D Kerkovich | PubMed Health

PubMed2000

Monocyte:astrocyte interactions regulate MCP-1 expression in both cell types.

As astrocytes are a source of monocyte chemoattractant protein-1 (MCP-1) and lie in close apposition to brain microvessels, interactions between astrocytes and infiltrating monocytes might regulate production of this chemokine. To investigate this possibility, a monocyte:astrocyte co-culture model was utilized to assess the respective roles of these two cell types in regulating MCP-1 production. Results indicate that, while neither monocytes nor astrocytes alone produce detectable levels of MCP-1, co-culture of these two cell types results in time-dependent production of this chemokine. Such production requires de novo protein synthesis and is dependent on physical contact between monocytes and astrocytes, involving engagement of the cell-adhesion molecules ICAM-1 and VCAM-1. Additionally, interleukin 1-beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) are soluble mediators of this response. These findings imply that monocyte extravasation into the CNS may be critically regulated at the blood-brain barrier by specialized monocyte:astrocyte interactions.

Astrocytes↗

PubMed1999

Expression of binding sites for beta chemokines on human astrocytes.

Astrocytes are major sources of chemokines and are thus critical effectors of central nervous system (CNS) inflammation. However, it is as yet unclear whether these cells, like leukocytes, also possess receptors for chemokines (CCRs). To address this issue, we utilized a novel fluorescence approach to detect qualitatively and quantitatively binding sites for biotinylated derivatives of the beta chemokines monocyte chemotactic protein-1 (MCP-1) and macrophage inflammatory protein-1alpha (MIP-1alpha) on cultured human fetal astrocytes. Both chemokines were found to bind to the surface of astrocytes in a specific and saturable manner and with the high-affinity typical of these chemokines' binding to leukocyte CCRs. Binding of labeled MCP-1 and of labeled MIP-1alpha was antagonized by the respective unlabeled homologue but not by the unlabeled heterologous chemokine. Binding of labeled MCP-1 was also inhibited by unlabeled MCP-3, both of which are ligands for CCR2. In a parallel manner, binding of labeled MIP-1alpha was first shown to be attenuated by unlabeled RANTES, both of which recognize CCR1 and CCR5, and then separately antagonized by MCP-3 and MIP-1beta, which bind to CCR1 and CCR5, respectively. Finally, binding of both labeled chemokines was observed to be modulated in response to astrocyte stimulation by proinflammatory cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), further indicating that these binding sites are subject to regulation and, thus, likely to be physiologically responsive. Collectively, these results indicate that binding sites exhibiting characteristics of chemokine receptors exist on human astrocytes. Such sites might function in the recruitment of both astrocytes and leukocytes to specified brain regions during physiological and pathophysiological processes.

Astrocytes↗