MBL Susceptibility of seasonal and pandemic 2009 viruses. (A) Plaques were visualized by immunostaining. To eliminate the effects of MBL, the mouse serum was diluted with DMEM containing 0.1 M mannose. (B and C) Inhibitory effect of mouse serum on seasonal and pandemic 2009 influenza viruses. The infectivity of each specimen was expressed as a percentage of the plaque number of the control (without mouse serum). Each value is the mean derived from two independent experiments.