Functional cell models of the gut and their applications in food microbiology--a review

Abstract

Animal experimentation has a long tradition for risk assessment of new drugs before they reach the clinic. To reduce expensive animal experimentation, attempts have been made to build inexpensive and convenient intestinal functional cell models to study toxicity and bioavailability of new substances along with providing relevant models to study interactions between the host, pathogens and intestinal microflora. We review the available cell lines and models of the intestine and their potential uses. Tumor derived cell lines such as Caco-2, T84 and HT-29 are widely used despite many drawbacks, which are discussed with respect to complexity of the gut, where various cell types interact with commensal microbiota and gut-associated lymphoid tissue. To address this complexity, 3D models of human and animal gut represent a promising in vitro system to mimic in vivo situation without the use of transformed cell lines.

Fig. 1

Schematic presentation of interactions in the small intestine. Intestinal epithelial cells are polarised cells with distinct apical (towards the lumen) and basolateral sides (towards the body). Tight junctions between the cells keep integrity of the epithelia. Underneath the epithelial barrier lay the mucosal lymphatic tissues, responsible for induction and regulation of the immune system. Nutrients and antigens are selectively sampled in the lumen and transported through the barrier. Besides enterocytes other cells populate the epithelial barrier (M, Goblet, Paneth, endocrine cells) with distinct specialised functions.

Fig. 2

Morphology of the epithelial cells: (a) SEM micrograph of a typical morphology of the cell with established epithelial character; (b) TEM micrograph of the epithelial cells: arrow indicates proper tight junctions formation between the adjacent epithelial cells; (c) SEM micrograph of apical surface microvilli of the fully differentiated epithelial cell. Establishment of densely packed epithelial layer is crucial for the barrier between the lumen and the body; layer morphology depends on the matrix, which is used to grow the cells.

Fig. 3

Intestinal epithelial cell lines: (a) Caco-2; (b) HIEC; (c) H4; (d) IPEC-J2; (e) IPEC-J2-3; (f) IPEC-J2-9. Magnification 200×. Caco-2, HIEC and H4 are human-derived cell lines while IPEC-J2 was isolated from a pig. Although all cells are classified as epithelial, there are morphological differences between them. Except for Caco-2, all the cell lines have a non-tumorigenic origin.

Fig. 4

Differences in growth morphology between normal intestinal epithelial (IPEC-J2) (a, c) and tumorigenic cells (Caco-2) (b, d) and growth type (a,b — simple monolayers on plastic; c,d — 3D growth). Magnification 100×. Both cell lines develop different surface morphology depending on the growth matrix (monolayer — 3D). 3D growth allows the cells to polarise with distinct apical and basolateral parts, mimicking the in vivo situation.

Fig. 5

Schematic presentation of the functional (3D) model of the gut and functional polarity of the intestinal epithelial cells growing in it. Cells growing on a microporous membrane develop transepithelial resistance (TER) and potential (TEP), measured between apical and basolateral compartments. Graphs represent time dependent development of TER/TEP after seeding on the membrane for three porcine intestinal epithelial cell line clones (PSI cl.1 (yellow); PSI cl. 3 (blue); PSI cl. 9 (magenta)).

Fig. 6

Cell lines (epithelial and monocytes/macrophages) developed in our laboratory to build 3D functional cell models of intestine: porcine (a) CLAB; (b) PSI; (c) PoM; ovine (d) OSI; goat (e) GIE; (f) GOMA; chicken (g) B1OXI; (h) COMA; human (i) TLT. Magnification 200×. PoM, GOMA and COMA are macrophages, while others are epithelial cells. All the cell lines are of non-tumorigenic origin, isolated from dissected animal tissue using limiting dilution technique.

Fig. 7

Infection of porcine monocyte/macrophage cell line PoM with hepatitis E virus (HEV): (a) PoM before inoculation; (b) control after 48 h; (c) infection with HEV after 48 h. Magnification 40×. In our laboratory developed intestinal/macrophage cell lines and 3D models of animal and human intestines can be used to study host–pathogen interactions, isolation of probiotics and for other studies in the intestine.

Fig. 8

Infection of porcine intestinal epithelial cell line PSI with tick-borne encephalitis virus (TBEV): (a) PSI before inoculation; (b) control after 5 days; (c) infection with TBEV after 5 days. Magnification 40×. 3D models of intestine can be applied in the research of new viruses and zoonotic diseases.