Astrocytes produce dendritic cell-attracting chemokines in vitro and in multiple sclerosis lesions

As a result of their close association with the blood-brain barrier, astrocytes play an important role in regulating the homing of different leukocyte subsets to the inflamed central nervous system (CNS). In this study, we investigated whether human astrocytes produce chemokines that promote the migration of myeloid dendritic cells (DCs). By reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay, we show that cultured human astrocytes stimulated with interleukin-1beta and tumor necrosis factor produce CCL2, CCL3, CCL4, CCL5, CCL20, and CXCL12 that act on immature DCs, but not CCL19 and CCL21, 2 chemokines specific for mature DCs. Compared with controls, supernatants of cytokine-stimulated astrocytes are more effective in promoting the migration of immature monocyte-derived DCs (iMDDCs). Desensitization of CXCR4 (receptor for CXCL12), CCR1-3-5 (shared receptors for CCL3-4-5), and CCR6 (receptor for CCL20) on iMDDC reduces cell migration toward astrocyte supernatants, indicating that astrocytes release biologically relevant amounts of iMDDC-attracting chemokines. By immunohistochemistry, we show that CXCL12 and, to a lesser extent, CCL20 are expressed by reactive astrocytes in multiple sclerosis lesions. These data lend support to the idea that astrocyte-derived chemokines may contribute to immature DC recruitment to the inflamed CNS.