Neutrophil elastase converts human immature dendritic cells into transforming growth factor-beta1-secreting cells and reduces allostimulatory ability

Secretory leukocyte protease inhibitor influences periarticular joint inflammation in Borrelia burgdorferi-infected mice

Lyme disease, caused by Borrelia burgdorferi, is the most common tick-borne infection in the United States. Arthritis is a major clinical manifestation of infection, and synovial tissue damage has been attributed to the excessive pro-inflammatory responses. The secretory leukocyte protease inhibitor (SLPI) promotes tissue repair and exerts anti-inflammatory effects. The role of SLPI in the development of Lyme arthritis in C57BL/6 mice, which can be infected with B. burgdorferi but only develop mild joint inflammation, was therefore examined. Slpi-deficient C57BL/6 mice challenged with B. burgdorferi had a higher infection load in the tibiotarsal joints and marked periarticular swelling compared to infected wild-type control mice. The ankle joint tissues of B. burgdorferi-infected Slpi-deficient mice contained significantly higher percentages of infiltrating neutrophils and macrophages. B. burgdorferi-infected Slpi-deficient mice also exhibited elevated serum levels of IL-6, neutrophil elastase, and MMP-8. Moreover, using a recently developed BASEHIT (BActerial Selection to Elucidate Host-microbe Interactions in high Throughput) library, we found that SLPI directly interacts with B. burgdorferi. These data demonstrate the importance of SLPI in suppressing periarticular joint inflammation in Lyme disease.

Neutrophils in Type 1 Diabetes: Untangling the Intricate Web of Pathways and Hypothesis

Neutrophils are increasingly recognized as key contributors to the pathogenesis of Type 1 Diabetes (T1D), yet their precise mechanistic role in disease onset and progression remains incompletely understood. While these innate immune cells reside in pancreatic tissue and support tissue homeostasis under physiological conditions, they can also drive tissue damage by triggering innate immune responses and modulating inflammation. Within the inflammatory milieu, neutrophils establish complex, bidirectional interactions with various immune cells, including macrophages, dendritic cells, natural killer cells, and lymphocytes. Once activated, they may enhance the innate immune response through direct or indirect crosstalk with immune cells, antigen presentation, and β-cell destruction or dysfunction. These mechanisms underscore the multifaceted and dynamic role of neutrophils in T1D, shaped by their intricate immunological interactions. Further research into the diverse functional capabilities of neutrophils is crucial for uncovering novel aspects of their involvement in T1D, potentially revealing new therapeutic targets to modulate disease progression.

Secretory leukocyte protease inhibitor influences periarticular joint inflammation in B. burgdorferi-infected mice

Lyme disease, caused by Borrelia burgdorferi, is the most common tick-borne infection in the United States. Arthritis is a major clinical manifestation of infection, and synovial tissue damage has been attributed to the excessive pro-inflammatory responses. The secretory leukocyte protease inhibitor (SLPI) promotes tissue repair and exerts anti-inflammatory effects. The role of SLPI in the development of Lyme arthritis in C57BL/6 mice, which can be infected with B. burgdorferi, but only develop mild joint inflammation, was therefore examined. SLPI-deficient C57BL/6 mice challenged with B. burgdorferi had a higher infection load in the tibiotarsal joints and marked periarticular swelling, compared to infected wild type control mice. The ankle joint tissues of B. burgdorferi-infected SLPI-deficient mice contained significantly higher percentages of infiltrating neutrophils and macrophages. B. burgdorferi-infected SLPI-deficient mice also exhibited elevated serum levels of IL-6, neutrophil elastase, and MMP-8. Moreover, using a recently developed BASEHIT (BActerial Selection to Elucidate Host-microbe Interactions in high Throughput) library, we found that SLPI directly interacts with B. burgdorferi. These data demonstrate the importance of SLPI in suppressing periarticular joint inflammation in Lyme disease.

Extracellular Mechanisms of Neutrophils in Immune Cell Crosstalk

Neutrophils are professional phagocytes that provide defense against invading pathogens through phagocytosis, degranulation, generation of ROS, and the formation of neutrophil extracellular traps (NETs). Although long been considered as short-lived effector cells with limited biosynthetic activity, recent studies have revealed that neutrophils actively communicate with other immune cells. Neutrophils employ various types of soluble mediators, including granules, cytokines, and chemokines, for crosstalk with immune cells. Additionally, ROS and NETs, major arsenals of neutrophils, are utilized for intercellular communication. Furthermore, extracellular vesicles play a crucial role as mediators of neutrophil crosstalk. In this review, we highlight the extracellular mechanisms of neutrophils and their roles in crosstalk with other cells.

The innate immune brakes of the lung

Respiratory mucosal surfaces are continuously exposed to not only innocuous non-self antigens but also pathogen-associated molecular patterns (PAMPs) originating from environmental or symbiotic microbes. According to either "self/non-self" or "danger" models, this should systematically result in homeostasis breakdown and the development of immune responses directed to inhaled harmless antigens, such as T helper type (Th)2-mediated asthmatic reactions, which is fortunately not the case in most people. This discrepancy implies the existence, in the lung, of regulatory mechanisms that tightly control immune homeostasis. Although such mechanisms have been poorly investigated in comparison to the ones that trigger immune responses, a better understanding of them could be useful in the development of new therapeutic strategies against lung diseases (e.g., asthma). Here, we review current knowledge on innate immune cells that prevent the development of aberrant immune responses in the lung, thereby contributing to mucosal homeostasis.

Vitamin D3 Priming of Dendritic Cells Shifts Human Neutrophil-Dependent Th17 Cell Development to Regulatory T Cells

Vitamin D3 (VD3) is a potential adjuvant for use in tolerogenic vaccine formulations that target dendritic cells (DCs) for the treatment of chronic inflammatory disorders, e.g., autoimmune diseases. These disorders are often associated with enhanced activity of IL-17-producing T helper 17 (Th17) cells which develop in a DC-driven and neutrophil-dependent fashion. Here, we investigated the effect of VD3 on Candida albicans-specific human T-cell differentiation, since C. albicans is a model pathogen for Th17 cell development. VD3 priming of DCs restricted neutrophil-dependent Th17 cell development and neutrophil-independent Th1 cell formation from naive CD4⁺ T cells. In line with this, the production of Th1/Th17-polarizing cytokines IL-12 and IL-23 by DCs was reduced by VD3 priming. Development of both FoxP3⁺CD127_lowCD25⁺ Tregs and IL-10-producing T cells was significantly enhanced in VD3-primed conditions, even in the presence of neutrophils. ICOS⁺ Tregs, major IL-10 producers, CD69⁺FoxP3⁺, and TIGIT⁺FoxP3⁺ Tregs were significantly induced by VD3 priming as well. Our data support the potential use of VD3 as an adjuvant to induce tolerance in the treatment of autoimmune disorders, including those in which neutrophils are involved in pathogenesis, since we show that Treg development is enhanced by VD3 even in the presence of neutrophils, while Th17 cell development is restricted.

