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A flow diagram of the different development pathways for the 5 subsets of ILC cell, starting from the common lymphoid progenitor, including the different transcription factors they each require for development
Schematic diagram of the development of ILCs, mainly based on mouse differentiation pathways.[1]

ILC2 cells, or type 2 innate lymphoid cells are a type of innate lymphoid cell. Not to be confused with the ILC. They are derived from common lymphoid progenitor and belong to the lymphoid lineage. These cells lack antigen specific B or T cell receptor because of the lack of recombination activating gene.[2] ILC2s produce type 2 cytokines (e.g. IL-4, IL-5, IL-9, IL-13) and are involved in responses to helminths, allergens,[3] some viruses, such as influenza virus[4] and cancer.[5][6][7]

The cell type was first described in 2001 as non-B/non-T cells, which produced IL-5 and IL-13 in response to IL-25 and expressed MHC class II and CD11c.[8] In 2006, a similar cell population was identified in a case of helminthic infection.[9] The name "ILC2" was not proposed until 2013.[10] They were previously identified in literature as natural helper cells,[11] nuocytes,[12] or innate helper 2 cells.[13] It is believed that ILC2s are rather old cell type with ancestor populations emerging in lamprey and bony fish.[14]

Parasitic infection

[edit]

ILC2s play the crucial role of secreting type 2 cytokines in response to large extracellular parasites. They express characteristic surface markers and receptors for chemokines, which are involved in distribution of lymphoid cells to specific organ sites. They require IL-7 for their development, which activates two transcription factors (both required by these cells)—RORα and GATA3. After stimulation with Th2 polarising cytokines, which are secreted mainly by epithelia (e.g. IL-25, IL-33, TSLP, prostaglandin D2 and leukotriene D4), ILC2s begin to produce IL-5, IL-13, IL-9, IL-4 rapidly. ILC2s are critical for primary responses to local Th2 antigens e.g. helminths and viruses and that is why ILC2s are abundant in the tissues of skin,[15][16] lungs, liver and gut.[17] It has been observed that ILC2s originate in the gut, enter lymphatic vessels and then circulate in the bloodstream so they can migrate to other organs to help fight the parasitic infection. The trafficking is partly sphingosine 1-phosphate-dependent.[16] For example, during an Nippostrongylus brasiliensis infection, ILC2s contribute to worm clearance by producing the essential cytokine IL-13.[18] IL-13 secreted by ILC2s also promotes migration of activated lung dendritic cells into the draining lymph node, which then results in naive T cell priming and differentiation into Th2 cells.[19]

Respiratory virus infection

[edit]

It has been observed, that ILC2s are activated upon respiratory virus infections in mice and humans. For instance, during Influenza A virus infection, which induces IL-33 production, ILC2s are activated and drive airway hyper-responsiveness. Another example is an Respiratory syncytial virus infection, where ILC2s contribute by being the main source of IL-13 early in the infection leading to airway hyper-responsiveness and increased mucus production.[18]

Allergy, atopic dermatitis, and asthma

[edit]

ILC2s play a variety of roles in allergy.[19] Primarily, they provide a source of the type 2 cytokines that orchestrate the allergic immune response. They produce a profile of signals in response to pro-allergenic cytokines IL-25 and IL-33 that is similar to those produced in response to helminthic infection. Their contribution to this signaling appears to be comparable to that of T cells. In response to allergen exposure in the lungs, ILC2s produce IL-13, a necessary cytokine in the pathogenesis of allergic reactions. This response appears to be independent of T and B cells. Further, allergic responses that resemble asthma-like symptoms have been induced in mice that lack T and B cells using IL-33. It has also been found that ILC2s are present in higher concentrations in tissues where allergic symptoms are present, such as in the nasal polyps of patients with chronic rhinosinusitis and the skin from patients with atopic dermatitis.[20][21][22]

Barrier function

[edit]

ILC2s are known to be enriched in the Fat-Associated Lymphoid Clusters (FALCs) within the mesenteries. IL-5 secreted by ILC2s is essential growth factor for B1 B cells and therefore important in the IgA antibody production. Besides the type 2 cytokines, ILC2s can also produce IL-6, which induces antibody production by B-cells, acts as a growth factor for plasmablasts and contributes in regulation of T follicular helper cells.[23][24]

ILC2s are also known to be present in the FALCs within the pleural cavity. After being stimulated via IL-33 during an infection, they begin to secrete IL-5, leading to an activation of B1 B cells and the production of IgM antibodies.[25] ILC2s are the dominant population of ILC in the lungs. By producing IL-13, they can initiate smooth muscle contraction and mucus secretion, but also goblet cell hyperplasia if the IL-13 is overexpressed. In addition, ILC2s help pulmonary wound healing after influenza infection by secreting amphiregulin. Besides lungs, ILC2 populations can also be found in human nasal and tonsil tissues.[18]

Adipose tissue homeostasis

[edit]

