Antibody Response to Influenza Hemagglutinin Conserved Stalk Domain after Sequential Immunization with Old Vaccine Strains

Figure 4

ELISA binding to the stalk domain of HA using purified recombinant chimeric HA; chimeric H6 head with H1 stalk (a) and chimeric H9 head with H1 stalk (b). Homologous-boosted mice (n = 10) were primed with inactivated pandemic 2009 influenza vaccine and boosted at week 4 and 8 with the same vaccine strain. Heterologous-boosted mice (n = 10) were primed with inactivated pandemic 2009 influenza vaccine and boosted with inactivated A/Puerto Rico/8/1934 influenza vaccine at week 4 and inactivated A/USSR/92/1977 influenza vaccine at week 8. The control group (n = 5) received PBS at the initial prime and at week 4 and 8 boost. The chimeric HAs were used to avoid binding to the HA globular head. Immunized mice did not have antibody response to H6 or H9 as the immunized antigens were H1. Therefore, the binding antibody that was detected in this ELISA belonged to the common HA stalk in the immunized and ELISA antigens. The asterisks indicate significant differences at (t test).

(a)

(b)