Abstract 4303: Heme Oxygenase 1 Expression in Dendritic Cells Drives Cd4+ T Cell Activation in Transplantation Atherosclerosis

Abstract

Although over-expression of heme oxygenase-1 (HO-1) attenuates transplantation arteriosclerosis, the mechanism by which HO-1 exerts its protective effect remains unclear. In order to investigate the effect of HO-1 expression specifically in the dendritic cell (DC) in the context of transplantation atherosclerosis, we studied the effect of HO1-deficient versus wildtype (WT) DCs on the T-cell priming response and outcome in a murine transplant arteriosclerosis model. At day 0 C57bl6 mice received either WT (N=7) or HO1-knockout DCs (N=7) pre-sensitized with Balb/c splenocytes lysate. At day 10 an allogenic aorta segment derived from Balb/c mice was transplanted into the carotid artery position of C57Bl6 mice. 14 days post transplantation, the grafts were harvested and analyzed by imumnohistology. Adoptive transfer of HO1-deficient DCs significantly increased neointimal hyperplasia as compared to WT DCs (116995 versus 38428 μm2 P<0.05). HO-1 deficient DCs also increased medial thickeness (15936 versus 12034 μm2 P<0.05), reduced intimal VSMCs content (46 versus 75% P<0.05) and resulted in more prominent medial cell infiltration (461 versus 232 μm2 P<0.05). In the transplanted aorta of the with HO-1 nullizygous DCs treated recipient group, an increase in CD4+ T-cell infiltration (9.5 versus 0.2% in WT P<0.05) and IgG deposition, concomitant to a decrease of CD8+ T cell infiltration (8.1 versus 14.3%, P<0.05) was observed. In line with these observations, in vitro analysis of HO-1 deficiency in DC function showed an increased priming potential for CD4+ T cells, thereby increasing the CD4+/CD8+ T cell ratio. Increased efficiency in CD4+ T cell priming by HO-1 deficient DCs was facilitated by a higher cell surface level of MHC II. Further studies indicated that HO-1 deficiency increased STAT1 phosphorylation, thereby enhancing CIITA gene expression that lead to increased MHC II levels on the DCs cell surface. HO-1 deficiency in dendritic cells increases vascular cell infiltration with a higher CD4+/CD8 T-cell ratio in vascular allografts resulting in an augmented form of transplantation arteriosclerosis. This effect is facilitated by a STAT1-CIITA-MHCII dependent intracellular pathway.