ILC2s are essential in the maintenance of homeostasis in lean and healthy adipose tissue. ILC2s resident in visceral adipose tissue produce IL-5, IL-13 and methionine-enkephalin peptides after prolonged exposure to IL-33. IL-5 secreted by ILC2s in adipose tissue is crucial for the recruitment and maintenance of eosinophils. Furthermore, production of IL-13 and IL-4 by ILC2 and eosinophils supports the maintenance of alternatively activated M2 macrophages and glucose homeostasis.[24]

Research identified dysregulated responses of ILC2s in adipose tissue as a factor in the development of obesity in mice since ILC2s also play important role in energy homeostasis. Methionine-enkephalin peptides produced by ILC2s act directly on adipocytes to upregulate UCP1 and promote emergence of beige adipocytes in white adipose tissue.[26] Beige and brown adipose tissue are specialized in thermogenesis.[24] The process of beiging leads to increased energy expenditure and decreased adiposity.[26]

References

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ILC2

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Type 2 innate lymphoid cells (ILC2s) are a subset of innate lymphoid cells (ILCs) that lack rearranged antigen-specific receptors and mirror the functions of CD4+ Th2 cells by rapidly producing type 2 cytokines, including interleukin (IL)-5, IL-9, and IL-13, upon activation by epithelial-derived alarmins such as IL-25, IL-33, and thymic stromal lymphopoietin (TSLP).[1][2] These cells are tissue-resident sentinels primarily located in mucosal barriers like the lungs, intestines, and skin, where they express the transcription factor GATA3 and respond to environmental cues to initiate early immune responses.[3][1] ILC2s develop from common lymphoid progenitors through a series of committed precursors, including common helper-like innate lymphoid precursors (CHILPs), with GATA3 being essential for their lineage specification and maintenance.[1] They are identified by surface markers such as CD127 (IL-7 receptor α chain), CD25 (IL-2 receptor α chain), and lack of lineage-specific markers (Lin-), distinguishing them from adaptive lymphocytes.[1] Unlike T cells, ILC2s provide immediate effector functions without prior sensitization, producing cytokines at levels up to 10-fold higher per cell than Th2 cells.[1] Recent studies highlight their plasticity, including the ability to transdifferentiate into regulatory subsets that produce IL-10 to dampen inflammation.[1] In immune responses, ILC2s are pivotal for type 2 immunity, driving eosinophil recruitment, goblet cell hyperplasia, and mucus production to expel helminth parasites, as seen in infections like Nippostrongylus brasiliensis.[2] They also secrete amphiregulin (AREG) to promote epithelial repair and tissue remodeling in contexts such as wound healing in the skin, lung, and intestine.[2] However, dysregulated ILC2 activity contributes to allergic diseases, including asthma, where IL-5 and IL-13 exacerbate airway inflammation and fibrosis.[1][2] ILC2s interact dynamically with their microenvironment, including epithelial cells that release activating signals, neurons via neuromediators like vasoactive intestinal peptide (VIP), and other immune cells such as eosinophils and T cells, forming regulatory circuits that balance protection and pathology.[3]

Overview

Definition

Innate lymphoid cells type 2 (ILC2s) are a specialized subset of innate lymphoid cells (ILCs), which constitute a family of immune cells that lack antigen-specific receptors characteristic of the adaptive immune system.[4] Unlike lymphocytes of the adaptive branch, such as T cells, ILC2s do not undergo gene rearrangement for receptor diversity and instead rely on germline-encoded receptors to sense environmental cues.[4] These cells are primarily enriched in mucosal and barrier tissues, where they contribute to early immune surveillance and maintenance of tissue homeostasis.[4] A key distinguishing feature of ILC2s from T helper 2 (Th2) cells is their ability to mount rapid responses to innate signals, such as alarmins released during epithelial damage or infection, without requiring prior antigen sensitization or clonal expansion. This innate activation allows ILC2s to initiate immune reactions within hours, providing an immediate bridge to adaptive immunity. In contrast, Th2 cells depend on T cell receptor recognition and co-stimulation for activation, which delays their response. The primary function of ILC2s lies in orchestrating type 2 immune responses through the secretion of signature cytokines, which drive anti-helminth defense, allergic inflammation, and tissue repair processes.[4] These responses are essential for host protection against multicellular parasites and for promoting wound healing and metabolic homeostasis in barrier sites. ILC2s exhibit evolutionary conservation across mammalian species, with orthologous populations identified in diverse vertebrates, underscoring their fundamental role in innate immunity.

