GZMB and infection: Indeed, B. coccoides colonization in Abx-treated mice restored frequency of GrB-secreting NK cells in PBMCs following EMCV infection to the level of PBS-treated controls at 3 dpi, whereas C. butyricum oral gavage did not improve the impairment of GrB secretion in NK cells exhibited in Abx-treated controls during infection (Fig. S5).