Szun Szun Tay

Cutaneous immunosurveillance and regulation of inflammation by group 2 innate lymphoid cells

Type 2 immunity is critical for defense against cutaneous infections but also underlies the development of allergic skin diseases. We report the identification in normal mouse dermis of an abundant, phenotypically unique group 2 innate lymphoid cell (ILC2) subset that depended on interleukin 7 (IL-7) and constitutively produced IL-13. Intravital multiphoton microscopy showed that dermal ILC2 cells specifically interacted with mast cells, whose function was suppressed by IL-13. Treatment of mice deficient in recombination-activating gene 1 (Rag1−/−) with IL-2 resulted in the population expansion of activated, IL-5-producing dermal ILC2 cells, which led to spontaneous dermatitis characterized by eosinophil infiltrates and activated mast cells. Our data show that ILC2 cells have both pro- and anti-inflammatory properties and identify a previously unknown interactive pathway between two innate populations of cells of the immune system linked to type 2 immunity and allergic diseases.

Hepatocyte entry leads to degradation of autoreactive CD8 T cells

Although most self-reactive T cells are eliminated in the thymus, mechanisms to inactivate or control T cells specific for extrathymic antigens are required and exist in the periphery. By investigating the site in which autoreactive T cells are tolerized, we identify a unique mechanism of peripheral deletion in which naïve autoreactive CD8 T cells are rapidly eliminated in the liver after intrahepatic activation. T cells actively invade hepatocytes, enter endosomal/lysosomal compartments, and are degraded. Blockade of this process leads to accumulation of autoreactive CD8 T cells in the liver and breach of tolerance, with the development of autoimmune hepatitis. Cell into cell invasion, or emperipolesis, is a long-observed phenomenon for which a physiological role has not been previously demonstrated. We propose that this “suicidal emperipolesis” is a unique mechanism of autoreactive T-cell deletion, a process critical for the maintenance of tolerance.

The Skin-Resident Immune Network

The skin provides an effective physical and biological barrier against environmental and pathogenic insults whilst ensuring tolerance against commensal microbes. This protection is afforded by the unique anatomy and cellular composition of the skin, particularly the vast network of skin-associated immune cells. These include the long-appreciated tissue-resident macrophages, dendritic cells, and mast cells, as well as the more recently described dermal γδ T cells and innate lymphoid cells. Collectively, these cells orchestrate the defense against a wide range of pathogens and environmental challenges, but also perform a number of homeostatic functions. Here, we review recent developments in our understanding of the various roles that leukocyte subsets play in cutaneous immunobiology, and introduce the newer members of the skin immune system. Implications for human disease are discussed.

Role of IL-4 and Th2 responses in allograft rejection and tolerance.

Purpose of reviewDue to the dominance of Th1 cytokines in rejection and the ability of Th2 cytokines, particularly IL-4, to inhibit Th1 responses, it has long been held that Th2 cytokines can improve transplant outcomes. Although there is some support for this, there is mounting evidence that IL-4 and Th2 cytokines can promote graft dysfunction. These disparate effects are reviewed. Recent findingsThe role of Th2 cytokines in graft dysfunction is not necessarily due to promotion of humoral immunity, but is due to their ability to drive T-cell and non-T-cell responses including alternative activation of macrophages. Alternatively, activated macrophages compete with classically activated macrophages for arginine and they are mutually exclusive, analogous to mutual competition between Th1 and Th2 cells. Recent findings also point to two subsets of regulatory T cells (Tregs), each dependent on either Th1 or Th2 cytokines. In addition to its effects on bone marrow-derived cells, IL-4 affects parenchymal cells by signalling through the type II receptor, which consists of the IL-4R alpha chain (IL-4Rα) and the IL-13Rα1, which also binds IL-13. SummaryThe effects of Th2 cytokines in transplantation depend on their cellular targets, the timing and form of administration and on Th2 cytokine-dependent Tregs.

IL-2 is a critical regulator of group 2 innate lymphoid cell function during pulmonary inflammation

BACKGROUND Group 2 innate lymphoid cells (ILC2) have been implicated in the pathogenesis of allergic lung diseases. However, the upstream signals that regulate ILC2 function during pulmonary inflammation remain poorly understood. ILC2s have been shown to respond to exogenous IL-2, but the importance of endogenous IL-2 in ILC2 function in vivo remains unclear. OBJECTIVE We sought to understand the role of IL-2 in the regulation of ILC2 function in the lung. METHODS We used histology, flow cytometry, immunohistochemistry, ELISA, and quantitative PCR with knockout and reporter mice to dissect pulmonary ILC2 function in vivo. We examined the role of ILC2s in eosinophilic crystalline pneumonia, an idiopathic type 2 inflammatory lung condition of mice, and the effect of IL-2 deficiency on this disease. We determined the effect of IL-2 administration on pulmonary ILC2 numbers and function in mice in the steady state and after challenge with IL-33. RESULTS We discovered an unexpected role for innate cell-derived IL-2 as a major cofactor of ILC2 function during pulmonary inflammation. Specifically, we found that IL-2 was essential for the development of eosinophilic crystalline pneumonia, a type 2 disease characterized by increased numbers of activated ILC2s. We show that IL-2 signaling serves 2 distinct functions in lung ILC2s, namely promoting cell survival/proliferation and serving as a cofactor for the production of type 2 cytokines. We further demonstrate that group 3 innate lymphoid cells are an innate immune source of IL-2 in the lung. CONCLUSION Innate cell-derived IL-2 is a critical cofactor in regulating ILC2 function in pulmonary type 2 pathology.