Discovery

The discovery of group 2 innate lymphoid cells (ILC2s) occurred in 2010 through independent studies that identified a novel population of lineage-negative lymphoid cells capable of rapidly producing type 2 cytokines in response to epithelial-derived alarmins. In one seminal report, researchers described these cells in mouse adipose tissue as "natural helper cells," which responded to interleukin-25 (IL-25) and IL-33 by secreting IL-5 and IL-13, highlighting their role in innate type 2 immunity independent of adaptive responses. Concurrently, another group identified a similar IL-25-responsive population in the lungs of mice during helminth infection, termed "nuocytes," which served as a major early source of IL-13 to drive expulsion of the parasite Nippostrongylus brasiliensis. These early descriptions built on prior recognition of other innate lymphoid cell subsets, such as ILC1s and ILC3s, but shifted attention to this type 2 cytokine-producing lineage, spurred by growing interest in allergic and anti-parasitic responses in the early 2010s. Additional studies around the same time reinforced the existence of these cells in mucosal tissues, further distinguishing them from T helper 2 cells by their lack of antigen-specific receptors and rapid activation profile. The initial nomenclature varied across reports—"natural helper cells," "nuocytes," and "innate lymphoid cells type 2"—reflecting the field's excitement and the need for consensus. Standardization came in 2013 with a proposal endorsed by the International Union of Immunological Societies (IUIS), which unified the terminology under "group 2 innate lymphoid cells" or ILC2s, categorizing them alongside ILC1s and ILC3s based on their signature cytokines (IL-5 and IL-13 for ILC2s) and key transcription factor (GATA3). This framework facilitated broader research integration, emphasizing ILC2s' contributions to barrier immunity and tissue homeostasis.

Characteristics

Cellular Markers

Innate lymphoid cells type 2 (ILC2s) are primarily identified through multicolor flow cytometry by their lineage-negative (Lin⁻) status, which excludes markers expressed on other hematopoietic lineages such as T cells (CD3ε⁻, CD5⁻), B cells (CD19⁻, B220⁻), natural killer (NK) cells (NK1.1⁻ or CD56⁻), and myeloid cells (CD11b⁻, CD11c⁻, Gr-1⁻, CD14⁻, CD16⁻).[5][6][7] This Lin⁻ gate is typically combined with CD45⁺ expression to select for leukocytes, forming the foundational population for ILC2 isolation across tissues.[5][7] Positive surface markers further define ILC2s within the Lin⁻ CD45⁺ compartment. In both mice and humans, CD127 (IL-7Rα)⁺ is a core marker essential for ILC development and survival.[5][6][7] Mouse ILC2s are commonly identified as CD90 (Thy1)⁺ and ST2 (IL-33R)⁺, with activated populations additionally expressing KLRG1⁺ and often Sca-1⁺ or CD25⁺.[6][7] In humans, ILC2s express CD127⁺ alongside CD161⁺ and ST2⁺, though CD90 expression is minimal or absent; CRTH2 serves as a distinctive marker for human ILC2s, co-regulated with type 2 cytokine production.[5][7] These markers vary by tissue context, such as higher KLRG1 expression in small intestine ILC2s versus ST2 in lung ILC2s in mice.[6] Intracellular transcription factors provide confirmatory identification of ILC2 identity. GATA3 acts as the master regulator, driving ILC2 differentiation and function, while RORα supports their maintenance and survival.[5][7] Additional factors like PLZF and Bcl11b are expressed at high levels in ILC2s, distinguishing them from other ILC subsets, with low or absent RORγt.[5] These profiles enable precise isolation but highlight species-specific nuances, such as reliance on CD90.2 in mice versus CD161 in humans for optimal gating.[7]

Cytokine Profile

Innate lymphoid cells type 2 (ILC2s) are defined by their production of signature type 2 cytokines, including interleukin-5 (IL-5), interleukin-13 (IL-13), and interleukin-9 (IL-9).[8] IL-5 primarily drives eosinophil activation and recruitment, supporting anti-parasitic defenses and allergic responses.[9] IL-13 contributes to goblet cell hyperplasia, mucus hypersecretion, and tissue repair processes at barrier sites.[8] IL-9 functions to amplify ILC2 responses by promoting their proliferation and survival.[10] ILC2 cytokine production is triggered by epithelial-derived alarmins such as IL-33, IL-25, and thymic stromal lymphopoietin (TSLP), which are released in response to tissue damage or allergens.[8] These signals act through specific receptors—ST2 for IL-33, IL-17RB for IL-25, and TSLPR for TSLP—to initiate rapid ILC2 activation and effector function.[11] Additionally, lipid mediators like prostaglandin D2 (PGD2) enhance ILC2 migration and cytokine secretion via the CRTH2 receptor, bridging innate and adaptive immunity in inflammatory contexts.[12] Key regulatory pathways underpin ILC2 cytokine expression. IL-7 signaling, essential for ILC2 homeostasis, activates the transcription factor STAT5 to maintain cell survival and basal responsiveness.[13] For IL-5 and IL-13, the master transcription factor GATA3 directly controls their expression by binding promoter regions, ensuring coordinated type 2 responses upon alarmin stimulation.[14] An important amplification mechanism involves IL-9, which engages autocrine signaling through its receptor on ILC2s to enhance survival, proliferation, and further type 2 cytokine output, thereby sustaining responses during prolonged inflammation.[10] This loop is particularly evident in recovery phases following tissue insult, where IL-9 reinforces ILC2 effector functions without requiring continuous external stimuli.[15]

