Studies on antibody responses following neonatal immunization with influenza hemagglutinin DNA or protein

Neonatal mice have immature immune systems with defects in several componen ts of inflammatory, innate, and specific immune responses and develop a pre ferential T helper type 2 response following immunization with many vaccine antigens. These studies were undertaken to determine whether 1-day-old neo natal mice immunized with plasmid DNA expressing influenza A/PR/8/34 hemagg lutinin (H1) by either intramuscular (im) or gene gun (gg) inoculation were capable of generating humoral responses comparable to those in mice immuni zed as adults. The newborn mice developed stable, long-lived, protective an ti-HI-specific IgG responses similar in titer to those of adult DNA-immuniz ed mice. However, unlike the adult im and gg DNA immunizations, which devel op polarized IgG2a and IgG1 responses, respectively, mice immunized as neon ates developed a variety of IgG1, IgG2a, and mixed lgG1/lgG2a responses reg ardless of the inoculation method. Boosting increased but did not change th ese antibody profiles. In contrast to the DNA immunizations, inoculations o f newborn mice with an A/PR/8/34 viral protein subunit preparation failed t o elicit an antibody response. Temporal studies revealed that both responsi veness to protein vaccination and development of polarized patterns of T he lp following DNA immunization appeared by 2 weeks of age. (C) 1999 Academic Press.