Vaccination with hemagglutinin or neuraminidase DNA protects BALB/c mice against influenza virus infection in presence of maternal antibody

Table 3 Protection against a lethal influenza virus challenge in offspring immunized with DNA vaccine born to the mothers immunized with inactivated vaccine^a

		Serum IgG titers^b in offspring
Dose (μg) of Inactivated vaccine for female mice	Plasmid for offspring	ELISA (2ⁿ)^c		NI assay (2ⁿ)^c		Lung virus titers^b (log₁₀ TCID₅₀)	Survival offspring/Tested offspring (3 weeks)
		21 days after primary immunization	7 days after booster	21 days after primary immunization	7 days after booster
1.00	30 μg HA	14.8 ± 0.50	13.3 ± 0.30			3.3 ± 0.35*	3/6
0.10	30 μg HA	11.7 ± 0.50	12.5 ± 0.60			3.8 ± 0.23*	3/7
0.01	30 μg HA	11.3 ± 0.60	13.0 ± 0.00			3.0 ± 0.71*	6/7*
1.00	30 μg NA			4.3 ± 0.60	7.0 ± 1.00	1.9 ± 0.58*	7/7*
0.10	30 μg NA			3.7 ± 0.60	7.2 ± 0.80	1.5 ± 0.24*	7/7*
0.01	30 μg NA			4.3 ± 0.60	8.0 ± 1.00	0.9 ± 0.83*	6/6*
Unimmunized	Unimmunized	<1	<1	<3	<3	5.3 ± 0.35	0/7

^a Female mice were immunized twice, 3 weeks apart, with various doses of inactivated vaccine. The offspring were immunized with 30 μg HA or 30 μg NA at ages of 1 and 4 weeks respectively. Serum samples from offspring were collected 3 weeks after primary immunization and 1 week after booster. The anti-HA antibody titers were measured by ELISA. The anti-NA antibody titers were measured by NI assay. One week after booster, the offspring were challenged with a lethal dose of A/PR/8/34 (20 × LD₅₀). Lungs were taken out from at least three mice in each group 3 days after challenge for virus titration by standard MDCK assay. Survival rates of mice were measured 3 weeks after challenge.
^b Values represent mean ± S.D. of each group.
^c The serum samples were diluted 2-fold serially and "n" represents the dilution factor.
*Significant difference (p < 0.05)

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