BCG persists and induces a durable cell-mediated immunity in mice.
(A–B) BALB/c mice were vaccinated with 1×106 CFU of BCG Copenhagen by intranasal (i.n.) or subcutaneous (s.c.) route. At 7 different time points after vaccination at the same time, mice were euthanized and their lungs and spleen were isolated. (A) BCG load in the two organs of individual mice was determined. Detection limit of the assay as shown by dotted line was 30 CFU/organ, and data shown are mean CFU ± s.e.m. in the lung (left) and spleen (right) from two independent experiments using 5 individually analyzed mice per group at each time point. The experiment was not performed at the104-week time point. (*P<0.05, ** P<0.01, *** P<0.001, **** P<0.0001 using 1-way analysis of variance (ANOVA) with Tukey's post-test). (B) In parallel, pooled cells from the lung (left) or spleen (right) of BCG-vaccinated and naïve mice (n = 4/time point/group) were stimulated with WCL in a cultured ELISPOT assay and IFN-γ, IL-4 and IL-17A SFU were enumerated. Data are means ± s.e.m. of individual cytokine SFU constituting the total cytokine responses of 2 (at week 3, 78 and 104), 3 (at week 32) or 4 (at week 6 and 12) independent experiments evaluated in triplicate. Responses are significant (P<0.001) in vaccinated compared to naïve mice at 6 time points after week 3 using 1-way ANOVA with Tukey's post-test.