Neutrophil Extracellular Traps in Cancer Therapy Resistance

Neutrophils and their products are increasingly recognized to have a key influence on cancer progression and response to therapy. Their involvement has been shown in nearly every aspect of cancer pathophysiology with growing evidence now supporting their role in resistance to a variety of cancer therapies. Recently, the role of neutrophils in cancer progression and therapy resistance has been further complicated with the discovery of neutrophil extracellular traps (NETs). NETs are web-like structures of chromatin decorated with a variety of microbicidal proteins. They are released by neutrophils in a process called NETosis. NET-dependent mechanisms of cancer pathology are beginning to be appreciated, particularly with respect to tumor response to chemo-, immuno-, and radiation therapy. Several studies support the functional role of NETs in cancer therapy resistance, involving T-cell exhaustion, drug detoxification, angiogenesis, the epithelial-to-mesenchymal transition, and extracellular matrix remodeling mechanisms, among others. Given this, new and promising data suggests NETs provide a microenvironment conducive to limited therapeutic response across a variety of neoplasms. As such, this paper aims to give a comprehensive overview of evidence on NETs in cancer therapy resistance with a focus on clinical applicability.

Myeloid-Derived Suppressor Cells in Prostate Cancer: Present Knowledge and Future Perspectives

Several lines of research are being investigated to better understand mechanisms implicated in response or resistance to immune checkpoint blockade in prostate cancer (PCa). Myeloid-derived suppressor cells (MDSCs) have emerged as a major mediator of immunosuppression in the tumor microenvironment that promotes progression of various tumor types. The main mechanisms underlying MDSC-induced immunosuppression are currently being explored and strategies to enhance anti-tumor immune response via MDSC targeting are being tested. However, the role of MDSCs in PCa remains elusive. In this review, we aim to summarize and present the state-of-the-art knowledge on current methodologies to phenotypically and metabolically characterize MDSCs in PCa. We describe how these characteristics may be linked with MDSC function and may influence the clinical outcomes of patients with PCa. Finally, we briefly discuss emerging strategies being employed to therapeutically target MDSCs and potentiate the long-overdue improvement in the efficacy of immunotherapy in patients with PCa.

Secretory Leukocyte Proteinase Inhibitor Protects Acute Kidney Injury Through Immune and Non-Immune Pathways

ABSTRACT

Acute kidney injury (AKI) is characterized by rapid loss of excretory function and is the clinical manifestation of several disorders affecting the kidney. The aim of the present study was to investigate the mechanism of action of Secretory Leukocyte Proteinase Inhibitor (SLPI) that protects the kidneys form AKI. In vivo and in vitro experiments were performed to assess the effect of SLPI on kidney injury. Animal models of kidney injury was generated by 40 min obstruction of kidney artery and vein (ischemia-reperfusion injury model) or daily administration of 60 mg/kg/day of gentamicine for 5 day (gentamicin-associated AKI model). For in vitro assessment, human renal epithelium HK-2 cells were cultured under serum starvation conditions or with tacrolimus. The administration of SLPI (250 μg/kg, i.p.) reduced elevated plasma creatinine and blood urea nitrogen levels, tissue myeloperoxidase content, and acute tubular necrosis induced by kidney damage. Furthermore, SLPI treatment reduced CD86, CD68, CD14, CCL2, TNFα, and IL-10 transcripts in kidney biopsies. To further analyze a direct effect of SLPI on renal epithelial cells, HK-2 cells from human renal epithelium were cultured under serum starvation conditions or with tacrolimus. Both conditions induced apoptosis of HK-2 cells which was reduced when SLPI was present in the culture medium. Furthermore, SLPI favored the proliferation and migration of HK-2 cells. An analysis of the gene profiles of HK-2 cells treated with calcineurin inhibitors affected inflammatory and non-inflammatory pathways that were reversed by SLPI. Among them, SLPI down modulated the expression of CCL2, SLC5A3, and BECN1 but up-regulated the expression of TLR4, ATF4, ATF6, HSP90B, BBC3 SLC2A1, and TNFRSF10B. Overall, these results suggest that SLPI, in addition to its activity on immune cells, may directly target tubular epithelial cells of the kidney to mediate the nephroprotective activity in AKI.

Targeting DCs for Tolerance Induction: Don't Lose Sight of the Neutrophils

Chronic inflammatory disorders (CID), such as autoimmune diseases, are characterized by overactivation of the immune system and loss of immune tolerance. T helper 17 (Th17) cells are strongly associated with the pathogenesis of multiple CID, including psoriasis, rheumatoid arthritis, and inflammatory bowel disease. In line with the increasingly recognized contribution of innate immune cells to the modulation of dendritic cell (DC) function and DC-driven adaptive immune responses, we recently showed that neutrophils are required for DC-driven Th17 cell differentiation from human naive T cells. Consequently, recruitment of neutrophils to inflamed tissues and lymph nodes likely creates a highly inflammatory loop through the induction of Th17 cells that should be intercepted to attenuate disease progression. Tolerogenic therapy via DCs, the central orchestrators of the adaptive immune response, is a promising strategy for the treatment of CID. Tolerogenic DCs could restore immune tolerance by driving the development of regulatory T cells (Tregs) in the periphery. In this review, we discuss the effects of the tolerogenic adjuvants vitamin D3 (VD3), corticosteroids (CS), and retinoic acid (RA) on both DCs and neutrophils and their potential interplay. We briefly summarize how neutrophils shape DC-driven T-cell development in general. We propose that, for optimization of tolerogenic DC therapy for the treatment of CID, both DCs for tolerance induction and the neutrophil inflammatory loop should be targeted while preserving the potential Treg-enhancing effects of neutrophils.

Cross-Talk among Polymorphonuclear Neutrophils, Immune, and Non-Immune Cells via Released Cytokines, Granule Proteins, Microvesicles, and Neutrophil Extracellular Trap Formation: A Novel Concept of Biology and Pathobiology for Neutrophils

Polymorphonuclear neutrophils (PMNs) are traditionally regarded as professional phagocytic and acute inflammatory cells that engulf the microbial pathogens. However, accumulating data have suggested that PMNs are multi-potential cells exhibiting many important biological functions in addition to phagocytosis. These newly found novel activities of PMN include production of different kinds of cytokines/chemokines/growth factors, release of neutrophil extracellular traps (NET)/ectosomes/exosomes and trogocytosis (membrane exchange) with neighboring cells for modulating innate, and adaptive immune responses. Besides, PMNs exhibit potential heterogeneity and plasticity in involving antibody-dependent cellular cytotoxicity (ADCC), cancer immunity, autoimmunity, inflammatory rheumatic diseases, and cardiovascular diseases. Interestingly, PMNs may also play a role in ameliorating inflammatory reaction and wound healing by a subset of PMN myeloid-derived suppressor cells (PMN-MDSC). Furthermore, PMNs can interact with other non-immune cells including platelets, epithelial and endothelial cells to link hemostasis, mucosal inflammation, and atherogenesis. The release of low-density granulocytes (LDG) from bone marrow initiates systemic autoimmune reaction in systemic lupus erythematosus (SLE). In clinical application, identification of certain PMN phenotypes may become prognostic factors for severe traumatic patients. In the present review, we will discuss these newly discovered biological and pathobiological functions of the PMNs.

