FIG 5.

Protective efficacy of immunized MHC-II KO mice and immune sera from MHC-II KO mice. (A and B) Protective efficacy of immunized MHC-II KO mice. (A) Body weight changes. (B) Survival rates. Naive B6 WT (n = 4), boost-immunized B6 wild-type (immu WT [n = 5]), and boost-immunized MHC-II KO (immu MHC-II KO [n = 4]) mice were intranasally challenged with a lethal infectious dose of A/PR/8/34 virus (5× LD₅₀). #, One mouse survived. (C and D) Protective efficacy of immune sera from MHC-II KO mice. (C) Body weight changes. (D) Survival rates. Naive BALB/c mice (n = 5/group) were intranasally infected with a lethal dose of A/PR/8/34 virus (10× LD₅₀) that had been preincubated with heat-inactivated sera (final 4-fold dilutions). Naive, A/PR/8/34 virus plus sera from naive B6 WT mice; Immu WT, A/PR/8/34 virus plus immune sera from prime boost-immunized B6 WT mice; Immu MHC-II KO, A/PR/8/34 virus plus immune sera from prime boost-immunized MHC-II KO mice. P values indicate significant differences between immu WT and immu MHC-II KO groups. *, P < 0.05; **, P < 0.01.