Interleukin-13 is the key effector Th2 cytokine in ulcerative colitis that affects epithelial tight junctions, apoptosis, and cell restitution.
OBJECTIVE
Ulcerative colitis (UC) is characterized by a Th2 immune response with inflammation and epithelial barrier dysfunction. So far, Th2 cytokines have not been shown to directly influence epithelial barrier function.


METHODS
Lamina propria mononuclear cells (LPMCs) were stimulated and interleukin (IL)-13 was measured by enzyme-linked immunosorbent assay. Functional IL-13 and IL-4 effects were studied on HT-29/B6 colonic epithelial cells in Ussing chambers and by conductance scanning. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assays. IL-13/IL-4 receptors were analyzed by reverse-transcription polymerase chain reaction and immunofluorescence. Western blotting combined with immunofluorescence was used to detect tight junction proteins. Furthermore, restitution velocity was measured. Finally, mucosal biopsy specimens from patients with UC were compared with cultured cells for these features.


RESULTS
LPMCs from patients with UC produced large amounts of IL-13 (985 +/- 73 pg/mL), much more than from controls or patients with Crohn's disease. IL-13Ralpha1 and IL-4Ralpha receptors were present in HT-29/B6 cells and colonic epithelial cells of control patients and patients with UC. IL-13 had a dose-dependent effect on transepithelial resistance of HT-29/B6 monolayers (reduction to 60% +/- 4%), whereas IL-4 had no effect. This was due to an increased number of apoptotic cells (5.6-fold +/- 0.9-fold) and an increased expression of the pore-forming tight junction protein claudin-2 to 295% +/- 37%, both of which contributed equally. Finally, epithelial restitution velocity decreased from 15.1 +/- 0.6 to 10.6 +/- 0.5 microm/h after treatment with IL-13. Parallel changes were observed in human samples, with an increase in claudin-2 expression to 956% +/- 252%.


CONCLUSIONS
IL-13 was identified as an important effector cytokine in UC that impairs epithelial barrier function by affecting epithelial apoptosis, tight junctions, and restitution velocity.
Heller
Frank
F
Department of Gastroenterology, Charité, Campus Benjamin Franklin, Berlin, Germany.
Florian
Peter
P
Bojarski
Christian
C
Richter
Jan
J
Christ
Melanie
M
Hillenbrand
Bernd
B
Mankertz
Joachim
J
Gitter
Alfred H
AH
Bürgel
Nataly
N
Fromm
Michael
M
Zeitz
Martin
M
Fuss
Ivan
I
Strober
Warren
W
Schulzke
Jörg D
JD
D000328:Adult; D017209:Apoptosis / Q000276:immunology* / Q000502:physiology; D015415:Biomarkers / Q000032:analysis; D001707:Biopsy, Needle; D015153:Blotting, Western; D049109:Cell Proliferation; D002478:Cells, Cultured; D003093:Colitis, Ulcerative / Q000276:immunology* / Q000473:pathology; D003424:Crohn Disease / Q000276:immunology / Q000473:pathology; D016207:Cytokines / Q000032:analysis / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D018793:Interleukin-13 / Q000032:analysis / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000276:immunology / Q000473:pathology; D008297:Male; D008875:Middle Aged; D011336:Probability; D011379:Prognosis; D012307:Risk Factors; D012494:Sampling Studies; D012680:Sensitivity and Specificity; D018418:Th2 Cells / Q000276:immunology; D019108:Tight Junctions / Q000276:immunology*
D015415:Biomarkers; D016207:Cytokines; D018793:Interleukin-13