Unconjugated bilirubin inhibits VCAM-1-mediated transendothelial leukocyte migration.
During lymphocyte migration, engagement of VCAM-1 stimulates the generation of endothelial cell-derived reactive oxygen species (ROS) and activation of matrix metalloproteinases, facilitating endothelial retraction. Because bilirubin is a potent antioxidant, we examined the hypothesis that this bile pigment inhibits VCAM-1-dependent cellular events. The migration of isolated murine splenic lymphocytes across monolayers of murine endothelial cell lines (which constitutively express VCAM-1) is significantly inhibited by physiological concentrations of bilirubin, in the absence of an effect on lymphocyte adhesion. Bilirubin administration also suppresses VCAM-1-stimulated ROS generation and reduces endothelial cell matrix metalloproteinase activity. In a murine asthma model characterized by VCAM-1-dependent airway inflammation, treatment of C57BL6/J mice with i.p. bilirubin decreases the total leukocyte count in the lung parenchyma and lavage fluid, through specific inhibition of eosinophil and lymphocyte infiltration. Blood eosinophil counts were increased in bilirubin-treated animals, while VCAM-1 expression in the capillary endothelium and cytokine levels in both lung lavage and supernatants from cultured lymph node lymphocytes were unchanged, suggesting that bilirubin inhibits leukocyte migration.


CONCLUSIONS
bilirubin blocks VCAM-1-dependent lymphocyte migration in vitro and ameliorates VCAM-1-mediated airway inflammation in vivo, apparently through the suppression of cellular ROS production. These findings support a potential role for bilirubin as an endogenous immunomodulatory agent.
Keshavan
Pavitra
P
Division of Digestive Diseases, University of Cincinnati, Cincinnati, OH 45267, USA. keshavpa@ucmail.uc.edu
Deem
Tracy L
TL
Schwemberger
Sandy J
SJ
Babcock
George F
GF
Cook-Mills
Joan M
JM
Zucker
Stephen D
SD
D000818:Animals; D001249:Asthma / Q000188:drug therapy / Q000276:immunology / Q000473:pathology; D001663:Bilirubin / Q000494:pharmacology*; D002460:Cell Line; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D004802:Eosinophilia / Q000188:drug therapy / Q000276:immunology / Q000473:pathology; D005260:Female; D007962:Leukocytes / Q000187:drug effects* / Q000502:physiology*; D008168:Lung / Q000187:drug effects / Q000276:immunology / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D010047:Ovalbumin / Q000276:immunology; D015398:Signal Transduction / Q000187:drug effects; D019010:Vascular Cell Adhesion Molecule-1 / Q000502:physiology*
D019010:Vascular Cell Adhesion Molecule-1; D010047:Ovalbumin; D001663:Bilirubin