Guards at the gate: physiological and pathological roles of tissue-resident innate lymphoid cells in the lung

Prediction of mortality risk in patients with severe community-acquired pneumonia in the intensive care unit using machine learning

The aim of this study was to develop and validate a machine learning-based mortality risk prediction model for patients with severe community-acquired pneumonia (SCAP) in the intensive care unit (ICU). We collected data from two centers as the development and external validation cohorts. Variables were screened using the Recursive Feature Elimination method. Five machine learning algorithms were used to build predictive models. Models were evaluated through nested cross-validation to select the best one. The model was interpreted using Shapley Additive Explanations. We selected the optimal model to generate the web calculator. A total of 23 predictive features were selected. The Light Gradient Boosting Machine (LightGBM) model had an area under the receiver operating characteristic curve (AUC) of 0.842 (95% CI: 0.757-0.927), with an external 5-fold cross-validation average AUC of 0.842 ± 0.038, which was superior to the other models. External validation results also demonstrated good performance by the LightGBM model with an AUC of 0.856 (95% CI: 0.792-0.921). Based on this, we generated a web calculator by combining five high importance predictive factors. The LightGBM model was confirmed to be efficient and stable in predicting the mortality risk of patients with SCAP admitted to the ICU. The web calculator based on the LightGBM model can provide clinicians with a prognostic evaluation tool.

Lung Immune Cell Niches and the Discovery of New Cell Subtypes

Immune cells in the lungs are important for maintaining lung function. The importance of immune cells in defending against lung diseases and infections is increasingly recognized. However, a primary knowledge gaps in current studies of lung immune cells is the understanding of their subtypes and functional heterogeneity. Increasing evidence supports the existence of novel immune cell subtypes that engage in the complex crosstalk between lung-resident immune cells, recruited immune cells, and epithelial cells. Therefore, further studies on how immune cells respond to perturbations in the pulmonary microenvironment are warranted. This review explores the processes behind the formation of the immune cell niche during lung development, and the characteristics and cell interaction modes of several major lung-resident immune cells. It indicates that distinct lung microenvironments or inflammatory niches can mediate the formation of different cell subtypes. These findings summarize and clarify paths to identify new cell subtypes that originate from resident progenitor cells and recruited peripheral cells, which are remodeled by the pulmonary microenvironment. The development of new techniques combining transcriptome analysis and location information is essential for identifying new immune cell subtypes and their relative immune niches, as well as for uncovering the molecular mechanisms of immune cell-mediated lung homeostasis.

Bimin Kang ameliorates the minimal persistent inflammation in allergic rhinitis by reducing BCL11B expression and regulating ILC2 plasticity

ETHNOPHARMACOLOGICAL RELEVANCE

Minimal persistent inflammation (MPI) is a major contributor to the recurrence of allergic rhinitis (AR). The traditional Chinese herbal medicine known as Bimin Kang Mixture (BMK) have been used in clinics for decades to treat AR, which can relieve AR symptoms, reduce inflammatory response and improve immune function. However, its mechanism in controlling MPI is still unclear.

AIM OF THE STUDY

This study aims to assess the therapeutic effect of BMK on MPI, and elaborate the mechanism involved in BMK intervention in BCL11B regulation of type 2 innate lymphoid cell (ILC2) plasticity in the treatment of MPI.

MATERIAL AND METHODS

The effect of BMK (9.1 ml/kg) and Loratadine (15.15 mg/kg) on MPI was evaluated based on symptoms, pathological staining, and ELISA assays. RT-qPCR and flow cytometry were also employed to assess the expression of BCL11B, IL-12/IL-12Rβ2, and IL-18/IL-18Rα signaling pathways associated with ILC2 plasticity in the airway tissues of MPI mice following BMK intervention.

RESULTS

BMK restored the airway epithelial barrier, and markedly reduced inflammatory cells (eosinophils, neutrophils) infiltration (P < 0.01) and goblet cells hyperplasia (P < 0.05). BCL11B expression positively correlated with the ILC2 proportion in the lungs and nasal mucosa of AR and MPI mice (P < 0.01). BMK downregulated BCL11B expression (P < 0.05) and reduced the proportion of ILC2, ILC3 and ILC3-like ILC2 subsets (P < 0.05). Moreover, BMK promoted the conversion of ILC2 into an ILC1-like phenotype through IL-12/IL-12Rβ2 and IL-18/IL-18Rα signaling pathways in MPI mice.