Development

Ontogeny

Innate lymphoid cells type 2 (ILC2s) originate from common lymphoid progenitors (CLPs) in the bone marrow, which differentiate into early innate lymphoid progenitors (EILPs) characterized by expression of α4β7 integrin.[16] These EILPs further progress to common innate lymphoid progenitors (CILPs), also known as common helper innate lymphoid progenitors (CHILPs), which are Lin⁻ Id2⁺ IL-7Rα⁺ α4β7⁺ Flt3⁻ CD25⁻ cells capable of giving rise to all helper-like ILC subsets, including ILC2s.[17] Interleukin-7 (IL-7) signaling through the IL-7 receptor α (IL-7Rα, or CD127) is essential for the survival, proliferation, and differentiation of these progenitors into mature ILC2s, as IL-7Rα deficiency severely impairs helper ILC development.[18] ILC2 ontogeny occurs in distinct embryonic and adult phases. During embryogenesis, committed ILC progenitors arise primarily in the fetal liver starting around embryonic day 13.5 (E13.5) in mice, seeding peripheral tissues such as the lung, intestine, and skin to establish resident populations.[19] In contrast, adult ILC2 pools are replenished by progenitors from the bone marrow, with postnatal differentiation contributing to tissue homeostasis, though some fetal-derived cells persist long-term in certain sites.[20] Seminal studies between 2013 and 2015 confirmed a shared common progenitor for ILC2s with ILC1s and ILC3s. Yang et al. (2015) identified TCF-1⁺ EILPs in the bone marrow as multipotent precursors with potential for all ILC lineages and natural killer cells.[21] Earlier, Klose et al. (2014) described the CHILP as an Id2-dependent progenitor downstream of CLPs that specifically generates helper ILCs, distinguishing them from conventional natural killer cells.[17] GATA3 acts as a key transcription factor specifying ILC2 identity from these common progenitors.[18] Recent studies as of 2025 have further elucidated roles of transcription factors like BACH2 in driving ILC2 development and function, with its ablation impairing lineage commitment.[22]

Tissue-Specific Differentiation

ILC2s exhibit tissue-specific maturation and adaptation following their initial seeding into peripheral tissues, where local microenvironments imprint distinct transcriptional and functional profiles to optimize their roles in immunity and homeostasis. This process involves integration of cytokine signals, transcription factor modulation, and environmental cues, leading to heterogeneous ILC2 subsets tailored to organ-specific demands. In the lungs, ILC2s develop enhanced responsiveness to IL-33 through elevated expression of the receptor ST2 (IL1RL1), which enables swift activation and proliferation in response to alveolar epithelial injury or allergen exposure.[23] This adaptation is driven by tissue-specific factors such as neuropilin-1 (Nrp1) and CCR2 expression, which promote retention and survival in the pulmonary niche.[24] Consequently, lung-resident ILC2s rapidly initiate type 2 responses, distinguishing them from circulating counterparts. In the gut, transcription factors such as aryl hydrocarbon receptor (Ahr) suppress IL-33 receptor expression to sustain gut-specific ILC2 functions. In the skin, ILC2s exhibit enhanced IL-18 responsiveness and CD103 expression for barrier maintenance.[25] These adaptations ensure ILC2s align with the unique microbial and structural demands of mucosal and cutaneous environments. ILC2s also demonstrate plasticity, with the capacity for transdifferentiation into ILC1-like states under exposure to IL-12 and IFN-γ, marked by reduced GATA3 levels, increased T-bet expression, and acquisition of IFN-γ production.[26] This shift occurs in inflammatory contexts, such as chronic lung diseases, allowing ILC2s to pivot toward type 1 immunity when needed.[27] Tissue-resident memory ILC2s form long-lived populations that persist in barrier sites, sustained primarily by IL-7 signaling, which supports survival and self-renewal through upregulation of anti-apoptotic factors.[28] Local survival factors, including TGF-β1 in the lung, further reinforce this residency by stabilizing tissue-specific markers like Nrp1, enabling enduring immune surveillance without reliance on continuous progenitor influx.[24]