Neutrophils acquire antigen-presenting cell features after phagocytosis of IgG-opsonized erythrocytes

Neutrophils are particularly well known for their antimicrobial function. Although historically they are regarded as strictly a phagocyte of the innate immune system, over time it has become clear that neutrophils are versatile cells with numerous functions including innate and adaptive immune regulation. We have previously described a role for human neutrophils in antibody-mediated red blood cell (RBC) clearance. Under homeostatic conditions, neutrophils do not take up RBCs. Yet, when RBCs are immunoglobulin G (IgG) opsonized, which can occur in alloimmunization or autoimmunization reactions, neutrophils can effectively phagocytose RBCs. In the present study, we show that human neutrophils acquire an antigen-presenting cell (APC) phenotype following RBC phagocytosis. Subsequent to RBC phagocytosis, neutrophils expressed major histocompatibility complex class II (MHC-II) and costimulatory molecules such as CD40 and CD80. Moreover, in classical APCs, the respiratory burst is known to regulate antigen presentation. We found that the respiratory burst in neutrophils is reduced after IgG-mediated RBC phagocytosis. Additionally, following RBC phagocytosis, neutrophils were demonstrated to elicit an antigen-specific T-cell response, using tetanus toxoid (TT) as an antigen to elicit an autologous TT-specific CD4⁺ T-cell response. Lastly, although the "don't eat me" signal CD47 is known to have a powerful restrictive role in the activation of immunity against RBCs in dendritic cells, CD47 does not seem to have a significant effect on the antigen-presenting function of neutrophils in this context. Overall, these findings reveal that besides their classical antimicrobial role, neutrophils show plasticity in their phenotype.

Depletion of CD11c+ dendritic cells in apolipoprotein E-deficient mice limits angiotensin II-induced abdominal aortic aneurysm formation and growth

OBJECTIVE

The role of chronic inflammation in abdominal aortic aneurysm (AAA) is controversial. CD11c+ antigen-presenting cells (APCs) (dendritic cells (DCs)) have been reported in human AAA samples but their role is unclear. The effect of conditional depletion of CD11c+ cells on experimental AAA was investigated in the angiotensin II (AngII)-infused apolipoprotein E-deficient (ApoE-/-) mouse model.

APPROACH

CD11c-diphtheria toxin (DT or D.tox) receptor (DTR), ovalbumin (OVA) fragment aa 140-386, and enhanced green fluorescent protein (eGFP)-ApoE-/- (CD11c.DOG.ApoE-/-) mice were generated and CD11c+ cell depletion achieved with D.tox injections (8 ng/g body weight, i.p., every-other-day). AAA formation and growth were assessed by measurement of supra-renal aortic (SRA) diameter in vivo by serial ultrasound and by morphometry assessment of harvested aortas at the end of the study.

RESULTS

Depletion of CD11c+ cells by administration of D.tox on alternative days was shown to reduce the maximum diameter of AAAs induced by 28 days AngII infusion compared with controls (D.tox, 1.58 ± 0.03 mm vs Vehicle control, 1.81 ± 0.06 mm, P<0.001). CD11c+ depletion commencing after AAA establishment by 14 days of AngII infusion, was also shown to lead to smaller AAAs than controls after a further 14 days (D.tox, 1.54 ± 0.04 mm vs Vehicle control, 1.80 ± 0.03 mm, P<0.001). Flow cytometry revealed significantly lower numbers of circulating CD44hi CD62Llo effector CD4 T cells, CD44hi CD62Llo effector CD8 T cells and B220+ B cells in CD11c+ cell-depleted mice versus controls. CD11c+ depletion attenuated SRA matrix degradation indicated by decreased neutrophil elastase activity (P=0.014), lower elastin degradation score (P=0.012) and higher collagen content (P=0.002).

CONCLUSION

CD11c+ cell-depletion inhibited experimental AAA development and growth associated with down-regulation of circulating effector T cells and attenuated matrix degradation. The findings suggest involvement of autoreactive immune cells in AAA pathogenesis.

Extracellular Vesicles as Mediators of Cellular Crosstalk Between Immune System and Kidney Graft

Extracellular vesicles (EVs) are known immune-modulators exerting a critical role in kidney transplantation (KT). EV bioactive cargo includes graft antigens, costimulatory/inhibitory molecules, cytokines, growth factors, and functional microRNAs (miRNAs) that may modulate expression of recipient cell genes. As paracrine factors, neutrophil- and macrophage-derived EVs exert immunosuppressive and immune-stimulating effects on dendritic cells, respectively. Dendritic cell-derived EVs mediate alloantigen spreading and modulate antigen presentation to T lymphocytes. At systemic level, EVs exert pleiotropic effects on complement and coagulation. Depending on their biogenesis, they can amplify complement activation or shed complement inhibitors and prevent cell lysis. Likewise, endothelial- and platelet-derived EVs can exert procoagulant/prothrombotic effects and also promote endothelial survival and angiogenesis after ischemic injury. Kidney endothelial- and tubular-derived EVs play a key role in ischemia-reperfusion injury (IRI) and during the healing process; additionally, they can trigger rejection by inducing both alloimmune and autoimmune responses. Endothelial EVs have procoagulant/pro-inflammatory effects and can release sequestered self-antigens, generating a tissue-specific autoimmunity. Renal tubule-derived EVs shuttle pro-fibrotic mediators (TGF-β and miR-21) to interstitial fibroblasts and modulate neutrophil and T-lymphocyte influx. These processes can lead to peritubular capillary rarefaction and interstitial fibrosis-tubular atrophy. Different EVs, including those from mesenchymal stromal cells (MSCs), have been employed as a therapeutic tool in experimental models of rejection and IRI. These particles protect tubular and endothelial cells (by inhibition of apoptosis and inflammation-fibrogenesis or by inducing autophagy) and stimulate tissue regeneration (by triggering angiogenesis, cell proliferation, and migration). Finally, urinary and serum EVs represent potential biomarkers for delayed graft function (DGF) and acute rejection. In conclusion, EVs sustain an intricate crosstalk between graft tissue and innate/adaptive immune systems. EVs play a major role in allorecognition, IRI, autoimmunity, and alloimmunity and are promising as biomarkers and therapeutic tools in KT.

Neutrophils from severe asthmatic patients induce epithelial to mesenchymal transition in healthy bronchial epithelial cells

BACKGROUND

Asthma is a heterogenous disease characterized by chronic inflammation and airway remodeling. An increase in the severity of airway remodeling is associated with a more severe form of asthma. There is increasing interest in the epithelial to mesenchymal transition process and mechanisms involved in the differentiation and repair of the airway epithelium, especially as they apply to severe asthma. Growing evidence suggests that Epithelial-Mesenchymal transition (EMT) could contribute to airway remodeling and fibrosis in asthma. Severe asthmatic patients with remodeled airways have a neutrophil driven inflammation. Neutrophils are an important source of TGF-β1, which plays a role in recruitment and activation of inflammatory cells, extracellular matrix (ECM) production and fibrosis development, and is a potent inducer of EMT.

