Neutrophil-derived CCL3 is essential for the rapid recruitment of dendritic cells to the site of Leishmania major inoculation in resistant mice

The pro-inflammatory responses of innate immune cells to Leishmania RNA virus 2-infected L. major support the survival and proliferation of the parasites

Infection of Leishmania by Leishmania RNA virus (LRV) has been proposed as a pathogenic factor that induces pro-inflammatory responses through the TLR3/TLR4 signaling pathway. We investigated the effect of L. major infection by LRV2 on innate immune cell responses (human neutrophil (HL-60) and macrophage (THP-1) cell lines). The expression levels of pro- and anti-inflammatory cytokine and chemokine genes as well as genes involved in the amino acid metabolism of arginine were then investigated by RT-qPCR. Moreover, the expression of TLR genes and their downstream signaling pathways were compared in THP-1 cells infected with the two isolates. Apoptosis was also evaluated in infected THP-1 and HL-60 cells using the PI/Annexin V flow cytometry assay. In both cell lines, the expression of pro-inflammatory cytokines increased in response to LRV2+ L. major (Lm+), and the expression of chemokines shifted toward macrophage recruitment. In contrast to LRV2- L. major (Lm-), Lm+ infected THP-1 cells acquired the M2-like phenotype. The presence of LRV2 increased the gene expression of TLRs and their signaling pathways, especially TLR3 and TLR4, which was proportional to the increase in pro-inflammatory cytokines. In addition, Lm+ increased the expression of IL-10 and IFN-β, which contribute to the survival and growth of the parasite in the phagolysosome. Altogether, our results showed that Lm+ could stimulate pro-inflammatory responses that promote parasite replication and stabilization in the host.

Hyperbaric oxygen-induced acute lung injury: A mouse model study on pathogenic characteristics and recovery dynamics

Oxygen is an essential substance for the maintenance of human life. It is also widely used in clinical and diving medicine. Although oxygen is crucial for survival, too much oxygen can be harmful. Excessive oxygen inhalation in a short period of time can lead to injury, and the lung is one of the main target organs. Acute lung injury (ALI) induced by hyperbaric oxygen (HBO) is notably more severe than that caused by normobaric oxygen, yet systematic research on such injury and its regression is scarce. In this study, two independent experiments were designed. In the first experiment, mice were exposed to 2 atmospheres absolute (ATA), ≥95% oxygen for 2, 4, 6, and 8 h. Changes in lung histopathology, inflammation and expression of chemokines, alveolar-capillary barrier, and 8-OHdG were detected before and after the exposure. In the second experiment, these parameters were measured at 0 h, 12 h, and 24 h following 6 h of exposure to 2 ATA of ≥95% oxygen. Research indicates that ALI induced by HBO is characterized histologically by alveolar expansion, atelectasis, inflammatory cell infiltration, and hemorrhage. At 2 ATA, significant changes in the alveolar-capillary barrier were observed after more than 95% oxygen exposure for 4 h, as evidenced by increased Evans blue (EB) extravasation (p = 0.0200). After 6 h of HBO exposure, lung tissue pathology scores, 8-OHdG levels, and inflammatory and chemotactic factors (such as Il6, CCL2, CCL3, CXCL5, and CXCL10), intercellular adhesion molecule 1 (ICAM1), and vascular cell adhesion molecule 1 (VCAM1) were significantly elevated. Compared to lung injury caused by normobaric oxygen, the onset time of injury was significantly shortened. Additionally, it was observed that these markers continued to increase after leaving the HBO environment, peaking at 12 h and starting to recover at 24 h, indicating that the peak of inflammatory lung injury occurs within 12 h post-exposure, with recovery beginning at 24 h. This contradicts the common belief that lung injury is alleviated upon removal from a high-oxygen environment. However, EB levels, which reflect damage to the alveolar-capillary barrier, and VE-Cadherin (VE-Cad), tight junction protein 1 (ZO-1), ICAM1, and VCAM1 remained significantly altered 24 h after leaving the HBO environment. This suggests that the alveolar-capillary barrier is the most sensitive and slowest recovering part of the lung injury induced by HBO. These findings can provide insights into the pathogenesis and progression of lung injury caused by HBO and offer references for identifying corresponding intervention targets.

Calcineurin-NFAT signaling controls neutrophils' ability of chemoattraction upon fungal infection

Calcineurin-nuclear factor of activated T cells (CN-NFAT) inhibitors are widely clinically used drugs for immunosuppression, but besides their required T cell response inhibition, they also undesirably affect innate immune cells. Disruption of innate immune cell function can explain the observed susceptibility of CN-NFAT inhibitor-treated patients to opportunistic fungal infections. Neutrophils play an essential role in innate immunity as a defense against pathogens; however, the effect of CN-NFAT inhibitors on neutrophil function was poorly described. Thus, we tested the response of human neutrophils to opportunistic fungal pathogens, namely Candida albicans and Aspergillus fumigatus, in the presence of CN-NFAT inhibitors. Here, we report that the NFAT pathway members were expressed in neutrophils and mediated part of the neutrophil response to pathogens. Upon pathogen exposure, neutrophils underwent profound transcriptomic changes with subsequent production of effector molecules. Importantly, genes and proteins involved in the regulation of the immune response and chemotaxis, including the chemokines CCL2, CCL3, and CCL4 were significantly upregulated. The presence of CN-NFAT inhibitors attenuated the expression of these chemokines and impaired the ability of neutrophils to chemoattract other immune cells. Our results amend knowledge about the impact of CN-NFAT inhibition in human neutrophils.

