Primary seasonal influenza virus infection elicits CD4 T cells specific for genetically conserved epitopes that can be mobilized for cross protective immunity to pandemic H1N1 influenza

In this study, a mouse model of primary and secondary influenza infection is developed by using a widely circulating seasonal H1N1 virus and the pandemic strain of H1N1 that emerged in Mexico in 2009, and several key issues are evaluated. The specificity of CD4 T cell reactivity toward epitopes conserved among H1N1 viruses or unique to the seasonal or pandemic strain was assessed by ELISpot assays. It was observed that a secondary challenge with the pandemic virus was associated with rapid expansion of memory CD4 T cells specific for shared determinants, decreased viral titers and accelerated neutralizing anti-influenza antibody responses to the serologically distant novel pandemic strain.