Group 2 Innate Lymphoid Cells Exhibit a Dynamic Phenotype in Allergic Airway Inflammation

Abstract

Group 2 innate lymphoid cells (ILC2) are implicated in allergic asthma as an early innate source of the type 2 cytokines IL-5 and IL-13. However, their induction in house dust mite (HDM)-mediated airway inflammation additionally requires T cell activation. It is currently unknown whether phenotypic differences exist between ILC2s that are activated in a T cell-dependent or T cell-independent fashion. Here, we compared ILC2s in IL-33- and HDM-driven airway inflammation. Using flow cytometry, we found that surface expression levels of various markers frequently used to identify ILC2s were dependent on their mode of activation, highly variable over time, and differed between tissue compartments, including bronchoalveolar lavage (BAL) fluid, lung, draining lymph nodes, and spleen. Whereas in vivo IL-33-activated BAL fluid ILC2s exhibited an almost uniform CD25+CD127+T1/ST2+ICOS+KLRG1+ phenotype, at a comparable time point after HDM exposure BAL fluid ILC2s had a very heterogeneous surface marker phenotype. A major fraction of HDM-activated ILC2s were CD25lowCD127+T1/ST2low ICOSlowKLRG1low, but nevertheless had the capacity to produce large amounts of type 2 cytokines. HDM-activated CD25low ILC2s in BAL fluid and lung rapidly reverted to CD25high ILC2s upon in vivo stimulation with IL-33. Genome-wide transcriptional profiling of BAL ILC2s revealed ~1,600 differentially expressed genes: HDM-stimulated ILC2s specifically expressed genes involved in the regulation of adaptive immunity through B and T cell interactions, whereas IL-33-stimulated ILC2s expressed high levels of proliferation-related and cytokine genes. In both airway inflammation models ILC2s were present in the lung submucosa close to epithelial cells, as identified by confocal microscopy. In chronic HDM-driven airway inflammation ILC2s were also found inside organized cellular infiltrates near T cells. Collectively, our findings show that ILC2s are phenotypically more heterogeneous than previously thought, whereby their surface marker and gene expression profile are highly dynamic.

Orchestration between ILC2s and Th2 cells in shaping type 2 immune responses

“…It has also been shown that in a mild HDM model, ILC2 induction requires T cell activation. 179,180 Therefore, future studies should also focus on how Th2 cells may modulate ILC2 activation and function in different disease models. ILCs and T helper cells are considered to be functionally redundant in host defense 181 ; however, a recent study has demonstrated that the functions of T cells cannot be replaced by ILCs.…”

Pulmonary group 2 innate lymphoid cells: surprises and challenges

“…Heterogeneity occurs in response to different stimuli with IL-33 inducing a uniform ILC2 phenotype, whereas HDM-induced ILC2s were heterogeneous but could still induce high levels of Th2 cytokines. 22 Transcriptional profiling showed 1,600 differentially expressed genes in BAL ILC2s involved in adaptive B and T cell responses, proliferation and cytokine production. ILC2s can also acquire a memory phenotype during allergic airway inflammation.…”

“…They arise from the common lymphoid progenitor (CLP) in the bone marrow which give rise to the more restricted ILC2 lineage-specific progenitor, ILC2p. The development of this progenitor relies on Gata3 [20][21][22][23] and the transcription factor retinoic acid receptor-related orphan nuclear receptor-α (RORα encoded by Rora gene). 24 A tight transcriptional network involving factors such as inhibitor of DNA binding-2 (Id2), Notch, 25 nuclear factor interleukin-3 (Nfil3), 26,27 promyelocytic leukemia zinc finger protein (PLZF, encoded by Btb16), T-cell factor-1 (TCF-1), 28,29 and zinc finger protein growth factor independent-1 (Gfi1) 30 are essential for the sequential specification and commitment of the ILC2 lineage.…”

Understanding Asthma Phenotypes, Endotypes, and Mechanisms of Disease

“…Akin to T-helper cells, heterogeneity and plasticity in relation to environmental signals in asthma have also recently been described in ILCs [86]. Together, both plasticity of T cell and ILCs add to the complexity of inflammation in severe asthma.…”