DAP12 Deficiency in Liver Allografts Results in Enhanced Donor DC Migration, Augmented Effector T Cell Responses and Abrogation of Transplant Tolerance

Abstract

Liver interstitial dendritic cells (DC) have been implicated in immune regulation and tolerance induction. We found that the transmembrane immuno-adaptor DNAX-activating protein of 12kDa (DAP12) negatively regulated conventional liver myeloid (m) DC maturation and their in vivo migratory and T cell allostimulatory ability. Livers were transplanted from C57BL/6(H2b) (B6) wild-type (wt) or DAP12−/− mice into wt C3H (H2k) recipients. Donor mDC (H2-Kb+CD11c+) were quantified in spleens by flow cytometry. Anti-donor T cell reactivity was evaluated by ex vivo CFSE-MLR and delayed-type hypersensitivity responses, while T effector and regulatory T cells (Treg) were determined by flow analysis. A 3–4-fold increase in donor-derived DC was detected in spleens of DAP12−/− liver recipients compared with those given wt grafts. Moreover, pro-inflammatory cytokine gene expression in the graft, IFNγ production by graft-infiltrating CD8+ T cells, and systemic levels of IFNγ were all elevated significantly in DAP12−/− liver recipients. DAP12−/− grafts also exhibited reduced incidences of CD4+Foxp3+ cells and enhanced CD8+ T cell IFNγ secretion in response to donor antigen challenge. Unlike wt grafts, DAP12−/− livers failed to induce tolerance and were rejected acutely. Thus, DAP12 expression in liver grafts regulates donor mDC migration to host lymphoid tissue, alloreactive T cell responses and transplant tolerance.

DNAX Activating Protein of 12 kDa/Triggering Receptor Expressed on Myeloid Cells 2 Expression by Mouse and Human Liver Dendritic Cells: Functional Implications and Regulation of Liver Ischemia–Reperfusion Injury

“…We have reported that, in vitro , DAP12 –/– or DAP12 small interfering RNA–treated liver DCs exhibited a more activated/mature phenotype and enhanced production of proinflammatory cytokines compared with WT liver DCs . When we examined the extent to which DAP12 regulated both major histocompatibility complex (MHC) Ⅱ (I‐A b and IA/IE) and costimulatory molecule expression by liver and spleen DCs following LPS stimulation in vivo , we found that the MFI of these molecules expressed by both liver and spleen DCs from LPS‐injected DAP12 –/– mice was increased compared with WT controls (Fig.…”

Graft‐infiltrating PD‐L1hi cross‐dressed dendritic cells regulate antidonor T cell responses in mouse liver transplant tolerance

“…For all (liver transplant) experiments, age‐matched animals were distributed randomly into experimental groups. Liver transplants were performed in male B6 donors to male C3H recipients because for anatomic/surgical reasons, male B6 (or B10) into male C3H is the model of choice for orthotopic allogeneic liver transplantation in the mouse . After surgery, each mouse was housed alone for the first week.…”

“…Molecular mechanisms whereby liver APCs regulate/inhibit T cell responses include their expression of programed death ligand‐1 (PD‐L1 = B7 homologue 1 [B7‐H1]), interleukin (IL)‐10, FasL, the Notch ligand Jagged 1, CD39, and the immunoreceptor tyrosine‐based activation motif–bearing transmembrane adaptor protein DNAX‐activating protein of 12 kDa (DAP12) . Of these molecules, PD‐L1, IL‐10, and DAP12 have been implicated in the regulation of mouse “spontaneous” liver transplant tolerance …”

Stellate Cells in Hepatic Immunological Tolerance

“…A role for LPS-induced increased expression of DNAX-activating protein of 12 kDa (DAP12), which is associated with IDO induction, is pertinent in this regard as DAP12-deficient DCs exhibit enhanced maturation upon TLR ligation [105,106]. This mechanism may be an important part of the phenomenon known as "endotoxin tolerance" [107].…”