A. Total IgG response after DNA immunization of four mice three times, two weeks apart with A27L, A27L+I, pA27L+R, pA27LOPT, pA27LOPT+I. Naïve and pVax1 were used as controls, One week after the last immunization, sera from each group of mice were diluted at 1:400, and incubated in a 96-well plate previously coated with recombinant VVWR A27 protein. B. Antigen-specific production of each IgG subtype shown was detected from each group. The plate was analyzed by scanning the absorption at 450 nm and the immune responses among groups of mice are presented as the mean ± standard error of the mean (SEM) of at least three independent experiment. A p value of less than 0.05 was considered significant.