Detection of IgG, IgG1, and IgG2a antibodies in the sera of Kunming mice. (A) Determination of IgG antibodies induced by DNA immunization at weeks 0, 2, 4, 6. (B) Determination of IgG1 and IgG2a in the sera of mice two weeks after the last immunization. Results are expressed as means ± SD (n = 3) with respect to absorbance at OD405 and statistical differences (p < 0.05) are indicated by (*). The bars represent the levels of IgG, IgG1, and IgG2a in the serum of mice.