Figure 3.

Immunofluorescent localization of claudin-1 and occludin in the colon of the preterm and term germ-free piglets. Cryosections of the colon of the preterm [(A,C)a,c] and the term [(B,D)b,d] germ-free piglets were stained for the tight junction proteins claudin-1 [(A,B)a,b] and occludin [(C,D)c,d]. Scale bars for claudin-1 (A,B) and occludin (C,D) are at 200 µm and 50 µm, respectively. Panels with small letters represent magnifications of ×2 for claudin-1 (a,b) and ×4 for occludin (c,d) of the selected area (outlined with dashed lines) in the corresponding panels denoted with capital letters. Claudin-1 is expressed uniformly from crypt to surface in epithelial lateral membranes in the colon of both piglet groups [(A,B)a,b]. In the preterm enterocytes, it is also extensively expressed in the cytoplasm (a). Occludin is expressed at the apical lateral membrane of crypt epithelial cells (c, star), but not in surface epithelial cells in the preterm germ-free piglets [(C), arrow]. It is expressed at the apical lateral membrane of crypt cells (not shown here) and at surface epithelial cells in the term piglets (d, arrows). Sections from five piglets were examined for each group.