PCNA and necrotizing enterocolitis: We again demonstrated that the bacteria–epithelial cell coculture in our NEC-on-a-Chip model resulted in increased expression of proinflammatory cytokines IL1B and IL8 (Figure 3B), as well as decreased expression of proliferation markers Ki67 and PCNA (Figure 3C) at 24 hours after inoculation compared with control chips.