Humoral response in BALB/c mice induced by DNA vaccination A. Determination of specific IgG antibodies in the sera of BALB/c mice at 0, 2, 4 and 6 weeks. B. Determination of the specific IgG antibody subclass profile (IgG1 or IgG2a) in the sera of BALB/c mice 2 weeks after the third immunization. Results are expressed as means of the OD405 ± SD (n = 3), and statistically significant differences (p < 0.05) are indicated by (*).