Aims: Human colon adenocarcinoma (Caco-2 cells), has the ability to spontaneously differentiate towards a normal intestinal epithelium phenotype in long-term culture. Since the junctional complex, brush border, and transcytosis contribute mainly to the function of enterocytes in absorption, morphological structure of these cells plays undeniable rule. However, full morphological characterization of these cells was not adequately investigated. Therefore, the aim of the present work is to carry full morphological characterization of the cultured intestinal epithelial cells versus the Caco-2 cells model.

Methods: Freshly isolated and late cultured jejunal cells of adult rabbits as well as Caco-2 cells were processed for transmission electron microscopy (TEM) and scanning electron microscopy (SEM) and examined with Philips CM100 at 80 KV, and Philips SEM XL 30 at 30 Kv; respectively. Immune-fluorescence examination was done using two primary antibodies: anti-pancytokeratin for detecting cells of epithelial origin and anti-HBB, specific for apical uptake of sucrase-isomaltase, then processed for DAB staining. Immune-electron microscopy was done by tracing the uptake and transport of IgG conjugated to HRP, stained with DAB cytochemistry, and then processed for TEM. Results: Cultured Intestinal epithelial cells expressed early cytokeratin, tight junctional complexes, desmosomes and long microvilli with TEM before deterioration and conversion into fibroblastic like cells on day 21. Caco-2 cells in culture gradually undergo spontaneous enterocytic differentiation, in the form of cytokeratin labeling and positive sucrase-isomaltase as detected by immunofluorescence. Examination by TEM and SEM showed high density surface microvilli, coated pits and vesicles, apical tubo-vesicular system and apical junctional complexes. Immunoelectron microscopy of the Caco-2 cells showed the uptake at the surface of microvilli and transcytosis of IgG-HRP reaching the basal region.

Conclusion: This investigation provides full morphological characterization of the cultured epithelial cells and Caco-2 cells model. Caco-2 cells model has proved to be a useful in vitro model that mimics the intestinal epithelium.

Keywords: Caco-2 cells, IgG HRP, Scanning electron microscopy, Transmission electron microscopy