Impaired calcineurin signaling in myeloid cells results in downregulation of pentraxin-3 and increased susceptibility to aspergillosis

Infections after organ transplantation and immune response

Organ transplantation has provided another chance of survival for end-stage organ failure patients. Yet, transplant rejection is still a main challenging factor. Immunosuppressive drugs have been used to avoid rejection and suppress the immune response against allografts. Thus, immunosuppressants increase the risk of infection in immunocompromised organ transplant recipients. The infection risk reflects the relationship between the nature and severity of immunosuppression and infectious diseases. Furthermore, immunosuppressants show an immunological impact on the genetics of innate and adaptive immune responses. This effect usually reactivates the post-transplant infection in the donor and recipient tissues since T-cell activation has a substantial role in allograft rejection. Meanwhile, different infections have been found to activate the T-cells into CD₄⁺ helper T-cell subset and CD₈⁺ cytotoxic T-lymphocyte that affect the infection and the allograft. Therefore, the best management and preventive strategies of immunosuppression, antimicrobial prophylaxis, and intensive medical care are required for successful organ transplantation. This review addresses the activation of immune responses against different infections in immunocompromised individuals after organ transplantation.

FK506 impairs neutrophil migration that results in increased polymicrobial sepsis susceptibility

OBJECTIVE

This study aimed to investigate the effects of FK506 on experimental sepsis immunopathology. It investigated the effect of FK506 on leukocyte recruitment to the site of infection, systemic cytokine production, and organ injury in mice with sepsis.

METHODS

Using a murine cecal ligation and puncture (CLP) peritonitis model, the experiments were performed with wild-type (WT) mice and mice deficient in the gene Nfat1 (Nfat1^-/-) in the C57BL/6 background. Animals were treated with 2.0 mg/kg of FK506, subcutaneously, 1 h before the sepsis model, twice a day (12 h/12 h). The number of bacteria colony forming units (CFU) was manually counted. The number of neutrophils in the lungs was estimated by the myeloperoxidase (MPO) assay. The expression of CXCR2 in neutrophils was determined using flow cytometry analysis. The expression of inflammatory cytokines in macrophage was determined using ELISA. The direct effect of FK506 on CXCR2 internalization was evaluated using HEK-293T cells after CXCL2 stimulation by the BRET method.

RESULTS

FK506 treatment potentiated the failure of neutrophil migration into the peritoneal cavity, resulting in bacteremia and an exacerbated systemic inflammatory response, which led to higher organ damage and mortality rates. Failed neutrophil migration was associated with elevated CXCL2 chemokine plasma levels and lower expression of the CXCR2 receptor on circulating neutrophils compared with non-treated CLP-induced septic mice. FK506 did not directly affect CXCL2-induced CXCR2 internalization by transfected HEK-293 cells or mice neutrophils, despite increasing CXCL2 release by LPS-treated macrophages. Finally, the CLP-induced response of Nfat1^-/- mice was similar to those observed in the Nfat1^+/+ genotype, suggesting that the FK506 effect is not dependent on the NFAT1 pathway.

CONCLUSION

Our data indicate that the increased susceptibility to infection of FK506-treated mice is associated with failed neutrophil migration due to the reduced membrane availability of CXCR2 receptors in response to exacerbated levels of circulating CXCL2.

Potential Antifungal Targets for Aspergillus sp. from the Calcineurin and Heat Shock Protein Pathways