Physiological Functions

Barrier Defense

ILC2s play a crucial role in maintaining epithelial barrier integrity at mucosal surfaces, such as the lungs and gut, by orchestrating type 2 immune responses that support tissue repair and homeostasis. These cells respond to environmental cues at barrier sites, producing cytokines that enhance epithelial defenses without necessarily involving adaptive immunity. Through their strategic positioning in tissues like the lung and intestinal lamina propria, ILC2s contribute to steady-state surveillance and rapid responses to perturbations, ensuring the structural and functional continuity of epithelial layers.[2] A key mechanism involves IL-13 production by ILC2s, which drives goblet cell hyperplasia and mucus production in both the lungs and gut, thereby strengthening the mucociliary barrier against potential threats. In the airways, ILC2-derived IL-13 promotes goblet cell metaplasia, increasing mucus secretion to trap and clear particulates, while in the intestinal epithelium, it similarly induces goblet cell expansion to bolster the mucus layer that separates luminal contents from host tissues.[29][30] ILC2s also coordinate with tuft cells through an IL-25/IL-13 feedback loop to facilitate epithelial repair following injury. Tuft cells sense damage or stressors and release IL-25, which activates nearby ILC2s to produce IL-13; this IL-13 in turn stimulates further tuft cell hyperplasia and goblet cell differentiation, amplifying the regenerative response at mucosal barriers. This circuit is particularly vital in the gut, where it promotes rapid turnover and fortification of the epithelium post-injury.[31] In wound healing processes, ILC2s secrete amphiregulin, an epidermal growth factor family member, to activate fibroblasts and promote angiogenesis, thereby supporting tissue remodeling and barrier restoration. This function is evident in lung tissues, where amphiregulin from ILC2s aids recovery after viral-induced damage by enhancing extracellular matrix deposition and vascularization without excessive inflammation. Additionally, during steady-state conditions, ILC2s maintain low-level IL-5 production to sustain eosinophil populations in tissues, which contribute to baseline barrier surveillance and homeostasis through anti-microbial activities and tissue remodeling support.[32][33]

Adipose Tissue Homeostasis

Innate lymphoid cells type 2 (ILC2s) were first identified in the visceral adipose tissue (VAT) of mice in 2010, where they reside as a distinct population responsible for maintaining local type 2 immune responses. These cells produce interleukin-5 (IL-5) and interleukin-13 (IL-13), which are essential for sustaining eosinophils and alternatively activated macrophages (AAMs, also known as M2 macrophages) in VAT. Specifically, IL-5 drives eosinophil recruitment and accumulation, while IL-13 promotes AAM polarization; depletion of ILC2s leads to a 12- to 14-fold reduction in VAT eosinophils and impairs AAM maintenance, highlighting their central regulatory role in adipose immune homeostasis.[34] The eosinophil-ILC2-macrophage axis in adipose tissue orchestrates metabolic adaptations, particularly the beiging of white adipose tissue (WAT), a process that converts energy-storing white adipocytes into thermogenic beige adipocytes expressing uncoupling protein 1 (UCP1). ILC2-derived IL-5 recruits eosinophils, which in turn secrete IL-4 to activate M2 macrophages; these macrophages release catecholamines that stimulate β-adrenergic signaling in adipocytes, upregulating UCP1 expression and enhancing non-shivering thermogenesis. Activation of ILC2s by IL-33 further amplifies this axis, significantly increasing the number of beige adipocytes in subcutaneous WAT and boosting oxygen consumption for caloric expenditure, independent of adaptive immunity but reliant on ILC2-intrinsic mechanisms like methionine-enkephalin peptide secretion. This pathway also improves systemic insulin sensitivity, as IL-33-elicited ILC2 responses in obese mice reduce glucose intolerance and enhance glucose homeostasis through UCP1-dependent thermogenesis.[35][36] High-fat diets (HFDs) disrupt ILC2 function in adipose tissue, contributing to obesity by suppressing ILC2 numbers and activity in both mice and humans. HFD feeding reduces VAT-resident ILC2s, alongside eosinophils and M2 macrophages, while promoting pro-inflammatory M1 macrophages via cytokines such as IFNγ and TNFα, which inhibit ILC2 proliferation. This suppression impairs beiging and thermogenesis, exacerbating weight gain and insulin resistance; conversely, adoptive transfer of activated ILC2s into HFD-fed obese mice limits fat accumulation and restores metabolic balance, underscoring the protective role of ILC2s against diet-induced adipose dysfunction.[37][38]

Roles in Infections

Parasitic Infections

Innate lymphoid cells type 2 (ILC2s) play a pivotal role in the host's defense against helminth parasitic infections by rapidly initiating type 2 immune responses. Upon infection with intestinal helminths such as Nippostrongylus brasiliensis, ILC2s are activated to produce high levels of interleukin-13 (IL-13), which promotes goblet cell hyperplasia and mucin production in the epithelium, facilitating worm expulsion.[39][40] This rapid IL-13 secretion occurs independently of adaptive immunity and is essential for the timely clearance of parasites, as depletion of ILC2s impairs expulsion and prolongs infection.[41] A key regulatory circuit amplifying this response involves tuft cells in the small intestine, which detect helminth-derived signals and produce IL-25 to activate resident ILC2s. Activated ILC2s then secrete IL-13, which acts on epithelial progenitors to drive tuft cell hyperplasia, creating a feed-forward loop that sustains type 2 immunity and enhances anti-helminth defenses.[42][43] This tuft cell-IL-25-ILC2 axis is particularly critical during primary infections, ensuring robust epithelial remodeling and parasite restriction in the gut mucosa.[44] Recent studies have identified IL-25-induced memory-like ILC2s that emerge during helminth infections, persist after clearance, and enforce enhanced mucosal type 2 immunity upon re-infection, contributing to long-term protection.[45] Additionally, ILC2s can rapidly mobilize from the intestine to distant sites like the lungs during infection, supporting systemic anti-helminth responses.[46] Following acute expulsion, ILC2s contribute to resolution and tissue homeostasis through IL-9 production, which acts in an autocrine manner to promote ILC2 survival and amplify effector cytokines like IL-5 and IL-13. This IL-9 signaling supports tissue repair by enhancing amphiregulin secretion and reducing inflammation in the recovery phase after helminth-induced damage, such as in the lungs during larval migration.[47][48] In humans, ILC2 involvement mirrors these mechanisms, with elevated circulating ILC2s observed in peripheral blood during Ascaris lumbricoides infections, marked by increased expression of activation markers like CD69 and CRTH2.[49] These cells likely contribute to systemic type 2 responses that aid in controlling helminth burdens. For protozoan infections, such as those caused by Entamoeba histolytica, ILC2s activated via IL-33 provide protective effects against colitis by promoting epithelial barrier integrity and IL-13-mediated repair.[50]