CONCLUSION

By downregulating BCL11B expression, BMK regulates ILC2 plasticity and decreases the proportion of ILC2, ILC3, and ILC3-like ILC2 subsets, promoting the conversion of ILC2 to ILC1, thus restoring balance of ILC subsets in airway tissues and control MPI.

The IL-25/ILC2 axis promotes lung cancer with a concomitant accumulation of immune-suppressive cells in tumors in humans and mice

Background

Group 2 innate lymphoid cells (ILC2) can be activated by interleukin (IL)-33 or IL-25. IL-25-activated ILC2 cells help protect the host against helminth infection while exacerbating allergic-like inflammation and tissue damage in the lung. In the context of cancer, IL-33-activated ILC2 cells were found to bear anti-tumoral functions in lung cancer while IL-25-activated ILC2 cells promoted tumorigenesis in colorectal cancer. The role of IL-25-activated ILC2 cells in lung cancer remains to be addressed.

Methods

We examined the overall survival of human non-small cell lung cancer (NSCLC) patients according to IL25 expression as well as the distribution of ILC2 cells and regulatory T cells (Tregs) in various NSCLC patient tissues and peripheral blood (PB) of healthy donors (HDs). We analyzed the effect of adoptive transfer of IL-25-activated ILC2 cells on tumor growth, metastasis and survival in a heterotopic murine model of lung cancer.

Results

We report that human NSCLC patients with high IL-25 expression have reduced overall survival. Moreover, NSCLC patients bear increased frequencies of ILC2s compared to HDs. Frequencies of Tregs were also increased in NSCLC patients, concomitantly with ILC2s. In mice bearing heterotopic lung cancer, adoptive transfer of IL-25-activated ILC2s led to increased tumor growth, increased metastasis and reduced survival. The frequencies of monocytic myeloid-derived suppressor cells (M-MDSCs) were found to be increased in the tumors of mice that received ILC2s as compared to controls.

Conclusion

Overall, our results indicate that the IL-25/ILC2 axis promotes lung cancer potentially by recruiting immune-suppressive cells to the tumors both in humans and in mice, and that it may therefore represent a suitable novel target for NSCLC immunotherapeutic development.

Intragraft immune cells: accomplices or antagonists of recipient-derived macrophages in allograft fibrosis?

Organ fibrosis caused by chronic allograft rejection is a major concern in the field of transplantation. Macrophage-to-myofibroblast transition plays a critical role in chronic allograft fibrosis. Adaptive immune cells (such as B and CD4⁺ T cells) and innate immune cells (such as neutrophils and innate lymphoid cells) participate in the occurrence of recipient-derived macrophages transformed to myofibroblasts by secreting cytokines, which eventually leads to fibrosis of the transplanted organ. This review provides an update on the latest progress in understanding the plasticity of recipient-derived macrophages in chronic allograft rejection. We discuss here the immune mechanisms of allograft fibrosis and review the reaction of immune cells in allograft. The interactions between immune cells and the process of myofibroblast formulation are being considered for the potential therapeutic targets of chronic allograft fibrosis. Therefore, research on this topic seems to provide novel clues for developing strategies for preventing and treating allograft fibrosis.

ILC3-like ILC2 subset increases in minimal persistent inflammation after acute type II inflammation of allergic rhinitis and inhibited by Biminkang: Plasticity of ILC2 in minimal persistent inflammation

Minimal persistent inflammation (MPI), the local inflammation that occurs after an acute type II immune response in patients with allergic rhinitis (AR), is responsible for airway hyperreactivity and the recurrence of AR. Innate lymphoid cells (ILCs) play a crucial role in mucosal immune homeostasis, but the changes of ILC subsets in the MPI stage remain unclear. In this study, the levels of ILC-secreting cytokines in nasal lavages were analyzed from 19 AR patients and 8 healthy volunteers. AR and MPI model mice were established to study the ILC subsets. The results showed that IL-17A was significantly increased in nasal lavage of AR patients in the MPI stage by MSD technology. When compared with the AR model mice, the frequency of IL-13⁺ ILC2 in the nasal mucosa and lungs decreased, while IL-5⁺ ILC2 remain high in MPI model mice. A part of the IL-5⁺ ILC2 subset displayed ILC3-like characteristics with elevated RORγt, IL-17A and IL-23R expression. Especially, these ILC3-like ILC2 exhibited up-regulation of GATA3⁺ RORγt⁺ were increased in MPI model mice. After the treatment of Biminkang, the frequencies of IL-5⁺ ILC2, IL-17A⁺ ILC3, and GATA3⁺ RORγt⁺ ILC3-like ILC2 were significantly reduced, and IL-23R expression was also decreased on ILC3-like-ILC2 subset. These results suggested that the elevated IL-17A in the MPI stage has been related to or at least partly due to the increased of ILC3-like ILC2. Biminkang could effectively decrease IL-17A⁺ ILC3 and inhibit ILC3-like ILC2 subset in the MPI stage. Biminkang is effective in administrating MPI by regulating airway ILC homeostasis.

