During early embryogenesis, microglia arise from yolk sac progenitors that populate the developing central nervous system (CNS), but how the tissue-resident macrophages are maintained throughout the organism's lifespan still remains unclear. Here, we describe a system that allows specific, conditional ablation of microglia in adult mice. We found that the microglial compartment was reconstituted within 1 week of depletion. Microglia repopulation relied on CNS-resident cells, independent from bone-marrow-derived precursors. During repopulation, microglia formed clusters of highly proliferative cells that migrated apart once steady state was achieved. Proliferating microglia expressed high amounts of the interleukin-1 receptor (IL-1R), and treatment with an IL-1R antagonist during the repopulation phase impaired microglia proliferation. Hence, microglia have the potential for efficient self-renewal without the contribution of peripheral myeloid cells, and IL-1R signaling participates in this restorative proliferation process.

Naturally occurring regulatory T cells (T reg cells) are a thymus-derived subset of T cells, which are crucial for the maintenance of peripheral tolerance by controlling potentially autoreactive T cells. However, the underlying molecular mechanisms of this strictly cell contact–dependent process are still elusive. Here we show that naturally occurring T reg cells harbor high levels of cyclic adenosine monophosphate (cAMP). This second messenger is known to be a potent inhibitor of proliferation and interleukin 2 synthesis in T cells. Upon coactivation with naturally occurring T reg cells the cAMP content of responder T cells is also strongly increased. Furthermore, we demonstrate that naturally occurring T reg cells and conventional T cells communicate via cell contact–dependent gap junction formation. The suppressive activity of naturally occurring T reg cells is abolished by a cAMP antagonist as well as by a gap junction inhibitor, which blocks the cell contact–dependent transfer of cAMP to responder T cells. Accordingly, our results suggest that cAMP is crucial for naturally occurring T reg cell–mediated suppression and traverses membranes via gap junctions. Hence, naturally occurring T reg cells unexpectedly may control the immune regulatory network by a well-known mechanism based on the intercellular transport of cAMP via gap junctions.

Interferon-regulatory factor 4 (IRF4) is essential for the development of T helper 2 (Th2) and Th17 cells. Herein, we report that IRF4 is also crucial for the development and function of an interleukin-9 (IL-9)-producing CD4(+) T cell subset designated Th9. IRF4-deficient CD4(+) T cells failed to develop into IL-9-producing Th9 cells, and IRF4-specific siRNA inhibited IL-9 production in wild-type CD4(+) T cells. Chromatin-immunoprecipitation (ChIP) analyses revealed direct IRF4 binding to the Il9 promoter in Th9 cells. In a Th9-dependent asthma model, neutralization of IL-9 substantially ameliorated asthma symptoms. The relevance of these findings is emphasized by the fact that the induction of IL-9 production also occurs in human CD4(+) T cells accompanied by the upregulation of IRF4. Our data clearly demonstrate the central function of IRF4 in the development of Th9 cells and underline the contribution of this T helper cell subset to the pathogenesis of asthma.

The tanption factors NF-KB and AP-1 have been Implicated in the inducible expression of a variety of gen involved in to oxidative stress and cellular defense mechanisms. Here, we report that thioredoxin, an important cellular protein oxidoreductase with antoxidant activity, exerts different effects on the activation of NF-icB and AP-1. Transient expression or exogenous application of thioredoxin resulted in a dose-dependent inhibition of NF-KB activly, as demonstrated in gel shift and transactivation experiments. AP-1-dependent transactivation, in contrast, was sltrongy enhanced by thioredoxin. A similar increase of AP-1 actiity was also observed with other, structurally unrelated antioxidants such as pyrrolidine dithiocarbamate and butylated hydroxyanisole, indicating that the thioredoxin-induced increase of AP-1 activation was indeed based on an antioidant effect. Moreover, the stimulatoy effect on AP-1 activity was found to involve de novo t cipton of the c-jun and c-fos components but to be independent of protein kinase C activation. These results suggest that thioredoxin plays an important role in the regulation of transcriptional processes and oppositely affects NF-ucB and AP-1 activation.

