Hallmarks of CD4 T cell immunity against influenza.

The mechanisms responsible for heterosubtypic immunity to influenza virus are not well understood but might hold the key for new vaccine strategies capable of providing lasting protection against both seasonal and pandemic strains. Memory CD4 T cells are capable of providing substantial protection against influenza both through direct effector mechanisms and indirectly through regulatory and helper functions. Here, we discuss the broad impact of memory CD4 T cells on heterosubtypic immunity against influenza and the prospects of translating findings from animal models into improved human influenza vaccines.