RNA Modification in Inflammatory Bowel Diseases

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder characterized by damage to the intestinal mucosa, which is caused by a combination of factors. These include genetic and epigenetic alterations, environmental influence, microorganism interactions, and immune conditions. Some populations with IBD show a cancer-prone phenotype. Recent studies have provided insight into the involvement of RNA modifications in the specific pathogenesis of IBD through regulation of RNA biology in epithelial and immune cells. Studies of several RNA modification-targeting reagents have shown preferable outcomes in patients with colitis. Here, we note a new awareness of RNA modification in the targeting of IBD and related diseases, which will contribute to early diagnosis, disease monitoring, and possible control by innovative therapeutic approaches.

Respiratory Influenza Virus Infection Causes Dynamic Tuft Cell and Innate Lymphoid Cell Changes in the Small Intestine

Influenza A viruses (IAV) can cause severe disease and death in humans. IAV infection and the accompanying immune response can result in systemic inflammation, leading to intestinal damage and disruption of the intestinal microbiome. Here, we demonstrate that a specific subset of epithelial cells, tuft cells, increase across the small intestine during active respiratory IAV infection. Upon viral clearance, tuft cell numbers return to baseline levels. Intestinal tuft cell increases were not protective against disease, as animals with either increased tuft cells or a lack of tuft cells did not have any change in disease morbidity after infection. Respiratory IAV infection also caused transient increases in type 1 and 2 innate lymphoid cells (ILC1 and ILC2, respectively) in the small intestine. ILC2 increases were significantly blunted in the absence of tuft cells, whereas ILC1s were unaffected. Unlike the intestines, ILCs in the lungs were not altered in the absence of tuft cells. This work establishes that respiratory IAV infection causes dynamic changes to tuft cells and ILCs in the small intestines and that tuft cells are necessary for the infection-induced increase in small intestine ILC2s. These intestinal changes in tuft cell and ILC populations may represent unexplored mechanisms preventing systemic infection and/or contributing to severe disease in humans with preexisting conditions. IMPORTANCE Influenza A virus (IAV) is a respiratory infection in humans that can lead to a wide range of symptoms and disease severity. Respiratory infection can cause systemic inflammation and damage in the intestines. Few studies have explored how inflammation alters the intestinal environment. We found that active infection caused an increase in the epithelial population called tuft cells as well as type 1 and 2 innate lymphoid cells (ILCs) in the small intestine. In the absence of tuft cells, this increase in type 2 ILCs was seriously blunted, whereas type 1 ILCs still increased. These findings indicate that tuft cells are necessary for infection-induced changes in small intestine type 2 ILCs and implicate tuft cells as regulators of the intestinal environment in response to systemic inflammation.

Non-atopic Neonatal Thymic Innate Lymphoid Cell Subsets (ILC1, ILC2, and ILC3) Identification and the Modulatory Effect of IgG From Dermatophagoides Pteronyssinus (Derp)-Atopic Individuals

Innate lymphoid cells (ILCs) are classified into distinct subsets termed ILC1, ILC2, and ILC3 cells. The existing literature lacks evidence identifying ILCs and their subsets in the human thymus but already demonstrates that they can exert several functions in regulating immune responses. Furthermore, it was already described that IgG's repertoires could modulate lymphocytes' maturation in the human thymus. Here we aimed to identify ILCs subsets in the human thymus and provide insight into the possible modulatory effect of purified IgG on these cells. Thymic tissues were obtained from 12 infants without an allergic background (non-atopic), and a literature-based peripheral ILCs staining protocol was used. Purified IgG was obtained from non-atopic individuals (n-At), atopic individuals reactive to allergens non-related to dust mites (nr-At), and atopic individuals reactive to the mite Dermatophagoides pteronyssinus (Derp-At). As with all tissues in which they have already been detected, thymic ILCs are rare, but we could detect viable ILCs in all tested tissues, which did not occur with the ILC1 subset. ILC2 and ILC3 NKp44+ subsets could be detected in all evaluated thymus, but ILC3 NKp44- subset could not. Next, we observed that Derp-At IgG could induce the expression of ILC2 phenotype, higher levels of IL-13, and lower levels of IL-4 when compared to IgG purified from non-atopic or non-related atopic (atopic to allergens excluding dust mites) individuals. These results contribute to the elucidation of human thymic ILCs and corroborate emerging evidence about IgG's premature effect on allergy development-related human lymphocytes' modulation.

