Adipose-tissue Treg cells restrain differentiation of stromal adipocyte precursors to promote insulin sensitivity and metabolic homeostasis.

Regulatory T (Treg) cells in epidydimal visceral adipose tissue (eVAT) of lean mice and humans regulate metabolic homeostasis. We found that constitutive or punctual depletion of eVAT-Treg cells reined in the differentiation of stromal adipocyte precursors. Co-culture of these precursors with conditional medium from eVAT-Treg cells limited their differentiation in vitro, suggesting a direct effect. Transcriptional comparison of adipocyte precursors, matured in the presence or absence of the eVAT-Treg-conditioned medium, identified the oncostatin-M (OSM) signaling pathway as a key distinction. Addition of OSM to in vitro cultures blocked the differentiation of adipocyte precursors, while co-addition of anti-OSM antibodies reversed the ability of the eVAT-Treg-conditioned medium to inhibit in vitro adipogenesis. Genetic depletion of OSM (specifically in Treg) cells or of the OSM receptor (specifically on stromal cells) strongly impaired insulin sensitivity and related metabolic indices. Thus, Treg-cell-mediated control of local progenitor cells maintains adipose tissue and metabolic homeostasis, a regulatory axis seemingly conserved in humans.

Airway injury induces alveolar epithelial and mesenchymal responses mediated by macrophages.

Acute injury in the airways or the lung activates local progenitors and stimulates changes in cell-cell interactions to restore homeostasis, but it is not appreciated how more distant niches are impacted. We utilized mouse models of airway-specific epithelial injury to examine secondary tissue-wide alveolar, immune, and mesenchymal responses. Single-cell transcriptomics and in vivo validation revealed transient, tissue-wide proliferation of alveolar type 2 (AT2) progenitor cells after club cell-specific ablation. The AT2 cell proliferative response was reliant on alveolar macrophages (AMs) via upregulation of Spp1 which encodes the secreted factor Osteopontin. A previously uncharacterized mesenchymal population we termed Mesenchymal Airway/Adventitial Niche Cell 2 (MANC2) also exhibited dynamic changes in abundance and a pro-fibrotic transcriptional signature after club cell ablation in an AM-dependent manner. Overall, these results demonstrate that acute airway damage can trigger distal lung responses including altered cell-cell interactions that may contribute to potential vulnerabilities for further dysregulation and disease.

Association between gut microbiota development and allergy in infants born during pandemic-related social distancing restrictions.

BACKGROUND: Several hypotheses link reduced microbial exposure to increased prevalence of allergies. Here we capitalize on the opportunity to study a cohort of infants (CORAL), raised during COVID-19 associated social distancing measures, to identify the environmental exposures and dietary factors that contribute to early life microbiota development and to examine their associations with allergic outcomes. METHODS: Fecal samples were sequenced from infants at 6 (n = 351) and repeated at 12 (n = 343) months, using 16S sequencing. Published 16S data from pre-pandemic cohorts were included for microbiota comparisons. Online questionnaires collected epidemiological information on home environment, healthcare utilization, infant health, allergic diseases, and diet. Skin prick testing (SPT) was performed at 12 (n = 343) and 24 (n = 320) months of age, accompanied by atopic dermatitis and food allergy assessments. RESULTS: The relative abundance of bifidobacteria was higher, while environmentally transmitted bacteria such as Clostridia was lower in CORAL infants compared to previous cohorts. The abundance of multiple Clostridia taxa correlated with a microbial exposure index. Plant based foods during weaning positively impacted microbiota development. Bifidobacteria levels at 6 months of age, and relative abundance of butyrate producers at 12 months of age, were negatively associated with AD and SPT positivity. The prevalence of allergen sensitization, food allergy, and AD did not increase over pre-pandemic levels. CONCLUSIONS: Environmental exposures and dietary components significantly impact microbiota community assembly. Our results also suggest that vertically transmitted bacteria and appropriate dietary supports may be more important than exposure to environmental microbes alone for protection against allergic diseases in infancy.

Macrophage phenotypes and functions: resolving inflammation and restoring homeostasis.

