CD38 and influenza: We first tested expression of these cell-surface receptors after seasonal influenza vaccination, a routine nonadjuvanted inoculation in which cTfh cell expansion has been well described (Bentebibel et al., 2013) and in which expression of ICOS and CD38 has been reported on cTfh cells (Bentebibel et al., 2013; Herati et al., 2017; Koutsakos et al., 2018).