Bilirubin suppresses Th17 immunity in colitis by upregulating CD39

Area of Science:

• Immunology
• Molecular Biology
• Gastroenterology

Background:

• Unconjugated bilirubin (UCB), a heme oxidation product, possesses immunosuppressive properties.
• The molecular mechanisms of UCB's immunosuppression, beyond antioxidant effects, are not fully understood.
• UCB influences T helper type 17 (Th17) immune responses and has shown protective effects in experimental colitis.

Purpose of the Study:

• To elucidate the molecular mechanisms by which UCB modulates Th17 immune responses.
• To investigate the role of CD39 ectonucleotidase and the aryl hydrocarbon receptor (AHR) in UCB-mediated immunomodulation.
• To assess the therapeutic potential of UCB in inflammatory bowel disease (IBD) models.

Main Methods:

• In vitro studies using human Th17 cells and in vivo experiments with Entpd1-/- and Ahrd mice models of experimental colitis.
• Analysis of FOXP3 and CD39 expression, cellular suppressor ability, and IL-10 production.
• Investigation of the interaction between UCB, AHR, and CD39 in regulating Th17 cell function.

Main Results:

• UCB enhances Th17 cell immunoregulatory properties, increasing FOXP3 and CD39 levels and suppressor ability.
• UCB-induced CD39 upregulation on Th17 cells is dependent on aryl hydrocarbon receptor (AHR) ligation.
• Genetic deletion of CD39 or AHR dysfunction abrogated UCB's protective effects in experimental colitis.
• UCB failed to induce immunosuppressive properties in Th17 cells from inflammatory bowel disease (IBD) samples due to decreased AHR levels.

Conclusions:

• UCB exerts immunosuppressive effects on Th17 cells through AHR-mediated upregulation of CD39.
• Th17 cell dysfunction in IBD may be linked to reduced AHR levels, impairing UCB's beneficial effects.
• Targeting AHR or CD39 could offer therapeutic strategies for Th17-related immune dysfunction in IBD.