Role of cytoskeleton and surface lectins in Giardia duodenalis attachment to Caco2 cells

An in vitro model of Giardia duodenalis and the Caco2 cell line enable the study of parameters that could play a part in trophozoite attachment. We explored the role of membranous lectins of G. duodenalis in attachment-inhibition studies using carbohydrates in solution. Attachment rates were reduced by 14% and 23% in the presence of 100 mmol/l mannose-6-phosphate and glucose, respectively, as compared with control values. No significant modification was observed after trophozoite trypsinization at room temperature or at 37 degrees C. The inhibitory effects of colchicine (35%) and nocodazole (70%) suggest a primordial role of the cytoskeleton; microtubules appear to be the principal effectors of trophozoite fixation. Scanning electron microscopy revealed circular imprints on the Caco2 brush border after trophozoite detachment. The mechanisms of attachment of G. duodenalis to intestinal enterocyte-like cells in culture are thus essentially of the mechanical or hydrodynamic type; surface lectins would appear to intervene in the specificity for duodenal cells.

Adherence and multiplication of Giardia intestinalis on human enterocyte-like differentiated cells in vitro

This report describes a technique for studying the adherence and growth of Giardia intestinalis trophozoites (strains PARIS/86/LCF/1, PARIS/86/LCF/2 and PARIS/88/LCF/8) using the human colon carcinoma cell line Caco2. Giardia trophozoites were cultured with Caco2 cells in a modified HSP3 culture medium. The biochemical differentiation of Caco2 cells was established by an increase in sucrase isomaltase activities to values of 4.51 +/- 0.90 and 10.39 +/- 3.00 milliunits/mg protein for 8- and 12-day-old cultures, respectively. Giardia, adherence to 8- and 12-day-old Caco2 cells reached a value of greater than 75% after 60 and 30 min, respectively. Adherence diminished significantly at 24 degrees C and was almost undetectable at 4 degrees C. Depletion of divalent cations reduced the proportion of adherent trophozoites by up to 46%. Adherence was pH-independent between pH 6.0 and 7.6. Parasite growth increased when Caco2 cell monolayers were used instead of axenic cultures. This in vitro human cell model may contribute to the study of the mechanisms and factors involved in the host-parasite interaction.

The biological effects of retinoids on cell differentiation and proliferation

The retinoids are the natural and synthetic analogues of retinol or vitamin A. These molecules are able to modulate differentiation and proliferation processes in several cell types. The presence of retinoids is essential for inducing or maintaining the differentiation of epithelial cells. On the other hand, when excess retinol is added to the culture medium, the differentiation of some mesenchymal cells is impaired. Retinoids also promote the differentiation of carcinoma cells of various origins: embryonal carcinoma, leukaemic and melanoma cells. While their effect on the proliferation of normal cells appears variable, these molecules inhibit the growth of cells treated with a tumoural promoter, or spontaneously transformed cells, and they prevent tumour promotion. Various mechanisms of action might be involved: retinoids could act at the level of the genome with or without the participation of their binding proteins. They might also influence glycoconjugate biosynthesis and interact, through certain glycosylation reactions, with growth factor receptors. The role of vitamin A and its structural analogues in cell differentiation and growth is of great therapeutic interest.