Viral Infections

During influenza A virus infection, damage to airway epithelial cells triggers the release of IL-33, which binds to the ST2 receptor on ILC2s, promoting their rapid expansion and activation in the lungs. Activated ILC2s then secrete high levels of IL-5 and IL-13, which drive eosinophil recruitment and accumulation, contributing to eosinophilia that peaks during the recovery phase. These cytokines also induce airway hyperreactivity by altering smooth muscle contractility and epithelial responses, potentially exacerbating respiratory symptoms.[51][52] ILC2s exhibit a dual role in the context of viral infections like influenza A. In the early stages, their production of type 2 cytokines such as IL-5 and IL-13 supports tissue repair by promoting epithelial cell proliferation and mucus clearance, aiding in the restoration of lung homeostasis following viral clearance. However, in severe or chronic cases, unchecked ILC2 expansion and excessive type 2 inflammation can worsen pathology by fostering persistent eosinophilic infiltration and goblet cell hyperplasia, which impair effective antiviral responses and prolong disease.[53][54] ILC2s also facilitate interactions with adaptive immunity during viral challenges. For instance, ILC2-derived IL-5 enhances B cell survival and differentiation in the lungs, supporting early antibody production against respiratory viruses such as Sendai virus, independent of T cell help. This mechanism helps bridge innate and humoral responses to promote mucosal defense.[55] In respiratory syncytial virus (RSV) infections, ILC2s contribute to detrimental outcomes, particularly in neonates. Activation of ILC2s by IL-33 leads to IL-13 secretion, which drives goblet cell metaplasia and excessive mucus production, resulting in airway obstruction and increased disease severity. Studies around 2014 highlighted how this ILC2-mediated pathway worsens RSV pathogenesis by promoting type 2 immunopathology that hinders viral clearance and amplifies bronchiolitis.[56][57]

SARS-CoV-2 Infections

Innate lymphoid cells type 2 (ILC2s) have been implicated in SARS-CoV-2 infections, with lower blood abundance associated with increased disease severity, including higher hospitalization odds (odds ratio 0.454 per twofold decrease in ILCs), longer hospital stays, and elevated inflammatory markers such as C-reactive protein. ILC2s promote disease tolerance by producing amphiregulin to support lung tissue repair and homeostasis following infection. However, reduced ILC2 levels, potentially exacerbated by age and sex differences, correlate with worse outcomes, while expanded subsets like CD117low ILC2s in patients may contribute to type 2 cytokine responses that aid repair but could exacerbate inflammation in severe cases.[58][59][60]

Roles in Diseases

Allergic Disorders

In allergic asthma, exposure to allergens triggers the release of epithelial-derived alarmins such as IL-33 and thymic stromal lymphopoietin (TSLP), which activate group 2 innate lymphoid cells (ILC2s) in the lungs.[61] Activated ILC2s produce IL-5, promoting eosinophil recruitment and survival, which contributes to eosinophilic inflammation.[62] Concurrently, IL-13 secretion from ILC2s drives airway hyperresponsiveness (AHR), goblet cell metaplasia, and mucus hypersecretion, exacerbating asthmatic symptoms.[63] This pathway underscores ILC2s as key initiators of type 2 immune responses in allergen-driven asthma pathogenesis.[64] Human studies have demonstrated elevated ILC2 numbers in the airways of patients with asthma, particularly correlating with disease severity.[65] In severe asthma, bronchoalveolar lavage fluid and sputum samples show increased ILC2 frequencies, with IL-5- and IL-13-producing ILC2s most prominent in eosinophilic subtypes.[66] These findings suggest ILC2s contribute to persistent inflammation and poor lung function in refractory cases.[67] Targeting this pathway with anti-IL-33 monoclonal antibodies has shown promise in reducing ILC2 activation and eosinophilia in clinical trials for moderate-to-severe asthma.[68] However, ILC2s exhibit plasticity, including a regulatory subtype (IL-10-producing ILC2s) that dampens type 2 inflammation in asthma. These cells reduce airway hyperresponsiveness and eosinophilia in murine models and are increased in human allergic individuals following allergen immunotherapy, correlating with symptom improvement as of 2023.[69] In allergic rhinitis, nasal allergen challenge induces rapid expansion and activation of ILC2s in the nasal mucosa.[70] Within hours of exposure, such as to cat dander, circulating CRTH2+ ILC2s increase, trafficking to the nasal tissues where they amplify type 2 cytokine production and local eosinophilic responses.[71] This expansion correlates with symptom severity, highlighting ILC2s' role in acute allergic nasal inflammation.[61] Therapeutic strategies targeting ILC2s have advanced, with biologics like anti-ST2 antibodies entering clinical trials since 2018 to mitigate their contributions to allergic disorders.[67] For instance, astegolimab, an anti-ST2 monoclonal antibody, has demonstrated efficacy in phase 2b trials by suppressing ILC2-driven exacerbations in severe asthma patients.[72] These approaches aim to block upstream alarmin signaling, offering potential for personalized treatment in type 2-high allergic conditions.[73]

