Two immunogenic passenger dendritic cell subsets in the rat liver have distinct trafficking patterns and radiosensitivities

The aim of this study was to investigate the trafficking patterns, radiation sensitivities, and functions of conventional dendritic cell (DC) subsets in the rat liver in an allotransplantation setting. We examined DCs in the liver, hepatic lymph, and graft tissues and recipient secondary lymphoid organs after liver transplantation from rats treated or untreated by sublethal irradiation. We identified two distinct immunogenic DC subsets. One was a previously reported population that underwent blood-borne migration to the recipient's secondary lymphoid organs, inducing systemic CD8+ T-cell responses; these DCs are a radiosensitive class II major histocompatibility complex (MHCII)+CD103+CD172a+CD11b-CD86+ subset. Another was a relatively radioresistant MHCII+CD103+CD172a+CD11b+CD86+ subset that steadily appeared in the hepatic lymph. After transplantation, the second subset migrated to the parathymic lymph nodes (LNs), regional peritoneal cavity nodes, or persisted in the graft. Irradiation completely eliminated the migration and immunogenicity of the first subset, but only partly suppressed the migration of the second subset and the CD8+ T-cell response in the parathymic LNs. The grafts were acutely rejected, and intragraft CD8+ T-cell and FoxP3+ regulatory T-cell responses were unchanged. The radioresistant second subset up-regulated CD25 and had high allostimulating activity in the mixed leukocyte reaction, suggesting that this subset induced CD8+ T-cell responses in the parathymic LNs and in the graft by the direct allorecognition pathway, leading to the rejection. Conclusion: Conventional rat liver DCs contain at least two distinct immunogenic passenger subsets: a radiosensitive blood-borne migrant and a relatively radioresistant lymph-borne migrant. LNs draining the peritoneal cavity should be recognized as a major site of the intrahost T-cell response by the lymph-borne migrant. This study provides key insights into liver graft rejection and highlights the clinical implications of immunogenic DC subsets. (HEPATOLOGY 2012)