Exportin 1 governs the immunosuppressive functions of myeloid-derived suppressor cells in tumors through ERK1/2 nuclear export

Myeloid-derived suppressor cells (MDSCs) are a main driver of immunosuppression in tumors. Understanding the mechanisms that determine the development and immunosuppressive function of these cells could provide new therapeutic targets to improve antitumor immunity. Here, using preclinical murine models, we discovered that exportin 1 (XPO1) expression is upregulated in tumor MDSCs and that this upregulation is induced by IL-6-induced STAT3 activation during MDSC differentiation. XPO1 blockade transforms MDSCs into T-cell-activating neutrophil-like cells, enhancing the antitumor immune response and restraining tumor growth. Mechanistically, XPO1 inhibition leads to the nuclear entrapment of ERK1/2, resulting in the prevention of ERK1/2 phosphorylation following the IL-6-mediated activation of the MAPK signaling pathway. Similarly, XPO1 blockade in human MDSCs induces the formation of neutrophil-like cells with immunostimulatory functions. Therefore, our findings revealed a critical role for XPO1 in MDSC differentiation and suppressive functions; exploiting these new discoveries revealed new targets for reprogramming immunosuppressive MDSCs to improve cancer therapeutic responses.

In silico prediction of CD8+ and CD4+ T cell epitopes in Leishmania major proteome: Using immunoinformatics

The leishmaniases are NDTs (neglected tropical diseases) that affect people all over the world. They are brought on by protozoans from the genus Leishmania and disseminated by phlebotomine flies that are afflicted with the disease. The best option to manage and lower the incidence of these diseases has been thought by the creation of a safe and effective vaccination. This research used an in silico based mining approach to look for high potential epitopes that might bind to MHC Class I and MHC Class II molecules (mainly; HLA-A*02:01 & HLA-DRB1*03:01) from human population in order to promote vaccine development. Based on the presence of signal peptides, GPI anchors, antigenicity predictions, and a subtractive proteomic technique, we have screened 17 putative antigenic proteins from the 8083 total proteins of L. major. After that thorough immunogenic epitope prediction were done using IEDB-AR tools. We isolated five immunogenic epitopes (three 9-mer & two 15-mer) from five antigenic proteins through docking and MD simulation analysis. Finally, these five anticipated epitopes, viz., TLPEIPVNV, ELMAPVFGL, TLAAAVALL, NSINIRLDGVTSAGF and NVPLVVDASSLFRVA have considerably stronger binding potential with their respective alleles and may trigger immunological responses. The goal of this work was to identify MHC restricted epitopes for CD8+ and CD4+ T cells activation using immunoinformatics in order to identify potential vaccine candidates against L. major parasites.

The different impact of drug-resistant Leishmania on the transcription programs activated in neutrophils

Drug resistance threatens the effective control of infections, including parasitic diseases such as leishmaniases. Neutrophils are essential players in antimicrobial control, but their role in drug-resistant infections is poorly understood. Here, we evaluated human neutrophil response to clinical parasite strains having distinct natural drug susceptibility. We found that Leishmania antimony drug resistance significantly altered the expression of neutrophil genes, some of them transcribed by specific neutrophil subsets. Infection with drug-resistant parasites increased the expression of detoxification pathways and reduced the production of cytokines. Among these, the chemokine CCL3 was predominantly impacted, which resulted in an impaired ability of neutrophils to attract myeloid cells. Moreover, decreased myeloid recruitment when CCL3 levels are reduced was confirmed by blocking CCL3 in a mouse model. Collectively, these findings reveal that the interplay between naturally drug-resistant parasites and neutrophils modulates the infected skin immune microenvironment, revealing a key role of neutrophils in drug resistance.

Lombana C, Beiting D, Novais F, P. Carvalho L, M. Carvalho E, Scott P. CCR5 promotes the migration of pathological CD8+ T cells to the leishmanial lesions

Cytolytic CD8+ T cells mediate immunopathology in cutaneous leishmaniasis without controlling parasites. Here, we identify factors involved in CD8+ T cell migration to the lesion that could be targeted to ameliorate disease severity. CCR5 was the most highly expressed chemokine receptor in patient lesions, and the high expression of CCL3 and CCL4, CCR5 ligands, was associated with delayed healing of lesions. To test the requirement for CCR5, Leishmania-infected Rag1-/- mice were reconstituted with CCR5-/- CD8+ T cells. We found that these mice developed smaller lesions accompanied by a reduction in CD8+ T cell numbers compared to controls. We confirmed these findings by showing that the inhibition of CCR5 with maraviroc, a selective inhibitor of CCR5, reduced lesion development without affecting the parasite burden. Together, these results reveal that CD8+ T cells migrate to leishmanial lesions in a CCR5-dependent manner and that blocking CCR5 prevents CD8+ T cell-mediated pathology.

CC Chemokine Family Members' Modulation as a Novel Approach for Treating Central Nervous System and Peripheral Nervous System Injury-A Review of Clinical and Experimental Findings

Despite significant progress in modern medicine and pharmacology, damage to the nervous system with various etiologies still poses a challenge to doctors and scientists. Injuries lead to neuroimmunological changes in the central nervous system (CNS), which may result in both secondary damage and the development of tactile and thermal hypersensitivity. In our review, based on the analysis of many experimental and clinical studies, we indicate that the mechanisms occurring both at the level of the brain after direct damage and at the level of the spinal cord after peripheral nerve damage have a common immunological basis. This suggests that there are opportunities for similar pharmacological therapeutic interventions in the damage of various etiologies. Experimental data indicate that after CNS/PNS damage, the levels of 16 among the 28 CC-family chemokines, i.e., CCL1, CCL2, CCL3, CCL4, CCL5, CCL6, CCL7, CCL8, CCL9, CCL11, CCL12, CCL17, CCL19, CCL20, CCL21, and CCL22, increase in the brain and/or spinal cord and have strong proinflammatory and/or pronociceptive effects. According to the available literature data, further investigation is still needed for understanding the role of the remaining chemokines, especially six of them which were found in humans but not in mice/rats, i.e., CCL13, CCL14, CCL15, CCL16, CCL18, and CCL23. Over the past several years, the results of studies in which available pharmacological tools were used indicated that blocking individual receptors, e.g., CCR1 (J113863 and BX513), CCR2 (RS504393, CCX872, INCB3344, and AZ889), CCR3 (SB328437), CCR4 (C021 and AZD-2098), and CCR5 (maraviroc, AZD-5672, and TAK-220), has beneficial effects after damage to both the CNS and PNS. Recently, experimental data have proved that blockades exerted by double antagonists CCR1/3 (UCB 35625) and CCR2/5 (cenicriviroc) have very good anti-inflammatory and antinociceptive effects. In addition, both single (J113863, RS504393, SB328437, C021, and maraviroc) and dual (cenicriviroc) chemokine receptor antagonists enhanced the analgesic effect of opioid drugs. This review will display the evidence that a multidirectional strategy based on the modulation of neuronal-glial-immune interactions can significantly improve the health of patients after CNS and PNS damage by changing the activity of chemokines belonging to the CC family. Moreover, in the case of pain, the combined administration of such antagonists with opioid drugs could reduce therapeutic doses and minimize the risk of complications.

