Purpose: This H1N1 A/Netherlands/602/2009 challenge was performedto assess if B- and T- cell subsets frequencies kinetics of mature B-cell subsets residing in the iliac lymph nodesafter immunization, can predict the protective efficacy of the used immunization regimen this murine challenge model. Method: We compared B and T cell subset frequencies between cohorts of mice subjected to immunization regimens inducing different levels of protection against lethal H1N1 influenza challenge. Naïve 8-weeks old mice were immunized three times, at days 0, 21 and 42 with different immunogens. One cohort of animals was vaccinated received a largely protective vaccine containing a high dose (30 µg) of a trimeric full-length H1 HA antigen (FL H1#2316) that provides heterologous protection against H1N1 A/Netherlands/602/2009 while a second cohort received a minimally protective vaccine containing a high dose (30 µg) of an HA stem-based monomeric antigen (UFV#4157) derived from FL H1#2316 To control for differences in immune responses related to the dose rather than intrinsically protective properties of the used immunization antigen, a lower but partiallly protective protective dose (0.3 µg) of FL H1#2316 was used for immunizations of a third cohort, while as a negative control for survival a fourth cohort was immunized with PBS only. All immunizations, including mock-immunizations with PBS, were adjuvanted with alum. To analyze cellular responses at early and late timepoints of GC reactions after prime or boost immunizations, 8 animals per cohort were sacrificed at 8 different timepoint (days 4, 7, 12, 19, 25, 28, 46 and 49). To assess the protective efficacy of the administered vaccine regimens, 10 animals per immunized cohort were challenged intranasally with a lethal dose of 25xLD50 H1N1 A/Netherlands/602/2009, heterologous to the parental H1 virus strain. Results: After influenza challenge we observed that high (30 µg) and low (0.3 µg) doses of FL H1#2316 conferred survival rates of 80% and 60% respectively, while a high ...