We have previously shown that two tumor necrosis factor (TNF) receptors (TNFR) exhibit antagonistic functions during neurodegenerative processes in vivo with TNFR1 aggravating and TNFR2 reducing neuronal cell loss, respectively. To elucidate the neuroprotective signaling pathways of TNFR2, we investigated glutamateinduced excitotoxicity in primary cortical neurons. TNFexpressing neurons from TNF-transgenic mice were found to be strongly protected from glutamate-induced apoptosis. Neurons from wild type and TNFR1 ؊/؊ mice prestimulated with TNF or agonistic TNFR2-specific antibodies were also resistant to excitotoxicity, whereas TNFR2 ؊/؊ neurons died upon glutamate and/or TNF exposures. Both protein kinase B/Akt and nuclear factor-B (NF-B) activation were apparent upon TNF treatment. Both TNFR1 and TNFR2 induced the NF-B pathway, yet with distinguishable kinetics and upstream activating components, TNFR1 only induced transient NF-B activation, whereas TNFR2 facilitated long term phosphatidylinositol 3-kinase-dependent NF-B activation strictly. Glutamate-induced triggering of the ionotropic N-methyl-Daspartate receptor was required for the enhanced and persistent phosphatidylinositol 3-kinase-dependent NF-B activation by TNFR2, indicating a positive cooperation of TNF and neurotransmitter-induced signal pathways. TNFR2-induced persistent NF-B activity was essential for neuronal survival. Thus, the duration of NF-B activation is a critical determinant for sensitivity toward excitotoxic stress and is dependent on a differential upstream signal pathway usage of the two TNFRs. Tumor necrosis factor (TNF)1 is a prominent proinflammatory mediator that has been causally associated with the pathophysiology of several acute and chronic diseases, in particular rheumatoid arthritis and Morbus Crohn (1, 2). Up-regulated TNF expression has also been found in various neurodegenerative diseases such as cerebral malaria, AIDS dementia, Alzheimer's disease, multiple sclerosis, and stroke, suggesting a potential pathogenic role of TNF in these diseases as well (3-7). The membrane-expressed form of TNF signals through both TNF receptors (TNFR1 and TNFR2), whereas soluble TNF proteolytically cleaved from the membrane form acts mainly via TNFR1 (8). Signal pathways initiated from the death domain-containing TNFR1, leading to both proapoptotic and antiapoptotic cellular responses, have been studied in great detail (9). In contrast, there is less information regarding the molecular mechanisms surrounding signal pathways and cellular responses solely initiated via TNFR2 because of concomitant TNFR1 signals in normal situations. The evaluation of the physiological role of TNFR2 by large depends on data obtained from TNFR1 Ϫ/Ϫ mice. We have recently investigated the role of TNF and its receptors in retinal ischemia and unraveled an antagonistic function of TNFR1 and TNFR2. TNFR2 exerts neuroprotection in a phosphatidylinositol 3-kinase (PI3K) dependent manner, which is counterbalanced by the neurodegenerative action of TNFR1 (10). TNFR1 h...

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Cytotoxic T lymphocytes are effector CD8+ T cells that eradicate infected and malignant cells. Here we show that the transcription factor NFATc1 controls the cytotoxicity of mouse cytotoxic T lymphocytes. Activation of Nfatc1 −/− cytotoxic T lymphocytes showed a defective cytoskeleton organization and recruitment of cytosolic organelles to immunological synapses. These cells have reduced cytotoxicity against tumor cells, and mice with NFATc1-deficient T cells are defective in controlling Listeria infection. Transcriptome analysis shows diminished RNA levels of numerous genes in Nfatc1 −/− CD8+ T cells, including Tbx21, Gzmb and genes encoding cytokines and chemokines, and genes controlling glycolysis. Nfatc1 −/−, but not Nfatc2 −/− CD8+ T cells have an impaired metabolic switch to glycolysis, which can be restored by IL-2. Genome-wide ChIP-seq shows that NFATc1 binds many genes that control cytotoxic T lymphocyte activity. Together these data indicate that NFATc1 is an important regulator of cytotoxic T lymphocyte effector functions.