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Macrophage inflammatory protein-3alpha/CCL20 is a recently identified chemokine that binds to CCR6 and acts as a chemoattractant for memory/differentiated T-cells, B-cells, and immature dendritic cells. We have previously reported that CCL20 and CCR6 mRNAs are expressed in the CNS of SJL mice with experimental autoimmune encephalomyelitis (EAE) and that CCL20 is produced by CNS-infiltrating leukocytes at disease onset and, additionally, by intraparenchymal astrocyte-like cells during disease relapses. In this study, we provide further immunohistochemical evidence that astrocytes represent the main CNS source of CCL20 during EAE. Moreover, we show that the proinflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha, but not interferon-gamma, induce expression of CCL20 mRNA and secretion of CCL20 protein in cultures of mouse brain-derived astrocytes. We also show that supernatants from cytokine-activated astrocytes stimulate the migration of polarized T helper cells and that this effect is partially inhibited by anti-CCL20 antibody. These findings suggest that, through secretion of CCL20, astrocytes could play an important role in orchestrating the recruitment of specific leukocyte subsets to the inflamed CNS and in regulating CNS-targeted immune responses., (Copyright 2003 Wiley-Liss, Inc.)

In the human immunodeficiency virus type 1 (HIV-1)-infected brain, the virus does not replicate in astrocytes, but a synthesis of viral regulatory proteins occurs in these cells, leading to accumulation of Nef. As an approach to understand the effects of Nef on astrocyte functional activity, we analyzed whether intracellular Nef interferes with the expression and activation of the enzyme protein kinase C (PKC), which is an important regulator of astroglial functions and HIV-1 replication. Astrocytoma clones (U251 MG) not expressing Nef (Neo), or expressing wild-type Nef (Bru) or nonmyristoylated Nef (TH) were used to monitor the expression and activation of 10 PKC isoforms. The same clones were used to evaluate the effect of Nef on the viral long terminal repeat (LTR) promoter after activation of PKC with the phorbol ester 12-myristate 13-acetate (PMA). PKC intracellular distribution and activation were evaluated by Western blot analysis of cytosolic and membrane fractions of control and Nef-expressing clones. PMA-induced LTR activation was analyzed in clones transfected with a plasmid encoding for the CAT reporter gene controlled by the LTR promoter, by using an enzyme-linked immunosorbent assay to measure CAT expression. Nef selectively downregulated the expression and activation of betaII and epsilon PKC isoforms in astrocytoma cells. Such downregulation correlated with an inhibition of LTR activation after PMA stimulation. The myristoylation of Nef and its membrane localization were essential for these effects. These results suggest that Nef may alter astrocytic functions by interfering with PKC expression and activation and contribute to the restriction of HIV-1 replication in astrocytes., (Copyright 1999 Wiley-Liss, Inc.)

Following brain injury, astrocytes express receptors for cytokines and neuropeptides and secrete several regulatory mediators that have a well established role in inflammation, immunity, and tissue development or repair. To elucidate the role of substance P (SP), a neurotransmitter peptide of the tachykinin family, in inducing astrocyte secretory activities, we have examined the expression of SP receptors and the functional consequences of their activation in cultured astrocytes from the human embryonic brain or spinal cord. Radioligand binding studies revealed that only one type of SP receptors, the high affinity NK-1 receptor, was present on human astrocytes and that spinal cord astrocytes expressed about 6 times as many SP binding sites as brain astrocytes. Following SP treatment, a substantial inositol phosphate formation was observed in spinal cord astrocytes only. Stimulation of spinal cord astrocytes with SP alone did not induce secretion of cytokines [interleukin-6 (IL-6), granulocyte-macrophage-CSF, macrophage chemoattractant protein-1 or leukemia inhibitory factor] or prostaglandin E2 (PGE2). Interestingly, however, SP selectively potentiated the inducing effect of IL-1beta on IL-6 and PGE2 secretion by spinal cord astrocytes without affecting the IL-1-beta-evoked secretion of other cytokines. SP also enhanced the small inducing effect of tumor necrosis factor-alpha (TNF-alpha) on IL-6 and PGE2 secretion and that of transforming growth factor-beta on PGE2 secretion. These results suggest that SP can enhance immunoregulatory and neurotrophic astroglial functions mediated by IL-6 and PGE2 by acting in concert with a set of cytokines whose cerebral expression has been reported during development and in a variety of diseases.