The intestinal barrier is dependent on three junctional complexes, the tight junction (TJ), the adherens junction and desmosomes. Of these, TJ complexes separate the external lumen from the underlying mucosa. Apical TJs consisting of integral transmembrane proteins including occludin, tricellulin and claudins form a dynamic multimolecular complex that selectively regulates the paracellular flux of ions and molecules through the small intestinal epithelium. The TJ complex also constitutes a highly resistant barrier to the entry of luminal pathogens and toxins, preventing infection of the underlying tissues. How the assembly and function of the TJ complex remains unclear. Evidence suggests TJ complex formation may be regulated by cycles of phosphorylation and dephosphorylation of occludin. Occludin seals the paracellular space between neighboring cells in epithelial and endothelial cell layers and targeted phosphorylation by cellular kinases affects occludin localisation and interaction with components of the TJ complex. Occludin comprises two extracellular loops, four transmembrane domains and two intracellular N- and C-terminus domains. The aim of my project is to investigate the role of occludin phosphorylation in TJ barrier formation in response to pathogen infection. To address this I have used the major protozoan parasite Toxoplasma gondii to assess TJ barrier integrity in the small intestinal epithelial cells (IEC-6). Recombinant protein fragments of occludin domains were used to assess invasion of the intestinal epithelium by Toxoplasma gondii. We established Toxoplasma gondii tachyzoites bind to the extracellular loops of occludin as a mechanism of invasion and transmigration of the small intestinal epithelium without disrupting TJ barrier function. Our results indicate that Toxoplasma gondii can associate with the occludin C-terminus to modulate occludin phosphorylation and assembly at the TJ. We have provided also evidence for targeted phosphorylation of occludin in response to Toxoplasma gondii infection using an in vitro kinase assay to identify IEC-6 kinases that target occludin. These findings represent a step towards understanding the pathogenesis of intestinal diseases associated with a disrupted TJ permeability barrier.