Aspergillus species, especially A. fumigatus, and to a lesser extent others (A. flavus, A. niger, A. terreus), although rarely pathogenic to healthy humans, can be very aggressive to immunocompromised patients (they are opportunistic pathogens). Although survival rates for such infections have improved in recent decades following the introduction of azole derivatives, they remain a clinical challenge. The fact that current antifungals act as fungistatic rather than fungicide, that they have limited safety, and that resistance is becoming increasingly common make the need for new, more effective, and safer therapies to become more acute. Over the last decades, knowledge about the molecular biology of A. fumigatus and other Aspergillus species, and particularly of calcineurin, Hsp90, and their signaling pathway proteins, has progressed remarkably. Although calcineurin has attracted much interest, its adverse effects, particularly its immunosuppressive effects, make it less attractive than it might at first appear. The situation is not very different for Hsp90. Other proteins from their signaling pathways, such as protein kinases phosphorylating the four SPRR serine residues, CrzA, rcnA, pmcA-pmcC (particularly pmcC), rfeF, BAR adapter protein(s), the phkB histidine kinase, sskB MAP kinase kinase, zfpA, htfA, ctfA, SwoH (nucleoside diphosphate kinase), CchA, MidA, FKBP12, the K27 lysine position from Hsp90, PkcA, MpkA, RlmA, brlA, abaA, wetA, other heat shock proteins (Hsp70, Hsp40, Hsp12) currently appear promising and deserve further investigation as potential targets for antifungal drug development.

The role of the gut microbiota in multiple sclerosis

During the past decade, research has revealed that the vast community of micro-organisms that inhabit the gut - known as the gut microbiota - is intricately linked to human health and disease, partly as a result of its influence on systemic immune responses. Accumulating evidence demonstrates that these effects on immune function are important in neuroinflammatory diseases, such as multiple sclerosis (MS), and that modulation of the microbiome could be therapeutically beneficial in these conditions. In this Review, we examine the influence that the gut microbiota have on immune function via modulation of serotonin production in the gut and through complex interactions with components of the immune system, such as T cells and B cells. We then present evidence from studies in mice and humans that these effects of the gut microbiota on the immune system are important in the development and course of MS. We also consider how strategies for manipulating the composition of the gut microbiota could be used to influence disease-related immune dysfunction and form the basis of a new class of therapeutics. The strategies discussed include the use of probiotics, supplementation with bacterial metabolites, transplantation of faecal matter or defined microbial communities, and dietary intervention. Carefully designed studies with large human cohorts will be required to gain a full understanding of the microbiome changes involved in MS and to develop therapeutic strategies that target these changes.

Transcriptional regulatory networks of circulating immune cells in type 1 diabetes: A community knowledgebase

Investigator-generated transcriptomic datasets interrogating circulating immune cell (CIC) gene expression in clinical type 1 diabetes (T1D) have underappreciated re-use value. Here, we repurposed these datasets to create an open science environment for the generation of hypotheses around CIC signaling pathways whose gain or loss of function contributes to T1D pathogenesis. We firstly computed sets of genes that were preferentially induced or repressed in T1D CICs and validated these against community benchmarks. We then inferred and validated signaling node networks regulating expression of these gene sets, as well as differentially expressed genes in the original underlying T1D case:control datasets. In a set of three use cases, we demonstrated how informed integration of these networks with complementary digital resources supports substantive, actionable hypotheses around signaling pathway dysfunction in T1D CICs. Finally, we developed a federated, cloud-based web resource that exposes the entire data matrix for unrestricted access and re-use by the research community.

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Re-use of transcriptomic type 1 diabetes (T1D) circulating immune cells (CICs) datasets

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We generated transcriptional regulatory networks for T1D CICs

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Use cases generate substantive hypotheses around signaling pathway dysfunction in T1D CICs

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Networks are freely accessible on the web for re-use by the research community

Calcineurin in development and disease

Calcineurin (CaN) is a unique calcium (Ca²⁺) and calmodulin (CaM)-dependent serine/threonine phosphatase that becomes activated in the presence of increased intracellular Ca²⁺ level. CaN then functions to dephosphorylate target substrates including various transcription factors, receptors, and channels. Once activated, the CaN signaling pathway participates in the development of multiple organs as well as the onset and progression of various diseases via regulation of different cellular processes. Here, we review current literature regarding the structural and functional properties of CaN, highlighting its crucial role in the development and pathogenesis of immune system disorders, neurodegenerative diseases, kidney disease, cardiomyopathy and cancer.

