ALLOGENEIC LIVER-DERIVED DENDRITIC CELL PROGENITORS FAIL TO STIMULATE INTRACELLULAR TH1 CYTOKINE PRODUCTION AND INDUCE ONLY LOW LEVELS OF ANTI-DONOR CTL: ASSOCIATION WITH `SPONTANEOUS' LIVER ALLOGRAFT ACCEPTANCE.

Abstract

491 Background: In vitro generated liver-derived dendritic cell (DC) progenitors do not stimulate allogeneicTcells (Lu L et al: J Exp Med 1994; 179: 1823) which may explain why liver is the least immunogenic of transplanted organs. In mice, CD4+T-helper (Th)1 cells secrete IL-2, INF-γ and TNF, whereas Th2 cells produce IL-5, IL-6, and the suppressive cytokines IL-4 and IL-10.Th2 cells have been implicated in the induction of tolerance. We hypothesized that liver-derived DC progenitors might induce minimal allogeneic Th1 cell activation predisposing to tolerance induction.Aims: The purpose of this study was to investigate the influence of liver-derived DC progenitors on cytokine production by allogeneic T cells and to determine the relationship to T cell proliferative and cytotoxic T cell(CTL) responses. Methods: Purified C3H (H-2k, I-Ek) T cells (2 × 106/well) were incubated with irradiated B10(H-2b, I-Ab) allogeneic liver-derived DC progenitors(105/well) or mature DC (positive control) grown from B10 bone marrow for 4 days. IL-4 and INF-γ were measured in supernatants at 24, 48, 72, 96 and 120 hr by ELISA. Activated T cells were stained for expression of intracellular cytokines using flow cytometry. Three-day primary MLR were performed using C3H T cells as responders, and liver DC progenitors or BM DC as stimulators. CTL assays were performed after 4 days of co-culture using a 4 hr isotope release assay, and donor-specific EL4 (H-2b) target cells.Results: T cell proliferation assays confirmed that liver-derived DC progenitors were poor stimulators of allogeneic T cells. CTL assays showed maximal target cell lysis by T cells stimulated with mature allogeneic BM DC, in contrast to liver DC progenitors that exhibited only minimal stimulation. Flow studies of T cells performed 72 hr post-stimulation by allogeneic BM DC revealed high expression of intracellular INF-γ compared to cells stimulated with allogeneic liver DC progenitors. This was accompanied by detection of significant levels of secreted INF-γ (129 pg/ml) in the former group. IL-4 production by both of these groups of cells was negligible. Restimulation of T cells with allogeneic spleen cells in secondary MLR indicated that donor hyporesponsiveness was not induced by liver DC progenitors. Conclusions: Low levels of MHC and costimulatory molecules on liver DC progenitors are associated with poor Th1 cytokine production, minimal T cell proliferation and weak CTL responses. These findings indicate that the comparative immune privilege of murine liver allografts may be influenced by the properties of donor-derived DC progenitors.