S.l. vaccination of PR8 split vaccine with LPSpa protected mice from viral challenge.

<p>BALB/c mice were divided into 3 groups and immunized twice s.c. with 0.1 μg PR8 vaccine or s.l. with PR8 vaccine (0.1 μg) and 5 μg LPSpa at weekly intervals. The titer of PR8-specific (A) serum IgG and (B) nasal IgA were assessed by ELISA (n = 4). Seven days after the last immunization, mice were challenged with a lethal dose (100×LD₅₀) of PR8 virus and (C) survival rates were recorded (n = 8–10). (D) Lung sections at 5 days after virus challenge were stained with hematoxylin-eosin to evaluate cellular infiltration (n = 3). Similar experiments were performed at least three times and one representative experiment is shown. <i>***P</i><0.001, by the log-rank test. N.D., not detectable.