The role of pentraxin3 in plasma and bronchoalveolar lavage fluid in COPD patients with invasive pulmonary aspergillosis

Background

The use of galactomannan (GM) testing in plasma and bronchoalveolar lavage fluid (BALF) has improved the diagnosis of invasive pulmonary aspergillosis (IPA) in patients with chronic obstructive pulmonary disease (COPD); however, the high false-positive rate leads to overdiagnosis. Pentraxin 3 (PTX3) as an indicator of inflammation plays an important role in resistance to Aspergillus infections. This study aimed to investigate the diagnostic value of PTX3 for diagnosing IPA with COPD.

Methods

We retrospectively collected data on patients with suspected COPD and IPA who had been hospitalized in the Third Affiliated Hospital of Soochow University between September 2017 and November 2020. PTX3 and GM were measured using enzyme-linked immunosorbent assays.

Results

A total of 165 patients were included in the study, of whom 35 had confirmed or probable IPA. The remaining 130 patients served as controls. The median plasma and BALF PTX3 levels were significantly higher in patients with IPA than in control patients (3.74 ng/mL vs. 1.29 ng/mL, P < 0.001; and 3.88 ng/mL vs. 1.58 ng/mL, P < 0.001 in plasma and BALF, respectively). The plasma GM, plasma PTX3, BALF GM, and BALF PTX3 assays had sensitivities of 60.0%, 77.1%, 78.6%, and 89.3%, respectively, and specificities of 73.8%, 69.2%, 80.7%, and 77.1%, respectively. The sensitivity of PTX3 in plasma and BALF was higher than that of GM. However, the specificity of PTX3 and GM did not differ significantly between the IPA group and the control group. The specificity of the assays for the diagnosis of IPA was > 90% in patients who were PTX3-positive and GM-positive in plasma and BALF.

Conclusions

BALF and plasma PTX3 levels were significantly higher in COPD patients with IPA. The sensitivity of PTX3 was superior to that of GM for diagnosing IPA in patients with COPD. The combination of GM and PTX3 is useful for the diagnosis of IPA in patients with COPD.

Aspergillosis: Emerging risk groups in critically ill patients

Information on invasive aspergillosis (IA) and other invasive filamentous fungal infections is limited in non-neutropenic patients admitted to the intensive care unit (ICU) and presenting with no classic IA risk factors. This review is based on the critical appraisal of relevant literature, on the authors' own experience and on discussions that took place at a consensus conference. It aims to review risk factors favoring aspergillosis in ICU patients, with a special emphasis on often overlooked or neglected conditions. In the ICU patients, corticosteroid use to treat underlying conditions such as chronic obstructive pulmonary disease (COPD), sepsis, or severe COVID-19, represents a cardinal risk factor for IA. Important additional host risk factors are COPD, decompensated cirrhosis, liver failure, and severe viral pneumonia (influenza, COVID-19). Clinical observations indicate that patients admitted to the ICU because of sepsis or acute respiratory distress syndrome are more likely to develop probable or proven IA, suggesting that sepsis could also be a possible direct risk factor for IA, as could small molecule inhibitors used in oncology. There are no recommendations for prophylaxis in ICU patients; posaconazole mold-active primary prophylaxis is used in some centers according to guidelines for other patient populations and IA treatment in critically ill patients is basically the same as in other patient populations. A combined evaluation of clinical signs and imaging, classical biomarkers such as the GM assay, and fungal cultures examination, remain the best option to assess response to treatment.

LAY SUMMARY

The use of corticosteroids and the presence of co-morbidities such as chronic obstructive pulmonary disease, acute or chronic advanced liver disease, or severe viral pneumonia caused by influenza or Covid-19, may increase the risk of invasive aspergillosis in intensive care unit patients.

Immunosuppression Affects Neutrophil Functions: Does Calcineurin-NFAT Signaling Matter?