Inflammation must be tightly regulated to both defend against pathogens and restore tissue homeostasis. The resolution of inflammatory responses is a dynamic process orchestrated by cells of the immune system. Macrophages, tissue-resident innate immune cells, are key players in modulating inflammation. Here, we review recent work highlighting the importance of macrophages in tissue resolution and the return to homeostasis. We propose that enhancing macrophage pro-resolution functions represents a novel and widely applicable therapeutic strategy to dampen inflammation, promote repair, and restore tissue integrity and function.

Atopic outcomes at 2 years in the CORAL cohort, born in COVID-19 lockdown.

INTRODUCTION: The CORAL study is a cohort of infants born during the first weeks of the first SARS-CoV-2 (COVID-19) lockdown. This cohort has had lower antibiotic exposure, higher breastfeeding rates and lower infection rates, especially in the first year of life. We hypothesized that the altered early-life environment of infants born during lockdown would change the incidence of allergic conditions. METHODS: This longitudinal, observational study followed 365 infants born between March and May 2020 from enrolment to the age of 2 years. Infants attended three research appointments at 6-, 12-, and 24-months and completed detailed questionnaires. At research appointments, children had skin prick testing, and atopic dermatitis (AD) assessment. Statistical analysis focused on changes within the group at different time points, the influence of specific environmental factors on allergic risk and compared the incidence of atopic conditions with a pre-pandemic Irish infant cohort, BASELINE. RESULTS: AD was more common in CORAL group at both 12 (26.5% vs. 15.5%; p < .001) and 24 months (21.3% vs. 15.9%; p = .02) compared with pre-pandemic BASELINE cohort. Within the CORAL group, those with AD at both 12- and 24-month appointments had a more severe AD phenotype associated with a higher risk of allergic sensitization. There was less milk (0% vs. 1%; p = .09), peanut (0.6% vs. 1.8%; p = .3), and egg allergy (0% vs. 2.9%; p < .001) in the CORAL group at 24 months compared with the BASELINE cohort. Aeroallergen sensitization increased between 12 and 24 months in the CORAL cohort (1.5% vs. 8.9%; p < .001), as did parent-reported wheezing episodes (9% vs. 24%; p < .001). CONCLUSIONS: Despite higher AD incidence in the CORAL cohort, the incidence of food sensitization and allergy are lower than expected pre-pandemic rates possibly reflecting the early introduction and maintenance of dietary allergens enhanced by changes in infant infections, antibiotic use, and breastfeeding in the first 2 years of life in the group. These beneficial effects of the lockdown could be outweighing the expected risk of less early-life microbial encounters outlined by the hygiene hypothesis.

Developmental and behavioural outcomes at 2 years in babies born during the COVID-19 pandemic: communication concerns in a pandemic birth cohort.

INTRODUCTION: The CORAL (Impact of Corona Virus Pandemic on Allergic and Autoimmune Dysregulation in Infants Born During Lockdown) study reported a reduction in social communication milestones in 12-month-old infants born into the COVID-19 pandemic. AIMS: To look at 24-month developmental and behavioural outcomes in the CORAL cohort. DESIGN: The CORAL study is a longitudinal prospective observational study of Irish infants born in the first 3 months of the pandemic. At 24 months of age, the Ages and Stages Developmental Questionnaire (ASQ24) and the Child Behaviour Checklist (CBCL) were completed and compared with prepandemic BASELINE (Babies After SCOPE: Evaluating the Longitudinal Impact Using Neurological and Nutritional Impact) cohort. RESULTS: 917 babies (312 CORAL infants and 605 BASELINE infants) were included. At 24 months of age, infants in the CORAL and BASELINE cohorts had similar developmental ASQ24 scores in fine motor, problem solving and personal and social domains but ASQ24 communication scores were significantly lower in the CORAL group compared with the BASELINE cohort (mean (SD) 49.5 (15.1) vs 53.7 (11.6), p<0.01). Infants from the CORAL cohort were more likely to score below standardised cut-offs for developmental concern in the communication domain (11.9% CORAL compared with 5.4% BASELINE, p<0.01). Unadjusted ASQ24 gross motor scores were lower for the pandemic cohort. Fewer CORAL infants fell under 2 SD cut-off in personal-social subdomain. For CBCL, there was no evidence of difference in scores between the cohorts on multivariable analysis. CONCLUSION: 24-month-old pandemic-born infants had largely similar developmental and behavioural scores compared with their prepandemic counterparts. Concerns have been raised in the communication developmental domain.

