C4A and infection: Consistent with the above observations, the immunoprotection assay showed that the accumulated survival rate of the ODN-C4 injected group was significantly (P < 0.05, Breslow test) increased by 80% compared with that of the control group (fish that only received mock PBS before infection) in the first 3 days after the infection with A. hydrophila (Fig. 6E), and the zebrafish that only received ODN-C4 without the infection (Mock) did not show an effect on mortality.