Neutrophils are innate immune cells with important roles in antimicrobial defense. However, impaired or dysregulated neutrophil function can result in host tissue damage, loss of homeostasis, hyperinflammation or pathological immunosuppression. A central link between neutrophil activation and immune outcomes is emerging to be the calcineurin-nuclear factor of activated T cells (NFAT) signaling pathway, which is activated by neutrophil detection of a microbial threat via pattern recognition receptors and results in inflammatory cytokine production. This potent pro-inflammatory pathway is also the target of several immunosuppressive drugs used for the treatment of autoimmune disorders, during solid organ and hematopoietic cell transplantations, and as a part of anti-cancer therapy: but what effects these drugs have on neutrophil function, and their broader consequences for immune homeostasis and microbial defense are not yet known. Here, we bring together the emerging literature describing pathology- and drug- induced neutrophil impairment, with particular focus on their effects on calcineurin-NFAT signaling in the innate immune compartment.

Future challenges and chances in the diagnosis and management of invasive mould infections in cancer patients

Diagnosis, treatment, and management of invasive mould infections (IMI) are challenged by several risk factors, including local epidemiological characteristics, the emergence of fungal resistance and the innate resistance of emerging pathogens, the use of new immunosuppressants, as well as off-target effects of new oncological drugs. The presence of specific host genetic variants and the patient's immune system status may also influence the establishment of an IMI and the outcome of its therapy. Immunological components can thus be expected to play a pivotal role not only in the risk assessment and diagnosis, but also in the treatment of IMI. Cytokines could improve the reliability of an invasive aspergillosis diagnosis by serving as biomarkers as do serological and molecular assays, since they can be easily measured, and the turnaround time is short. The use of immunological markers in the assessment of treatment response could be helpful to reduce overtreatment in high risk patients and allow prompt escalation of antifungal treatment. Mould-active prophylaxis could be better targeted to individual host needs, leading to a targeted prophylaxis in patients with known immunological profiles associated with high susceptibility for IMI, in particular invasive aspergillosis. The alteration of cellular antifungal immune response through oncological drugs and immunosuppressants heavily influences the outcome and may be even more important than the choice of the antifungal treatment. There is a need for the development of new antifungal strategies, including individualized approaches for prevention and treatment of IMI that consider genetic traits of the patients.

Lay Abstract

Anticancer and immunosuppressive drugs may alter the ability of the immune system to fight invasive mould infections and may be more important than the choice of the antifungal treatment. Individualized approaches for prevention and treatment of invasive mold infections are needed.

NFAT signaling in human mesenchymal stromal cells affects extracellular matrix remodeling and antifungal immune responses

Mesenchymal stromal cells (MSCs) combined with calcineurin-nuclear factor of activated T cell (CN-NFAT) inhibitors are being tested as a treatment for graft-versus-host disease (GvHD). The immunosuppressive properties of MSCs seem beneficial; however, their response during fungal infection, which is an important cause of mortality in patients with GvHD , is unknown. We report that MSCs phagocytose the fungal component zymosan, resulting in phosphorylation of spleen tyrosine kinase (Syk), increase in cytosolic calcium levels, and ultimately, increase in NFAT1 nuclear translocation. RNA sequencing analysis of zymosan-treated MSCs showed that CN-NFAT inhibition affects extracellular matrix (ECM) genes but not cytokine expression that is under the control of the NF-κB pathway. When coculturing MSCs or decellularized MSC-ECM with human peripheral blood mononuclear cells (PBMCs), selective NFAT inhibition in MSCs decreased cytokine expression by PBMCs. These findings reveal a dual mechanism underlying the MSC response to zymosan: while NF-κB directly controls inflammatory cytokine expression, NFAT impacts immune-cell functions by regulating ECM remodeling.