OBJECTIVE

As there is little data examining the contribution of neutrophils and/or their mediators to the induction of EMT in airway epithelial cells, the objective of this study was to better understand the potential role of neutrophils in severe asthma in regards to EMT.

METHODS

We used an in vitro system to investigate the neutrophil-epithelial cell interaction. We obtained peripheral blood neutrophils from severe asthmatic patients and control subjects and examined for their ability to induce EMT in primary airway epithelial cells.

RESULTS

Our data indicate that neutrophils from severe asthmatic patients induce changes in morphology and EMT marker expression in bronchial epithelial cells consistent with the EMT process when co-cultured. TGF-β1 levels in the culture medium of severe asthmatic patients were increased compared to that from co-cultures of non-asthmatic neutrophils and epithelial cells.

CONCLUSIONS AND CLINICAL RELEVANCE

As an inducer of EMT and an important source of TGF-β1, neutrophils may play a significant role in the development of airway remodeling and fibrosis in severe asthmatic airways.

Orchestration of Adaptive T Cell Responses by Neutrophil Granule Contents

Neutrophils are the most abundant leukocytes in peripheral blood and respond rapidly to danger, infiltrating tissues within minutes of infectious or sterile injury. Neutrophils were long thought of as simple killers, but now we recognise them as responsive cells able to adapt to inflammation and orchestrate subsequent events with some sophistication. Here, we discuss how these rapid responders release mediators which influence later adaptive T cell immunity through influences on DC priming and directly on the T cells themselves. We consider how the release of granule contents by neutrophils—through NETosis or degranulation—is one way in which the innate immune system directs the phenotype of the adaptive immune response.

The enigmatic role of the neutrophil in asthma: Friend, foe or indifferent?

Whilst severe asthma has classically been categorized as a predominantly Th2-driven pathology, there has in recent years been a paradigm shift with the realization that it is a heterogeneous disease that may manifest with quite disparate underlying inflammatory and remodelling profiles. A subset of asthmatics, particularly those with a severe, corticosteroid refractory disease, present with a prominent neutrophilic component. Given the potential of neutrophils to impart extensive tissue damage and promote inflammation, it has been anticipated that these cells are closely implicated in the underlying pathophysiology of severe asthma. However, uncertainty persists as to why the neutrophil is present in the asthmatic lung and what precisely it is doing there, with evidence supporting its role as a protagonist of pathology being primarily circumstantial. Furthermore, our view of the neutrophil as a primitive, indiscriminate killer has evolved with the realization that neutrophils can exhibit a marked anti-inflammatory, pro-resolving and wound healing capacity. We suggest that the neutrophil likely exhibits pleiotropic and potentially conflicting roles in defining asthma pathophysiology-some almost certainly detrimental and some potentially beneficial-with context, timing and location all critical confounders. Accordingly, indiscriminate blockade of neutrophils with a broad sword approach is unlikely to be the answer, but rather we should first seek to understand their complex and multifaceted roles in the disease state and then target them with the same subtleties and specificity that they themselves exhibit.

Revisiting the Page & Schroeder model: the good, the bad and the unknowns in the periodontal host response 40 years later

In their classic 1976 paper, Page & Schroeder described the histopathologic events and the types of myeloid cells and lymphocytes involved in the initiation and progression of inflammatory periodontal disease. The staging of periodontal disease pathogenesis as 'initial', 'early', 'established' and 'advanced' lesions productively guided subsequent research in the field and remains fundamentally valid. However, major advances regarding the cellular and molecular mechanisms underlying the induction, regulation and effector functions of immune and inflammatory responses necessitate a reassessment of their work and its integration with emerging new concepts. We now know that each type of leukocyte is actually represented by functionally distinct subsets with different, or even conflicting, roles in immunity and inflammation. Unexpectedly, neutrophils, traditionally regarded as merely antimicrobial effectors in acute conditions and protagonists of the 'initial' lesion, are currently appreciated for their functional versatility and critical roles in chronic inflammation. Moreover, an entirely new field of study, osteoimmunology, has emerged and sheds light on the impact of immunoinflammatory events on the skeletal system. These developments and the molecular dissection of crosstalk interactions between innate and adaptive leukocytes, as well as between the immune system and local homeostatic mechanisms, offer a more nuanced understanding of the host response in periodontitis, with profound implications for treatment. At the same time, deeper insights have generated new questions, many of which remain unanswered. In this review, 40 years after Page & Schroeder proposed their model, we summarize enduring and emerging advances in periodontal disease pathogenesis.

The role of extracellular vesicles when innate meets adaptive

Innate immune cells are recognized for their rapid and critical contribution to the body's first line of defense against invading pathogens and harmful agents. These actions can be further amplified by specific adaptive immune responses adapted to the activating stimulus. Recently, the awareness has grown that virtually all innate immune cells, i.e., mast cells, neutrophils, macrophages, eosinophils, basophils, and NK cells, are able to communicate with dendritic cells (DCs) and/or T and B cells, and thereby significantly contribute to the orchestration of adaptive immune responses. The means of communication that are thus far primarily associated with this function are cell-cell contacts and the release of a broad range of soluble mediators. Moreover, the possible contribution of innate immune cell-derived extracellular vesicles (EVs) to the modulation of adaptive immunity will be outlined in this review. EVs are submicron particles composed of a lipid bilayer, proteins, and nucleic acids released by cells in a regulated fashion. EVs are involved in intercellular communication between multiple cell types, including those of the immune system. A good understanding of the mechanisms by which innate immune cell-derived EVs influence adaptive immune responses, or vice versa, may reveal novel insights in the regulation of the immune system and can open up new possibilities for EVs (or their components) in controlling immune responses, either as a therapy, target, or as an adjuvant in future immune modulating treatments.

Cementoin-SLPI fusion protein binds to human monocytes and epithelial cells and shows higher biological activity than SLPI

Secretory Leukocyte Proteinase Inhibitor (SLPI) is an antiinflammatory peptide that blocks the activity of serine proteases, primarily the neutrophil elastase. In an attempt to direct the activity of SLPI on inflamed sites, a chimera consisting of the transglutaminase II substrate domain of trappin 2 (cementoin), and the mature SLPI protein was constructed. Cell attachment and biological activity were compared between SLPI and this chimera. By using whole cell ELISA, fluorescence microscopy and flow cytometry assays we observed that the cementoin-SLPI fusion protein (FP) but not SLPI attached to a human lung epithelial cell line and monocytes. A maximum attachment was achieved 15 min after FP was added to the cell cultures. In an elastase activity assay, we observed that FP retained its antiprotease activity and that at equimolar amount of proteins, FP was more efficient than SLPI in the inhibition. Both, FP and SLPI inhibits IL-2-induced lymphocyte proliferation, however, lower amounts of FP were required to achieve this inhibition. Furthermore, FP binds to mycobacteria and maintained the bactericidal activity observed for SLPI. Overall, these results show that this new chimera is able to attach to the cell surfaces retaining and improving some biological activities described for SLPI.

