Figure 6: HA-specific IgG and IgM Production in purified IgM+ splenocyte culture. In experiment I (6a and 6b), splenocytes were harvested from old (24 months of age) and young (4 months of age) two weeks after primary infection with the same dosage of influenza A/Taiwan/1/86 virus (FV) as in Figure 5 and IgM+ cells isolated with AutoMax system were cultured with IL-4 and 60Co-irradiated FV-infected splenocytes in an effecter/stimulator ratio of 5:1. ELISPOT assay was performed on the 1.6 × 106 cells (in eight wells) prior to and day 3 following culture for IgM and IgG spots, respectively. The decreased mean IgM spot number and increased IgG spot number were exhibited from day 0 to day 3 in both old and young mice, but significant changes were only shown in young mice. The data were presented in means ± SE for 5 mice in each group. In Experiment II (6c and 6d), the supernatant of above culture on day 3 following culture were harvested and FV HA- specific IgM and IgG were measured with ELISA. The level of FV HA-specific IgM in the purified IgM+ cell culture of old mice is higher compared to the young mice, while the levels of FV HA-specific IgG in both purified IgM+ cell culture and IgM+ cell-depleted culture of old mice are significantly lower in the old mice compared to the young mice. The data were presented in means ± SE for 5 mice in each group