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Anaphylactic shock is characterized by elevated immunoglobulin-E (IgE) antibodies that signal via the high affinity Fcε receptor (FcεRI) to release inflammatory mediators. Here we report that the novel cytokine interleukin-33 (IL-33) potently induces anaphylactic shock in mice and is associated with the symptom in humans. IL-33 is a new member of the IL-1 family and the ligand for the orphan receptor ST2. In humans, the levels of IL-33 are substantially elevated in the blood of atopic patients during anaphylactic shock, and in inflamed skin tissue of atopic dermatitis patients. In murine experimental atopic models, IL-33 induced antigen-independent passive cutaneous and systemic anaphylaxis, in a T cell–independent, mast cell–dependent manner. In vitro , IL-33 directly induced degranulation, strong eicosanoid and cytokine production in IgE-sensitized mast cells. The molecular mechanisms triggering these responses include the activation of phospholipase D1 and sphingosine kinase1 to mediate calcium mobilization, Nuclear factor–κB activation, cytokine and eicosanoid secretion, and degranulation. This report therefore reveals a hitherto unrecognized pathophysiological role of IL-33 and suggests that IL-33 may be a potential therapeutic target for anaphylaxis, a disease of considerable unmet medical need.

Atopic allergy is characterized by an increase in IgE antibodies that signal through the high-affinity Fcepsilon receptor (FcepsilonRI) to induce the release of inflammatory mediators from mast cells. For unknown reasons, the prevalence of allergic diseases has recently increased steeply in the developed world. However, this increase has not been mirrored in developing countries, even though IgE concentrations are often greatly elevated in individuals from these countries, owing to nonspecific IgE induction by universally present parasitic worms. Here we offer one explanation for this paradox based on the properties of ES-62, a molecule secreted by filarial nematodes. We found that highly purified, endotoxin-free ES-62 directly inhibits the FcepsilonRI-induced release of allergy mediators from human mast cells by selectively blocking key signal transduction events, including phospholipase D-coupled, sphingosine kinase-mediated calcium mobilization and nuclear factor-kappaB activation. ES-62 mediates these effects by forming a complex with Toll-like receptor 4, which results in the sequestration of protein kinase C-alpha (PKC-alpha). This causes caveolae/lipid raft-mediated, proteasome-independent degradation of PKC-alpha, a molecule important for the coupling of FcepsilonRI to phospholipase D and mast cell activation. We also show that ES-62 is able to protect mice from mast cell-dependent hypersensitivity in the skin and lungs, indicating that it has potential as a novel therapeutic for allergy.

Aggregation of receptors specific for the constant region of immunoglobulin G activates a repertoire of monocyte responses that can lead ultimately to targeted cell killing via antibody-directed cellular cytotoxicity. The high affinity receptor, Fc␥RI, contains no recognized signaling motif in its cytoplasmic tail but rather utilizes the ␥-chain of Fc⑀RI as an accessory molecule to recruit tyrosine kinases for signal transduction. We show here that, in a human monocytic cell line primed with interferon-␥, Fc␥RI mobilizes intracellular calcium stores using a novel pathway that involves tyrosine kinase coupling to phospholipase D and resultant downstream activation of sphingosine kinase. Moreover, Fc␥RI is not coupled to phospholipase C; hence, calcium release from intracellular stores occurred in the absence of any measurable rise in inositol triphosphate. Finally, as this novel activation pathway is also shown to be responsible for mediating the vesicular trafficking of internalized immune complexes for degradation, it is likely to play a key role in controlling intracellular events triggered by Fc␥RI.

Multipotent mesenchymal stem cells (MSC) are reported to be immunoprivileged as well as immunosuppressive. Hence, they are ideal candidates for allogeneic transplantation to induce regeneration of diseased tissues and organs. However, it is not known whether MSC would retain their immunoprivileged and immunomodulatory properties after differentiating into the local cell types of the transplantation site. This study sought to investigate this question with a novel New Zealand White rabbit osteogenesis model. Results showed that osteogenic cells differentiated from MSC (DOC) in vitro did not express the MHC class II molecule, were incapable of inducing allogeneic lymphocyte proliferation in mixed lymphocyte culture or generating CTL, were inhibitory in ongoing lymphocyte proliferation, and secreted anti-inflammatory cytokines (IL-10 and TGF-β). There was a significantly higher secretion of IL-10 by DOC than that by MSC, while there was no significant difference between the TGF-β secretion of MSC and DOC in vitro. However, after IFN-γ treatment, TGF-β secretion by DOC significantly decreased despite the increased production by MSC. Four weeks after local DOC implantation, despite MHC class II expression, second-set allogeneic skin rejection showed similar survival to first-set allogeneic skin rejection and DOC appeared to function as osteoblasts. In conclusion, DOC retained their immunoprivileged and immunomodulatory properties in vitro, but the latter was lost following transplantation.

