Food grade titanium dioxide (fgTiO2) is a biologically persistent microparticle with an average diameter of 130 nm. It is an additive in the human diet and an excipient in some capsules, tablets, and toothpastes with a median intake of ~2.5 mg per person per day in the UK. Its impact, if any, is not understood. In particular, understanding which gut cells are targeted by fgTiO2 and any potential effects of this requires clarification. This thesis reports a detailed understanding of cellular uptake of fgTiO2 in the mammalian gastrointestinal tract. Having reviewed the relevant literature it was clear that methodology for fgTiO2 detection in tissues merited careful attention. This work identifies reflectance microscopy, with a confocal microscope, as a suitable technique for per particle analysis in intestinal tissue and subsequently demonstrates that this can be used quantitatively, and single particle detection was validated against electron microscopy with microanalysis. Employing the same tools, methodology for quantitative immunofluorescence of the immune cell marker PD-L1, also at the per-cell level, was developed to allow co-detection of this and fgTiO2. With appropriate methodology firmly established, I investigate sites of particle uptake in the murine gut and describe the subepithelial dome of the Peyer’s patch as a newly recognised site of accumulation. I then demonstrate the marked similarities between this and fgTiO2 accumulation in human Peyer’s patches through the study of six separate samples from each species. Following this, I sought to determine how a mildly pathogenic Salmonella inoculation would modulate particle accumulation in the Peyer’s patch cells. A loss of fgTiO2 from the subepithelial dome region was demonstrated when compared to non-inoculated control mice; I propose that pathogen-induced particle-cell migration occurs but found no evidence that this was to elsewhere in the patch. Thus, further work should consider mesenteric lymph nodes as a potential target in such situations. Finally, I show that fgTiO2 does not alter subepithelial dome expression of PD-L1 whether in the presence or absence of Salmonella. Overall, I conclude that ingested fgTiO2 selectively migrates to phagocytic cells of intestinal Peyer’s patches, especially in the subepithelial dome region. However, if the local system is perturbed by this accumulation, PD-L1 is not modulated so inflammation is unlikely to occur. Conversely, a mild Salmonella challenge led to particle migration. Thus, establishing where fgTiO2 goes and how it gets there, should form the basis for future research.