Expression of β‐chemokines and chemokine receptors in human fetal astrocyte and microglial co‐cultures: Potential role of chemokines in the developing CNS

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Abstract
Chemokines play specific roles in directing the recruitment of leukocyte subsets into inflammatory foci within the central nervous system (CNS). The involvement of these cytokines as mediators of inflammation is widely accepted. Recently, it has become evident that cells of the CNS (astrocytes, microglia, and neurons) not only synthesize, but also respond functionally or chemotactically to chemokines. We previously reported developmental events associated with colonization of the human fetal CNS by mononuclear phagocytes (microglial precursors), which essentially takes place within the first two trimesters of life. As part of the array of signals driving colonization, we noted specific anatomical distribution of chemokines and chemokine receptors expressed during this period. In order to further characterize expression of these molecules, we have isolated and cultured material from human fetal CNS. We demonstrate that unstimulated subconfluent human fetal glial cultures express high levels of CCR2 and CXCR4 receptors in cytoplasmic vesicles. Type I astrocytes, and associated ameboid microglia in particular, express high levels of surface and cytoplasmic CXCR4. Of the chemokines tested (MIP‐1α, MIP‐1β, MCP‐1, MCP‐3, RANTES, SDF‐1, IL‐8, IP‐10), only MIP‐1α, detected specifically on microglia, was expressed both constitutively and consistently. Low variable levels of MCP‐1, MIP‐1α, and RANTES were also noted in unstimulated glial cultures. Recombinant human chemokines rhMCP‐1 and rhMIP‐1α also displayed proliferative effects on glial cultures at [10 ng/ml], but displayed variable effects on CCR2 levels on these cells. rhMCP‐1 specifically upregulated CCR2 expression on cultured glia at [50 ng/ml]. It is gradually becoming evident that chemokines are important in embryonic development. The observation that human fetal glial cells and their progenitors express specific receptors for chemokines and can be stimulated to produce MCP‐1, as well as proliferate in response to chemokines, supports a role for these cytokines as regulatory factors during development. GLIA 37:64–75, 2002.