Allergic asthma is a chronic inflammation of the airways mediated by an adaptive type 2 immune response. Upon allergen exposure, group 2 innate lymphoid cells (ILC2s) can be rapidly activated and represent an early innate source of IL-5 and IL-13. Here, we used a house dust mite (HDM)-driven asthma mouse model to study the induction of ILC2s in allergic airway inflammation. In BALF, lungs, and lymph nodes, ILC2 activation is critically dependent on prior sensitization with HDM. Importantly, T cells are required for ILC2 induction, whereby T-cell activation precedes ILC2 induction. During HDM-driven allergic airway inflammation the accumulation of ILC2s in BALF is IL-33 independent, although infiltrating ILC2s produce less cytokines in Il33 −/− mice. Transfer of in vitro polarized OVA-specific OT-II Th2 cells alone or in combination with Th17 cells followed by OVA and HDM challenge is not sufficient to induce ILC2, despite significant eosinophilic inflammation and T-cell activation. In this asthma model, ILC2s are therefore not an early source of Th2 cytokines, but rather contribute to type 2 inflammation in which Th2 cells play a key role. Taken together, ILC2 induction in HDM-mediated allergic airway inflammation in mice critically depends on activation of T cells.Keywords: Allergy · Asthma · Group 2 innate lymphoid cells (ILC2s) · House dust mite · Th2 cellsAdditional supporting information may be found in the online version of this article at the publisher's web-site IntroductionAsthma is a heterogeneous disease involving chronic inflammation of the airways and is characterized by episodes of coughing, wheezing, and shortness of breath. Multiple genetic predispositions and environmental factors contribute to asthma development and it is estimated that ß300 million people are affected worldwide. The asthma syndrome is divided into distinct disease entities with specific mechanisms, which have been called asthma endotypes [1,2]. The most prevalent endotype is allergic asthma, showing a strong association between exacerbations and repeated Correspondence: Dr. Rudi W. Hendriks e-mail: r.hendriks@erasmusmc.nl exposure to allergens such as pollen, fungi, or house dust mite (HDM). Allergic asthma is thought to be a classic Th2-mediated disease in which the signature effector cytokines IL-4, IL-5, and IL-13 are key orchestrators of persistent inflammation, airway hyperresponsiveness and remodeling, smooth muscle cell hyperplasia, mucous cell metaplasia, and increased angiogenesis (reviewed in [2,3]).Although production of IL-5 and IL-13 by a non-T/non-B lymphocyte population in response to IL-25 was first reported by Fort et al. [4], only recently these cells were accurately characterized and defined as a novel cell population that is negative for classic hematopoietic lineage markers and expresses Sca-1, CD117 (c-kit), CD25 (IL-2Rα), CD127 (IL-7Rα), and T1/ST2 (IL-33R) [5][6][7]. These innate cells are currently referred to as group 2 innate lymphoid cells (ILC2s) and were found to produce IL-13, which is [24]. Ho...

ILC2s in AI use a flexible epigenome that couples adaptation to new microenvironments with functional plasticity. Importantly, we reveal strong correlations between gene regulatory mechanisms in ILC2s and the genetic basis of asthma, supporting a pathogenic role for ILC2s in patients with allergic asthma.

Influenza virus infection is an important cause of severe asthma exacerbations, but it remains unclear how a Th1-mediated antiviral response triggers a prototypical Th2 disease. We investigated CD4 T cells and group 2 innate lymphoid cells (ILC2s) in influenza virus-infected mice. We found that ILC2s accumulated in the lung rapidly after influenza virus infection, but the induction of IL-5 and IL-13 secretion was delayed and concomitant with T cell activation. In an influenza-induced exacerbation of allergic airway inflammation model we noticed an initial reduction of ILC2 numbers and cytokine production in broncho-alveolar lavage compared to chronic house dust mite (HDM)-mediated airway inflammation alone. ILC2s phenotype was characterized by low T1/ST2, ICOS, KLRG1, and CD25 expression, resembling naïve ILC2s. The contribution of ILC2s to type 2 cytokine production in the early stage of the influenza-induced exacerbation was limited. In contrast, T cells showed increased IL-4 and IL-5 production when exposed to both HDM and influenza virus. Upon virus clearance, ILC2s regained an activated T1/ST2 ICOS KLRG1 CD25 phenotype paired with cytokine production and were major contributors to the type 2 cytokine milieu. Collectively, our data indicate that both T cells and ILC2s contribute to influenza-induced exacerbation of allergic airway inflammation, but with different kinetics.