Testosterone affects type I/type II interferon response of neutrophils during hepatic amebiasis

Differences in immune response between men and women may influence the outcome of infectious diseases. Intestinal infection with Entamoeba histolytica leads to hepatic amebiasis, which is more common in males. Previously, we reported that innate immune cells contribute to liver damage in males in the murine model for hepatic amebiasis. Here, we focused on the influences of sex and androgens on neutrophils in particular. Infection associated with neutrophil accumulation in the liver was higher in male than in female mice and further increased after testosterone treatment in both sexes. Compared with female neutrophils, male neutrophils exhibit a more immature and less activated status, as evidenced by a lower proinflammatory N1-like phenotype and deconvolution, decreased gene expression of type I and type II interferon stimulated genes (ISGs) as well as downregulation of signaling pathways related to neutrophil activation. Neutrophils from females showed higher protein expression of the type I ISG viperin/RSAD2 during infection, which decreased by testosterone substitution. Moreover, ex vivo stimulation of human neutrophils revealed lower production of RSAD2 in neutrophils from men compared with women. These findings indicate that sex-specific effects on neutrophil physiology associated with maturation and type I IFN responsiveness might be important in the outcome of hepatic amebiasis.

How Neutrophils Shape the Immune Response: Reassessing Their Multifaceted Role in Health and Disease

Neutrophils are the most abundant of the circulating immune cells and are the first to be recruited to sites of inflammation. Neutrophils are a heterogeneous group of immune cells from which are derived extracellular traps (NETs), reactive oxygen species, cytokines, chemokines, immunomodulatory factors, and alarmins that regulate the recruitment and phenotypes of neutrophils, macrophages, dendritic cells, T cells, and B cells. In addition, cytokine-stimulated neutrophils can express class II major histocompatibility complex and the internal machinery necessary for successful antigen presentation to memory CD4+ T cells. This may be relevant in the context of vaccine memory. Neutrophils thus emerge as orchestrators of immune responses that play a key role in determining the outcome of infections, vaccine efficacy, and chronic diseases like autoimmunity and cancer. This review aims to provide a synthesis of current evidence as regards the role of these functions of neutrophils in homeostasis and disease.

CCR5 promotes the migration of CD8+ T cells to the leishmanial lesions

Cytolytic CD8+ T cells mediate immunopathology in cutaneous leishmaniasis without controlling parasites. Here, we identify factors involved in CD8+ T cell migration to the lesion that could be targeted to ameliorate disease severity. CCR5 was the most highly expressed chemokine receptor in patient lesions, and the high expression of CCL3 and CCL4, CCR5 ligands, was associated with delayed healing of lesions. To test the requirement for CCR5, Leishmania-infected Rag1-/- mice were reconstituted with CCR5-/- CD8+ T cells. We found that these mice developed smaller lesions accompanied by a reduction in CD8+ T cell numbers compared to controls. We confirmed these findings by showing that the inhibition of CCR5 with maraviroc, a selective inhibitor of CCR5, reduced lesion development without affecting the parasite burden. Together, these results reveal that CD8+ T cells migrate to leishmanial lesions in a CCR5-dependent manner and that blocking CCR5 prevents CD8+ T cell-mediated pathology.

Characterization of Chemotaxis-Associated Gene Dysregulation in Myeloid Cell Populations in the Lungs during Lipopolysaccharide-Mediated Acute Lung Injury

During endotoxin-induced acute lung injury (ALI), immune cell recruitment resulting from chemotaxis is mediated by CXC and CC chemokines and their receptors. In this study, we investigated the role of chemokines and their receptors in the regulation of myeloid cell populations in the circulation and the lungs of C57BL/6J mice exhibiting LPS-mediated ALI using single-cell RNA sequencing. During ALI, there was an increase in the myeloid cells, M1 macrophages, monocytes, neutrophils, and other granulocytes, whereas there was a decrease in the residential alveolar macrophages and M2 macrophages. Interestingly, LPS triggered the upregulation of CCL3, CCL4, CXCL2/3, and CXCL10 genes associated with cellular migration of various subsets of macrophages, neutrophils, and granulocytes. Furthermore, there was an increase in the frequency of myeloid cells expressing CCR1, CCR3, CCR5, and CXCR2 receptors during ALI. MicroRNA sequencing studies of vehicle versus LPS groups identified several dysregulated microRNAs targeting the upregulated chemokine genes. This study suggests that chemokine ligand-receptors interactions are responsible for myeloid cell heterogenicity and cellular recruitment to the lungs during ALI. The single-cell transcriptomics allowed for an in-depth assessment and characterization of myeloid cells involved in immune cell trafficking during ALI.

