BCG Pasteur strain induced higher specific IgG and IgG1 titers, higher proliferation of splenocytes, higher percentages of CD4(+) or CD8(+) T cells, and higher concentration of secreted IFN-gamma than BCG China strain. However, there were no significant differences in IgG2a titer and IL-4 concentration between both strains. In conclusion, our study shows that immune responses to BCG vaccine differ by strain, which may account for variable outcomes of BCG immunization.