Figure 5: ELISPOT analysis for influenza virus-specific IgG+ and IgM+ cells in old and young mice. Bone marrow cells and splenocytes of old (24 months of age) and young (4 months of age) were harvested 12th day after secondary infection (challenge) with 10 MID50 of influenza A/Taiwan/1/86 virus (FV) or after the second vaccination with inactivated FV. Cells were assessed for the numbers of influenza virus-specific IgM (5a) and IgG (5b) positive cells with two-color ELISPOT assay. Compared to young mice, inactivated virus- vaccinated old mice exhibited significantly decreased number of IgG (P<0.05-0.001) positive spots (5b). Only one spot was found in live virus infection groups. IgM positive spots (5a) in bone marrow cells from both live virus-infected and inactivated virus-vaccinated old mice and in splenic cells from live virus-infected mice were all significantly increased when compared to those from young mice (P<0.01-0.001). The data were presented in means SE for 5 mice in each group.