Innate lymphoid cells (ILCs) are increasingly appreciated as important participants in homeostasis and inflammation. Substantial plasticity and heterogeneity among ILC populations have been reported. Here we have delineated the heterogeneity of human ILCs through single-cell RNA sequencing of several hundreds of individual tonsil CD127(+) ILCs and natural killer (NK) cells. Unbiased transcriptional clustering revealed four distinct populations, corresponding to ILC1 cells, ILC2 cells, ILC3 cells and NK cells, with their respective transcriptomes recapitulating known as well as unknown transcriptional profiles. The single-cell resolution additionally divulged three transcriptionally and functionally diverse subpopulations of ILC3 cells. Our systematic comparison of single-cell transcriptional variation within and between ILC populations provides new insight into ILC biology during homeostasis, with additional implications for dysregulation of the immune system.

The etiology of upper airway collapsibility in patients with snoring and obstructive sleep apnea (OSA) remains unclear. Local muscular abnormalities, including neurogenic lesions, could be a contributory factor. The aim of this study was to histologically evaluate the hypothesis of a progressive snorers disease. Biopsies of palatopharyngeal muscle were obtained from 21 patients with habitual snoring and different degrees of upper airway obstruction (10 patients with OSA) and 10 nonsnoring control subjects. Morphological abnormalities, including neurogenic signs (e.g., type grouping), were blindly quantified. The degree of abnormality was significantly increased in patients compared with control subjects. The individual score of abnormalities was significantly correlated to the percentage periodic obstructive breathing but not to oxygen desaturation index. Analyses of the individual fiber-size spectra demonstrated a significantly increased number of hypertrophied and/or atrophied fibers in patients compared with controls. The subjects were also divided into three groups according to their type of nocturnal breathing, i.e., nonsnorers, patients with < 20%, and patients with > or = 45% obstructive breathing. These groups correlated significantly with the degree of abnormality and pathological fiber-size spectra. In conclusion, these results support the hypothesis of a progressive local neurogenic lesion, caused by the trauma of snoring, as a possible contributory factor to upper airway collapsibility.

Natural killer (NK) cells are cytotoxic lymphocytes and play a vital role in controlling viral infections and cancer. In contrast to B and T lymphopoiesis where cellular and regulatory pathways have been extensively characterized, the cellular stages of early human NK cell commitment remain poorly understood. Here we demonstrate that a Lin(-)CD34(+)CD38(+)CD123(-)CD45RA(+)CD7(+)CD10(+)CD127(-) population represents a NK lineage-restricted progenitor (NKP) in fetal development, umbilical cord blood, and adult tissues. The newly identified NKP has robust NK cell potential both in vitro and in vivo, generates functionally cytotoxic NK cells, and lacks the ability to produce T cells, B cells, myeloid cells, and innate lymphoid-like cells (ILCs). Our findings identify an early step to human NK cell commitment and provide new insights into the human hematopoietic hierarchy.

BackgroundGroup 2 innate lymphoid cells (ILC2s) are involved in the initial phase of type 2 inflammation and can amplify allergic immune responses by orchestrating other type 2 immune cells. Prostaglandin (PG) E2 is a bioactive lipid that plays protective roles in the lung, particularly during allergic inflammation.ObjectiveWe set out to investigate how PGE2 regulates human ILC2 function.MethodsThe effects of PGE2 on human ILC2 proliferation and intracellular cytokine and transcription factor expression were assessed by means of flow cytometry. Cytokine production was measured by using ELISA, and real-time quantitative PCR was performed to detect PGE2 receptor expression.ResultsPGE2 inhibited GATA-3 expression, as well as production of the type 2 cytokines IL-5 and IL-13, from human tonsillar and blood ILC2s in response to stimulation with a combination of IL-25, IL-33, thymic stromal lymphopoietin, and IL-2. Furthermore, PGE2 downregulated the expression of IL-2 receptor α (CD25). In line with this observation, PGE2 decreased ILC2 proliferation. These effects were mediated by the combined action of E-type prostanoid receptor (EP) 2 and EP4 receptors, which were specifically expressed on ILC2s.ConclusionOur findings reveal that PGE2 limits ILC2 activation and propose that selective EP2 and EP4 receptor agonists might serve as a promising therapeutic approach in treating allergic diseases by suppressing ILC2 function.

No abstract

Cross-reactive CD4 + T cells that recognize SARS-CoV-2 are more commonly detected in the peripheral blood of unexposed individuals compared to SARS-CoV-2-reactive CD8 + T cells. However, large numbers of memory CD8 + T cells reside in tissues, feasibly harboring localized SARS-CoV-2-specific immune responses. To test this idea, we performed a comprehensive functional and phenotypic analysis of virusspecific T cells in tonsils, a major lymphoid tissue site in the upper respiratory tract, and matched peripheral blood samples obtained from children and adults before the emergence of COVID-19. We found that SARS-CoV-2-specific memory CD4 + T cells could be found at similar frequencies in the tonsils and peripheral blood in unexposed individuals, whereas functional SARS-CoV-2-specific memory CD8 + T cells were almost only detectable in the tonsils. Tonsillar SARS-CoV-2-specific memory CD8 + T cells displayed a follicular homing and tissue-resident memory phenotype, similar to tonsillar Epstein-Barr virus-specific memory CD8 + T cells, but were functionally less potent than other virus-specific memory CD8 + T cell responses. The presence of pre-existing tissue-resident memory CD8 + T cells in unexposed individuals could potentially enable rapid sentinel immune responses against SARS-CoV-2.

No abstract

Human innate lymphoid cells have been described to exist in different organs, with functional deregulation of these cells contributing to several disease states. Here, we performed the first detailed characterization of the phenotype, tissue-residency properties, and functionality of ILC1s, ILC2s, and ILC3s in the human adult and fetal liver. In addition, we investigated changes in the ILC compartment in liver fibrosis. A unique composition of tissue-resident ILCs was observed in nonfibrotic livers as compared with that in mucosal tissues, with NKp44 ILC3s accounting for the majority of total intrahepatic ILCs. The frequency of ILC2s, representing a small fraction of ILCs in nonfibrotic livers, increased in liver fibrosis and correlated directly with the severity of the disease. Notably, intrahepatic ILC2s secreted the profibrotic cytokine IL-13 when exposed to IL-33 and thymic stromal lymphopoetin (TSLP); these cytokines were produced by hepatocytes, hepatic stellate cells (HSCs), and Kupffer cells in response to TLR-3 stimulation. In summary, the present results provide the first detailed characterization of intrahepatic ILCs in human adult and fetal liver. The results indicate a role for ILC2s in human liver fibrosis, implying that targeting ILC2s might be a novel therapeutic strategy for its treatment.