FIG. 4.

Immunization with DNA vaccines increases the frequency of antigen-specific IFN-γ-secreting cells early in infection. Ten mice were immunized with DNA-85B or the control vector (100 μg, intramuscularly). Four weeks later, half of each treatment group (five/group) was then challenged with aerosol M. tuberculosis H37Rv (100 CFU). All groups were analyzed at the same time point. Early in infection (day 17 [gray bars]) and just after the peak of infection (week 5 [hatched bars]), the numbers of splenocytes secreting IFN-γ in response to Ag85B were measured by ELIspot as described in Materials and Methods. The levels of significance of the differences between groups at day 17 were calculated by Student’s t test. The level of significance of the difference between group 1 and group 2 was P < 0.001 (†), and that between group 1 and group 3 was P < 0.005 (∗). Error bars indicate the standard errors of the means.