The role of polymorphonuclear neutrophils during HIV-1 infection

It is well-recognized that human immunodeficiency virus type-1 (HIV-1) mainly targets CD4⁺ T cells and macrophages. Nonetheless, during the past three decades, a huge number of studies have reported that HIV-1 can directly or indirectly target other cellular components of the immune system including CD8⁺ T cells, B cells, dendritic cells, natural killer cells, and polymorphonuclear neutrophils (PMNs), among others. PMNs are the most abundant leukocytes in the human circulation, and are known to play principal roles in the elimination of invading pathogens, regulating different immune responses, healing of injured tissues, and maintaining mucosal homeostasis. Until recently, little was known about the impact of HIV-1 infection on PMNs as well as the impact of PMNs on HIV-1 disease progression. This is because early studies focused on neutropenia and recurrent microbial infections, particularly, during advanced disease. However, recent studies have extended the investigation area to cover new aspects of the interactions between HIV-1 and PMNs. This review aims to summarize these advances and address the impact of HIV-1 infection on PMNs as well as the impact of PMNs on HIV-1 disease progression to better understand the pathophysiology of HIV-1 infection.

Host DNA released by NETosis promotes rhinovirus-induced type-2 allergic asthma exacerbation

Respiratory viral infections represent the most common cause of allergic asthma exacerbations. Amplification of the type-2 immune response is strongly implicated in asthma exacerbation, but how virus infection boosts type-2 responses is poorly understood. We report a significant correlation between the release of host double-stranded DNA (dsDNA) following rhinovirus infection and the exacerbation of type-2 allergic inflammation in humans. In a mouse model of allergic airway hypersensitivity, we show that rhinovirus infection triggers dsDNA release associated with the formation of neutrophil extracellular traps (NETs), known as NETosis. We further demonstrate that inhibiting NETosis by blocking neutrophil elastase or by degrading NETs with DNase protects mice from type-2 immunopathology. Furthermore, the injection of mouse genomic DNA alone is sufficient to recapitulate many features of rhinovirus-induced type-2 immune responses and asthma pathology. Thus, NETosis and its associated extracellular dsDNA contribute to the pathogenesis and may represent potential therapeutic targets of rhinovirus-induced asthma exacerbations.

Neutrophil extracellular traps downregulate lipopolysaccharide-induced activation of monocyte-derived dendritic cells

Polymorphonuclear neutrophils (PMN) play a central role in inflammation and participate in its control, notably by modulating dendritic cell (DC) functions via soluble mediators or cell-cell contacts. Neutrophil extracellular traps (NETs) released by PMN could play a role in this context. To evaluate NET effects on DC maturation, we developed a model based on monocyte-derived DC (moDC) and calibrated NETs isolated from fresh human PMN. We found that isolated NETs alone had no discernable effect on moDC. In contrast, they downregulated LPS-induced moDC maturation, as shown by decreased surface expression of HLA-DR, CD80, CD83, and CD86, and by downregulated cytokine production (TNF-α, IL-6, IL-12, IL-23), with no increase in the expression of tolerogenic DC genes. Moreover, the presence of NETs during moDC maturation diminished the capacity of these moDC to induce T lymphocyte proliferation in both autologous and allogeneic conditions, and modulated CD4(+) T lymphocyte polarization by promoting the production of Th2 cytokines (IL-5 and IL-13) and reducing that of Th1 and Th17 cytokines (IFN-γ and IL-17). Interestingly, the expression and activities of the lymphoid chemokine receptors CCR7 and CXCR4 on moDC were not altered when moDC matured in the presence of NETs. Together, these findings reveal a new role for NETs in adaptive immune responses, modulating some moDC functions and thereby participating in the control of inflammation.

Tolerogenic signaling by pulmonary CD1c+ dendritic cells induces regulatory T cells in patients with chronic obstructive pulmonary disease by IL-27/IL-10/inducible costimulator ligand

BACKGROUND

Increased mortality rates in patients with chronic obstructive pulmonary disease (COPD) are largely due to severe infectious exacerbations. Impaired respiratory immunity is linked to the enhanced susceptibility to infections. Dendritic cells (DCs) direct host immune responses toward immunity or tolerance. Pulmonary CD1c(+) DCs elicit robust antiviral immune responses in healthy subjects. Nevertheless, their functional specialization in patients with COPD remains unexplored.

OBJECTIVE

We sought to better understand the mechanisms that suppress respiratory immunity in patients with COPD by examining the immunostimulatory and tolerogenic properties of pulmonary CD1c(+) DCs.

METHODS

We analyzed the expression of costimulatory and tolerogenic molecules by pulmonary CD1c(+) DCs from patients with COPD (CD1c(+)DCCOPD) and former smokers without COPD. We isolated lung CD1c(+) DCs and determined their ability to stimulate allogeneic T-cell responses. The suppressive effects of lung CD1c(+) DCs and CD1c(+) DC-primed T cells on mixed leukocyte reactions were examined. An experimental human model of COPD exacerbation was used to investigate the levels of critical immunosuppressive molecules in vivo.

RESULTS

CD1c(+) DCs from patients with COPD hinder T-cell effector functions and favor the generation of suppressive IL-10-secreting CD4(+) T cells that function through IL-10 and TGF-β. IL-27, IL-10, and inducible T-cell costimulator ligand signaling are essential for CD1c(+)DCCOPD-mediated differentiation of IL-10-producing suppressive T cells. Exposure of lung CD1c(+) DCs from nonobstructed subjects to lungs of patients with COPD confers tolerogenic properties. IL-27 and IL-10 levels are increased in the lung microenvironment on rhinovirus-induced COPD exacerbation in vivo.

CONCLUSION

We identify a novel tolerogenic circuit encompassing suppressive CD1c(+) DCs and regulatory T cells in patients with COPD that might be implicated in impaired respiratory immunity and further highlight IL-10 and IL-27 as potent therapeutic targets.

Systems biology approaches to understanding Epithelial Mesenchymal Transition (EMT) in mucosal remodeling and signaling in asthma

A pathological hallmark of asthma is chronic injury and repair, producing dysfunction of the epithelial barrier function. In this setting, increased oxidative stress, growth factor- and cytokine stimulation, together with extracellular matrix contact produces transcriptional reprogramming of the epithelial cell. This process results in epithelial-mesenchymal transition (EMT), a cellular state associated with loss of epithelial polarity, expression of mesenchymal markers, enhanced mobility and extracellular matrix remodeling. As a result, the cellular biology of the EMT state produces characteristic changes seen in severe, refractory asthma: myofibroblast expansion, epithelial trans-differentiation and subepithelial fibrosis. EMT also induces profound changes in epithelial responsiveness that affects innate immune signaling that may have impact on the adaptive immune response and effectiveness of glucocorticoid therapy in severe asthma. We discuss how this complex phenotype is beginning to be understood using systems biology-level approaches through perturbations coupled with high throughput profiling and computational modeling. Understanding the distinct changes induced by EMT at the systems level may provide translational strategies to reverse the altered signaling and physiology of refractory asthma.

