Fig. 1.

Experimental intestinal cell model settings. Epithelial cells can be grown on plastic or on microporous membranes (filter inserts) in the presence of immune cells, leading to better cell polarization and differentiation due more accurate simulation of the in vivo intestinal environment (A = apical; B = basolateral). Cells can be grown in a conventional manner with apical side upwards, or alternatively, the filter with polarized cells can be inverted, so that the top of the membrane is equivalent to the basolateral side. In both conventional and inverted setting co-cultured immune cells, substances and microorganisms can be added to apical or basolateral side, enabling functional studies described in the main text on both sides of the epithelia. The inverted setting is particularly appropriate for mechanistic studies of the basolateral side of the epithelia with underlying (immune) cells, since gravity forces the cells to make closer contacts.