The cytokine/chemokine response in Leishmania/HIV infection and co-infection

HIV infection progressively weakens the immune system by infecting and destroying cells involved in host defense. Viral infection symptoms are generated and aggravated as immunosuppression progresses, triggered by the presence of opportunistic infections: among these is leishmaniasis, a disease caused by the intracellular parasite Leishmania. The incidence of this co-infection is growing progressively due to the geographic distribution overlap. Both pathogens infect monocytes/macrophages and dendritic cells, although they can also modulate the activity of other cells without co-infecting, such as T and B lymphocytes. Leishmania/HIV co-infection could be described as a system comprising modulations of cell surface molecule expression, production of soluble factors, and intracellular death activities, leading ultimately to the potentiation of infectivity, replication, and spread of both pathogens. This review describes the cytokine/chemokine response in Leishmania/HIV infection and co-infection, discussing how these molecules modulate the course of the disease and analyzing the therapeutic potential of targeting this network.

NLRP12-expressing dendritic cells mediate both dissemination of infection and adaptive immune responses in visceral leishmaniasis

The NLR protein NLRP12 contributes to innate immunity, but the mechanism remains elusive. Infection of Nlrp12 -/- or wild-type mice with Leishmania infantum led to aberrant parasite tropism. Parasites replicated to higher levels in livers of Nlrp12 -/- mice than in the livers of WT mice and failed to disseminate to spleens. Most retained liver parasites resided in dendritic cells (DCs), with correspondingly fewer infected DCs in spleens. Furthermore, Nlrp12 -/- DCs expressed lower CCR7 than WT DCs, failed to migrate toward CCL19 or CCL21 in chemotaxis assays, and migrated poorly to draining lymph nodes after sterile inflammation. Leishmania-infected Nlpr12 -/- DCs were significantly less effective at transporting parasites to lymph nodes than WT DCs. Consistently, adaptive immune responses were also impaired in infected Nlrp12 -/- mice. We hypothesize that Nlrp12-expressing DCs are required for efficient dissemination and immune clearance of L. infantum from the site of initial infection. This is at least partly due to the defective expression of CCR7.

Neutrophil-T cell crosstalk and the control of the host inflammatory response

While fundamental in their innate role in combating infection and responding to injury, neutrophils are emerging as key modulators of adaptive immune responses. Such functions are attained via both soluble and nonsoluble effectors that enable at least two major downstream outcomes: first, to mediate and control acute inflammatory responses and second, to regulate adaptive immunity and ultimately promoting the development and maintenance of immune tolerance either by releasing immuno-modulatory factors, including cytokines, or by directly interacting with cells of the adaptive immune system. Herein, we review these novel properties of neutrophils and redefine the pathophysiological functions of these fascinating multi-tasking cells, exploring the different mechanisms through which neutrophils are able to either enhance and orchestrate T cell pro-inflammatory responses or inhibit T cell activity to maintain immune tolerance.

Gasdermin-D activation promotes NLRP3 activation and host resistance to Leishmania infection

Intracellular parasites from the Leishmania genus cause Leishmaniasis, a disease affecting millions of people worldwide. NLRP3 inflammasome is key for disease outcome, but the molecular mechanisms upstream of the inflammasome activation are still unclear. Here, we demonstrate that despite the absence of pyroptosis, Gasdermin-D (GSDMD) is active at the early stages of Leishmania infection in macrophages, allowing transient cell permeabilization, potassium efflux, and NLRP3 inflammasome activation. Further, GSDMD is processed into a non-canonical 25 kDa fragment. Gsdmd-/- macrophages and mice exhibit less NLRP3 inflammasome activation and are highly susceptible to infection by several Leishmania species, confirming the role of GSDMD for inflammasome-mediated host resistance. Active NLRP3 inflammasome and GSDMD are present in skin biopsies of patients, demonstrating activation of this pathway in human leishmaniasis. Altogether, our findings reveal that Leishmania subverts the normal functions of GSDMD, an important molecule to promote inflammasome activation and immunity in Leishmaniasis.

Neutrophil Heterogeneity and its Roles in the Inflammatory Network after Ischemic Stroke

As the first peripheral immune cells to enter the brain after ischemic stroke, neutrophils are important participants in stroke-related neuroinflammation. Neutrophils are quickly mobilized from the periphery in response to a stroke episode and cross the blood-brain barrier to reach the ischemic brain parenchyma. This process involves the mobilization and activation of neutrophils from peripheral immune organs (including the bone marrow and spleen), their chemotaxis in the peripheral blood, and their infiltration into the brain parenchyma (including disruption of the blood-brain barrier, inflammatory effects on brain tissue, and interactions with other immune cell types). In the past, it was believed that neutrophils aggravated brain injuries through the massive release of proteases, reactive oxygen species, pro-inflammatory factors, and extracellular structures known as neutrophil extracellular traps (NETs). With the failure of early clinical trials targeting neutrophils and uncovering their underlying heterogeneity, our view of their role in ischemic stroke has become more complex and multifaceted. As neutrophils can be divided into N1 and N2 phenotypes in tumors, neutrophils have also been found to have similar phenotypes after ischemic stroke, and play different roles in the development and prognosis of ischemic stroke. N1 neutrophils are dominant during the acute phase of stroke (within three days) and are responsible for the damage to neural structures via the aforementioned mechanisms. However, the proportion of N2 neutrophils gradually increases in later phases, and this has a beneficial effect through the release of anti-inflammatory factors and other neuroprotective mediators. Moreover, the N1 and N2 phenotypes are highly plastic and can be transformed into each other under certain conditions. The pronounced differences in their function and their high degree of plasticity make these neutrophil subpopulations promising targets for the treatment of ischemic stroke.

