Vijay et al. show that an age-dependent increase of phospholipase A2 group IID (PLA2G2D) in the lung contributes to worse outcomes in mice infected with SARS-CoV. Mice lacking (PLA2G2D) had increased survival to lethal infection with enhanced DC migration to the dLN and augmented T cell responses. The results suggest that targeting (PLA2G2D) in elderly patients with respiratory infections could represent an attractive therapeutic strategy.

Antigen-mediated cross-linking of IgE bound to mast cells via the high affinity receptor for IgE triggers a signaling cascade that results in the release of intracellular calcium stores, followed by an influx of extracellular calcium. The collective increase in intracellular calcium is critical to the release of the granular contents of the mast cell, which include the mediators of acute anaphylaxis. We show that the sensitivity of the mast cell to antigen-mediated degranulation through this pathway can be dramatically influenced by the A2b adenosine receptor. Loss of this Gs-coupled receptor on mouse bone marrow–derived mast cells results in decreased basal levels of cyclic AMP and an excessive influx of extracellular calcium through store-operated calcium channels following antigen activation. Mice lacking the A2b receptor display increased sensitivity to IgE-mediated anaphylaxis. Collectively, these findings show that the A2b adenosine receptor functions as a critical regulator of signaling pathways within the mast cell, which act in concert to limit the magnitude of mast cell responsiveness when antigen is encountered.

The contribution of NLRP3, a member of the nucleotide-binding domain leucine-rich repeat containing (NLR) family, in the development of allergic airway disease is currently controversial. Here, we used multiple allergic asthma models to examine the physiologic role of NLRP3. We found no significant differences in airway eosinophilia, histopathology, mucus production and airway hyperreactivity between wild type and Nlrp3-/- mice in either acute (alum-dependent) or chronic (alum-independent) OVA models. In addition to the OVA model, we also did not detect a role for NLRP3 in the development of allergic airway disease induced by either acute or chronic house dust mite (HDM) antigen exposure. While we did not observe significant phenotypic differences in any of the models tested, we did observe a significant reduction of IL-13 and IL-33 in Nlrp3-/- mice compared to wild type controls in the chronic OVA model without added alum. In all of the allergic airway disease models, the levels of the NLRP3 inflammasome associated cytokines IL-1β and IL-18 in the lung were below the level of detection. In sum, this report surveyed four different allergic asthma models and found a modest and selected role for NLRP3 in the alum-free OVA model. However this difference did not greatly alter the clinical outcome of the disease. This suggests that the role of NLRP3 in allergic asthma has to be re-evaluated.

Background-The mechanisms responsible for the development of airway hyperresponsiveness in asthma are poorly understood. Adenosine levels are high in the lungs of patients with asthma, but a role for adenosine in the development of this cardinal feature of asthma has not been previously reported.

BelgiumAdenosine triphosphate has previously been shown to induce semi-mature human monocyte-derived dendritic cells (DC). These are characterized by the up-regulation of co-stimulatory molecules, the inhibition of IL-12 and the up-regulation of some genes involved in immune tolerance, such as thrombospondin-1 and indoleamine 2,3-dioxygenase. The actions of adenosine triphosphate are mediated by the P2Y 11 receptor; since there is no functional P2Y 11 gene in the murine genome, we investigated the action of adenine nucleotides on murine DC. Adenosine 5 0 -(3-thiotriphosphate) and adenosine inhibited the production of IL-12p70 by bone marrow-derived DC (BMDC). These inhibitions were relieved by 8-p-sulfophenyltheophylline, an adenosine receptor antagonist. The use of selective ligands and A 2B -/-BMDC indicated the involvement of the A 2B receptor. A microarray experiment, confirmed by quantitative PCR, showed that, in presence of LPS, 5 0 -(N-ethylcarboxamido) adenosine (NECA, the most potent A 2B receptor agonist) regulated the expression of several genes: arginase I and II, thrombospondin-1 and vascular endothelial growth factor were up-regulated whereas CCL2 and CCL12 were downregulated. We further showed that NECA, in combination with LPS, increased the arginase I enzymatic activity. In conclusion, the described actions of adenine nucleotides on BMDC are mediated by their degradation product, adenosine, acting on the A 2B receptor, and will possibly lead to an impairment of Th1 response or tolerance.

