Abstract Campylobacter JeJum IS the leading cause of foodborne gastroenteritis worldwide, yet despite the organism's prevalence, relatively little is known about the mechanisms of pathogenesis. This is mainly due to the lack of a convenient small animal model of infection combined with certain inherent weaknesses with widely used in vitro models. The aim was to develop two improved models to study C. jejuni interactions with intestinal epithelial cells. The Ex Vivo Organ Culture (EVOC) model involves co-culturing C. jejuni with human intestinal biopsies. C. jejuni 11168H and 81-176 wild-type strains were demonstrated to induce the secretion of human beta-defensins 2 and 3 (hBD-2 and hBD-3). Furthermore, the supernatants of infected biopsies were demonstrated to contain significantly higher levels of IL-l~, IL-6, IL-12 and IL-23 compared to uninfected controls. Experiments using 11168H flaA and neuBl mutants demonstrated that the induced defensin response was not due to host recognition of either flagellin or the terminal sialic acid residue of C. jejuni illS. The Vertical Diffusion Chamber (VDC) model involves co-culturing C. jejuni with polarised human intestinal epithelial cells (lECs) with micro aerobic conditions at the apical surface and aerobic conditions at the basolateral surface. Survival and integrity of the IECs under these conditions over 24 hours was demonstrated. Co- culture experiments under these conditions resulted in an increase in both C. jejuni interaction with and invasion of IECs. This was mirrored by an increased, polarised host innate immune response. Transcriptional analysis of aerobically and microaerobically co-cultured C. jejuni 11168H identified several genes that may playa role in these increased interactions. The levels of interaction and invasion of defined C. jejuni 11168H mutants with Caco-2 cells were analysed to identify bacterial factors that contribute to these increased interactions. Both 11168HflaA and rpoN mutants exhibited lower levels of interaction and invasion than the wild-type strain, suggesting the involvement of bacterial motility in the increased interactions under micro aerobic conditions. The reduction in this increased interaction phenotype was more pronounced at shorter co-incubation times, suggesting that motility is particularly important during the early phases of interaction. The development of these two model systems should allow· future 3 experiments to more accurately investigate host-pathogen interactions during C. jejuni infection of the human intestinal tract