As noted, oral gavage with an AIEC isolate NRG857c caused a rapid epithelial apoptosis in ileal epithelium5, marked by an increase of active Caspase-3+ crypts at the early stage of infection (Fig. 1a, b), and a corresponding epithelial regeneration evidenced by an increase of CD24-/low Ki67+ proliferating crypts which mostly represent transit-amplifying (TA) cells (Figs. 1c, 2b)24,25. Here, MKI67 is linked to infection.