Social communication skill attainment in babies born during the COVID-19 pandemic: a birth cohort study.

INTRODUCTION: The SARS-CoV-2 (COVID-19) pandemic was managed with sustained mass lockdowns to prevent spread of COVID-19 infection. Babies born during the early stages of the pandemic missed the opportunity of meeting a normal social circle of people outside the family home. METHODS: We compared 10 parentally reported developmental milestones at 12-month assessment in a cohort of 309 babies born at the onset of the pandemic (CORAL cohort) and 1629 babies from a historical birth cohort (BASELINE cohort recruited between 2008 and 2011). RESULTS: Compared with a historical cohort, babies born into lockdown appeared to have some deficits in social communication. Fewer infants in the pandemic cohort had one definite and meaningful word (76.6% vs 89.3%), could point (83.8% vs 92.8%) or wave bye-bye (87.7% vs 94.4%) at 12-month assessment. Adjusted log-binomial regression analyses demonstrated significant differences in social communication in the CORAL cohort compared with the BASELINE cohort: one definite and meaningful word (relative risk (RR): 0.86 (95% CI: 0.80 to 0.92)), pointing (RR: 0.91 (95% CI: 0.86 to 0.96)) and waving bye-bye (RR: 0.94 (95% CI: 0.90 to 0.99)). DISCUSSION: Parentally reported developmental outcomes in a birth cohort of babies born into lockdown during the COVID-19 pandemic may indicate some potential deficits in early life social communication. It must be noted that milestones are parentally reported and comparison is with a historical cohort with associated limitations. Further studies with standardised testing is required to validate these findings. CONCLUSION: Pandemic-associated social isolation may have impacted on the social communication skills in babies born during the pandemic compared with a historical cohort. Babies are resilient and inquisitive by nature, and it is hoped that with societal re-emergence and increase in social circles, their social communication skills will improve.

Macrophages control pathological interferon responses during viral respiratory infection.

Antiviral immune mediators, including interferons and their downstream effectors, are critical for host defense yet can become detrimental when uncontrolled. Here, we identify a macrophage-mediated anti-inflammatory mechanism that limits type I interferon (IFN-I) responses. Specifically, we found that cellular stress and pathogen recognition induce Oncostatin M (OSM) production by macrophages. OSM-deficient mice succumbed to challenge with influenza or a viral mimic due to heightened IFN-I activation. Macrophage-derived OSM restricted excessive IFN-I production by lung epithelial cells following viral stimulation. Furthermore, reconstitution of OSM in the respiratory tract was sufficient to protect mice lacking macrophage-derived OSM against morbidity, indicating the importance of local OSM production. This work reveals a host strategy to dampen inflammation in the lung through the negative regulation of IFN-I by macrophages.

Tumor-associated macrophages expressing the transcription factor IRF8 promote T cell exhaustion in cancer.

Tumors are populated by antigen-presenting cells (APCs) including macrophage subsets with distinct origins and functions. Here, we examined how cancer impacts mononuclear phagocytic APCs in a murine model of breast cancer. Tumors induced the expansion of monocyte-derived tumor-associated macrophages (TAMs) and the activation of type 1 dendritic cells (DC1s), both of which expressed and required the transcription factor interferon regulatory factor-8 (IRF8). Although DC1s mediated cytotoxic T lymphocyte (CTL) priming in tumor-draining lymph nodes, TAMs promoted CTL exhaustion in the tumor, and IRF8 was required for TAMs' ability to present cancer cell antigens. TAM-specific IRF8 deletion prevented exhaustion of cancer-cell-reactive CTLs and suppressed tumor growth. Tumors from patients with immune-infiltrated renal cell carcinoma had abundant TAMs that expressed IRF8 and were enriched for an IRF8 gene expression signature. Furthermore, the TAM-IRF8 signature co-segregated with CTL exhaustion signatures across multiple cancer types. Thus, CTL exhaustion is promoted by TAMs via IRF8.

