FIG 4.

Passive serum transfer and CD4⁺ cells induced by 1V270/1Z105-adjuvanted rHA contribute to protection from lethal influenza virus challenge. Immune sera were generated from mice by immunization with rPR/8 or rCal/09 HA adjuvanted with 1V270/1Z105 or no adjuvant at 0 and 3 weeks and administered to recipient mice. Mice immunized with rPR/8 were challenged with homologous PR/8 virus and followed for morbidity (A), as assayed by weight loss, and mortality (B). Mice receiving immune sera from either rPR/8- or rCal/09-vaccinated animals were challenged with NL/09 virus, such that heterologous protection was assayed using homologous protection as the control group, and these animals were followed for morbidity (C), based on body weight loss, and mortality (D). Statistical significance of weight loss was assessed by multiple t tests, comparing the 1V270/1Z015 versus no adjuvant groups (A) and the Cal/09 homologous control (C), as indicated by the colors of the asterisks. (E and F) Mice were immunized with rPR/8 HA plus 1V270/1Z105, and 3 to 4 weeks later they were treated with the MAb GK 1.5 to deplete CD4⁺ cells or the MAb LTF-2 (isotype) as a control. Two days after administration of the MAbs, mice were challenged with homologous PR/8 virus and assayed for morbidity, based on weight loss, and mortality (animal survival data are shown in parentheses) (E) or with heterologous NL/09 virus and assayed for morbidity by weight loss and mortality (animal survival data are shown in parentheses) (F). For the heterologous challenge, two independent experiments with 10 mice/group and 19 to 20 mice/group were conducted and combined. Statistical significance of weight loss was assessed based on multiple t tests. Statistical significance of survival was assessed with the Mantel-Cox test. *, P < 0.05; **, P < 0.01.