It is known that influenza virus infection induces the differentiation of host CD4+ T cells into Tfh cells, which in turn contribute to humoral immunity-mediated virus clearance.22–25 To examine the role of Peli1-modulated Tfh cells in regulating viral infection, we adoptively transferred WT or Peli1-deficient CD4+ T cells with WT B cells into Rag1-KO mice and then infected these mice with H1N1 influenza virus. Here, RAG1 is linked to viral infectious disease.