Autoimmune and Other Conditions

In atopic dermatitis, skin-resident ILC2s are elevated in lesional tissue and produce IL-13, which drives Th2 cell skewing and exacerbates epidermal barrier disruption by impairing tight junction integrity and promoting inflammation through interactions with mast cells and basophils.[74] Studies in human AD patients have shown that ILC2-derived IL-13 enhances the migration of activated dendritic cells to lymph nodes, further amplifying Th2 responses and chronic skin inflammation.[75] ILC2s exhibit context-dependent roles in autoimmunity, providing protection in some conditions while contributing to pathogenesis in others. In models of colitis, ILC2s exert a protective effect by secreting IL-13, which promotes goblet cell differentiation, mucus production, and epithelial barrier repair, thereby mitigating intestinal inflammation and tissue damage.[76] Conversely, in psoriasis, skin ILC2s demonstrate plasticity, converting to an ILC3-like state under IL-23 stimulation and producing IL-22, which drives keratinocyte hyperproliferation and sustains the inflammatory milieu characteristic of psoriatic lesions.[77] This conversion has been observed in both murine models and human dermal samples, highlighting ILC2s' contribution to IL-17/IL-22-mediated autoimmunity.[78] In cancer, ILC2s display dual functions depending on the tumor type and exhibit heterogeneity that confers tissue-specific pro- and anti-tumor effects, influencing prognosis across various malignancies as of 2025.[79] In lung cancer, ILC2s promote tumor progression by secreting VEGF-A, which induces angiogenesis and vascular permeability, facilitating nutrient supply and metastatic spread in preclinical models.[80] In contrast, in melanoma, ILC2s mediate anti-tumor immunity through IL-5 and GM-CSF production, which recruits and activates eosinophils to infiltrate tumors, enhancing cytotoxicity against melanoma cells and improving survival outcomes in both mouse models and human patients.[81] PD-1 blockade further unleashes this ILC2-eosinophil axis, amplifying therapeutic responses.[82] Dysregulated ILC2s in adipose tissue contribute to metabolic diseases such as obesity and type 2 diabetes by failing to maintain anti-inflammatory macrophage polarization, leading to chronic low-grade inflammation and insulin resistance.[83] In obese models, LKB1 deficiency upregulates PD-1 on adipose ILC2s, impairing mitochondrial function and exacerbating insulin resistance; PD-1 blockade restores ILC2 effector functions and reverses these metabolic deficits as of 2024.[84] Research from the 2020s has identified therapeutic potential in targeting ILC2s; for instance, DR3 agonists stimulate adipose-resident ILC2s to boost IL-13 production, reversing insulin resistance and improving glucose homeostasis in obese mouse models.[83] Similarly, CB2 receptor agonists activate ILC2s via AKT/ERK/CREB signaling, enhancing type 2 cytokine output and ameliorating established type 2 diabetes in preclinical studies, with implications for human therapy.[85]

