HA tri-stalk specific seroreactivity in mice.

(A) Serial dilutions of HA tri-stalk protein (0.15625, 0.3125, 0.625, 1.25, 2.5, 5.0 and 10.0 μg/mL) tested against 1:2700 dilution of sera from LAH-PP7 vaccinated mice or naïve mice. (B) Total IgG ELISA was used to determine the HA tri-stalk specific seroreactivity induced by vaccination with LAH-PP7 or by sublethal infection (s.i.) of A/Luxembourg/46/2009 pandemic H1N1 (pH1N1), A/Texas/36/91 seasonal H1N1 (sH1N1), A/Puerto Rico/8/34 H1N1 (PR8), A/Lux/01/2005 seasonal H3N2 (sH3N2), A/Aïshi/68 H3N2 (X-31), or B/Lee/40 virus. Total HA tri-stalk specific IgG titers were assayed in sera after the third immunization with LAH-PP7 or after 2 weeks post sublethal virus infection. (C) Comparison of HA tri-stalk specific IgG endpoint titers (n = 8 mice/group; **p<0.001, ****p<0.00001).