Age-dependent nasal immune responses in non-hospitalized bronchiolitis children

Bronchiolitis in children is associated with significant rates of morbidity and mortality. Many studies have been performed using samples from hospitalized bronchiolitis patients, but little is known about the immunological responses from infants suffering from mild/moderate bronchiolitis that do not require hospitalization. We have studied a collection of nasal lavage fluid (NLF) samples from outpatient bronchiolitis children as a novel strategy to unravel local humoral and cellular responses, which are not fully characterized. The children were age-stratified in three groups, two of them (GI under 2-months, GII between 2-4 months) presenting a first episode of bronchiolitis, and GIII (between 4 months and 2 years) with recurrent respiratory infections. Here we show that elevated levels of pro-inflammatory cytokines (IL1β, IL6, TNFα, IL18, IL23), regulatory cytokines (IL10, IL17A) and IFNγ were found in the three bronchiolitis cohorts. However, little or no change was observed for IL33 and MCP1, at difference to previous results from bronchiolitis hospitalized patients. Furthermore, our results show a tendency to IL1β, IL6, IL18 and TNFα increased levels in children with mild pattern of symptom severity and in those in which non RSV respiratory virus were detected compared to RSV+ samples. By contrast, no such differences were found based on gender distribution. Bronchiolitis NLFs contained more IgM, IgG1, IgG3 IgG4 and IgA than NLF from their age-matched healthy controls. NLF from bronchiolitis children predominantly contained neutrophils, and also low frequency of monocytes and few CD4+ and CD8+ T cells. NLF from infants older than 4-months contained more intermediate monocytes and B cell subsets, including naïve and memory cells. BCR repertoire analysis of NLF samples showed a biased VH1 usage in IgM repertoires, with low levels of somatic hypermutation. Strikingly, algorithmic studies of the mutation profiles, denoted antigenic selection on IgA-NLF repertoires. Our results support the use of NLF samples to analyze immune responses and may have therapeutic implications.

Mechanisms regulating neutrophil responses in immunity, allergy, and autoimmunity

Neutrophil granulocytes, or neutrophils, are the most abundant circulating leukocytes in humans and indispensable for antimicrobial immunity, as exemplified in patients with inborn and acquired defects of neutrophils. Neutrophils were long regarded as the foot soldiers of the immune system, solely destined to execute a set of effector functions against invading pathogens before undergoing apoptosis, the latter of which was ascribed to their short life span. This simplistic understanding of neutrophils has now been revised on the basis of insights gained from the use of mouse models and single-cell high-throughput techniques, revealing tissue- and context-specific roles of neutrophils in guiding immune responses. These studies also demonstrated that neutrophil responses were controlled by sophisticated feedback mechanisms, including directed chemotaxis of neutrophils to tissue-draining lymph nodes resulting in modulation of antimicrobial immunity and inflammation. Moreover, findings in mice and humans showed that neutrophil responses adapted to different deterministic cytokine signals, which controlled their migration and effector function as well as, notably, their biologic clock by affecting the kinetics of their aging. These mechanistic insights have important implications for health and disease in humans, particularly, in allergic diseases, such as atopic dermatitis and allergic asthma bronchiale, as well as in autoinflammatory and autoimmune diseases. Hence, our improved understanding of neutrophils sheds light on novel therapeutic avenues, focusing on molecularly defined biologic agents.

Context-dependent function of TSLP and IL-1β in skin allergic sensitization and atopic march

Atopic diseases, including atopic dermatitis (AD) and asthma, affect a large proportion of the population, with increasing prevalence worldwide. AD often precedes the development of asthma, known as the atopic march. Allergen sensitization developed through the barrier-defective skin of AD has been recognized to be a critical step leading to asthma, in which thymic stromal lymphopoietin (TSLP) was previously shown to be critical. In this study, using a laser-assistant microporation system to disrupt targeted skin layers for generating micropores at a precise anatomic depth of mouse skin, we model allergen exposure superficially or deeply in the skin, leading to epicutaneous sensitization or dermacutaneous sensitization that is associated with a different cytokine microenvironment. Our work shows a differential requirement for TSLP in these two contexts, and identifies an important function for IL-1β, which is independent of TSLP, in promoting allergen sensitization and subsequent allergic asthma.

Allergic sensitisation in the skin can lead to allergic dermatitis and further to airway asthma in a process of atopic march. Here the authors examine the difference between superficial or deep skin sensitisation, characterise the immune cells generated and show differential TSLP and IL-1β involvement.

The Dynamic Contribution of Neutrophils in the Chronic Respiratory Diseases

Asthma, chronic obstructive pulmonary disease, and idiopathic pulmonary fibrosis are representative chronic respiratory diseases (CRDs). Although they differ in terms of disease presentation, they are all thought to arise from unresolved inflammation. Neutrophils are not only the first responders to acute inflammation, but they also help resolve the inflammation. Notably, emerging clinical studies show that CRDs are associated with systemic and local elevation of neutrophils. Moreover, murine studies suggest that airway-infiltrating neutrophils not only help initiate airway inflammation but also prolong the inflammation. Given this background, this review describes neutrophil-mediated immune responses in CRDs and summarizes the completed, ongoing, and potential clinical trials that test the therapeutic value of targeting neutrophils in CRDs. The review also clarifies the importance of understanding how neutrophils interact with other immune cells and how these interactions contribute to chronic inflammation in specific CRDs. This information may help identify future therapeutic strategies for CRDs.

The tick and I: Parasite-host interactions between ticks and humans

Ticks, particularly hard ticks (Ixodidae), which are among the most important vectors of dangerous infectious agents, feed on their hosts for extended periods of time. With this lifestyle, numerous adaptations have evolved in ticks and their hosts, the pharmacological importance of which is increasingly being recognized. Many bioactive substances in tick saliva are being considered as the basis of new drugs. For example, components of tick cement can be developed into tissue adhesives or wound closures. Analgesic and antipruritic salivary components inhibit histamine or bradykinin, while other tick-derived molecules bind opioid or cannabinoid receptors. Tick saliva inhibits the extrinsic, intrinsic, or common pathway of blood coagulation with implications for the treatment of thromboembolic diseases. It contains vasodilating substances and affects wound healing. The broad spectrum of immunomodulatory and immunosuppressive effects of tick saliva, such as inhibition of chemokines or cellular immune responses, allows development of drugs against inflammation in autoimmune diseases and/or infections. Finally, modern vaccines against ticks can curb the spread of serious infections. The medical importance of the complex tick-host interactions is increasingly being recognized and translated into first clinical applications. Using selected examples, an overview of the mutual adaptations of ticks and hosts is given here, focusing on their significance to medical advance.

