Factors regulating the effect of IL-4 on intestinal epithelial barrier function.
BACKGROUND
Inflammatory bowel disease is associated with an imbalance in cytokine production and defective intestinal barrier function. Previous studies indicate that IL-4, a cytokine increased in food allergy and in early Crohn's disease, enhances epithelial permeability. Here, we characterized the mechanism of action of IL-4 on cultured epithelial cells and examined if the anti-inflammatory cytokines, TGF-beta or IL-10, can modulate the effects of IL-4.


METHODS
Confluent monolayers of human T84 epithelial cells were cultured with IL-4 alone or in combination with IL-10 or TGF-beta or with inhibitors of protein synthesis and blockers of IL-4 receptor signalling pathways. Permeability was evaluated by measuring transepithelial resistance (TER), flux of (3)H-fMLP (a small bacterial tripeptide) and horseradish peroxidase (HRP) (a macromolecule).


RESULTS
T84 cells cultured with IL-4 showed a significant drop in TER as well as an increased flux of (3)H-fMLP and HRP. Co-treatment with IL-10 did not improve TER, whereas TGF-beta attenuated the resistance drop. However, neither TGF-beta nor IL-10 were able to correct the increased (3)H-fMLP flux. In contrast, the increased HRP flux caused by IL-4 was inhibited by both IL-10 and TGF-beta. TGF-beta and IL-10 significantly reduced IL-4-enhanced values for endosomal area and paracellular spaces containing HRP. Inhibitor studies indicated the requirement for protein synthesis and the involvement of phosphatidylinositol 3-kinase.


CONCLUSIONS
These results provide new insights into the regulation of intestinal barrier function and may suggest a novel approach in the treatment of intestinal inflammation.
Di Leo
Vincenza
V
Intestinal Disease Research Programme, McMaster University, Hamilton, Ont, Canada.
Yang
Ping-Chang
PC
Berin
M Cecilia
MC
Perdue
Mary H
MH
D001692:Biological Transport / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D003513:Cycloheximide / Q000494:pharmacology; D006735:Horseradish Peroxidase / Q000187:drug effects; D006801:Humans; D015847:Interleukin-4 / Q000493:pharmacokinetics / Q000494:pharmacology / Q000502:physiology*; D007413:Intestinal Mucosa / Q000187:drug effects / Q000502:physiology*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014655:Vascular Resistance / Q000187:drug effects
D011500:Protein Synthesis Inhibitors; D016212:Transforming Growth Factor beta; D015847:Interleukin-4; D009240:N-Formylmethionine Leucyl-Phenylalanine; D003513:Cycloheximide; D006735:Horseradish Peroxidase