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Stimulation of MSCs with zymosan activates NFAT and NF-kB via the dectin1-Syk axis

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Calcineurin-NFAT inhibition impacts the expression of extracellular matrix genes

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NF-kB pathway regulates cytokine expression in zymosan-stimulated MSCs

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Selective NFAT inhibition in MSCs impacts cytokine secretion of MSC-PBMC cocultures

Inositol 1,4,5-trisphosphate 3-kinase B promotes Ca2+ mobilization and the inflammatory activity of dendritic cells

Innate immune responses to Gram-negative bacteria depend on the recognition of lipopolysaccharide (LPS) by a receptor complex that includes CD14 and TLR4. In dendritic cells (DCs), CD14 enhances the activation not only of TLR4 but also that of the NFAT family of transcription factors, which suppresses cell survival and promotes the production of inflammatory mediators. NFAT activation requires Ca²⁺ mobilization. In DCs, Ca²⁺ mobilization in response to LPS depends on phospholipase C γ2 (PLCγ2), which produces inositol 1,4,5-trisphosphate (IP₃). Here, we showed that the IP₃ receptor 3 (IP₃R3) and ITPKB, a kinase that converts IP₃ to inositol 1,3,4,5-tetrakisphosphate (IP₄), were both necessary for Ca²⁺ mobilization and NFAT activation in mouse and human DCs. A pool of IP₃R3 was located on the plasma membrane of DCs, where it colocalized with CD14 and ITPKB. Upon LPS binding to CD14, ITPKB was required for Ca²⁺ mobilization through plasma membrane-localized IP₃R3 and for NFAT nuclear translocation. Pharmacological inhibition of ITPKB in mice reduced both LPS-induced tissue swelling and the severity of inflammatory arthritis to a similar extent as that induced by the inhibition of NFAT using nanoparticles that delivered an NFAT-inhibiting peptide specifically to phagocytic cells. Our results suggest that ITPKB may represent a promising target for anti-inflammatory therapies that aim to inhibit specific DC functions.

Aspergillus fumigatus and Aspergillosis in 2019

Aspergillus fumigatus is a saprotrophic fungus; its primary habitat is the soil. In its ecological niche, the fungus has learned how to adapt and proliferate in hostile environments. This capacity has helped the fungus to resist and survive against human host defenses and, further, to be responsible for one of the most devastating lung infections in terms of morbidity and mortality. In this review, we will provide (i) a description of the biological cycle of A. fumigatus; (ii) a historical perspective of the spectrum of aspergillus disease and the current epidemiological status of these infections; (iii) an analysis of the modes of immune response against Aspergillus in immunocompetent and immunocompromised patients; (iv) an understanding of the pathways responsible for fungal virulence and their host molecular targets, with a specific focus on the cell wall; (v) the current status of the diagnosis of different clinical syndromes; and (vi) an overview of the available antifungal armamentarium and the therapeutic strategies in the clinical context. In addition, the emergence of new concepts, such as nutritional immunity and the integration and rewiring of multiple fungal metabolic activities occurring during lung invasion, has helped us to redefine the opportunistic pathogenesis of A. fumigatus.

Fungal Infections with Ibrutinib and Other Small-Molecule Kinase Inhibitors

Purpose of review

Small molecule kinase inhibitors (SMKIs) have revolutionized the management of malignant and autoimmune disorders. Emerging clinical reports point toward an increased risk for invasive fungal infections (IFIs) in patients treated with certain SMKIs. In this mini-review, we highlight representative examples of SMKIs that have been associated with or are expected to give rise to IFIs.

Recent findings

The clinical use of the Bruton's tyrosine kinase inhibitor ibrutinib as well as other FDA-approved SMKIs has been associated with IFIs. The fungal infection susceptibility associated with the clinical use of certain SMKIs underscores their detrimental effects on innate and adaptive antifungal immune responses.

Summary

The unprecedented development and clinical use of SMKIs is expected to give rise to an expansion of iatrogenic immunosuppressive factors predisposing to IFIs (and other opportunistic infections). Beyond increased clinical surveillance, better understanding of the pathogenesis of SMKI-associated immune dysregulation should help devising improved risk stratification and prophylaxis strategies in vulnerable patients.

Host defense mechanisms against Aspergillus fumigatus lung colonization and invasion

The human lung is continually exposed to airborne conidia of the fungus Aspergillus fumigatus (AF) and related species. The innate immune system efficiently eliminates inhaled AF conidia from the lung in normal individuals, but immunocompromised patients are at risk for highly lethal invasive aspergillosis (IA). Some individuals not at risk for IA may still suffer from failed clearance of AF in the form of noninvasive colonization associated with conditions such as allergic bronchopulmonary aspergillosis. Understanding of normal innate immune function against AF as well as failures of these functions will enable better treatment of these patient groups. In this review, we will focus on recent research that elucidates mechanisms of host defense and their failures resulting in colonization as well as tissue invasion.