Role of Chemokines in the Pathogenesis of Visceral Leishmaniasis

Abstract:

Visceral leishmaniasis (VL; also known as kala-azar), caused by the protozoan parasite Leishmania donovani is characterized by the inability of the host to generate an effective immune response. The manifestations of the disease depends on involvement of various immune components such as activation of macrophages, cell mediated immunity, secretion of cytokines and chemokines, etc. Macrophages are the final host cells for Leishmania parasites to multiply, and they are the key to a controlled or aggravated response that leads to clinical symptoms. The two most common macrophage phenotypes are M1 and M2. The pro-inflammatory microenvironment (mainly by IL-1β, IL-6, IL-12, IL-23, and TNF-α cytokines) and tissue injury driven by classically activated macrophages (M1-like) and wound healing driven by alternatively activated macrophages (M2-like) in an anti-inflammatory environment (mainly by IL-10, TGF-β, chemokine ligand (CCL)1, CCL2, CCL17, CCL18, and CCL22). Moreover, on polarized Th cells, chemokine receptors are expressed differently. Typically, CXCR3 and CCR5 are preferentially expressed on polarized Th1 cells, whereas CCR3, CCR4 and CCR8 have been associated with the Th2 phenotype. Further, the ability of the host to produce a cell-mediated immune response capable of regulating and/or eliminating the parasite is critical in the fight against the disease. Here, we review the interactions between parasites and chemokines and chemokines receptors in the pathogenesis of VL.

IBD Subtype-Regulators IFNG and GBP5 Identified by Causal Inference Drive More Intense Innate Immunity and Inflammatory Responses in CD Than Those in UC

Background: The pathological differences between Crohn’s disease (CD) and ulcerative colitis (UC) are substantial and unexplained yet. Here, we aimed to identify potential regulators that drive different pathogenesis of CD and UC by causal inference analysis of transcriptome data.

Methods: Kruskal–Wallis and Dunnett’s tests were performed to identify differentially expressed genes (DEGs) among CD patients, UC patients, and controls. Subsequently, differentially expressed pathways (DEPs) between CD and UC were identified and used to construct the interaction network of DEPs. Causal inference was performed to identify IBD subtype-regulators. The expression of the subtype-regulators and their downstream genes was validated by qRT-PCR with an independent cohort.

Results: Compared with the control group, we identified 1,352 and 2,081 DEGs in CD and UC groups, respectively. Multiple DEPs between CD and UC were closely related to inflammation-related pathways, such as NOD-like receptor signaling, IL-17 signaling, and chemokine signaling pathways. Based on the priori interaction network of DEPs, causal inference analysis identified IFNG and GBP5 as IBD subtype-regulators. The results with the discovery cohort showed that the expression level of IFNG, GBP5, and NLRP3 was significantly higher in the CD group than that in the UC group. The regulation relationships among IFNG, GBP5, and NLRP3 were confirmed with transcriptome data from an independent cohort and validated by qRT-PCR.

Conclusion: Our study suggests that IFNG and GBP5 were IBD subtype-regulators that trigger more intense innate immunity and inflammatory responses in CD than those in UC. Our findings reveal pathomechanical differences between CD and UC that may contribute to personalized treatment for CD and UC.

Local Release of TGF-β Inhibitor Modulates Tumor-Associated Neutrophils and Enhances Pancreatic Cancer Response to Combined Irreversible Electroporation and Immunotherapy

Pancreatic cancer is a deadly disease with little response to standard therapies. Irreversible electroporation (IRE) has emerged as a novel ablative technique for the clinical treatment of pancreatic cancer. Combinations of IRE and immunotherapies, including anti-programmed death 1 (αPD1) immune checkpoint blockade, have shown promising efficacy in both preclinical and clinical studies. However, tumor recurrence remains an obstacle that needs to be overcome. It herein is shown that IRE induces a substantial infiltration of neutrophils into pancreatic tumors. These neutrophils are then polarized into a protumor phenotype by immunosuppressive cues, in particular transforming growth factor β (TGF-β). Using glutathione-responsive degradable mesoporous silica nanoparticles loaded with SB525334, an inhibitor of TGF-β1 receptor, it is demonstrated that local inhibition of TGF-β within the tumor microenvironment promotes neutrophil polarization into an antitumor phenotype, enhances pancreatic cancer response to combined IRE and αPD1 therapy, and induces long-term antitumor memory. The therapeutic efficacy is also attributed to tumor infiltration by CD8⁺ cytotoxic T cells, depletion of regulatory T cells, and maturation of antigen-presenting dendritic cells. Thus, modulating neutrophil polarization with nanomedicine is a promising strategy for treating pancreatic cancer.

Neutrophil-dendritic cell interaction plays an important role in live attenuated Leishmania vaccine induced immunity

Background

Neutrophils are involved in the initial host responses to pathogens. Neutrophils can activate T cell responses either independently or through indirect involvement of Dendritic cells (DCs). Recently we have demonstrated direct neutrophil-T cell interactions that initiate adaptive immune responses following immunization with live attenuated Leishmania donovani centrin deleted parasite vaccine (LdCen^-/-). However, neutrophil-DC interactions in T cell priming in vaccine immunity in general are not known. In this study we evaluated the interaction between neutrophils and DCs during LdCen^-/- infection and compared with wild type parasite (LdWT) both in vitro and in vivo.

