Figure 7: Relationships between total IgG and antigen-specific IgG for young and old mice. Total IgG and influenza A/Taiwan/1/86 virus (FV) HA-specific IgG were all measured with ELISA. The animals and infection approach are the same as above Figure 2. The young mice exhibited significant positive correlations between total IgG levels and FVHA-specific IgG levels on both day 28 and 42 after primary infection (7a and 7b) but old mice did not (7c and 7d).