PDCD1 and influenza: For this, we analyzed TFH (CD4+CD44+CXCR5+PD-1+) cells compared to Teff (CD4+CD44+CXCR5−PD-1−) cells following LCMV, influenza, T. muris, H. polygyrus and C. rodentium infection (Extended Data Fig. 5a).