Myeloid hypoxia-inducible factor 1α prevents airway allergy in mice through macrophage-mediated immunoregulation

Hypoxia-inducible factor (HIF) has important roles in promoting pro-inflammatory and bactericidal functions in myeloid cells. Conditional genetic ablation of its major subunit Hif1α in the myeloid lineage consequently results in decreased inflammatory responses in classical models of acute inflammation in mice. By contrast, we report here that mice conditionally deficient for Hif1α in myeloid cells display enhanced sensitivity to the development of airway allergy to experimental allergens and house-dust mite antigens. We support that upon allergen exposure, MyD88-dependent upregulation of Hif1α boosts the expression of the immunosuppressive cytokine interleukin (IL)-10 by lung interstitial macrophages (IMs). Hif1α-dependent IL-10 secretion is required for IMs to block allergen-induced dendritic cell activation and consequently for preventing the development of allergen-specific T-helper cell responses upon allergen exposure. Thus, this study supports that, in addition to its known pro-inflammatory activities, myeloid Hif1α possesses immunoregulatory functions implicated in the prevention of airway allergy.

The B cell helper side of neutrophils

Neutrophils use opsonizing antibodies to enhance the clearance of intruding microbes. Recent studies indicate that splenic neutrophils also induce antibody production by providing helper signals to B cells lodged in the MZ of the spleen. Here, we discuss the B cell helper function of neutrophils in the context of growing evidence indicating that neutrophils function as sophisticated regulators of innate and adaptive immune responses.

Neutrophil myeloperoxidase regulates T-cell-driven tissue inflammation in mice by inhibiting dendritic cell function

Myeloperoxidase (MPO) is important in intracellular microbial killing by neutrophils but extracellularly causes tissue damage. Its role in adaptive immunity and T-cell-mediated diseases is poorly understood. Here, T-cell responses in lymph nodes (LNs) were enhanced by MPO deletion or in vivo inhibition, causing enhanced skin delayed-type hypersensitivity and antigen (Ag)-induced arthritis. Responses of adoptively transferred OT-II T cells were greater in MPO-deficient than wild-type (WT) recipients. MPO, deposited by neutrophils in LNs after Ag injection, interacted with dendritic cells (DCs) in vivo. Culture of murine or human DCs with purified MPO or neutrophil supernatant showed that enzymatically dependent MPO-mediated inhibition of DC activation occurs via MPO-generated reactive intermediates and involves DC Mac-1. Transfer of DCs cultured with WT, but not MPO-deficient, neutrophil supernatant attenuated Ag-specific immunity in vivo. MPO deficiency or in vivo inhibition increased DC activation in LNs after immunization. Studies with DQ-ovalbumin showed that MPO inhibits Ag uptake/processing by DCs. In vivo DC transfer and in vitro studies showed that MPO inhibits DC migration to LNs by reducing their expression of CCR7. Therefore, MPO, via its catalytic activity, inhibits the generation of adaptive immunity by suppressing DC activation, Ag uptake/processing, and migration to LNs to limit pathological tissue inflammation.

Anti-tumor effect of SLPI on mammary but not colon tumor growth

Secretory leukocyte protease inhibitor (SLPI) is a serine protease inhibitor that was related to cancer development and metastasis dissemination on several types of tumors. However, it is not known the effect of SLPI on mammary and colon tumors. The aim of this study was to examine the effect of SLPI on mammary and colon tumor growth. The effect of SLPI was tested on in vitro cell apoptosis and in vivo tumor growth experiments. SLPI over-expressing human and murine mammary and colon tumor cells were generated by gene transfection. The administration of murine mammary tumor cells over-expressing high levels of SLPI did not develop tumors in mice. On the contrary, the administration of murine colon tumor cells over-expressing SLPI, developed faster tumors than control cells. Intratumoral, but not intraperitoneal administration of SLPI, delayed the growth of tumors and increased the survival of mammary but not colon tumor bearing mice. In vitro culture of mammary tumor cell lines treated with SLPI, and SLPI producer clones were more prone to apoptosis than control cells, mainly under serum deprivation culture conditions. Herein we demonstrated that SLPI induces the apoptosis of mammary tumor cells in vitro and decreases the mammary but not colon tumor growth in vivo. Therefore, SLPI may be a new potential therapeutic tool for certain tumors, such as mammary tumors.

Ectosomes of polymorphonuclear neutrophils activate multiple signaling pathways in macrophages

Ectosomes are vesicles shed directly from the cell surface. Human polymorphonuclear neutrophils release ectosomes (PMN-Ect) upon their activation. PMN-Ect expose phosphatidylserine (PS) on the outer leaflet of the plasma membrane, and down-modulate the inflammatory response of human macrophages and dendritic cells exposed to TLR-2 and -4 ligands. This down-modulation is mediated by PS via the engagement and activation of the Mer receptor tyrosine kinase (MerTK). In the present study, we demonstrate that exposure of macrophages to PMN-Ect activates directly 2 additional pathways, an immediate Ca(2+) flux and a rapid release of TGF-β1. As expected, the Ca(2+) flux was necessary for the activation of TLR-2 pathway with the release of cytokines. However, MerTK blockade with antibodies did not modify the Ca(2+) flux, indicating an independent activation of Ca(2+) by PMN-Ect. Striking was that the rapid release of TGF-β1 was independent of the MerTK pathway and did not require a Ca(2+) flux. TGF-β1 was present in cytosolic storage pools, which were depleted after exposure of the macrophages to PMN-Ect, and no increase in TGF-β1 mRNA could be detected in the 3 first hours when maximal release had occurred. The release of TGF-β1 by macrophages was seen only for PMN-Ect and not for PS-liposomes or erythrocyte ectosomes, which express PS. However, blocking the PS of PMN-Ect inhibited TGF-β1 release, suggesting that PS expression was necessary although not sufficient for this release. Interestingly, the effects of PMN-Ect pre-exposure were lasting for 24h with the macrophages being less receptive to TLR-2 activation and TGF-β1 stores remaining low. In sum, PMN-Ect induce several signaling pathways in resting and stimulated macrophages, which include independently the MerTK pathway, Ca(2+) flux and the release of stored TGF-β1, and each might influence the immunomodulatory effects of macrophages.

