IL-33 is a novel member of the IL-1 cytokine family and a potent inducer of type 2 immunity, as mast cells and Th2 CD4+ T cells respond to IL-33 with the induction of type 2 cytokines such as IL-13. IL-33 mRNA levels are extremely high in the CNS, and CNS glia possess both subunits of the IL-33R, yet whether IL-33 is produced by and affects CNS glia has not been studied. Here, we demonstrate that pathogen-associated molecular patterns (PAMPs) significantly increase IL-33 mRNA and protein expression in CNS glia. Interestingly, IL-33 was localized to the nucleus of astrocytes. Further, CNS glial and astrocyte-enriched cultures treated with a PAMP followed by an ATP pulse had significantly higher levels of supernatant IL-1beta and IL-33 than cultures receiving any single treatment (PAMP or ATP). Supernatants from PAMP + ATP-treated glia induced the secretion of IL-6, IL-13, and MCP-1 from the MC/9 mast cell line in a manner similar to exogenous recombinant IL-33. Further, IL-33 levels and activity were increased in the brains of mice infected with the neurotropic virus Theiler's murine encephalomyelitis virus. IL-33 also had direct effects on CNS glia, as IL-33 induced various innate immune effectors in CNS glia, and this induction was greatly amplified by IL-33-stimulated mast cells. In conclusion, these results implicate IL-33-producing astrocytes as a potentially critical regulator of innate immune responses in the CNS.

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the central nervous system (CNS). Here we document for the first time that the cytokine IL-33 is upregulated in both the periphery and the CNS of MS patients. Plasma IL-33 was elevated in MS patients compared to normal subjects and a three-month treatment of MS patients with interferon β-1a resulted in significant decrease of IL-33 levels. Similarly, stimulated cultured lymphocytes and macrophages from MS patients had elevated IL-33 levels compared to normal subjects. In parallel, the transcription factor NF-κB that mediates IL-33 transcription was also elevated in leukocytes of MS patients. IL-33 was elevated in normal-appearing white matter and plaque areas from MS brains and astrocytes were identified as an important source of IL-33 expression in the CNS. In summary, IL-33 levels are elevated in the periphery and CNS of MS patients, implicating IL-33 in the pathogenesis of MS.

The protein tyrosine phosphatase SHP-1 is a crucial negative regulator of cytokine signaling and inflammatory gene expression, both in the immune system and in the central nervous system (CNS). Mice genetically lacking SHP-1 (me/me) display severe inflammatory demyelinating disease following inoculation with the Theiler's murine encephalomyelitis virus (TMEV) compared to infected wild-type mice. Therefore, it became essential to investigate the mechanisms of TMEV-induced inflammation in the CNS of SHP-1-deficient mice. Herein, we show that the expression of several genes relevant to inflammatory demyelination in the CNS of infected me/me mice is elevated compared to that in wild-type mice. Furthermore, SHP-1 deficiency led to an abundant and exclusive increase in the infiltration of high-level-CD45-expressing (CD45 hi ) CD11b Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS) that remains a major cause of disability (76). Several studies demonstrated that MS lesions contain multiple leukocyte cell types, including lymphocytes, macrophages, and dendritic cells, all of which are believed to contribute to lesion formation by various distinct and interacting mechanisms (54, 61). Among these leukocyte subsets, infiltrating macrophages have been identified as major effectors of demyelination in both MS and animal models for MS (17,44,59,102). In accord with these studies, it was recently reported that the dominant mechanism of demyelination in MS is macrophage mediated (15). Indeed, in some models for MS, the requirement for lymphocytes is negligible and macrophages are the sole mediators of demyelination (6, 72).These findings have stimulated intense interest in the function of macrophages in lesion formation, including signaling events that draw these cells into the CNS white matter and trigger the effector mechanisms by which these cells damage myelin. For instance, macrophages have been identified as the major responders to CNS chemokines and producers of a number of proinflammatory cytokines, chemokines, and toxic molecules known to promote demyelination (32,44,63,85,90,91,93,103). Interestingly, both the brains of MS patients and the brains of experimental animals with MS-like diseases contain activated transcription factors like NF-B (34, 40), STAT1 (35,37,40), and STAT6 (18,21,109), which can lead to enhanced expression of these inflammatory molecules. Based on the findings of our previous work, we propose that the modulation of inflammatory signaling via these transcriptional pathways may be deficient in the leukocytes, including the macrophages, of MS patients and that this deficiency is responsible for susceptibility to inflammatory demyelinating processes within the CNS.SHP-1 is a protein tyrosine phosphatase with two Src homology 2 domains which acts as a negative regulator of both innate and acquired immune cytokine signaling via NF-B (52, 67), STAT1 (29,68), and STAT6 (13,43,45,50). Mice genetically lacking SHP-1 (motheaten mice) display myelin de...

Recent studies in mice have demonstrated that the protein tyrosine phosphatase SHP-1 is a crucial negative regulator of pro-inflammatory cytokine signaling, TLR signaling, and inflammatory gene expression. Furthermore, mice genetically lacking SHP-1 (me/me) display a profound susceptibility to inflammatory CNS demyelination relative to wild type mice. In particular, SHP-1 deficiency may act predominantly in inflammatory macrophages to increase CNS demyelination as SHP-1-deficient macrophages display co-expression of inflammatory effector molecules and increased demyelinating activity in me/me mice. Recently, we reported that PBMCs of multiple sclerosis (MS) patients have a deficiency in SHP-1 expression relative to normal control subjects indicating that SHP-1 deficiency may play a similar role in MS as to that seen in mice. Therefore, it became essential to examine the specific expression and function of SHP-1 in macrophages from MS patients. Herein, we document that macrophages of MS patients have deficient SHP-1 protein and mRNA expression relative to those of normal control subjects. To examine functional consequences of the lower SHP-1, the activation of STAT6, STAT1, and NF-κB was quantified and macrophages of MS patients showed increased activation of these transcription factors. In accordance with this observation, several STAT6-, STAT1-, and NF-κB-responsive genes that mediate inflammatory demyelination were increased in macrophages of MS patients following cytokine and TLR agonist stimulation. Supporting a direct role of SHP-1 deficiency in altered macrophage function, experimental depletion of SHP-1 in normal subject macrophages resulted in an increased STAT/NF-κB activation and increased inflammatory gene expression to levels seen in macrophages of MS patients. In conclusion, macrophages of MS patients display a deficiency of SHP-1 expression, heightened activation of STAT6, STAT1, and NF-κB and a corresponding inflammatory profile that may be important in controlling macrophage-mediated demyelination in MS.