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.

The IKK␤ and NEMO/IKK␥ subunits of the NF-B-activating signalsome complex are known to be essential for activating NF-B by inflammatory and other stresslike stimuli. However, the IKK␣ subunit is believed to be dispensable for the latter responses and instead functions as an in vivo mediator of other novel NF-B-dependent and -independent functions. In contrast to this generally accepted view of IKK␣'s physiological functions, we demonstrate in mouse embryonic fibroblasts (MEFs) that, akin to IKK␤ and NEMO/IKK␥, IKK␣ is also a global regulator of tumor necrosis factor ␣-and IL-1-responsive IKK signalsome-dependent target genes including many known NF-B targets such as serum amyloid A3, C3, interleukin (IL)-6, IL-11, IL-1 receptor antagonist, vascular endothelial growth factor, Ptx3, ␤ 2 -microglobulin, IL-1␣, Mcp-1 and -3, RANTES (regulated on activation normal T cell expressed and secreted), Fas antigen, Jun-B, c-Fos, macrophage colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor. Only a small number of NF-B-dependent target genes were preferentially dependent on IKK␣ or IKK␤. Constitutive expression of a trans-dominant I B␣ superrepressor (I B␣SR) in wild type MEFs confirmed that these signalsome-dependent target genes were also dependent on NF-B. A subset of NF-B target genes were IKK-dependent in the absence of exogenous stimuli, suggesting that the signalsome was also required to regulate basal levels of activated NF-B in established MEFs. Overall, a sizable number of novel NF-B/IKK-dependent genes were identified including Secreted Frizzled, cadherin 13, protocadherin 7, CCAAT/enhancer-binding protein-␤ and -␦, osteoprotegerin, FOXC2 and FOXF2, BMP-2, p75 neurotrophin receptor, caspase-11, guanylate-binding proteins 1 and 2, ApoJ/clusterin, interferon (␣ and ␤) receptor 2, decorin, osteoglycin, epiregulin, proliferins 2 and 3, stromal cell-derived factor, and cathepsins B, F, and Z. SOCS-3, a negative effector of STAT3 signaling, was found to be an NF-B/IKK-induced gene, suggesting that IKKmediated NF-B activation can coordinately illicit negative effects on STAT signaling.The NF-B transcription factors are pivotal regulators of gene expression programs culminating in stress-like responses and the genesis of innate and acquired immunity (reviewed in Refs. 1-4). A host of extracellular stimuli including inflammatory cytokines, viral and bacterial infections, oxidative and DNA-damaging agents, UV light, and osmotic shock can all result in NF-B activation (1, 3-5). NF-B transcription factors bind to DNA as hetero-or homodimers that are selectively derived from five possible subunits (RelA/p65, c-Rel, RelB, p50, and p52) with each binding to half of a conserved 10-base pair consensus sequence (GGGRNWTYCC) (1, 5). Whereas the RelA/p65 and p50 subunits are ubiquitously expressed, the p52, c-Rel, and RelB subunits are more functionally important in specific differentiated cell types (1, 6). Cytoplasmic p50/p65 heterodimers, c-Rel homodimers, and RelB are bound to I Bs (inhibitors of NF-B...

No abstract

Recent studies have shown that gamma-interferon (IFN-gamma) induces the expression of Ia antigen on astrocytes. This observation is of immunological significance because such activated astrocytes can act as antigen-presenting cells, as demonstrated with myelin basic protein for antigen-specific encephalitogenic T-cell lines. However, the lack of lymphatic drainage in brain and the presence of the so-called blood-brain barrier restricting traffic of cells and macromolecules suggests that IFN-gamma may not be readily available, at least during the initial phases of viral infections. The question therefore arises as to whether astrocytes can be induced to express Ia antigens by other signals directly related to viral infection and possibly independent of IFN-gamma. In the present report we demonstrate that a neurotropic murine hepatitis virus induces expression of Ia antigen on astrocytes in tissue culture without infection, rendering these brain cells competent to participate directly in the immune response to a viral infection.