Parenting a newborn baby during the COVID-19 pandemic: a qualitative survey.

OBJECTIVE: The COVID-19 pandemic caused long periods of lockdown, social isolation and intense challenges for parents. This study examines parenting in an infant cohort born at the pandemic onset. METHODS: The CORAL study is a prospective longitudinal observational study looking at allergy, immune function and neurodevelopmental outcome in babies born between March and May 2020. Demographic information was collected, babies were reviewed at 6-monthly intervals, and serology for COVID-19 infection was recorded. When babies were 12 months old, parents were asked for 3-5 words to describe raising a baby during the pandemic. Frequency of word usage was compared between first time parents and parents with other children, and parents of babies with and without a diagnosis of COVID-19 infection. RESULTS: 354 babies were recruited to CORAL study. Social circles were small. At 6 months the median number of people (including parents) who had kissed the baby was 3, and by 12 months one-quarter of babies had never met another child of similar age. 304 parents completed the word choice. Commonly reported words were lonely (44.4%), isolating (31.9%) and strong bond (15.8%). 12 of those 304 babies had COVID-19 in their first year of life and there was no significant difference in reported negative or positive word number compared with parents of babies without a COVID-19 infection, or by first time parents or those who already had children. CONCLUSION: The lockdowns and social restrictions made raising an infant challenging for all parents in Ireland. It is important parents know this was a shared experience.

Microenvironmental sensing by fibroblasts controls macrophage population size.

Animal tissues comprise diverse cell types. However, the mechanisms controlling the number of each cell type within tissue compartments remain poorly understood. Here, we report that different cell types utilize distinct strategies to control population numbers. Proliferation of fibroblasts, stromal cells important for tissue integrity, is limited by space availability. In contrast, proliferation of macrophages, innate immune cells involved in defense, repair, and homeostasis, is constrained by growth factor availability. Examination of density-dependent gene expression in fibroblasts revealed that Hippo and TGF-ß target genes are both regulated by cell density. We found YAP1, the transcriptional coactivator of the Hippo signaling pathway, directly regulates expression of Csf1, the lineage-specific growth factor for macrophages, through an enhancer of Csf1 that is specifically active in fibroblasts. Activation of YAP1 in fibroblasts elevates Csf1 expression and is sufficient to increase the number of macrophages at steady state. Our data also suggest that expression programs in fibroblasts that change with density may result from sensing of mechanical force through actin-dependent mechanisms. Altogether, we demonstrate that two different modes of population control are connected and coordinated to regulate cell numbers of distinct cell types. Sensing of the tissue environment may serve as a general strategy to control tissue composition.

IL-34 and protein-tyrosine phosphatase receptor type-zeta-dependent mechanisms limit arthritis in mice.

Myeloid cell mediated mechanisms regulate synovial joint inflammation. IL-34, a macrophage (Mø) growth and differentiation molecule, is markedly expressed in neutrophil and Mø-rich arthritic synovium. IL-34 engages a newly identified independent receptor, protein-tyrosine phosphatase, receptor-type, zeta (PTPRZ), that we find is expressed by Mø. As IL-34 is prominent in rheumatoid arthritis, we probed for the IL-34 and PTPRZ-dependent myeloid cell mediated mechanisms central to arthritis using genetic deficient mice in K/BxN serum-transfer arthritis. Unanticipatedly, we now report that IL-34 and PTPRZ limited arthritis as intra-synovial pathology and bone erosion were more severe in IL-34 and PTPRZ KO mice during induced arthritis. We found that IL-34 and PTPRZ: (i) were elevated, bind, and induce downstream signaling within the synovium in arthritic mice and (ii) were upregulated in the serum and track with disease activity in rheumatoid arthritis patients. Mechanistically, IL-34 and PTPRZ skewed Mø toward a reparative phenotype, and enhanced Mø clearance of apoptotic neutrophils, thereby decreasing neutrophil recruitment and intra-synovial neutrophil extracellular traps. With fewer neutrophils and neutrophil extracellular traps in the synovium, destructive inflammation was restricted, and joint pathology and bone erosion diminished. These novel findings suggest that IL-34 and PTPRZ-dependent mechanisms in the inflamed synovium limit, rather than promote, inflammatory arthritis.

