Fig. 2: A mouse feeding study demonstrates fgTiO2 specificity for Peyer’s patches.
From: Immunocompetent cell targeting by food-additive titanium dioxide
a Single-cell analysis of a tilescanned ileal tissue section. As in humans (Fig. 1a/f), fgTiO2 loaded into the subepithelial dome (SED) and there was evidence of precursor pigment cell formation along the follicle base. Beyond the follicle, two positive cells (a, insets) were found in the villous mucosa. In contrast to the human findings (Fig. 1c) both were caused by luminal fgTiO2 trapped in the invaginated space of goblet cells. b–d To investigate the sensitivity of fgTiO2 detection by confocal reflectance microscopy, a tissue-region containing a single, reflectant foci was milled out under correlative SEM. e-i Transfer of the lamella to a transmission electron microscope enabled imaging and X-ray (EDX) and electron diffraction analysis. A (g, h) single particle of fgTiO2 with an (i) anatase diffraction pattern (i.e., as added to the diet) was confirmed responsible for the single reflectant foci observed. j Caecal patches (adjacent at the top of the colon) were almost completely devoid of fgTiO2 (n = 4 animals). k Immunofluorescence microscopy showed fgTiO2 access to Peyer’s patches was via GP2-positive microfold (M) cells. l Single-cell analysis of a longitudinal ileal section consistently showed the close association between an M-cell rich, follicle-associated epithelium and fgTiO2 uptake. m, n Guided by CD11c and CD3 labelling for phagocytic mononuclear cells and T-lymphocytes (respectively) image-sets were collected from the SED, germinal centre (GC) T-cell zone (TCZ) or overlying villous mucosa (VM) tissue regions (n = 4 mice per diet-group). Some fgTiO2 signal was observed in the GC and TCZ regions but the majority was in the SED. In keeping with (a), and in contrast to the human findings (Fig. 1c), in all four mice, no uptake was seen in the villous mucosa demonstrating specificity for M-cell mediated, Peyer’s patch targeting. Scale bars: a = 500 μm with insets 5 μm; b = 50 μm; c = 10 μm; d = 5 μm; e = 500 nm; g = 200 nm; h = 20 nm; i = 10 1/nm; j = 500 μm with insets 10 μm; k = 10 μm; l, m = 500 μm.
