Isolation and phenotyping of normal mouse liver dendritic cells by an improved method

Dendritic cells (DCs) are bone marrow-derived cells, which migrate to lymphoid and non-lymphoid organs via blood. Liver DCs are believed to play an important role in the regulation of hepatic allograft acceptance. However, because of inherent difficulties in isolating adequate numbers of DCs from liver, limited information is available on the phenotype and functions of liver DCs. To address this issue, we isolated DCs from normal C57BL/6 mouse liver using a modified procedure and described their immunophenotypic characteristics. Non-parenchymal cells (NPCs) were obtained by collagenase digestion of perfused liver fragments and density gradient centrifugation (14.5% nycodenz column). After overnight (18 hr) incubation of the NPCs, enrichment for transiently adherent, low- density cells on 13% nycodenz gradients permitted the recovery of low numbers of cells (approximately 1.2-1.5 x 10(5) per liver), many of which displayed distinct DCs morphology (abundant cytoplasm with prominent projections and irregularly shaped nuclei). Flowcytometric analysis revealed that most of these cells were recognized by anti-CD11c (60-70%). The results obtained from double staining with PE and FITC conjugated monoclonal antibodies indicated that these cells were CD11c(+)/MHC-II(+) (53%), CD11c(+)/CD86(+) (53.5%), CD11c(+)/ CD8α(+) (36%) and CD11c(+)/CD11b(+) (45%). These findings indicate that the purity of DCs isolated by nycodenz gradient is higher than other reported methods. Considering the similar ratio of lymphoid (CD11c(+)/CD8α(+)) and myeloid (CD11c(+)/CD11b(+)) DCs in the liver, and the known role of lymphoid DCs in tolerance induction, it seems that this subpopulation of DCs is not the main reason of liver tolerogenecity. Therefore, other factors such as the immaturity of liver DCs or the effect of liver microenvironment on these cells, etc. may explain the acceptance of hepatic allograft.