Protective effects of neuropeptide Y against elastase-induced pulmonary emphysema

Neuropeptide Y (NPY) is a neuropeptide widely expressed in not only the central nervous system but also immune cells and the respiratory epithelium. Patients with chronic obstructive pulmonary disease (COPD) reportedly exhibit decreased NPY expression in the airway epithelium, but the involvement of NPY in the pathophysiology of COPD has not been defined. We investigated the role of NPY in elastase-induced emphysema. NPY-deficient (NPY^-/-) mice and wild-type (NPY^+/+) mice received intratracheal instillation of porcine pancreas elastase (PPE). The numbers of inflammatory cells and the levels of cytokines and chemokines in the bronchoalveolar lavage (BAL) fluid and lung homogenates were determined along with quantitative morphometry of lung sections. Intratracheal instillation of PPE induced emphysematous changes and increased NPY levels in the lungs. Compared with NPY^+/+ mice, NPY^-/- mice had significantly enhanced PPE-induced emphysematous changes and alveolar enlargement. Neutrophilia seen in BAL flu12id of NPY^+/+ mice on day 4 after PPE instillation was also enhanced in NPY^-/- mice, and the enhancement was associated with increased levels of neutrophil-related and macrophage-related chemokines and IL-17A as well as increased numbers of type 3 innate lymphoid cells in the airways. Treatment with NPY significantly reduced PPE-induced emphysematous changes. Conversely, treatment with a NPY receptor antagonist exacerbated PPE-induced emphysematous changes. These observations indicate that NPY has protective effects against elastase-induced emphysema, and suggest that targeting NPY in emphysema has potential as a therapeutic strategy for delaying disease progression.

Pulmonary Guardians and Special Regulatory Devices in the Lung of Nile Monitor Lizard (Varanus niloticus) with Special Attention to the Communication Between Telocyte, Pericyte, and Immune Cells

Monitor lizards are acclimatized to a variety of environments. Most of the monitor species are terrestrial, although there are arboreal and semiaquatic monitors. Such accommodation requires unique cellular structure and regulatory devices in various organs, particularly their lungs. This study aimed to report the pulmonary guardians and special regulatory devices that may guard and promote the function of the lungs of the Nile monitor lizards (Varanus niloticus). Specially structured vessels were recorded in the pulmonary tissue involving atypical glomus vessels, vessels with variable wall thickness, and a venule with specialized internal elastic membrane. Moreover, numerous lung resident guardians could be identified including both alveolar and interstitial macrophages, dendritic cells, mast cells, and B- and T-lymphocytes. Pericytes were demonstrated surrounding the capillary endothelium with a characteristic direct hetero-cellular junction with telocytes. Telocytes established a microenvironment through an indirect hetero-cellular junction with the interstitial macrophage, dendritic cells, and pneumocyte type II. Collectively, these data indicate a significant role played by the specially structured vessels and the resident immune cells in guarding the pulmonary tissue of the Nile monitor lizards and promoting its function. Telocytes are suggested to play a key role in angiogenesis and cellular communication to promote the function of the immune cells.

PPARɣ drives IL-33-dependent ILC2 pro-tumoral functions

Group 2 innate lymphoid cells (ILC2s) play a critical role in protection against helminths and in diverse inflammatory diseases by responding to soluble factors such as the alarmin IL-33, that is often overexpressed in cancer. Nonetheless, regulatory factors that dictate ILC2 functions remain poorly studied. Here, we show that peroxisome proliferator-activated receptor gamma (PPARγ) is selectively expressed in ILC2s in humans and in mice, acting as a central functional regulator. Pharmacologic inhibition or genetic deletion of PPARγ in ILC2s significantly impair IL-33-induced Type-2 cytokine production and mitochondrial fitness. Further, PPARγ blockade in ILC2s disrupts their pro-tumoral effect induced by IL-33-secreting cancer cells. Lastly, genetic ablation of PPARγ in ILC2s significantly suppresses tumor growth in vivo. Our findings highlight a crucial role for PPARγ in supporting the IL-33 dependent pro-tumorigenic role of ILC2s and suggest that PPARγ can be considered as a druggable pathway in ILC2s to inhibit their effector functions. Hence, PPARγ targeting might be exploited in cancer immunotherapy and in other ILC2-driven mediated disorders, such as asthma and allergy.

