GZMB and infection: Further, upon ex vivo infection with influenza A/H3N2 virus, ∼50% of the total CD8+ T cell population express GrB in the absence of Perf (Kumar et al., 2017) and can play an important role in immune pathology resulting in the loss of tissue function and integrity (Choy et al., 2004; Tschopp et al., 2006; Granville, 2010; Hendel et al., 2010; Russo et al., 2018; Turner et al., 2019; Matsubara et al., 2020).