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Genome-wide association studies (GWAS) have implicated the IL33 locus in asthma, but the underlying mechanisms remain unclear. Here, we identify a 5 kb region within the GWAS-defined segment that acts as a strong regulatory element in vivo and in vitro. Chromatin conformation capture showed that this 5 kb region loops to the IL33 promoter, potentially regulating its expression. We show that genotype at the asthma-associated SNP rs1888909, located within the 5 kb region, is associated with IL33 gene expression in human airway epithelial cells and IL-33 protein expression in human plasma, potentially through differential binding of OCT-1 (POU2F1) to the asthma-risk allele. Our data demonstrate that asthma-associated variants at the IL33 locus mediate allele-specific regulatory activity and IL33 expression, providing a novel mechanism through which a regulatory SNP contributes to genetic risk of asthma.

Genome-wide association studies (GWAS) have implicated the IL33 locus in asthma, but the underlying mechanisms remain unclear. Here, we identify a 5 kb region within the GWAS-defined segment that acts as a strong regulatory element in vivo and in vitro. Chromatin conformation capture showed that this 5 kb region loops to the IL33 promoter, potentially regulating its expression. Supporting this notion, we show that genotype at an asthma-associated SNP, rs1888909, located within the 5 kb region, is associated with IL33 gene expression in human airway epithelial cells and IL-33 protein expression in human plasma, potentially through differential binding of OCT-1 (POU2F1) to the asthma-risk allele. Our data demonstrate that asthma-associated variants at the IL33 locus mediate allele-specific regulatory activity and IL33 expression, providing a novel mechanism through which a regulatory SNP contributes to genetic risk of asthma.

Expression of the transcription factor interferon regulatory factor 4 (IRF4) is required for the development of lung conventional DCs type 2 (cDC2s) that elicit Th2 responses, yet how IRF4 functions in lung cDC2s throughout the acute and memory allergic response is not clear. Here, we used a mouse model that loses IRF4 expression after lung cDC2 development to demonstrate that mice with IRF4-deficient DCs display impaired memory responses to allergen. This defect in the memory response was a direct result of ineffective Th2 induction and impaired recruitment of activated effector T cells to the lung after sensitization. IRF4-deficient DCs demonstrated defects in their migration to the draining lymph node and in T cell priming. Finally, T cells primed by IRF4-competent DCs mediated potent memory responses independently of IRF4-expressing DCs, demonstrating that IRF4-expressing DCs are not necessary during the memory response. Thus, IRF4 controlled a program in mature DCs governing Th2 priming and effector responses, but IRF4-expressing DCs were dispensable during tissue-resident memory T cell-dependent memory responses.

Allergic asthma affects more than 300 million people worldwide and is characterized by airway hypersensitivity and eosinophilia. A prevalent feature of allergic asthma is increased serum IL-33 levels, and asthma GWAS have demonstrated that SNPs in the IL-33 locus are significantly associated with disease. While IL-33 and its downstream type 2 responses have been extensively studied in murine models of asthma, much less is known about the regulation of human IL33. Analysis of the mouse and human IL33 loci reveals little genomic conservation between the two species in non-coding regions. We generated a novel BAC transgenic mouse strain containing the human IL-33 locus with a fluorescent reporter to interrogate the regulation and expression of human IL-33. Surprisingly, the mice expressed human IL-33 primarily in endothelial cells, whereas murine IL-33 was expressed primarily in epithelial cells. These results mirror the expression profiles of IL-33 in primary human lung cells from the LungGENS database, thus demonstrating that our novel mouse model faithfully replicates human IL-33 expression. To understand how human IL-33 in the lung is regulated and expressed during inflammation, we examined BAC transgenic mice challenged with either house dust mite extract (HDM) or poly(I:C). In contrast to murine IL-33, expression of human IL-33 was reduced during allergic inflammation. We tested whether IL-33 is able to autoregulate itself via a negative feedback loop. Indeed, IL-33 administration downregulated the expression of human IL-33 in lung endothelial cells. Together, these data emphasize a distinct and novel role in humans for lung endothelial cells in allergic airway disease by producing and responding to IL-33.