Menacing Mold: Recent Advances in Aspergillus Pathogenesis and Host Defense

The genus Aspergillus is ubiquitous in the environment and contains a number of species, primarily A. fumigatus, that cause mold-associated disease in humans. Humans inhale several hundred to several thousand Aspergillus conidia (i.e., vegetative spores) daily and typically clear these in an asymptomatic manner. In immunocompromised individuals, Aspergillus conidia can germinate into tissue-invasive hyphae, disseminate, and cause invasive aspergillosis. In this review, we first discuss novel concepts in host defense against Aspergillus infections and emphasize new insights in fungal recognition and signaling, innate immune activation, and fungal killing. Second, the review focuses on novel concepts of Aspergillus pathogenesis and highlights emerging knowledge regarding fungal strain heterogeneity, stress responses, and metabolic adaptations on infectious outcomes. Mechanistic insight into the host-pathogen interplay is thus critical to define novel druggable fungal targets and to exploit novel immune-based strategies to improve clinical outcomes associated with aspergillosis in vulnerable patient populations.

Calcineurin inhibitors reduce NFAT-dependent expression of antifungal pentraxin-3 by human monocytes

Calcineurin (CN) inhibitors are effective clinical immunosuppressants but leave patients vulnerable to potentially fatal fungal infections. This study tested the hypothesis that CN inhibition interferes with antifungal immune defenses mediated by monocytes. We showed that NFAT is expressed by human monocytes, and is activated by exposure to fungal ligands. We confirmed that NFAT translocation potently activated target gene transcription using a human monocytic reporter cell line. Inhibition of CN‐NFAT by cyclosporine A significantly reduced monocyte production of TNF‐α, IL‐10, and MCP‐1 proteins in response to pattern recognition receptor ligands as well as to Aspergillus fumigatus conidia. Moreover, we revealed that human monocytes express the antifungal protein pentraxin‐3 under control of NFAT. In conclusion, clinical CN inhibitors have the potential to interfere with the novel NFAT‐dependent pentraxin‐3 pathway as well as antifungal cytokine production in human monocytes, thereby impeding monocyte‐mediated defenses against fungal infection in immune‐suppressed patients.

It takes a village: Phagocytes play a central role in fungal immunity

Phagocytosis is an essential step in the innate immune response to invasive fungal infections. This process is carried out by a proverbial "village" of professional phagocytic cells, which have evolved efficient machinery to recognize and ingest pathogens, namely macrophages, neutrophils and dendritic cells. These innate immune cells drive early cytokine production, fungicidal activity, antigen presentation and activation of the adaptive immune system. Despite the development of antifungal agents with potent activity, the biological activity of professional phagocytic innate immune cells has proven indispensable in protecting a host from invasive fungal infections. Additionally, an emerging body of evidence suggests non-professional phagocytes, such as airway epithelial cells, carry out phagocytosis and may play a critical role in the elimination of fungal pathogens. Here, we review recent advances of phagocytosis by both professional and non-professional phagocytes in response to fungal pathogens, with a focus on invasive aspergillosis as a model disease.

Antifungal immune responses: emerging host-pathogen interactions and translational implications

Understanding the complex and highly dynamic interactions between fungi and host cells in a tissue-specific manner is crucial to facilitate the development of new therapeutic approaches to infections. Here, we discuss recent studies that are revealing the mechanisms underlying this context-dependent interplay.