References

  1. Development and function of regulatory innate lymphoid cells
  2. Innate lymphoid cells control signaling circuits to regulate tissue ...
  3. Group 2 innate lymphoid cells and their surrounding environment
  4. Group 2 Innate Lymphoid Cells (ILC2): Type 2 Immunity and ... - MDPI
  5. Optimal Identification of Human Conventional and ... - PubMed Central
  6. Flow cytometric analysis of innate lymphoid cells - NIH
  7. Isolation and Identification of Innate Lymphoid Cells (ILCs) for ... - NIH
  8. Group 2 Innate Lymphoid Cells in Health and Disease - PMC
  9. Type 2 Innate Lymphoid Cells in Allergic Disease - PubMed - NIH
  10. IL-9-mediated survival of type 2 innate lymphoid cells ... - PubMed
  11. Type-2 Innate Lymphoid Cells in Asthma and Allergy - ATS Journals
  12. Subset- and tissue-defined STAT5 thresholds control homeostasis ...
  13. Group 2 innate lymphoid cells utilize the IRF4-IL-9 module ... - Nature
  14. Development and differentiation of early innate lymphoid progenitors
  15. https://www.cell.com/cell/fulltext/S0092-8674(14
  16. https://www.cell.com/immunity/fulltext/S1074-7613(14
  17. Embryonic ILC-poiesis across tissues - Frontiers
  18. https://doi.org/10.1016/j.immuni.2018.07.015
  19. https://doi.org/10.1038/s41420-024-02096-y
  20. https://doi.org/10.1016/j.it.2020.08.009
  21. Tissue microenvironment induces tissue specificity of ILC2 - PMC
  22. https://doi.org/10.1038/ni.3444
  23. https://doi.org/10.1038/s41467-020-16004-1
  24. https://doi.org/10.4049/jimmunol.1500779
  25. ILC2 Diversity, Location, and Function in Pulmonary Disease - PMC
  26. Heterogeneity of ILC2s in the Intestine; Homeostasis and Pathology
  27. A tuft cell - ILC2 signaling circuit provides therapeutic targets to ...
  28. The Tec kinase ITK is essential for ILC2 survival and epithelial ...
  29. Group 2 innate lymphoid cells are a non-redundant source ... - Nature
  30. Innate lymphoid type 2 cells sustain visceral adipose tissue ...
  31. Group 2 innate lymphoid cells promote beiging of adipose and limit ...
  32. ILC2s and Adipose Tissue Homeostasis: Progress to Date and ... - NIH
  33. IL-33-driven ILC2/eosinophil axis in fat is induced by sympathetic ...
  34. ILC2s mediate systemic innate protection by priming mucus ...
  35. IL‐4/IL‐13‐producing ILC2s are required for timely control of ...
  36. Group-2 innate lymphoid cell/T cell interactions in helminth expulsion
  37. Tuft-cell-derived IL-25 regulates an intestinal ILC2 ... - PubMed - NIH
  38. A Metabolite-Triggered Tuft Cell-ILC2 Circuit Drives Small Intestinal ...
  39. The IL-25-dependent tuft cell circuit driven by intestinal helminths ...
  40. IL-9–mediated survival of type 2 innate lymphoid cells promotes ...
  41. Food for thought – ILC metabolism in the context of helminth infections
  42. Elevated circulating group-2 innate lymphoid cells expressing ...
  43. The IL-33-ILC2 pathway protects from amebic colitis - Nature
  44. Group 2 Innate Lymphoid Cell Production of IL-5 Is Regulated by ...
  45. Innate lymphoid cells promote lung-tissue homeostasis after ...
  46. LUNG group 2 innate lymphoid cells as a new adjuvant target to ...
  47. BATF promotes group 2 innate lymphoid cell–mediated lung tissue ...
  48. Group 2 Innate Lymphoid Cells Promote An Early Antibody ...
  49. Respiratory Syncytial Virus Disease Is Mediated by Age-Variable IL-33
  50. Respiratory syncytial virus infection activates IL-13–producing group ...
  51. The Role of Type 2 Innate Lymphoid Cells in Allergic Diseases
  52. Type 2 innate lymphoid cells: at the cross-roads in allergic asthma
  53. The modulation of pulmonary group 2 innate lymphoid cell function ...
  54. The role of type 2 innate lymphoid cells in eosinophilic asthma - Salter
  55. ILC2s: team players in regulating asthma - PMC - PubMed Central
  56. Allergen-induced Increases in Sputum Levels of Group 2 Innate ...
  57. Group 2 innate lymphoid cells in human asthma - ScienceDirect.com
  58. Targeting interleukin-33 and thymic stromal lymphopoietin pathways ...
  59. Allergen challenge in allergic rhinitis rapidly induces increased ...
  60. Mucosal Type 2 Innate Lymphoid Cells Are a Key Component of the ...
  61. Safety and tolerability of astegolimab, an anti-ST2 monoclonal ... - NIH
  62. Immunotherapy for asthma | Cellular & Molecular Immunology - Nature
  63. Innate lymphoid cells: a new key player in atopic dermatitis - PMC
  64. https://doi.org/10.3389/fimmu.2023.1277120
  65. Innate Lymphoid Cells in Intestinal Homeostasis and Inflammatory ...
  66. Tissue-Specific Diversity of Group 2 Innate Lymphoid Cells in the Skin
  67. https://doi.org/10.1038/s41586-021-03188-w
  68. https://pubmed.ncbi.nlm.nih.gov/29382598/
  69. Blockade of the co-inhibitory molecule PD-1 unleashes ILC2 ... - NIH
  70. https://doi.org/10.1038/s41590-021-00943-z
  71. DR3 stimulation of adipose resident ILC2s ameliorates type ... - Nature
  72. https://www.cell.com/cell-reports/fulltext/S2211-1247(24
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