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Antigen-specific serum IgM (A), IgA (B), and IgG (C) following primary and secondary infection of chickens with S. Virchow and S. Typhimurium. Data shown are based on five birds per group at each time point. Error bars represent the standard error of the mean. An asterisk indicates that there was a significant difference between group 1 and group 2 (*) or group 3 and group 4 (**) (P < 0.05).
