Maternal immunization with both hemagglutinin- and neuraminidase-expressing DNAs provides an enhanced protection against a lethal influenza virus challenge in infant and adult mice.

Maternal immunization is the major form of protection against many infectious diseases in early life. In this report, transmission of vaccine-specific maternal antibodies and protection of offspring against a lethal influenza virus challenge were studied. Adult female BALB/c mice were immunized intramuscularly with plasmid DNAs encoding influenza virus hemagglutinin (HA), neuraminidase (NA), or mixture of the two plasmids. The levels of specific antibodies in sera of offspring at different ages and the survival rates following the lethal viral challenge were valued. The results showed effective transmission of maternal antibodies and long-lasting protection in offspring. Along with the growth of offspring, the antibody titers in vivo decreased and the ability against virus infection decreased accordingly. The HA-specific maternal antibodies protected the offspring from a lethal influenza infection up to 2 weeks old, and the NA-specific maternal antibodies protected offspring up to 4 weeks old. Furthermore, antibodies transferred by the mother immunized with the mixture of HA and NA DNAs protected the offspring up to 6 weeks old. This suggests that maternal immunization with a mixture of HA and NA DNAs provide the most effective protection against the virus challenge for the offspring of mice.