Mass food challenges in a vacant COVID-19 stepdown facility: Exceptional opportunity provides a model for the future.

BACKGROUND: Internationally, the COVID-19 pandemic severely curtailed access to hospital facilities for those awaiting elective/semi-elective procedures. For allergic children in Ireland, already waiting up to 4 years for an elective oral food challenge (OFC), the restrictions signified indefinite delay. At the time of the initiative, there were approx 900 children on the Children's Health Ireland (CHI) waiting list. In July 2020, a project was facilitated by short-term (6 weeks) access to an empty COVID stepdown facility built, in a hotel conference centre, commandeered by the Health Service Executive (HSE), Ireland. The aim of this study was to achieve the rapid roll-out of an offsite OFC service, delivering high throughput of long waiting patients, while aligning with existing hospital policies and quality standards, international allergy guidelines and national social distancing standards. METHODS: The working group engaged key stakeholders to rapidly develop an offsite OFC facility. Consultant paediatric allergists, consultant paediatricians, trainees and allergy clinical nurse specialists were seconded from other duties. The facility was already equipped with hospital beds, bedside monitors (BP, pulse and oxygen saturation) and bedside oxygen. All medication and supplies had to be brought from the base hospital. Daily onsite consultant anaesthetic cover was resourced and a resuscitation room equipped. Standardized food challenge protocols were created. Access to the onsite hotel chef facilitated food preparation. A risk register was established. RESULTS: After 6 weeks of planning, the remote centre became operational on 7/9/2020, with the capacity of 27 OFC/day. 474 challenges were commenced: 465 (98%) were completed and 9 (2%) were inconclusive. 135 (29%) OFCs were positive, with 25 (5%) causing anaphylaxis. No child required advanced airway intervention. 8 children were transferred to the base hospital. The CHI allergy waiting list was reduced by almost 60% in only 24 days. CONCLUSIONS: Oral food challenges remain a vital tool in the care of allergic children, with their cost saving and quality-of-life benefits negatively affected by a delay in their delivery. This project has shown it is possible to have huge impacts on a waiting list efficiently, effectively and safely with good planning and staff buy-in-even in a pandemic. Adoption of new, flexible and efficient models of service delivery will be important for healthcare delivery in the post-COVID-19 era.

Fibroblasts and macrophages: Collaborators in tissue homeostasis.

Fibroblasts and macrophages are universal cell types across all mammalian tissues. These cells differ in many ways including their cellular origins; dynamics of renewal, recruitment, and motility within tissues; roles in tissue structure and secretion of signaling molecules; and contributions to the activation and progression of immune responses. However, many of the features that make these two cell types unique are not opposing, but instead complementary. This review will present cell-cell communication in this context and discuss how complementarity makes fibroblasts and macrophages highly compatible partners in the maintenance of tissue homeostasis.

Tissue Homeostasis and Inflammation.

There is a growing interest in understanding tissue organization, homeostasis, and inflammation. However, despite an abundance of data, the organizing principles of tissue biology remain poorly defined. Here, we present a perspective on tissue organization based on the relationships between cell types and the functions that they perform. We provide a formal definition of tissue homeostasis as a collection of circuits that regulate specific variables within the tissue environment, and we describe how the functional organization of tissues allows for the maintenance of both tissue and systemic homeostasis. This leads to a natural definition of inflammation as a response to deviations from homeostasis that cannot be reversed by homeostatic mechanisms alone. We describe how inflammatory signals act on the same cellular functions involved in normal tissue organization and homeostasis in order to coordinate emergency responses to perturbations and ultimately return the system to a homeostatic state. Finally, we consider the hierarchy of homeostatic and inflammatory circuits and the implications for the development of inflammatory diseases.

Untangling iNKT Cell Function in Adipose Tissue Homeostasis.

iNKT cells are important regulatory cells in metabolic health and disease. In this issue of Cell Metabolism, LaMarche et al. (2020) clarify the origin and heterogeneity of these unconventional T cells and identify the specific signals in adipose tissues that direct their function.