Review Biologicals & Immunologicals; The Chemokine Receptor Family

EBI1/CCR7 Is a New Member of Dendritic Cell Chemokine Receptor That Is Up-Regulated upon Maturation

Dendritic cells (DC) that are stimulated with inflammatory mediators can maturate and migrate from nonlymphoid tissues to lymphoid organs to initiate T cell-mediated immune responses. This migratory step is closely related to the maturation of the DC. In an attempt to identify chemokine receptors that might influence migration and are selectively expressed in mature DC, we have discovered that the chemokine receptor, EBI1/CCR7, is strikingly up-regulated upon maturation in three distinct culture systems: 1) mouse bone marrow-derived DC, 2) mouse epidermal Langerhans cells, and 3) human monocyte-derived DC. The EBI1/CCR7 expressed in mature DC is functional because ELC/MIP-3β, recently identified as a ligand of EBI1/CCR7, induces a rise in intracellular free calcium concentrations and directional migration of human monocyte-derived mature DC (HLA-DRhigh, CD1alow, CD14−, CD25+, CD83+, and CD86high) in a dose-dependent manner, but not of immature DC (HLA-DRlow, CD1ahigh, CD14−, CD25−, CD83−, and CD86−). In contrast, macrophage inflammatory protein-1α (MIP-1α), monocyte chemotactic protein-3 (MCP-3), and RANTES are active on immature DC but not on mature DC. Thus, it seems likely that MIP-1α, MCP-3, and RANTES can mediate the migration of immature DC located in peripheral sites, whereas ELC/MIP-3β can direct the migration of Ag-carrying DC from peripheral inflammatory sites, where DC are stimulated to up-regulate the expression of EBI1/CCR7, to lymphoid organs. It is postulated that different chemokines and chemokine receptors are involved in DC migration in vivo, depending on the maturation state of DC.

Cloning, in vitro expression, and functional characterization of a novel human CC chemokine of the monocyte chemotactic protein (MCP) family (MCP-4) that binds and signals through the CC chemokine receptor 2B

Here we describe the characterization of a novel human CC chemokine, tentatively named monocyte chemotactic protein (MCP-4). This chemokine was detected by random sequencing of expressed sequence tags in cDNA libraries. The full-length cDNA revealed an open reading frame for a 98-amino acid residue protein, and a sequence alignment with known CC chemokines showed high levels of similarity (59-62%) with MCP-1, MCP-3, and eotaxin. MCP-4 cDNA was cloned into Drosophila S2 cells, and the mature protein (residues 24-98) was purified from the conditioned medium. Recombinant MCP-4 induced a potent chemotactic response (EC50 = 2.88 +/- 0.15 nM) and a transient rise in cytosolic calcium concentration in fresh human peripheral blood monocytes but not in neutrophils. Binding studies in monocytes showed that MCP-4 and MCP-3 were very potent in displacing high affinity binding of 125I-MCP-1 (IC50 for MCP-4, MCP-3, and unlabeled MCP-1 of 2.1 +/- 1.4, 0.85-1.6, and 0.7 +/- 0.2 nM respectively), suggesting that all three chemokines interact with the CC chemokine receptor-2 (MCP-1 receptor). This was confirmed in binding studies with Chinese hamster ovary cells, stably transfected with the CC chemokine 2B receptor. Northern blot analysis in extracts of normal human tissues showed expression of mRNA for MCP-4 in small intestine, thymus, and colon, but the level of protein expression was too low to be detected in Western blot analysis. However, expression of MCP-4 protein was demonstrated by immunohistochemistry in human atherosclerotic lesion and found to be associated with endothelial cells and macrophages.

Chemokines: molecular double agents

Chemokines are best known as signalling molecules that attract leukocytes to sites of inflammation, but recent results show they are also important regulators of hematopoiesis during development.

Cytokines in inflammatory brain lesions: helpful and harmful

Multiple sclerosis (MS) is thought to be an autoimmune disease. In healthy individuals, the T cells of the immune system, when activated by an infectious agent, regularly traffic across an intact blood-brain barrier, survey the CNS and then leave. In MS, for reasons that are only gradually being understood, certain events in the peripheral immune response and in the brain cause some autoreactive T cells to stay in the CNS. Their presence initiates infiltration by other leukocytes and activation and recruitment of endogenous glia to the inflammatory process, ultimately leading to the destruction of myelin and the myelin-producing cell, the oligodendrocyte, and the dysfunction of axons. The key mediators in the subsequent cycles of histological damage and repair, and clinical relapse and remission are thought to be adhesion molecules, chemokines and cytokines.