Calcineurin-NFAT signalling in myeloid leucocytes: new prospects and pitfalls in immunosuppressive therapy

Myeloid leucocytes mediate host protection against infection and critically regulate inflammatory responses in body tissues. Pattern recognition receptor signalling is crucial for myeloid cell responses to pathogens, but growing evidence suggests an equally potent role for Calcineurin–NFAT signalling in control of myeloid cell function. All major subsets of myeloid leucocytes employ Calcineurin–NFAT signalling during immune responses to pathogens and/or tissue damage, but the influence this pathway exerts on pathogen clearance and host susceptibility to infection is not fully understood. Recent data from experimental models indicate that Calcineurin‐NFAT signalling is essential for infection control, and calcineurin inhibitors used in transplantation medicine (including cyclosporine A and tacrolimus) are now being tested for efficacy in a diverse range of inflammatory conditions and autoimmune pathologies. Efforts to repurpose calcineurin inhibitor drugs for new therapeutic applications may yield rapid improvements in clinical outcomes, but the potential impact of these compounds on myeloid cell function in treated patients is largely unknown. Here we discuss Calcineurin–NFAT control of myeloid leucocyte function in the context of recent therapeutic developments and ongoing clinical studies.

Calcineurin-mediated IL-2 production by CD11chighMHCII+ myeloid cells is crucial for intestinal immune homeostasis

The intestinal immune system can respond to invading pathogens yet maintain immune tolerance to self-antigens and microbiota. Myeloid cells are central to these processes, but the signaling pathways that underlie tolerance versus inflammation are unclear. Here we show that mice lacking Calcineurin B in CD11c^highMHCII⁺ cells (Cnb1^CD11c mice) spontaneously develop intestinal inflammation and are susceptible to induced colitis. In these mice, colitis is associated with expansion of T helper type 1 (Th1) and Th17 cell populations and a decrease in the number of FoxP3⁺ regulatory T (Treg) cells, and the pathology is linked to the inability of intestinal Cnb1-deficient CD11c^highMHCII⁺ cells to express IL-2. Deleting IL-2 in CD11c^highMHCII⁺ cells induces spontaneous colitis resembling human inflammatory bowel disease. Our findings identify that the calcineurin–NFAT–IL-2 pathway in myeloid cells is a critical regulator of intestinal homeostasis by influencing the balance of inflammatory and regulatory responses in the mouse intestine.

Treg cells can maintain intestinal homeostasis and limit intestinal bowel disease. Here the authors use a mouse model of spontaneous colitis to show that calcineurin-NFAT-induced IL-2 production by dendritic cells regulates the balance between Treg and effector T cells in the gut lamina propria.

Contact, Collaboration, and Conflict: Signal Integration of Syk-Coupled C-Type Lectin Receptors

Several spleen tyrosine kinase-coupled C-type lectin receptors (CLRs) have emerged as important pattern recognition receptors for infectious danger. Because encounter with microbial pathogens leads to the simultaneous ligation of several CLRs and TLRs, the signals emanating from different pattern recognition receptors have to be integrated to achieve appropriate biological responses. In this review, we briefly summarize current knowledge about ligand recognition and core signaling by Syk-coupled CLRs. We then address mechanisms of synergistic and antagonistic crosstalk between different CLRs and with TLRs. Emerging evidence suggests that signal integration occurs through 1) direct interaction between receptors, 2) regulation of expression levels and localization, and 3) collaborative or conflicting signaling interference. Accordingly, we aim to provide a conceptual framework for the complex and sometimes unexpected outcome of CLR ligation in bacterial and fungal infection.

Innate Lung Defense during Invasive Aspergillosis: New Mechanisms

Invasive aspergillosis (IA) is one of the most difficult to treat and, consequently, one of the most lethal fungal infections known to man. Continued use of immunosuppressive agents during chemotherapy and organ transplantation often leads to the development of neutropenia, the primary risk factor for IA. However, IA is also becoming more appreciated in chronic diseases associated with corticosteroid therapy. The innate immune response to Aspergillus fumigatus, the primary agent in IA, plays a pivotal role in the recognition and elimination of organisms from the pulmonary system. This review highlights recent findings about innate host defense mechanisms, including novel aspects of innate cellular immunity and pathogen recognition, and the inflammatory mediators that control infection with A. fumigatus.