Neutrophils in the activation and regulation of innate and adaptive immunity

Neutrophils have long been viewed as the final effector cells of an acute inflammatory response, with a primary role in the clearance of extracellular pathogens. However, more recent evidence has extended the functions of these cells. The newly discovered repertoire of effector molecules in the neutrophil armamentarium includes a broad array of cytokines, extracellular traps and effector molecules of the humoral arm of the innate immune system. In addition, neutrophils are involved in the activation, regulation and effector functions of innate and adaptive immune cells. Accordingly, neutrophils have a crucial role in the pathogenesis of a broad range of diseases, including infections caused by intracellular pathogens, autoimmunity, chronic inflammation and cancer.

Neutrophils in the activation and regulation of innate and adaptive immunity

Neutrophils have long been viewed as the final effector cells of an acute inflammatory response, with a primary role in the clearance of extracellular pathogens. However, more recent evidence has extended the functions of these cells. The newly discovered repertoire of effector molecules in the neutrophil armamentarium includes a broad array of cytokines, extracellular traps and effector molecules of the humoral arm of the innate immune system. In addition, neutrophils are involved in the activation, regulation and effector functions of innate and adaptive immune cells. Accordingly, neutrophils have a crucial role in the pathogenesis of a broad range of diseases, including infections caused by intracellular pathogens, autoimmunity, chronic inflammation and cancer.

Lactobacilli secreting a tumor antigen and IL15 activates neutrophils and dendritic cells and generates cytotoxic T lymphocytes against cancer cells

Lactobacillus rhamnosus GG (LGG) has been used to successfully induce tumor regression in an orthotopic model of bladder cancer. Increased infiltration of neutrophils and macrophages into the tumor mass was observed after therapy. This study evaluates the potential of LGG to induce a directed anti-tumor response. Lactobacilli were modified to secrete the prostate specific antigen (PSA) or IL15 and PSA (IL-15-PSA). Neutrophils and DC were exposed to LGG for 2 h as in clinical therapy for bladder cancer. Recombinant LGG activated neutrophils (elevated MHC class I expression) induced DC maturation (increased expression of CD86, CD80, CD40, MHC II and CD83), T cell proliferation and PSA specific cytotoxic T lymphocytes (CTL) activity. IL15 enhanced direct DC activation of CTL. Thus LGG secreting tumor antigens may activate antigen specific immune responses when instilled intravesically and IL15 could enhance this response.

Micro-encapsulated secretory leukocyte protease inhibitor decreases cell-mediated immune response in autoimmune orchitis

AIMS

We previously reported that recombinant human Secretory Leukocyte Protease Inhibitor (SLPI) inhibits mitogen-induced proliferation of human peripheral blood mononuclear cells. To determine the relevance of this effect in vivo, we investigated the immuno-regulatory role of SLPI in an experimental autoimmune orchitis (EAO) model.

MAIN METHODS

In order to increase SLPI half life, poly-ε-caprolactone microspheres containing SLPI were prepared and used for in vitro and in vivo experiments. Multifocal orchitis was induced in Sprague-Dawley adult rats by active immunization with testis homogenate and adjuvants. Microspheres containing SLPI (SLPI group) or vehicle (control group) were administered s.c. to rats during or after the immunization period.

KEY FINDINGS

In vitro SLPI-release microspheres inhibited rat lymphocyte proliferation and retained trypsin inhibitory activity. A significant decrease in EAO incidence was observed in the SLPI group (37.5%) versus the control group (93%). Also, SLPI treatment significantly reduced severity of the disease (mean EAO score: control, 6.33±0.81; SLPI, 2.72±1.05). In vivo delayed-type hypersensitivity and ex vivo proliferative response to testicular antigens were reduced by SLPI treatment compared to control group (p<0.05).

SIGNIFICANCE

Our results highlight the in vivo immunosuppressive effect of released SLPI from microspheres which suggests its feasible therapeutic use.

Serine leucocyte proteinase inhibitor-treated monocyte inhibits human CD4(+) lymphocyte proliferation

Serine leucocyte proteinase inhibitor (SLPI) is the main serine proteinase inhibitor produced by epithelial cells and has been shown to be a pleiotropic molecule with anti-inflammatory and microbicidal activities. However, the role of SLPI on the adaptive immune response is not well established. Therefore, we evaluated the effect of SLPI on lymphocyte proliferation and cytokine production. Human peripheral blood mononuclear cells (PBMC) were treated with mitogens plus SLPI and proliferation was assessed by [(3) H]thymidine uptake. The SLPI decreased the lymphocyte proliferation induced by interleukin-2 (IL-2) or OKT3 monoclonal antibodies in a dose-dependent manner. Inhibition was not observed when depleting monocytes from the PBMC and it was restored by adding monocytes and SLPI. SLPI-treated monocyte slightly decreased MHC II and increased CD18 expression, and secreted greater amounts of IL-4, IL-6 and IL-10 in the cell culture supernatants. SLPI-treated monocyte culture supernatant inhibited the CD4(+) lymphocyte proliferation but did not affect the proliferation of CD8(+) cells. Moreover, IL-2 increased T-bet expression and the presence of SLPI significantly decreased it. Finally, SLPI-treated monocyte culture supernatant dramatically decreased interferon-γ but increased IL-4, IL-6 and IL-10 in the presence of IL-2-treated T cells. Our results demonstrate that SLPI target monocytes, which in turn inhibit CD4 lymphocyte proliferation and T helper type 1 cytokine secretion. Overall, these results suggest that SLPI is an alarm protein that modulates not only the innate immune response but also the adaptive immune response.

Neutrophil elastase treated dendritic cells promote the generation of CD4(+)FOXP3(+) regulatory T cells in vitro

We have previously shown that neutrophilic elastase converts human immature dendritic cells (DCs) into TGF-β secreting cells and reduces its allostimulatory ability. Since TGF-β has been involved in regulatory T cells (Tregs) induction we analyzed whether elastase or neutrophil-derived culture supernatant treated DCs induce CD4(+)FOXP3(+) Tregs in a mixed lymphocyte reaction (MLR). We found that elastase or neutrophil-derived culture supernatant treated DCs increased TGF-β and decreased IL-6 production. Together with this pattern of cytokines, we observed a higher number of CD4(+)FOXP3(+) cells in the MLR cultures induced by elastase or neutrophil-derived culture supernatant treated DCs but not with untreated DCs. The higher number of CD4(+)FOXP3(+) T cell population was not observed when the enzymatic activity of elastase was inhibited with an elastase specific inhibitor and also when a TGF-β1 blocking antibody was added during the MLR culture. The increased number of CD4(+) that express FOXP3 was also seen when CD4(+)CD25(-) purified T cells were cocultured with the TGF-β producing DCs. Furthermore, these FOXP3(+) T cells showed suppressive activity in vitro. These results identify a novel mechanism by which the tolerogenic DCs generated by elastase exposure contribute to the immune regulation and may be relevant in the pathogenesis of several lung diseases where the inflammatory infiltrate contains high numbers of neutrophils and high elastase concentrations.