The specific mechanisms by which DCs initiate Th2 responses are not completely understood. We previously found that mice lacking the transcription factor IRF4 in DCs do not develop type 2 lung inflammation in response to house dust mite extract (HDM). Further, IRF4-deficient DCs had a reduced capacity for restimulating T cells towards a Th2 phenotype ex vivo. We hypothesized that IRF4 is necessary for DCs to perform one or more of the functions required to successfully initiate Th2 responses in vivo. Here we demonstrate that during in vivo HDM sensitization, IRF4 in DCs is required neither for CD11b+ CD24+ cDCs to take up allergen in the lungs, nor for the lung DCs to process antigens. Instead, IRF4-deficient lung DCs display lower levels of the Th2-associated costimulatory molecule OX40L and express less of the Th2-promoting cytokines IL-33 and IL-10 during sensitization. While HDM-bearing DCs lacking IRF4 arrive in the lung-draining lymph nodes at proportions comparable to WT DCs and are capable of processing antigens, reduced numbers migrate to the lung-draining lymph nodes in the absence of IRF4. Following HDM sensitization, mice with IRF4-deficient DCs display impaired CD4+ effector/memory T cell recruitment to the lung parenchyma and reduced T cell expression of CD69. Thus, IRF4 controls a pro-Th2 program in DCs including expression of OX40L, IL-10, and IL-33 as well as migration to the draining lymph nodes, culminating in Th2 priming in response to HDM.

(See the editorial commentary by Emery on pages 169–71, and the major articles by Lichtner et al on pages 178–86.) 10.1093/infdis/jiu419 10.1093/infdis/jiu417 Despite effective administration of combination antiretroviral therapy to human immunodeficiency virus type 1 (HIV-1)–infected pregnant women, mother-to-child transmission (MTCT) of HIV-1 remains a significant global public health concern. Several copathogens that pose threats to the developing fetus during gestation, such as cytomegalovirus (CMV), malaria parasites, and Mycobacterium tuberculosis, may also facilitate in utero transmission of HIV-1 and contribute to the high incidence of MTCT within specific populations [1–3]. These pathogens can promote transmission through increases in proviral load, immune activation, local inflammation, and maternal stimulation of fetal CD4+cells to increase cellular susceptibility to HIV-1 infection. CMV, a highly prevalent beta herpesvirus, infects >90% and 50%–80% of reproductive-age women in developing and developed countries, respectively. HIV-1–infected infants who acquire CMV infection in the first 18 months of life have a significantly higher rate of disease progression than those infected with HIV-1 alone [4, 5]. Studies have shown that CMV induces increases in T-cell activation in peripheral blood mononuclear cells (PBMCs) from HIV-1–infected infants [6] and memory cell differentiation [7]. Strong associations between in utero CMV infection and a higher incidence of MTCT of HIV-1 have been documented [8, 9]; however, the mechanisms that increase neonatal HIV-1 transmission remain unknown. Several in vitro studies demonstrate increased viral transcription and replication in phytohemagglutinin (PHA)/interleukin 2 (IL-2)–activated cord blood mononuclear cells (CBMCs), compared with adult PBMCs. However, these conditions do not mimic the in utero environment, which is normally immunoquiescent and associated with a low risk of HIV-1 transmission (7%) in vivo. In contrast, immune activation may facilitate HIV-1 infection following in utero exposure to CMV antigens. Increased T-cell activation may be associated with CCR5 expression and susceptibility of CBMCs to HIV-1. The goal of the current study is to examine the targets and mechanisms that affect fetal susceptibility to HIV-1 in utero. We demonstrate that the fraction of CD4+CCR5+ and CD4+CD45RO+ T cells in cord blood is significantly lower, compared with adult PBMCs, which may reflect that the low level of in utero HIV-1 transmission is due to a lack of target cells. However, upon in vitro stimulation with CMV antigens or PHA/IL-2, CBMCs undergo increased proliferation and upregulate the fraction of T central memory (TCM) cells and expression of CCR5 among CD4+ T cells. This upregulation of CCR5 was more pronounced in TCM cells, compared with naive CD4+ CBMCs. Unstimulated CD4+ CBMCs that lack CCR5 and CD45RO showed reduced levels of HIV-1 infection and replication in vitro, compared with PBMCs. However, priming CBMCs with CMV antigens influenced the proliferation and activation of CCR5+ TCM cells, rendering these more susceptible to HIV-1 infection in vitro.