Purpose: This H1N1 A/Netherlands/602/2009 challenge was performed to assess if B- and T- cell subsets frequencies kinetics of mature B-cell subsets residing in the iliac lymph nodes after 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 ...