CD4 and influenza: Furthermore, we found that there was a trend (P = 0.0727) of increased TIGIT expression on pTfh cells in IL-21–treated animals (Figure 3D), and influenza HAI titers day 14 after B1 correlated with both TIGIT+CD4+ Tcm (r = 0.6808, P = 0.0120) (Figure 3B) and TIGIT+ pTfh (r = 0.7387, P = 0.0112) cells (Figure 3E).