Dendritic cells and MPIF-1: chemotactic activity and inhibition of endogenous chemokine production by IFN-gamma and CD40 ligation.

We have examined the biological activity of the CC chemokine myeloid progenitor inhibitory factor 1 (MPIF-1) on human dendritic cells. MPIF-1 has chemotactic activity on dendritic cells derived from either peripheral blood monocytes or cord blood CD34+ progenitors. However, chemokine treatment did not induce further cell activation or maturation. In addition, MPIF-1 is constitutively released by monocyte-derived dendritic cells but not macrophages or monocytes (resting or stimulated). The proinflammatory stimuli lipopolysaccharide and tumor necrosis factor alpha, which induced the release of monocyte chemotactic protein-1, macrophage inflammatory protein-1alpha (MIP-1alpha), MIP-1beta, and interleukin-8, did not affect MPIF-1 release. In contrast, CD40 ligation and interferon-gamma treatment, while stimulating the production of the other chemokines, caused a pronounced reduction of MPIF-1 transcript and protein release. Thus, in dendritic cells the regulation of the production and release of MPIF-1 is distinct in comparison to other CC and CXC chemokines.

Characterization of the signal transduction pathway activated in human monocytes and dendritic cells by MPIF-1, a specific ligand for CC chemokine receptor 1.

The receptor specificity and signal transduction pathway has been identified and characterized for a truncated form of myeloid progenitor inhibitory factor-1 (MPIF-1(24-99)). MPIF-1 binds specifically to sites, in particular CCR1, shared with macrophage inflammatory protein-1alpha (MIP-1alpha) on the surface of human monocytes and dendritic cells, as inferred by its ability to compete for [125I]MIP-1alpha, but not for [125I]MIP-1beta or [125I]monocyte chemotactic protein-1(MCP-1) binding to intact cells. Based on calcium flux, MPIF-1 is an agonist on CCR1-transfected HEK-293 cells, monocytes, and dendritic cells, but not on CCR5-, CCR8-, or CX3CR1-transfected cells. The inhibitory effect of guanosine 5'-O-(3-thio-triphosphate) (GTP-gammaS) or pertussis toxin pretreatment on MPIF-1 binding and calcium mobilization, respectively, indicates the involvement of G proteins in the interaction of MPIF-1 and its receptor(s). The increase in intracellular free calcium concentration following MPIF-1 treatment is mainly due to the influx of calcium from an extracellular pool. However, a portion of the intracellular free calcium concentration is derived from a phospholipase C inhibitor-sensitive intracellular pool. MPIF-1 induces a rapid dose-dependent release of [3H]arachidonic acid from monocytes that is dependent on extracellular calcium and is blocked by phospholipase A2 (PLA2) inhibitors. Furthermore, PLA2 activation is shown to be necessary for filamentous actin formation in monocytes. Thus, the MPIF-1 signal transduction pathway appears to include binding to CCR1; transduction by G proteins; effector function by phospholipase C, protein kinase C, calcium flux, and PLA2; and cytoskeletal remodeling.