Figure 4.

IIV vaccination does not recall broadly reactive IgA antibodies in young and elderly subjects. (A) Levels of HA-reactive IgA antibodies against rHAs from three H1N1 influenza viruses (CA/09, NC/99 and Sing/86) in the serum of young adults and elderly subjects prior to and post-vaccination. (B) Level of H1 stem-directed IgA antibodies in the serum of young adults and elderly subjects prior to and post-vaccination, measured by ELISA as described in the M&M section. (C) Frequency of stem-directed IgA antibodies relative to total rHA binding, in the serum of young adults and elderly subjects prior to and post-vaccination. *p < 0.05, **p < 0.01, ***p < 0.001.