Since Tfh cells have been established as a separate CD4 T cell lineage that is specialized in providing help to B cells in the context of affinity maturation, several studies have investigated CD4 T cell responses following seasonal influenza vaccination with a special focus on cells with a Tfh phenotype (i.e. co-expression of PD-1 and CXCR5). This evidence concerns the gene CXCR5 and influenza.