Methodology/findings

LdCen^-/- parasite induced increased expression of CCL3 in neutrophils caused higher recruitment of DCs capable of inducing a strong proinflammatory response and elevated co-stimulatory molecule expression compared to LdWT infection. To further illustrate neutrophil-DCs interactions in vivo, we infected LYS-eGFP mice with red fluorescent LdWT/LdCen^-/- parasites and sort selected DCs that engulfed the neutrophil containing parasites or DCs that acquired the parasites directly in the ear draining lymph nodes (dLN) 5d post infection. The DCs predominantly acquired the parasites by phagocytosing infected neutrophils. Specifically, DCs containing LdCen^-/- parasitized neutrophils exhibited a proinflammatory phenotype, increased expression of costimulatory molecules and initiated higher CD4⁺T cell priming ex-vivo. Notably, potent DC activation occurred when LdCen^-/- parasites were acquired indirectly via engulfment of parasitized neutrophils compared to direct engulfment of LdCen^-/- parasites by DCs. Neutrophil depletion in LdCen^-/- infected mice significantly abrogated expression of CCL3 resulting in decreased DC recruitment in ear dLN. This event led to poor CD4⁺Th1 cell priming ex vivo that correlated with attenuated Tbet expression in ear dLN derived CD4⁺ T cells in vivo.

Conclusions

Collectively, LdCen^-/- containing neutrophils phagocytized by DC markedly influence the phenotype and antigen presenting capacity of DCs early on and thus play an immune-regulatory role in shaping vaccine induced host protective response.

Visceral Leishmaniasis (VL), caused by the protozoan parasites of the genus Leishmania is a neglected tropical disease. Leishmania donovani is the principal causative agent of VL in East Africa and the Indian subcontinent whereas in Europe, North Africa, and Latin America VL is mainly caused by Leishmania infantum. No licensed vaccine exists against VL. We have reported previously that live attenuated centrin gene-deleted L. donovani (LdCen^-/-) parasite vaccine induced strong innate immunity which leads to a protective Th1 response in animal models. We recently demonstrated that neutrophils play an indispensable role following immunization with LdCen^-/- parasites in inducing protective Th1 immune response. However, neutrophils also secrete chemokines that attract other innate cells such as dendritic cells and regulate their activities. In the current study we analyzed the interplay between neutrophils and DCs, and its effects on T cell activation during LdCen^-/- infection and compared with wild type parasite (LdWT) infection. We observed that higher recruitment of DCs occurred in LdCen^-/- infected mice ear draining lymph nodes compared to LdWT. This recruitment is facilitated by increased secretion of the chemokine CCL3 by neutrophils. A markedly decreased DC recruitment was observed in LdCen^-/- infected mice following CCL3 neutralization indicating the key role of neutrophils in DC recruitment. Further, we demonstrated that DCs that ingest LdCen^-/- infected neutrophils are better activated than those that acquire the parasites independent of neutrophils. Notably neutrophil depletion in LdCen^-/- infected mice also attenuated activation of DCs in the ear dLN that resulted in poor CD4⁺T cell priming. Our results reveal that interaction between neutrophils and DCs play an important role in shaping proinflammatory immune response induced by a live attenuated Leishmania vaccine.

Modulation of Host Immune Response during Leishmania infantum Natural Infection: A Whole-Transcriptome Analysis of the Popliteal Lymph Nodes in Dogs

Leishmania infantum, the etiological agent of canine leishmaniosis (CanL) in Europe, was responsible of the largest outbreak of human leishmaniosis in Spain. The parasite infects and survives within myeloid lineage cells, causing a potentially fatal disease if left untreated. The only treatment option relies on chemotherapy, although immunotherapy strategies are being considered as novel approaches to prevent progression of the disease. To this aim, a deeper characterization of the molecular mechanisms behind the immunopathogenesis of leishmaniosis is necessary. Thus, we evaluated, for the first time, the host immune response during L. infantum infection through transcriptome sequencing of the popliteal lymph nodes aspirates of dogs with CanL. Differential expression and weighted gene co-expression network analyses were performed, resulting in the identification of 5,461 differentially expressed genes (DEGs) and four key modules in sick dogs, compared to controls. As expected, defense response was the highest enriched biological process in the DEGs, with six genes related to immune response against pathogens (CHI3L1, SLPI, ACOD1, CCL5, MPO, BPI) included among the ten most expressed genes; and two of the key co-expression modules were associated with regulation of immune response, which also positively correlated with clinical stage and blood monocyte concentration. In particular, sick dogs displayed significant changes in the expression of Th1, Th2, Th17 and Tr1 cytokines (e. g. TNF-α, IFN-γ, IL-21, IL-17, IL-15), markers of T cell and NK cell exhaustion (e. g. LAG3, CD244, Blimp-1, JUN), and B cell, monocyte and macrophage disrupted functionality (e. g. CD40LG, MAPK4, IL-1R, NLRP3, BCMA). In addition, we found an overexpression of XBP1 and some other genes involved in endoplasmic reticulum stress and the IRE1 branch of the unfolded protein response, as well as one co-expression module associated with these processes, which could be induced by L. infantum to prevent host cell apoptosis and modulate inflammation-induced lymphangiogenesis at lymph nodes. Moreover, 21 lncRNAs were differentially expressed in sick dogs, and one key co-expression module was associated with chromatin organization, suggesting that epigenetic mechanisms could also contribute to dampening host immune response during natural L. infantum infection in the lymph nodes of dogs suffering from clinical leishmaniosis.

Exploring the paradox of defense between host and Leishmania parasite

Leishmaniasis, a neglected tropical disease, still remains a global concern for the healthcare sector. The primary causative agents of the disease comprise diverse leishmanial species, leading to recurring failures in disease diagnosis and delaying the initiation of appropriate chemotherapy. Various species of the Leishmania parasite cause diverse clinical manifestations ranging from skin ulcers to systemic infections. Therefore, host immunity in response to different forms of infecting species of Leishmania becomes pivotal in disease progression or regression. Thus, understanding the paradox of immune arsenals during host and parasite interface becomes crucial to eliminate this deadly disease. In the present review, we have elaborated on the immunological perspectives of the disease and discussed primary host immune cells that form a defense line to counteract parasite infection. Furthermore, we also have shed light on the immune cells and effector molecules responsible for parasite survival in host lethal milieu/ environment. Next, we have highlighted recent molecules/compounds showing potent leishmanicidal activities pertaining to their pro-oxidant and immuno-modulatory mechanisms. This review addresses an immuno-biological overview of the factors influencing the parasitic disease, as this knowledge can aid in the unraveling/ identification of potential biomarkers, novel therapeutics, and vaccine candidates against leishmaniasis.