High levels of adenosine can be measured from the lungs of asthmatics, and it is well recognized that aerosolized 5'AMP, the precursor of adenosine, elicits robust bronchoconstriction in patients with this disease. Characterization of mice with elevated adenosine levels secondary to the loss of adenosine deaminase (ADA) expression, the primary metabolic enzyme for adenosine, further support a role for this ubiquitous mediator in the pathogenesis of asthma. To begin to identify pathways by which adenosine can alter airway tone, we examined adenosine-induced bronchoconstriction in four mouse lines, each lacking one of the receptors for this nucleoside. We show, using direct measures of airway mechanics, that adenosine can increase airway resistance and that this increase in resistance is mediated by binding the A(1) receptor. Further examination of this response using pharmacologically, surgically, and genetically manipulated mice supports a model in which adenosine-induced bronchoconstriction occurs indirectly through the activation of sensory neurons.

SUMMARY Background Osteopontin (OPN) is a multifunctional protein which has recently been linked to allergic diseases. Clara cell 10-kDa protein (CC10) is another protein linked to allergy, and has been suggested to have an inhibitory role in inflammatory airway diseases. At this time, it is not known whether OPN is involved in allergic rhinitis (AR) or if there is any association between CC10 and OPN in AR. Objective To study the expression of OPN and its potential association with CC10 in AR. Methods The expression of CC10 and OPN in nasal mucosa of AR patients was investigated. AR animal models were established by employing wild-type and CC10-knockout mice. In some experiments, human recombinant CC10 protein was given to AR mice during either sensitization or challenge. The phenotypic changes were examined by histology and real-time RT-PCR. The direct effect of CC10 on OPN expression in spleen mononuclear cells and on OPN-induced inflammatory cytokine expression in BEAS-2B cells was measured through in vitro cell culture. Results OPN expression was up-regulated, with a concomitant down-regulation of CC10, in AR patients, showing a significant negative correlation between their expression. Compared with control mice sensitized with PBS, OPN expression was significantly increased in AR mice; such increase was more prominent in CC10-knockout mice, compared to wild-type. Administration of CC10 during both sensitization and challenge could markedly ameliorate Th2-skewed inflammation and OPN expression in nasal mucosa. CC10 administration at the sensitization phase could also reduce spleen OPN expression. The in vitro study showed that CC10 directly down-regulated OPN expression in spleen mononuclear cells stimulated with OVA and suppressed OPN-induced expression of Th2 cytokines and proinflammatory cytokines in BEAS-2B cells. Conclusion In the context of allergic airway responses, CC10 can inhibit OPN expression and suppress the Th2 promoting function of OPN, resulting in CC10’s inhibitory biological effects.

Asthma is a chronic inflammatory disease affecting the lung, characterized by breathing difficulty during an attack following exposure to an environmental trigger. Calcitonin gene-related peptide (CGRP) is a neuropeptide that may have a pathological role in asthma. The CGRP receptor is comprised of two components, which include the G-protein coupled receptor, calcitonin receptor-like receptor (CLR), and receptor activity-modifying protein 1 (RAMP1). RAMPs, including RAMP1, mediate ligand specificity in addition to aiding in the localization of receptors to the cell surface. Since there has been some controversy regarding the effect of CGRP on asthma, we sought to determine the effect of CGRP signaling ablation in an animal model of asthma. Using gene-targeting techniques, we generated mice deficient for RAMP1 by excising exon 3. After determining that these mice are viable and overtly normal, we sensitized the animals to ovalbumin prior to assessing airway resistance and inflammation after methacholine challenge. We found that mice lacking RAMP1 had reduced airway resistance and inflammation compared to wildtype animals. Additionally, we found that a 50% reduction of CLR, the G-protein receptor component of the CGRP receptor, also ameliorated airway resistance and inflammation in this model of allergic asthma. Interestingly, the loss of CLR from the smooth muscle cells did not alter the airway resistance, indicating that CGRP does not act directly on the smooth muscle cells to drive airway hyperresponsiveness. Together, these data indicate that signaling through RAMP1 and CLR plays a role in mediating asthma pathology. Since RAMP1 and CLR interact to form a receptor for CGRP, our data indicate that aberrant CGRP signaling, perhaps on lung endothelial and inflammatory cells, contributes to asthma pathophysiology. Finally, since RAMP-receptor interfaces are pharmacologically tractable, it may be possible to develop compounds targeting the RAMP1/CLR interface to assist in the treatment of asthma.