Chemokine and chemokine receptor expression by liver-derived dendritic cells: MIP-1alpha production is induced by bacterial lipopolysaccharide and interaction with allogeneic T cells.

Dendritic cells (DC) are highly-specialized antigen-presenting cells (APC), that initiate and modulate immune responses. Their specialized migratory and tissue-homing properties are regulated by small molecular weight proteins (chemokines) that govern leukocyte migration and activation. Little is known about the capacity of liver DC to produce or respond to chemokines. Here we examined chemokine and chemokine receptor (CR) gene expression in both immature DC progenitors (DCp) and comparatively mature DC generated from mouse liver. Factors affecting production of the chemokine macrophage inflammatory protein (MIP)-1alpha, and the influence of MIP-1alpha on liver DC migration were also investigated. Dendritic cells were propagated in response to granulocyte-macrophage colony stimulating factor (GM-CSF) +/- interleukin (IL)-4 from bone marrow (BM) cells or liver non-parenchymal cells (NPC) isolated from normal mice, or from mice treated with the hematopoietic growth factor Flt3 ligand (FL). Their phenotype and allostimulatory function were assessed by monoclonal antibody (mAb) staining and flow cytometry, and by the capacity to induce mixed leukocyte reactions, respectively. Specific chemokine and CR gene expression was studied using the RNase protection assay (RPA). Production of MIP-1alpha was determined by enzyme-linked immunoabsorbent assay (ELISA), and the migratory activity of liver DC induced by MIP-1alpha quantitated using microchemotaxis chambers. Like DC generated simultaneously from BM, liver-derived DC expressed mRNA for a variety of CC and CXC chemokines. RANTES (regulated upon activation, normal T cell expressed and secreted) transcripts were the most strongly expressed. Gene transcripts for the receptor CCR1, that binds RANTES and MIP-1alpha were also readily detected, as was CCR2, the receptor for the monocyte chemotactic proteins (MCP)1-4. No major differences in chemokine or CR mRNA expression were detected between immature and more mature liver DC. MIP-1alpha production by liver-derived DC was stimulated by bacterial lipopolysaccharide (LPS), and high levels were also detected in co-cultures of hepatic DC and allogeneic T cells. Chemotactic migration of liver-derived DC was stimulated by MIP-1alpha. Thus, liver-derived DC express mRNA for several CC and CXC chemokines and their receptors that may play key roles in the regulation of hepatic inflammatory responses. Production of MIP-1alpha by liver DC, and their migratory responses to this chemokine, suggest that MIP-1alpha and other chemokines may play significant roles in the regulation of liver DC function and in interactions of liver DC with other leukocytes, under normal and inflammatory conditions.