We administered an unadjuvanted quadrivalent influenza vaccine (Afluria Influenza A+B, 2010–2011 formulation) to 8-week-old C57BL/6 mice and 10 days later sorted total follicular T cells (gated as CD4+CXCR5+CD19–; Tfh and Tfr together) from the dLN and blood (Supplemental Figure 1A; supplemental material available online with this article; https://doi.org/10.1172/jci.insight.187271DS1). Here, CD19 is linked to influenza.