Correlation Between Immune Lymphoid Cells and Plasmacytoid Dendritic Cells in Human Colon Cancer

Background

Innate lymphoid cells (ILCs), so far studied mostly in mouse models, are important tissue-resident innate immune cells that play important roles in the colorectal cancer microenvironment and maintain mucosal tissue homeostasis. Plasmacytoid dendritic cells (pDCs) present complexity in various tumor types and are correlated with poor prognosis. pDCs can promote HIV-1-induced group 3 ILC (ILC3) depletion through the CD95 pathway. However, the role of ILC3s in human colon cancer and their correlation with other immune cells, especially pDCs, remain unclear.

Methods

We characterized ILCs and pDCs in the tumor microenvironment of 58 colon cancer patients by flow cytometry and selected three patients for RNA sequencing.

Results

ILC3s were negatively correlated, and pDCs were positively correlated, with cancer pathological stage. There was a negative correlation between the numbers of ILC3s and pDCs in tumor tissues. RNA sequencing confirmed the correlations between ILC3s and pDCs and highlighted the potential function of many ILC- and pDC-associated differentially expressed genes in the regulation of tumor immunity. pDCs can induce apoptosis of ILC3s through the CD95 pathway in the tumor-like microenvironment.

Conclusions

One of the interactions between ILC3s and pDCs is via the CD95 pathway, which may help explain the role of ILC3s in colon cancer.

The Role of Innate Immunity in Pulmonary Infections

Innate immunity forms a protective line of defense in the early stages of pulmonary infection. The primary cellular players of the innate immunity against respiratory infections are alveolar macrophages (AMs), dendritic cells (DCs), neutrophils, natural killer (NK) cells, and innate lymphoid cells (ILCs). They recognize conserved structures of microorganisms through membrane-bound and intracellular receptors to initiate appropriate responses. In this review, we focus on the prominent roles of innate immune cells and summarize transmembrane and cytosolic pattern recognition receptor (PRR) signaling recognition mechanisms during pulmonary microbial infections. Understanding the mechanisms of PRR signal recognition during pulmonary pathogen infections will help us to understand pulmonary immunopathology and lay a foundation for the development of effective therapies to treat and/or prevent pulmonary infections.

Mucosal immunity and tRNA, tRF, and tiRNA

Mucosal immunity has crucial roles in human diseases such as respiratory tract infection, inflammatory bowel diseases (IBD), and colorectal cancer (CRC). Recent studies suggest that the mononuclear phagocyte system, cancer cells, bacteria, and viruses induce the mucosal immune reaction by various pathways, and can be major factors in the pathogenesis of these diseases. Transfer RNA (tRNA) and its fragments, including tRNA-derived RNA fragments (tRFs) and tRNA-derived stress-induced RNAs (tiRNAs), have emerged as a hot topic in recent years. They not only are verified as essential for transcription and translation but also play roles in cellular homeostasis and functions, such as cell metastasis, proliferation, and apoptosis. However, the specific relationship between their biological regulation and mucosal immunity remains unclear to date. In the present review, we carry out a comprehensive discussion on the specific roles of tRNA, tRFs, and tiRNAs relevant to mucosal immunity and related diseases.

Target the Host, Kill the Bug; Targeting Host Respiratory Immunosuppressive Responses as a Novel Strategy to Improve Bacterial Clearance During Lung Infection

The lung is under constant pressure to protect the body from invading bacteria. An effective inflammatory immune response must be tightly orchestrated to ensure complete clearance of any invading bacteria, while simultaneously ensuring that inflammation is kept under strict control to preserve lung viability. Chronic bacterial lung infections are seen as a major threat to human life with the treatment of these infections becoming more arduous as the prevalence of antibiotic resistance becomes increasingly commonplace. In order to survive within the lung bacteria target the host immune system to prevent eradication. Many bacteria directly target inflammatory cells and cytokines to impair inflammatory responses. However, bacteria also have the capacity to take advantage of and strongly promote anti-inflammatory immune responses in the host lung to inhibit local pro-inflammatory responses that are critical to bacterial elimination. Host cells such as T regulatory cells and myeloid-derived suppressor cells are often enhanced in number and activity during chronic pulmonary infection. By increasing suppressive cell populations and cytokines, bacteria promote a permissive environment suitable for their prolonged survival. This review will explore the anti-inflammatory aspects of the lung immune system that are targeted by bacteria and how bacterial-induced immunosuppression could be inhibited through the use of host-directed therapies to improve treatment options for chronic lung infections.

