Involvement of heme oxygenase-1 in suppression of T cell activation by quercetin

Introduction: Although expression of heme oxygenase-1 (HO1) attenuates transplantation arteriosclerosis, the mechanism by which HO1 exerts its protective effect remains unclear. We studied the effect of HO1-deficient vs. wildtype (WT) dendritic cells (DCs) on the T-cell priming response and outcome in a murine transplant arteriosclerosis model. Methods: At day 0 C57bl6 mice received either WT (n=6) or HO1-knockout DCs (n=6) pre-sensitized with Balb/c splenocytes lysate to accelerate the development of arteriosclerosis. At day 10 an aorta segment from Balb/c mice was transplanted into the carotid artery position of C57Bl6 mice.14 days after transplantation allografts were excised and processed for immunohistochemical analysis. Results: HO1-deficient DCs significantly increased neointimal hyperplasia as compared to WT DCs (116995 vs. 46114μm 2 P<0.05) and incidence of intima formation (83 vs. 50% in WT DC). HO1 deficient DCs also increased medial thickeness (15936 vs.12034 μm 2 P<0.05) and intimal VSMCs content (76 vs. 46% P<0.05) and resulted in more prominent medial cell infiltration (461μm 2 vs. 232μm 2 P<0.05). Although HO1 deficient and WT DCs could be detected in allografts, HO1-nullizygous DCs induced an increase in CD4+ T-cell infiltration (9.5 vs. 0.1% in WT P<0.05) concomitant to a decrease of CD8+ T cell infiltration (8 vs.14%, P<0.05). In line with these observations Affymetrix microarray analysis confirmed that HO1 deletion in DCs was associated with a significant downregulation of MHCII-H2A expression (associated with CD4+T-cell activation) and induction of inhibitors of MHCII expression (including IK protein) whereas MHC I expression remained unchanged. Conclusions: HO1 expression in dendritic cells increases vascular cell infiltration with a higher CD8+/CD4+ T-cell ratio by stabilizing MHCII expression in vascular allografts resulting in inhibition of neointima formation and hence improved allograft survival.

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Identification of crassin acetate as a new immunosuppressant triggering heme oxygenase-1 expression in dendritic cells

Blood ◽

10.1182/blood-2009-02-204297 ◽

2009 ◽

Vol 114 (1) ◽

pp. 64-73 ◽

Cited By ~ 7

Author(s):

Hironori Matsushima ◽

Hiroaki Tanaka ◽

Norikatsu Mizumoto ◽

Akira Takashima

Keyword(s):

Dendritic Cells ◽

Heme Oxygenase ◽

T Cell Activation ◽

Large Scale ◽

Cell Activation ◽

Contact Hypersensitivity ◽

Heme Oxygenase 1 ◽

Mixed Leukocyte Reaction ◽

Cellular Targets ◽

Dc Maturation

Abstract By screening 720 natural compounds in a standard 2-way allogeneic mixed leukocyte reaction assay, we identified a potent immunosuppressive capacity of crassin acetate (CRA), a coral-derived cembrane diterpenoid. CRA efficiently inhibited allogeneic mixed leukocyte reaction as well as antigen-specific activation of CD4 T cells by bone marrow–derived dendritic cells (DCs). With regard to cellular targets, CRA suppressed not only mitogen-triggered T-cell activation, but also lipopolysaccharide-induced DC maturation, indicating dual functionality. Treatment with CRA at nontoxic doses induced heme oxygenase-1 (HO-1) mRNA/protein expression and HO-1 enzymatic activity in DCs, suggesting a unique mechanism of action. In fact, lipopolysaccharide-induced DC maturation was also inhibited by structurally unrelated compounds known to induce HO-1 expression or carbon monoxide (CO) release. Allergic contact hypersensitivity response to oxazolone and oxazolone-induced Langerhans cell migration from epidermis were both prevented almost completely by systemic administration of CRA. Not only do our results support the recent concept that HO-1/CO system negatively regulates immune responses, they also form both conceptual and technical frameworks for a more systematic, large-scale drug discovery effort to identify HO-1/CO-targeted immunosuppressants with dual target specificity.

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