Fig. 3

Sialic acid distribution in the beef cattle intestinal tract. (A-H) Confocal microscopy images of fluorescently labeled lectins Sambucus nigra (SNA, FITC, green) specific for sialic acid (SA) α2,6-Gal, Maackia amurensis II (MAL II, DyLight 650, red) specific for SA α2,3-Galβ (1–3) GlcNAc, and Maackia amurensis I (MAL I, FITC, green) specific for SA α2,3-Galβ (1–4) GlcNAc. Blue represents nuclear staining using DAPI; scale bar = 20 µM. Representative merged images showing SNA/MAL II binding (A–D) and MAL I/MAL II binding (E–H). The epithelial lining of the small and large intestine shows MAL II labeling (insets of A, C), which was evident in the quantitative image analysis (arrow) (Aiii, Ciii). Goblet cells located in the crypt and apical region of the intestines show abundant MAL II labeling (A–D). SNA labeling was limited to lamina propria (asterisk) (A, B) and goblet cells in the crypt region of the intestines (arrowhead) (B, D). MAL I and MAL II were labeled largely co-localized (E–H) in both the epithelial lining and goblet cells. Quantitative image analysis indicates MAL II was comparatively higher in the co-localized areas (arrow) (insets of E, G, Eiii, Giii). Uniform labeling of MAL I in goblet cells distributed toward apical or crypt regions of the small intestine (Ei, Fi). Note the gradient decrease in MAL I labeling in the goblet cells distributed toward the apical to crypt regions of the large intestine (Gi, Hi). (I–L) Confocal images of small and large intestines showing SA N-glycolylneuraminic acid (Neu5Gc, FITC, green) following immunofluorescence staining. The SA Neu5Gc was expressed on the epithelial lining and goblet cells of the small intestine (I, J). Neu5Gc expression was more scattered in the large intestine, and there was no evident expression on the epithelial lining (K, L).