Critical Roles of Balanced Innate Lymphoid Cell Subsets in Intestinal Homeostasis, Chronic Inflammation, and Cancer

Innate lymphoid cells (ILCs) comprise a recently identified subset of innate immune cells that are mainly localized to mucosa-associated tissues. Although they have not yet been fully characterized, they can generally be divided into ILC1s, ILC2s, and ILC3s. ILCs and their corresponding cytokines act as important mediators of the early stages of the immune response during inflammation, tissue repair, and the maintenance of epithelial integrity. Consequently, the dysregulation of ILC subsets might promote inflammation and cancer. Numerous studies have demonstrated that these cells play an important role in maintaining the microecological balance of the small intestine; however, their specific roles in mediating inflammation in this tissue and tumorigenesis remain unclear and controversial. In this review, we focus on recent progress that has helped to gain a better understanding of the role of ILCs in intestinal homeostasis, chronic inflammation, and cancer. Further focused research on the regulation and role of ILCs in intestinal homeostasis and pathology will help to reveal valuable diagnostic and therapeutic targets for the treatment of intestinal diseases.

Innate Lymphoid Cells in Mucosal Immunity

Innate lymphoid cells (ILCs) are innate counterparts of T cells that contribute to immune responses by secreting effector cytokines and regulating the functions of other innate and adaptive immune cells. ILCs carry out some unique functions but share some tasks with T cells. ILCs are present in lymphoid and non-lymphoid organs and are particularly abundant at the mucosal barriers, where they are exposed to allergens, commensal microbes, and pathogens. The impact of ILCs in mucosal immune responses has been extensively investigated in the gastrointestinal and respiratory tracts, as well as in the oral cavity. Here we review the state-of-the-art knowledge of ILC functions in infections, allergy and autoimmune disorders of the mucosal barriers.

Isolation and Identification of Innate Lymphoid Cells (ILCs) for Immunotoxicity Testing

Innate lymphoid cells (ILCs) comprise a family of innate immune cells that orchestrate mucosal immune responses: initiating, sustaining, and even curbing immune responses. ILCs are relatively rare (≤1% of lymphocytes in mucosal tissues), lack classical cell-surface markers, and can be divided into three subsets (type 1-3 ILCs) based on differences in cytokine production, phenotype, and developmental pathway. Because ILCs can only be identified by combinations of cell-surface markers and cytokine production, multicolor flow cytometry is the most reliable method to purify, characterize, and assess the functionality of ILCs. Here, we describe the methods for cell preparation, flow cytometric analysis, and purification of murine ILCs from the lung.

Role of Mast Cells and Type 2 Innate Lymphoid (ILC2) Cells in Lung Transplantation

The multifunctional role of mast cells (MCs) in the immune system is complex and has not fully been explored. MCs reside in tissues and mucous membranes such as the lung, digestive tract, and skin which are strategically located at interfaces with the external environment. These cells, therefore, will encounter external stimuli and pathogens. MCs modulate both the innate and the adaptive immune response in inflammatory disorders including transplantation. MCs can have pro- and anti-inflammatory functions, thereby regulating the outcome of lung transplantation through secretion of mediators that allow interaction with other cell types, particularly innate lymphoid cells (ILC2). ILC2 cells are a unique population of hematopoietic cells that coordinate the innate immune response against a variety of threats including infection, tissue damage, and homeostatic disruption. In addition, MCs can modulate alloreactive T cell responses or assist in T regulatory (Treg) cell activity. This paper outlines the current understanding of the role of MCs in lung transplantation, with a specific focus on their interaction with ILC2 cells within the engrafted organ.

Re-thinking our understanding of immunity: Robustness in the tissue reconstruction system

Robustness, understood as the maintenance of specific functionalities of a given system against internal and external perturbations, is pervasive in today's biology. Yet precise applications of this notion to the immune system have been scarce. Here we show that the concept of robustness sheds light on tissue repair, and particularly on the crucial role the immune system plays in this process. We describe the specific mechanisms, including plasticity and redundancy, by which robustness is achieved in the tissue reconstruction system (TRS). In turn, tissue repair offers a very important test case for assessing the usefulness of the concept of robustness, and identifying different varieties of robustness.