(A) Wild type mice were immunized intraperitoneally with rNP using LPS/alum adjuvant; controls were mock immunized with adjuvant alone. After 21 days, mice were challenged intranasally with H1N1 influenza, followed 5 days later with Spn. On days 20 and 22, mice were treated with CD8 mAb or a combination of CD4 and CD8 mAb; controls received a rat IgG2b control mAb. Survival was not compromised significantly in mice treated with CD8 or CD4 and CD8 mAb (n=8–10 mice/group). (B/C) Wild type (WT) and B cell-deficient μMT mice (B) or circulating antibody-deficient AID.μS mice (C) were immunized intraperitoneally with rNP using LPS/alum adjuvant; controls were mock immunized with adjuvant alone. After 21 days, mice were challenged intranasally with H1N1 influenza, followed 5 days later with Spn. Among mice immunized with rNP, WT mice showed significantly increased survival when compared to either μMT or AID.μS mice (both p<0.0001 by Log rank tests; n=10 mice/group).