Repeated DNA vaccination induced neonatal tolerance against Escherichia coli beta-galactosidase in immune-competent mice

Abstract

Objectives: To induce neonatal immune tolerance in immune competent animals by repeated DNA vaccination. Materials and Methods: We used two groups of neonatal immune competent mice, C57BL/6, six in each. Mice in one study group received subcutaneous injection of 2 μg of endotoxin-free plasmid, pCBLacZ, at the posterior neck area. Concentration of the plasmid was 0.5 mg/mL. This plasmid encoded a potent immunogen, Escherichia coil beta-galactosidase. Mice in the other study group received intrarectal injection of same amount of pCBLacZ. All the animals received injection at the second day of birth and 5 consecutive injections of the same dose of pCBLacZ at an interval of 7 days. Seven days after the last shoot, the mice received an intramuscular injection of 50 μg of endotoxin-free pCBLacZ at a concentration of 2 mg/mL at the left anterior tibialis. We used 6 naive adult C57BL/6 as the control. These animals received an intramuscular injection of 50 μg of pCBLacZ at the left anterior tibialis at age of 42 days. Results: We examined the expression of beta-galactosidase in muscle fibers 6 days after the last intramuscular injection. The average numbers of fibers expressing beta-galactosidase was 168.2 in the mice receiving intrarectal immunization as compared with 0 in the mice receiving subcutaneous injection and 16.2 in their little mates. (p=0.001 by likelihood ratio test). There were two mice got 409 and 513 blue fibers respectively. Serum IgG against the beta-galactosidase was lower in the animals receiving intrarectal injection as compared with the mice in the other two groups by nonparametric Mann-Whitney test. Conclusions: Repeated DNA vaccination in the neonatal stage can induce immune tolerance against a potent immunogen in the immune competent animals. The ways of administration determine the success of tolerance induction.