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Activation of T lymphocytes by human pathogens is a key step in the development of immune-mediated neurologic diseases. Because of their ability to invade the CNS and their increased secretion of proinflammatory cytokines, activated CD4+ T cells are thought to play a crucial role in pathogenesis. In the present study, we examined the expression of inflammatory mediators the cytokine-induced metalloproteinases (MMP-2, -3, and -9) and their endogenous inhibitors, tissue inhibitors of metalloproteinases (TIMP-1, -2, and -3), in human astrocytes in response to activated T cells. We used a model system of CD4+ T lymphocytes activated by persistent viral infection (human T lymphotropic virus, HTLV-I) in transient contact with human astrocytes. Interaction with T cells resulted in increased production of MMP-3 and active MMP-9 in astrocytes despite increased expression of endogenous inhibitors, TIMP-1 and TIMP-3. These data suggest perturbation of the MMP/TIMP balance. These changes in MMP and TIMP expression were mediated, in part, by soluble factors (presumably cytokines) secreted by activated T cells. Integrin-mediated cell adhesion is also involved in the change in MMP level, since blockade of integrin subunits (α1, α3, α5, and β1) on T cells resulted in less astrocytic MMP-9-induced expression. Interestingly, in CNS tissues from neurological HTLV-I-infected patients, MMP-9 was detected in neural cells within the perivascular space, which is infiltrated by mononuclear cells. Altogether, these data emphasize the importance of the MMP-TIMP axis in the complex interaction between the CNS and invading immune cells in the context of virally mediated T cell activation.

In absence epilepsy, epileptogenic processes are suspected of involving an imbalance between GABAergic inhibition and glutamatergic excitation. Here, we describe alteration of the expression of glutamate transporters in rats with genetic absence (the Genetic Absence Epilepsy Rats from Strasbourg: GAERS). In these rats, epileptic discharges, recorded in the thalamo-cortical network, appear around 40 days after birth. In adult rats no alteration of the protein expression of the glutamate transporters was observed. In 30-day-old GAERS protein levels (quantified by western blot) were lower in the cortex by 21% and 35% for the glial transporters GLT1 and GLAST, respectively, and by 32% for the neuronal transporter EAAC1 in the thalamus compared to control rats. In addition, the expression and activity of GLAST were decreased by 50% in newborn GAERS cortical astrocytes grown in primary culture. The lack of modification of the protein levels of glutamatergic transporters in adult epileptic GAERS, in spite of mRNA variations (quantified by RT-PCR), suggests that they are not involved in the pathogeny of spike-and-wave discharges. In contrast, the alteration of glutamate transporter expression, observed before the establishment of epileptic discharges, could reflect an abnormal maturation of the glutamatergic neurone-glia circuitry. Keywords: cortex, EAAC1, GAERS, GLAST, GLT1, thalamus. Absence epilepsy is mainly a childhood disease. Seizures occur as frequently as several hundred times per day and are detrimental to children's education and health. While convulsive epilepsy has been widely investigated, little is known about the pathophysiology of absence seizures. In GAERS (Genetic Absence Epilepsy Rats from Strasbourg), a genetic model of absence epilepsy (Vergnes et al. 1982), epileptic seizures occur around 40 days after birth and persist throughout lifetime. As in the human disease, the neuronal hyperexcitation and hypersynchronization, which induce spike-and-wave discharges (SWDs) in GAERS, are generated in a cortico-thalamic loop, involving reciprocal glutamatergic projections between the thalamus and the cortex, as well as GABAergic interneurones. Involvement of GABA and glutamate in the initiation and spreading of epileptic discharges in this model is supported by electrophysiological and pharmacological studies. A significantly increased amplitude of the voltage-dependent low-threshold Ca 2+ current observed in the reticular thalamic nucleus of GAERS with established epilepsy suggests an alteration of the GABAergic neurones in this structure (Tsakiridou et al. 1995). GABA A and GABA B agonists increase the duration of SWDs, while GABA B antagonists suppress SWDs. In addition, agonists of the glutamate receptor AMPA increase SWDs, while AMPA and NMDA antagonists decrease and suppress them, respectively. Density of GABAergic or glutamatergic neurones, glutamate decarboxylase expression (GABA synthesizing enzyme) and density of GABA

In the neurological disease associated with HTLV-1 infected T lymphocytes infiltrated within the CNS are suspected of playing a prominent role in pathogenesis via inflammatory cytokines and the viral protein Tax-1. We hypothesized that T lymphocytes initiate functional perturbation in astrocytes, resulting in neuronal alteration as glial cells have a crucial role in CNS homeostasis. In particular, astrocytes manage the steady state level of glutamate and continuously provide metabolite precursors to neurons and oligodendrocytes. Using a model system of HTLV-1-infected T cells-astrocytes interaction, we show that after contact with T cells, astrocyte acquire a phenotype typical of gliosis: secretion of proinflammatory cytokines (TNF-alpha, IL-1alpha, IL-6) and matrix metalloproteinases (MMP-9, MMP-3). The concomitant increase in the expression of MMPs and of their endogenous inhibitors (TIMP-1 and TIMP-3) suggests a perturbation in MMP/TIMP balance. This may alter the extracellular matrix and, in turn, the cell environment. At a functional level, glutamate transport and catabolism are impaired in astrocytes. A decrease in glutamate uptake is associated with downregulated expression of glutamate transporters GLAST and GLT1. The expression of astrocytic enzyme of glutamate metabolism is modified with up-regulation of glutamine synthetase and down-regulation of glutamate dehydrogenase. The involvement of Tax-1 in these alterations, directly or indirectly via TNF-alpha, is shown. Altered glutamate uptake and catabolism associated with impairment in cell connectivity via MMP/TIMP imbalance could compromise the functional integrity of the CNS in general and that of neurons and oligodendrocytes in particular.

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