OBJECTIVETo track the location of the transfused apoptotic allogeneic lymphocytes and asses the process of their accumulation and phagocytosis removal as consequences on allograft tolerance in recipient mice.

METHODSDonor spleen lymphocytes were labeled by CFSE and induced to apoptosis by dexamethasone incubation. After purification by anti-annexin V-conjugated magnetic beads isolation, apoptotic lymphocytes were transfused into recipient mice through the tail veins. Tissue samples from various organs were taken at various time points to analyze the fates of the apoptotic allogeneic lymphocytes and the phagocytosis of them by organ resident APCs.

RESULTSUsing fluorescent microscopy and flow cytometry, after the apoptotic cells were recognized and uptaken, the largest amount of labeled cells were accumulated in the livers and disappeared within not more than 12 hours. Recipient liver APCs were highly efficacious in phagocytosis of apoptotic allogeneic lymphocytes; the removal was completed within 15 minutes after incubation. LSEC, KC and LDC all phagocytosized the apoptotic allogeneic lymphocytes but with significantly different rates. Considering the numbers of those cells in a normal liver, it could be calculated that LSEC and KC had greater effects in this activity.

CONCLUSIONSThe liver deserves foremost attention for study of the mechanism of allografts tolerance induced by pre-transfusion of apoptotic donor spleen lymphocytes. LSEC and KC are the main functional APCs to the alloantigens.