Using 4get/KN2 dual reporter mice, which faithfully report cells that have actively transcribed from the Il4 locus and cells actively producing IL-4 [225], Reinhardt and colleagues demonstrated that during infection with the type-2 pathogens L. major or N. brasilienis, IL-4 production in draining lymph nodes was restricted to bona fide TFH cells that were phenotypically and functionally distinct from canonical TH2 cells [226]. This evidence concerns the gene IL4 and infection.