Bowman-Birk inhibitor attenuates dystrophic pathology in mdx mice

Bowman-Birk inhibitor concentrate (BBIC), a serine protease inhibitor, has been shown to diminish disuse atrophy of skeletal muscle. Duchenne muscular dystrophy (DMD) results from a loss of dystrophin protein and involves an ongoing inflammatory response, with matrix remodeling and activation of transforming growth factor (TGF)-β(1) leading to tissue fibrosis. Inflammatory-mediated increases in extracellular protease activity may drive much of this pathological tissue remodeling. Hence, we evaluated the ability of BBIC, an extracellular serine protease inhibitor, to impact pathology in the mouse model of DMD (mdx mouse). Mdx mice fed 1% BBIC in their diet had increased skeletal muscle mass and tetanic force and improved muscle integrity (less Evans blue dye uptake). Importantly, mdx mice treated with BBIC were less susceptible to contraction-induced injury. Changes consistent with decreased degeneration/regeneration, as well as reduced TGF-β(1) and fibrosis, were observed in the BBIC-treated mdx mice. While Akt signaling was unchanged, myostatin activitation and Smad signaling were reduced. Given that BBIC treatment increases mass and strength, while decreasing fibrosis in skeletal muscles of the mdx mouse, it should be evaluated as a possible therapeutic to slow the progression of disease in human DMD patients.

Secretory leukocyte protease inhibitor and elafin/trappin-2: versatile mucosal antimicrobials and regulators of immunity

Elafin and secretory leukocyte protease inhibitor (SLPI) are pleiotropic molecules chiefly synthesized at the mucosal surface that have a fundamental role in the surveillance against microbial infections. Their initial discovery as anti-proteases present in the inflammatory milieu in chronic pathologies such as those of the lung suggested that they may play a role in keeping in check extracellular proteases released during the excessive activation of innate immune cells such as neutrophils. This soon proved to be a simplistic explanation, as other functions were also soon ascribed to these molecules (antimicrobial, modulation of innate and adaptive immunity, regulation of tissue repair). Data emanating from patients with chronic pathologies (in the lung and elsewhere) have shown that SLPI and elafin are often inactivated in inflammatory secretions, either through the action of host or microbial products, justifying attempts at antiprotease supplementation in clinical protocols. Although these have been sparse, proof of principle has been demonstrated, and future challenges will undoubtedly rest with improvements in methods of delivery in the context of tissue inflammation and in careful selection of patients more likely to benefit from SLPI/elafin augmentation.

The impact of vector-mediated neutrophil recruitment on cutaneous leishmaniasis

The dynamic process of pathogen transmission by the bite of an insect vector combines several biological processes that have undergone extensive co-evolution. Whereas the host response to an insect bite is only occasionally confronted with the parasitic pathogens that competent vectors might transmit, the transmitted parasites will always be confronted with the acute, wound-healing response that is initiated by the bite itself. Invariably, this response involves neutrophils. In the case of Leishmania, infection is initiated in the skin following the bite of an infected sand fly, suggesting that Leishmania must possess some means to survive their early encounter with recruited neutrophils at the bite site. Here, we review the literature regarding the impact of neutrophils on the outcome of infection with Leishmania, with special attention to the role of the sand fly bite.

Osteopontin promotes fibrosis in dystrophic mouse muscle by modulating immune cell subsets and intramuscular TGF-beta

Duchenne muscular dystrophy (DMD) is an X-linked, degenerative muscle disease that is exacerbated by secondary inflammation. Here, we characterized the immunological milieu of dystrophic muscle in mdx mice, a model of DMD, to identify potential therapeutic targets. We identified a specific subpopulation of cells expressing the Vbeta8.1/8.2 TCR that is predominant among TCR-beta+ T cells. These cells expressed high levels of osteopontin (OPN), a cytokine that promotes immune cell migration and survival. Elevated OPN levels correlated with the dystrophic process, since OPN was substantially elevated in the serum of mdx mice and muscle biopsies after disease onset. Muscle biopsies from individuals with DMD also had elevated OPN levels. To test the role of OPN in mdx muscle, mice lacking both OPN and dystrophin were generated and termed double-mutant mice (DMM mice). Reduced infiltration of NKT-like cells and neutrophils was observed in the muscle of DMM mice, supporting an immunomodulatory role for OPN in mdx muscle. Concomitantly, an increase in CD4+ and FoxP3+ Tregs was also observed in DMM muscle, which also showed reduced levels of TGF-beta, a known fibrosis mediator. These inflammatory changes correlated with increased strength and reduced diaphragm and cardiac fibrosis. These studies suggest that OPN may be a promising therapeutic target for reducing inflammation and fibrosis in individuals with DMD.

Secretory leukocyte protease inhibitor: a secreted pattern recognition receptor for mycobacteria

RATIONALE

Human secretory leukocyte protease inhibitor (SLPI) displays bactericidal activity against pathogens such as Escherichia coli and Streptococcus. Furthermore, it has been reported that murine SLPI shows potent antimycobacterial activity.

OBJECTIVES

The aim of the present study was to investigate whether human recombinant SLPI not only kills mycobacteria but also acts as a pattern recognition receptor for the host immune system.

METHODS

For the in vivo experiment, BALB/c mice were infected by intranasal instillation with Mycobacterium bovis BCG and viable BCG load in lung homogenates was later determined. For the in vitro experiments, SLPI was incubated overnight with a suspension of M. bovis BCG or the virulent strain Mycobacterium tuberculosis H37Rv, and the percentage survival as well as the binding of SLPI to mycobacteria was determined. Furthermore, bacteria phagocytosis was also determined by flow cytometry.

MEASUREMENTS AND MAIN RESULTS

Intranasal SLPI treatment decreased the number of colony-forming units recovered from lung homogenates, indicating that SLPI interfered with M. bovis BCG infection. Moreover, SLPI decreased the viability of both M. bovis BCG and H37Rv. We demonstrated that SLPI attached to the surface of the mycobacteria by binding to pathogen-associated molecular pattern mannan-capped lipoarabinomannans and phosphatidylinositol mannoside. Furthermore, we found that in the sputum of patients with tuberculosis, mycobacteria were coated with endogenous SLPI. Finally, we showed that phagocytosis of SLPI-coated mycobacteria was faster than that of uncoated bacteria.

CONCLUSIONS

The present results demonstrate for the first time that human SLPI kills mycobacteria and is a new pattern recognition receptor for them.

Neutrophil elastase (NE) and NE inhibitors: canonical and noncanonical functions in lung chronic inflammatory diseases (cystic fibrosis and chronic obstructive pulmonary disease)

Proteases and antiproteases have multiple important roles both in normal homeostasis and during inflammation. Antiprotease molecules may have developed in a parallel network, consisting of "alarm" and "systemic" inhibitors. Their primary function was thought until recently to mainly prevent the potential injurious effects of excess release of proteolytic enzymes, such as neutrophil elastase (NE), from inflammatory cells. However, recently, new potential roles have been ascribed to these antiproteases. We will review "canonical" and new "noncanonical" functions for these molecules, and more particularly, those pertaining to their role in innate and adaptive immunity (antibacterial activity and biasing of the adaptive immune response).