BackgroundSevere acute respiratory syndrome (SARS) emerged in later February 2003, as a new epidemic form of life-threatening infection caused by a novel coronavirus. However, the immune-pathogenesis of SARS is poorly understood. To understand the host response to this pathogen, we investigated the gene expression profiles of peripheral blood mononuclear cells (PBMCs) derived from SARS patients, and compared with healthy controls.ResultsThe number of differentially expressed genes was found to be 186 under stringent filtering criteria of microarray data analysis. Several genes were highly up-regulated in patients with SARS, such as, the genes coding for Lactoferrin, S100A9 and Lipocalin 2. The real-time PCR method verified the results of the gene array analysis and showed that those genes that were up-regulated as determined by microarray analysis were also found to be comparatively up-regulated by real-time PCR analysis.ConclusionsThis differential gene expression profiling of PBMCs from patients with SARS strongly suggests that the response of SARS affected patients seems to be mainly an innate inflammatory response, rather than a specific immune response against a viral infection, as we observed a complete lack of cytokine genes usually triggered during a viral infection. Our study shows for the first time how the immune system responds to the SARS infection, and opens new possibilities for designing new diagnostics and treatments for this new life-threatening disease.

Mast cell activation triggers Ca2؉ signals and the release of enzyme-containing granules, events that play a major role in allergic/hypersensitivity reactions. However, the precise molecular mechanisms that regulate antigen-triggered degranulation and Ca 2؉ fluxes in human mast cells are still poorly understood. Here we show, for the first time, that a receptor can trigger Ca 2؉ via two separate molecular mechanisms. Using an antisense approach, we show that IgE-antigen stimulation of human bone marrow-derived mast cells triggers a sphingosine kinase (SPHK) 1-mediated fast and transient Ca 2؉ release from intracellular stores. However, phospholipase C (PLC) ␥1 triggers a second (slower) wave of calcium release from intracellular stores, and it is this PLC␥1-generated signal that is responsible for Ca 2؉ entry. Surprisingly, Fc⑀RI (a high affinity receptor for IgE)-triggered mast cell degranulation depends on the first, sphingosine kinase-mediated Ca 2؉ signal. These two pathways act independently because antisense knock down of either enzyme does not interfere with the activity of the other enzyme. Of interest, similar to PLC␥1, SPHK1 translocates rapidly to the membrane after Fc⑀RI cross-linking. Here we also show that SPHK1 activity depends on phospholipase D1 and that Fc⑀RI-triggered mast cell degranulation depends primarily on the activation of both phospholipase D1 and SPHK1.Aggregation of the high affinity receptor for IgE (Fc⑀RI) on mast cells triggers the Ca 2ϩ -dependent release and production of a wide range of mediators responsible for the major symptoms of immediate hypersensitivity reactions (1-3). Although some of the signaling cascades triggered by Fc⑀RI have been characterized, the regulatory mechanisms governing mast cell degranulation and calcium release from internal stores are only partially understood. Fc⑀RI is a heterotrimeric receptor complex (␣␤␥ 2 ) that contains immunoreceptor tyrosine-based activation motifs in both the ␤ and ␥ subunit cytoplasmic domains (4). The protein-tyrosine kinase Lyn is associated with the ␤ subunit in resting cells (5), and its activation is promoted by Fc⑀RI cross-linking (6). Activated Lyn phosphorylates immunoreceptor tyrosine-based activation motifs of the ␤ and ␥ subunits, resulting in the recruitment of other Src-like as well as Syk protein tyrosine kinases through Src homology 2 domain-mediated interactions with phosphotyrosine residues (7,8). Activation of these newly recruited protein tyrosine kinases, in turn, facilitates the translocation and phosphorylation of multiple signaling molecules, including phospholipase C (PLC) 1 ␥ isoforms and phosphoinositide 3-kinases (9). Activated PLC␥ hydrolyses phosphatidylinositol 4,5-bisphosphate to D-myo-inositol 1,4,5-trisphosphate and diacylglycerol, which induce the release of Ca 2ϩ from intracellular stores and the activation of protein kinase C isoforms, respectively. The amplitude and duration of the Ca 2ϩ response potentially modulate the activation of different transcription factors (10), regulating diff...

During sepsis, activation of phagocytes leads to the overproduction of proinflammatory cytokines, causing systemic inflammation. Despite substantial information regarding the underlying molecular mechanisms that lead to sepsis, several elements in the pathway remain to be elucidated. We found that the enzyme sphingosine kinase 1 (SphK1) is up-regulated in stimulated human phagocytes and in peritoneal phagocytes of patients with severe sepsis. Blockade of SphK1 inhibited phagocyte production of endotoxin-induced proinflammatory cytokines. We observed protection against sepsis in mice treated with a specific SphK1 inhibitor that was enhanced by treatment with a broad-spectrum antibiotic. These results demonstrated a critical role for SphK1 in endotoxin signaling and sepsis-induced inflammatory responses and suggest that inhibition of SphK1 is a potential therapy for septic shock.