IL-33 is a tissue-derived cytokine that induces and amplifies eosinophilic inflammation and has emerged as a promising new drug target for asthma and allergic disease. Common variants at IL33 and IL1RL1, encoding the IL-33 receptor ST2, associate with eosinophil counts and asthma. Through whole-genome sequencing and imputation into the Icelandic population, we found a rare variant in IL33 (NM_001199640:exon7:c.487-1G>C (rs146597587-C), allele frequency = 0.65%) that disrupts a canonical splice acceptor site before the last coding exon. It is also found at low frequency in European populations. rs146597587-C associates with lower eosinophil counts (β = -0.21 SD, P = 2.5×10–16, N = 103,104), and reduced risk of asthma in Europeans (OR = 0.47; 95%CI: 0.32, 0.70, P = 1.8×10–4, N cases = 6,465, N controls = 302,977). Heterozygotes have about 40% lower total IL33 mRNA expression than non-carriers and allele-specific analysis based on RNA sequencing and phased genotypes shows that only 20% of the total expression is from the mutated chromosome. In half of those transcripts the mutation causes retention of the last intron, predicted to result in a premature stop codon that leads to truncation of 66 amino acids. The truncated IL-33 has normal intracellular localization but neither binds IL-33R/ST2 nor activates ST2-expressing cells. Together these data demonstrate that rs146597587-C is a loss of function mutation and support the hypothesis that IL-33 haploinsufficiency protects against asthma.

Macrophage activation is critical in the innate immune response and can be regulated by the nucleotide receptor P2X 7 . In this regard, P2X 7 signaling is not well understood but has been implicated in controlling reactive oxygen species (ROS) generation by various leukocytes. Although ROS can contribute to microbial killing, the role of ROS in nucleotide-mediated cell signaling is unclear. In this study, we report that the P2X 7 agonists ATP and 3′-O-(4-benzoyl) benzoic ATP (BzATP) stimulate ROS production by RAW 264.7 murine macrophages. These effects are potentiated in lipopolysaccharide-primed cells, demonstrating an important interaction between extracellular nucleotides and microbial products in ROS generation. In terms of nucleotide receptor specificity, RAW 264.7 macrophages that are deficient in P2X 7 are greatly reduced in their capacity to generate ROS in response to BzATP treatment (both with and without LPS priming), thus supporting a role for P2X 7 in this process. Because MAP kinase activation is key for nucleotide regulation of macrophage function, we also tested the hypothesis that P2X 7 -mediated MAP kinase activation is dependent on ROS production. We observed that BzATP stimulates MAP kinase (ERK1/ ERK2, p38, and JNK1/JNK2) phosphorylation, and that the antioxidants N-acetyl-cysteine and ascorbic acid strongly attenuate BzATP-mediated JNK1/JNK2 and p38 phosphorylation but only slightly reduce BzATP-induced ERK1/ERK2 phosphorylation. These studies reveal that P2X 7 can contribute to macrophage ROS production, that this effect is potentiated upon lipopolysaccharide exposure, and that ROS are important participants in the extracellular nucleotide-mediated activation of several MAP kinase systems.

Summary Viral infections affect wheezing and asthma in children and adults of all ages. In infancy, wheezing illnesses are usually viral in origin, and children with more severe wheezing episodes are more likely to develop recurrent episodes of asthma and to develop asthma later in childhood. Children who develop allergen-specific immunoglobulin E (allergic sensitization), and those who wheeze with rhinoviruses (HRV) are at especially high risk for asthma. In older children and adults, HRV infections generally cause relatively mild respiratory illnesses and yet contribute to acute and potentially severe exacerbations in patients with asthma. These findings underline the importance of understanding the synergistic nature of allergic sensitization and infections with HRV in infants relative to the onset of asthma and in children and adults with respect to exacerbations of asthma. This review discusses clinical and experimental evidence of virus/allergen interactions and evaluates theories which relate immunologic responses to respiratory viruses and allergens to the pathogenesis and disease activity of asthma. Greater understanding of the relationship between viral respiratory infections, allergic inflammation, and asthma is likely to suggest new strategies for the prevention and treatment of asthma.

Extracellular ATP has been proposed to act as a danger signal to alert the immune system of cell damage. Release of high local concentrations of ATP activates the nucleotide receptor P2RX7 on monocytic cells, which promotes the processing/release of pro-inflammatory mediators. Although the pro-inflammatory actions of P2RX7 are well recognized, little is known regarding the potential function of P2RX7 in repair responses. Because the resolution of inflammation is characterized by monocytic cell-dependent production of pro-angiogenic factors, we evaluated the contribution of P2RX7 to this process. We observed that both transient and long-term P2RX7 activation promotes the robust release of VEGF from primary human monocytes. This VEGF release is calcium-dependent and associated with reactive oxygen species production. This previously unrecognized action of P2RX7 suggests that it may not only participate in inflammation and cell death, but that it is also likely to be important in the control of angiogenesis and wound repair.

The nucleotide receptor P2X7 is an attractive therapeutic target and potential biomarker for multiple inflammatory and neurologic disorders, and it is expressed in several immune, osteogenic and neurologic cell types. Aside from its role in the nervous system, it is activated by ATP released at sites of tissue damage, inflammation and infection. Ligand binding to P2X7 stimulates many cell responses, including calcium fluxes, MAPK activation, inflammatory mediator release, and apoptosis. Much work has centered on P2X7 action in cell death and mediator processing (e.g., pro-interleukin-1 cleavage by the inflammasome), but the contribution of P2X7 to transcriptional regulation is less well defined. In this review, we will focus on the growing evidence for the importance of nucleotide-mediated gene expression, we will highlight several animal model, human genetic, and clinical studies that support P2X7 as a therapeutic target, and we will discuss the latest developments in anti-P2X7 clinical trials.