Characterization of epithelial IL-8 response to inflammatory bowel disease mucosal E. coli and its inhibition by mesalamine.
BACKGROUND
Mucosally adherent E. coli are found in inflammatory bowel disease (IBD) and colon cancer. They promote release of the proinflammatory cytokine interleukin-8 (IL-8). We explored mechanisms for this release and its inhibition by drugs.


METHODS
IL-8 release from colon epithelial cells in response to mucosal E. coli isolates from IBD, colon cancer, and controls was characterized at the cellular and molecular level.


RESULTS
IL-8 response of HT29 cells was greater with Crohn's disease (689 +/- 298 [mean +/- SD] pg IL-8/mL at 4 hours, n = 7) and colon cancer isolates (532 +/- 415 pg/mL, n = 14) than with ulcerative colitis (236 +/- 58 pg/mL, n = 6) or control isolates (236 +/- 100 pg/mL, n = 6, P < 0.0001). Bacterial supernatants contained shed flagellin that triggered IL-8 release. For whole bacteria the IL-8 response to E. coli that agglutinate red blood cells (548 +/- 428 pg IL-8/mL, n = 16), a function that correlates with epithelial invasion, was greater than for nonhemagglutinators (281 +/- 253 pg/mL, n = 17; P < 0.0001). This was particularly marked among E. coli that, although flagellate, could not release IL-8 from TLR5-transfected HEK293 cells. IL-8 release was mediated by extracellular-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) and inhibited by mesalamine, but not hydrocortisone, at therapeutic concentrations.


CONCLUSIONS
Mucosa-associated E. coli shed flagellin that elicits epithelial IL-8 release but this may only become relevant when the mucosal barrier is weakened to expose basolateral TLR5. Adherent and invasive IBD and colon cancer E. coli isolates also elicit a flagellin-independent IL-8 response that may be relevant when the mucosal barrier is intact. The IL-8 release is MAPK-dependent and inhibited by mesalamine.
Subramanian
Sreedhar
S
Division of Gastroenterology, University School of Clinical Science, Liverpool, UK.
Rhodes
Jonathan M
JM
Hart
C Anthony
CA
Tam
Ben
B
Roberts
Carol L
CL
Smith
Shirley L
SL
Corkill
John E
JE
Winstanley
Craig
C
Virji
Mumtaz
M
Campbell
Barry J
BJ
D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D016022:Case-Control Studies; D002478:Cells, Cultured; D003110:Colonic Neoplasms / Q000276:immunology / Q000382:microbiology; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000276:immunology*; D005408:Flagellin / Q000235:genetics / Q000276:immunology; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000276:immunology* / Q000382:microbiology*; D016209:Interleukin-8 / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000276:immunology / Q000382:microbiology; D020935:MAP Kinase Signaling System; D019804:Mesalamine / Q000494:pharmacology*
D000894:Anti-Inflammatory Agents, Non-Steroidal; D016209:Interleukin-8; D005408:Flagellin; D019804:Mesalamine