Expression of binding sites for beta chemokines on human astrocytes

Astrocytes are major sources of chemokines and are thus critical effecters of central nervous system (CNS) inflammation. However, it is as yet unclear whether these cells, like leukocytes, also possess receptors for chemokine s (CCRs). To address this issue, we utilized a novel fluorescence approach to detect qualitatively and quantitatively binding sites for biotinylated d erivatives of the beta chemokines monocyte chemotactic protein-1 (MCP-1) an d macrophage inflammatory protein-1 alpha (MIP-1 alpha) on cultured human f etal astrocytes. Both chemokines were found to bind to the surface of astro cytes in a specific and saturable manner and with the high-affinity typical of these chemokines' binding to leukocyte CCRs. Binding of labeled MCP-1 a nd of labeled MIP-1 alpha was antagonized by the respective unlabeled homol ogue but not by the unlabeled heterologous chemokine. Binding of labeled MC P-1 was also inhibited by unlabeled MCP-S, both of which are ligands for CC R2. In a parallel manner, binding of labeled MIP-1 alpha was first shown to be attenuated by unlabeled RANTES, both of which recognize CCR1 and CCR5, and then separately antagonized by MCP-S and MIP-1 beta, which bind to CCR1 and CCR5, respectively. Finally, binding of both labeled chemokines was ob served to be modulated in response to astrocyte stimulation by proinflammat ory cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alph a (TNF-alpha), further indicating that these binding sites are subject to r egulation and, thus, likely to be physiologically responsive. Collectively, these results indicate that binding sites exhibiting characteristics of ch emokine receptors exist on human astrocytes. Such sites might function in t he recruitment of both astrocytes and leukocytes to specified brain regions during physiological and pathophysiological processes. (C) 1999 Wiley-Liss , Inc.