The well regulated activities of microglia and T cells specific to central nervous system (CNS) antigens can contribute to the protection of CNS neural cells and their renewal from adult neural stem/progenitor cells (aNPCs). Here we report that T cell-based vaccination of mice with a myelin-derived peptide, when combined with transplantation of aNPCs into the cerebrospinal fluid (CSF), synergistically promoted functional recovery after spinal cord injury. The synergistic effect was correlated with modulation of the nature and intensity of the local T cell and microglial response, expression of brain-derived neurotrophic factor and noggin protein, and appearance of newly formed neurons from endogenous precursor-cell pools. These results substantiate the contention that the local immune response plays a crucial role in recruitment of aNPCs to the lesion site, and suggest that similar immunological manipulations might also serve as a therapeutic means for controlled migration of stem/progenitor cells to other acutely injured CNS sites.

The role of activated microglia (MG) in demyelinating neurodegenerative diseases such as multiple sclerosis is controversial. Here we show that high, but not low, levels of IFN-g (a cytokine associated with inflammatory autoimmune diseases) conferred on rodent MG a phenotype that impeded oligodendrogenesis from adult neural stem/progenitor cells. IL-4 reversed the impediment, attenuated TNF-a production, and overcame blockage of IGF-I production caused by IFN-g. In rodents with acute or chronic EAE, injection of IL-4-activated MG into the cerebrospinal fluid resulted in increased oligodendrogenesis in the spinal cord and improved clinical symptoms. The newly formed oligodendrocytes were spatially associated with MG expressing MHC class II proteins and IGF-I. These results point to what we believe to be a novel role for MG in oligodendrogenesis from the endogenous stem cell pool. IntroductionRecovery from acute insults or chronic inflammatory and noninflammatory degenerative disorders in the CNS has been attributed to a limited capacity for neurogenesis and oligodendrogenesis, poor regeneration of injured nerves, and extreme vulnerability to degenerative conditions. Studies have demonstrated that the adult CNS contains stem cells that can give rise, albeit to a limited extent, both to neurons (1) and to oligodendrocytes (2) throughout life. Knowledge of the factors allowing such stem cells to exist, proliferate, and differentiate in the adult individual is a prerequisite for understanding and promoting the conditions conducive to CNS repair. This in turn can be expected to lead to the development of interventions aimed at boosting neural cell renewal from the endogenous stem cell pool or from exogenously applied stem cells.Studies have shown that inflammation within the CNS blocks neurogenesis (3, 4) and causes structural damage to myelin (5, 6). Moreover, "paralysis" of microglia (MG) and/or macrophages arrests progression of the transient monophasic disease EAE (7, 8). All of those findings were interpreted as evidence in support of the traditional view that the effect of local immune cells in the CNS is detrimental, and hence that recovery would require blockage, arrest, or elimination of local immune responses. Likewise, the limited regeneration and excessive vulnerability of CNS neurons under inflammatory conditions or after an acute insult were put down to the poor ability of the CNS to tolerate the immune-derived defensive activity that is often associated with local inflammation and cytotoxicity mediated, for example, by 9) or nitric oxide (10). More recent studies have shown, however, that although an uncontrolled local immune response indeed impairs

Fighting off neuronal degeneration requires a well controlled T-cell response against self-antigens residing in sites of the CNS damage. The ability to evoke this response is normally suppressed by naturally occurring CD4 ϩ CD25ϩ regulatory T-cells (Treg). No physiological compound that controls Treg activity has yet been identified. Here, we show that dopamine, acting via type 1 dopamine receptors (found here to be preferentially expressed by Treg), reduces the suppressive activity and the adhesive and migratory abilities of Treg. Treg activity was correlated with activation of the ERK1/2 (extracellular signal-regulated kinase 1/2) signaling pathway. Systemic injection of dopamine or an agonist of its type 1 receptors significantly enhanced, via a T-cell-dependent mechanism, protection against neuronal death after CNS mechanical and biochemical injury. These findings shed light on the physiological mechanisms controlling Treg and might open the way to novel therapeutic strategies for downregulating Treg activity (e.g., in neuronal degeneration) or for strengthening it (in autoimmune diseases).

autoimmunity ͉ neuroprotection ͉ neurodegenerative conditions ͉ hippocampal slice cultures ͉ immune regulation T he systemic adaptive T cell-dependent immune response plays a key role in the ability of neurons in the central nervous system (CNS) to withstand injurious conditions (1-3). Studies from our laboratory have shown that, after a CNS injury, T cells nonselectively migrate to the site of injury (4), and suggest that homing T cells, which encounter their relevant antigens at the lesion site, are the ones that contribute to the repair. Such T cells become locally activated to produce neurotrophic factors (5) and cytokines, which are capable of affecting the activity of resident microglia and hence the fate of threatened neurons. We further showed that the T cell-dependent protection evoked after an axonal injury, being an anti-self-response (6), is constitutively limited by naturally occurring CD4 ϩ CD25 ϩ regulatory T cells (Treg) (6). It is, however, amenable to therapeutic boosting, either by postinjury immunization with antigens derived from dominant proteins residing in the site of damage or by depletion of Treg (2).Treg comprise Ϸ10% of the CD4 ϩ T cell population, and have been widely viewed as safeguards against the pathogenic effects of autoimmune CD4 ϩ CD25