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.
Neonatal human autologous dendritic cells pulsed with recombinant protein antigen prime the generation of non-polarized CD4 T-cell effectors