Adeno-associated virus serotypes for gene therapeutics

Gene transfer vectors based on adeno-associated virus (AAV) are showing exciting therapeutic promise in early phase clinical trials. The ability to cross-package the prototypic AAV2 vector genome into different capsids is a powerful way of conferring novel tropism and biology, with evolving capsid engineering technologies and directed evolution approaches further enhancing the utility and flexibility of these vectors. Novel properties of specific capsids show unpredictable species and cell-type specificity. Therefore, full realisation of the therapeutic potential of AAV vectors requires the development of more therapeutically predictive preclinical methods for evaluating capsid performance. This will strongly complement an iterative approach to the evaluation of capsid variants in the clinic and, should wherever possible, include the determination of gene transfer efficiencies.

Antigen expression level threshold tunes the fate of CD8 T cells during primary hepatic immune responses

Significance The liver possesses unique immunological properties, with the capability of inducing tolerance upon transplantation, yet is also the target of immune-mediated damage in chronic viral hepatitis. To investigate the basis of these dichotomous outcomes, we manipulated several determinants capable of influencing outcomes of hepatic–immune interactions. Our findings reveal that a threshold of antigen expression within the liver is the dominant factor determining the fate of CD8 T cells recognizing intrahepatic antigen, irrespective of their affinity for antigen or the site of initial antigen encounter, with high-level antigen expression leading to exhaustion of T cell function. To our knowledge, for the first time, this study provides a unified model explaining the divergent consequences of hepatic–immune interactions. CD8 T-cell responses to liver-expressed antigens range from deletional tolerance to full effector differentiation resulting in overt hepatotoxicity. The reasons for these heterogeneous outcomes are not well understood. To identify factors that govern the fate of CD8 T cells activated by hepatocyte-expressed antigen, we exploited recombinant adenoassociated viral vectors that enabled us to vary potential parameters determining these outcomes in vivo. Our findings reveal a threshold of antigen expression within the liver as the dominant factor determining T-cell fate, irrespective of T-cell receptor affinity or antigen cross-presentation. Thus, when a low percentage of hepatocytes expressed cognate antigen, high-affinity T cells developed and maintained effector function, whereas, at a high percentage, they became functionally exhausted and silenced. Exhaustion was not irreversibly determined by initial activation, but was maintained by high intrahepatic antigen load during the early phase of the response; cytolytic function was restored when T cells primed under high antigen load conditions were transferred into an environment of low-level antigen expression. Our study reveals a hierarchy of factors dictating the fate of CD8 T cells during hepatic immune responses, and provides an explanation for the different immune outcomes observed in a variety of immune-mediated liver pathologic conditions.

miR‐181a mediates TGF‐β‐induced hepatocyte EMT and is dysregulated in cirrhosis and hepatocellular cancer

Epithelial–mesenchymal transition (EMT) has been implicated in the processes of embryogenesis, tissue fibrosis and carcinogenesis. Transforming growth factor‐β (TGF‐β) has been identified as a key driver of EMT and plays a key role in the pathogenesis of cirrhosis and hepatocellular carcinoma (HCC). The aim was to identify microRNA (miR) expression in TGF‐β‐induced hepatocyte EMT.

The Skin Immune Atlas: Three-Dimensional Analysis of Cutaneous Leukocyte Subsets by Multiphoton Microscopy

Site-specific differences in skin response to pathogens and in the course of cutaneous inflammatory diseases are well appreciated. The composition and localization of cutaneous leukocytes has been studied extensively using histology and flow cytometry. However, the precise three-dimensional (3D) distribution of distinct immune cell subsets within skin at different body sites requires visualization of intact living skin. We used intravital multiphoton microscopy in transgenic reporter mice in combination with quantitative flow cytometry to generate a 3D immune cell atlas of mouse skin. The 3D location of innate and adaptive immune cells and site-specific differences in the densities of macrophages, T cells and mast cells at four defined sites (ear, back, footpad, tail) is presented. The combinatorial approach further demonstrates an as yet unreported age-dependent expansion of dermal gamma-delta T cells. Localization of dermal immune cells relative to anatomical structures was also determined. While dendritic cells were dispersed homogeneously within the dermis, mast cells preferentially localized to the perivascular space. Finally, we show the functional relevance of site-specific mast cell disparities using the passive cutaneous anaphylaxis model. These approaches are applicable to assessing immune cell variations and potential functional consequences in the setting of infection as well as the pathogenesis of inflammatory skin conditions.

Two lymph nodes draining the mouse liver are the preferential site of DC migration and T cell activation.

BACKGROUND & AIMS Lymph nodes (LNs) play a critical role in host defence against pathogens. In rodents, lymphatic anatomy and drainage have been characterized for many different organs. Surprisingly, the LNs draining the mouse liver have not been clearly identified. This knowledge is of central importance to allow accurate characterization of immune responses to pathogens infecting the liver. It is also important for exploring immune responses in hepatic tumour models, and mechanisms underlying the relative tolerogenic properties of the liver. In this study, we used both anatomical and immunological approaches to identify the LN(s) draining the mouse liver. METHODS Evans Blue and purified dendritic cells were directly injected into the hepatic parenchyma. RESULTS Using Evans Blue, we identified three LNs adjacent to the liver that stained with the dye within the first 5 min, which we termed portal, coeliac, and first mesenteric LNs. We also provide evidence that dendritic cells (DCs) injected under the liver capsule preferentially migrate to the coeliac and portal nodes, leading to local activation of antigen-specific naïve CD8 and CD4 T cells, suggesting this is a route of lymphatic drainage from the liver. Consistent with this result, cell-associated antigen injected under the liver capsule was also cross-presented to CD8 T cells in these nodes. CONCLUSIONS These results suggest for the first time that the coeliac and portal nodes are the main LNs draining the liver, and that DCs exiting the liver can elicit primary T cell activation within these lymph nodes; first mesenteric nodes play a secondary role. We propose this nomenclature to be used as common designations for the observed structures.