Toxoplasma gondii-Induced Neutrophil Extracellular Traps Amplify the Innate and Adaptive Response

Toxoplasmosis affects one-third of the human population worldwide. Humans are accidental hosts and are infected after consumption of undercooked meat and water contaminated with Toxoplasma gondii cysts and oocysts, respectively. Neutrophils have been shown to participate in the control of T. gondii infection in mice through a variety of effector mechanisms, such as reactive oxygen species (ROS) and neutrophil extracellular trap (NET) formation. However, few studies have demonstrated the role of neutrophils in individuals naturally infected with T. gondii. In the current study, we evaluated the activation status of neutrophils in individuals with acute or chronic toxoplasmosis and determined the role of T. gondii-induced NET formation in the amplification of the innate and adaptive immune responses. We observed that neutrophils are highly activated during acute infection through increased expression of CD66b. Moreover, neutrophils from healthy donors (HDs) cocultured with tachyzoites produced ROS and formed NETs, with the latter being dependent on glycolysis, succinate dehydrogenase, gasdermin D, and neutrophil elastase. Furthermore, we observed elevated levels of the chemokines (CXC motif) CXCL8 and (CC motif) CCL4 ligands in plasma from patients with acute toxoplasmosis and production by neutrophils from HDs exposed to T. gondii. Finally, we showed that T. gondii-induced NETs activate neutrophils and promote the recruitment of autologous CD4⁺ T cells and the production of interferon gamma (IFN-γ), tumor necrosis factor (TNF), interleukin 6 (IL-6), IL-17, and IL-10 by peripheral blood mononuclear cells. In conclusion, we demonstrated that T. gondii activates neutrophils and promotes the release of NETs, which amplify human innate and adaptive immune responses.

The Paradox of a Phagosomal Lifestyle: How Innate Host Cell-Leishmania amazonensis Interactions Lead to a Progressive Chronic Disease

Intracellular phagosomal pathogens represent a formidable challenge for innate immune cells, as, paradoxically, these phagocytic cells can act as both host cells that support pathogen replication and, when properly activated, are the critical cells that mediate pathogen elimination. Infection by parasites of the Leishmania genus provides an excellent model organism to investigate this complex host-pathogen interaction. In this review we focus on the dynamics of Leishmania amazonensis infection and the host innate immune response, including the impact of the adaptive immune response on phagocytic host cell recruitment and activation. L. amazonensis infection represents an important public health problem in South America where, distinct from other Leishmania parasites, it has been associated with all three clinical forms of leishmaniasis in humans: cutaneous, muco-cutaneous and visceral. Experimental observations demonstrate that most experimental mouse strains are susceptible to L. amazonensis infection, including the C57BL/6 mouse, which is resistant to other species such as Leishmania major, Leishmania braziliensis and Leishmania infantum. In general, the CD4⁺ T helper (Th)1/Th2 paradigm does not sufficiently explain the progressive chronic disease established by L. amazonensis, as strong cell-mediated Th1 immunity, or a lack of Th2 immunity, does not provide protection as would be predicted. Recent findings in which the balance between Th1/Th2 immunity was found to influence permissive host cell availability via recruitment of inflammatory monocytes has also added to the complexity of the Th1/Th2 paradigm. In this review we discuss the roles played by innate cells starting from parasite recognition through to priming of the adaptive immune response. We highlight the relative importance of neutrophils, monocytes, dendritic cells and resident macrophages for the establishment and progressive nature of disease following L. amazonensis infection.

Deoxyhypusine synthase promotes a pro-inflammatory macrophage phenotype

The metabolic inflammation (meta-inflammation) of obesity is characterized by proinflammatory macrophage infiltration into adipose tissue. Catalysis by deoxyhypusine synthase (DHPS) modifies the translation factor eIF5A to generate a hypusine (Hyp) residue. Hypusinated eIF5A (eIF5A^Hyp) controls the translation of mRNAs involved in inflammation, but its role in meta-inflammation has not been elucidated. Levels of eIF5A^Hyp were found to be increased in adipose tissue macrophages from obese mice and in murine macrophages activated to a proinflammatory M1-like state. Global proteomics and transcriptomics revealed that DHPS deficiency in macrophages altered the abundance of proteins involved in NF-κB signaling, likely through translational control of their respective mRNAs. DHPS deficiency in myeloid cells of obese mice suppressed M1 macrophage accumulation in adipose tissue and improved glucose tolerance. These findings indicate that DHPS promotes the post-transcriptional regulation of a subset of mRNAs governing inflammation and chemotaxis in macrophages and contributes to a proinflammatory M1-like phenotype.

Ly6G deficiency alters the dynamics of neutrophil recruitment and pathogen capture during Leishmania major skin infection

Neutrophils represent one of the first immune cell types recruited to sites of infection, where they can control pathogens by phagocytosis and cytotoxic mechanisms. Intracellular pathogens such as Leishmania major can hijack neutrophils to establish an efficient infection. However the dynamic interactions of neutrophils with the pathogen and other cells at the site of the infection are incompletely understood. Here, we have investigated the role of Ly6G, a homolog of the human CD177 protein, which has been shown to interact with cell adhesion molecules, and serves as a bona fide marker for neutrophils in mice. We show that Ly6G deficiency decreases the initial infection rate of neutrophils recruited to the site of infection. Although the uptake of L. major by subsequently recruited monocytes was tightly linked with the concomitant uptake of neutrophil material, this process was not altered by Ly6G deficiency of the neutrophils. Instead, we observed by intravital 2-photon microscopy that Ly6G-deficient neutrophils entered the site of infection with delayed initial recruitment kinetics. Thus, we conclude that by promoting neutrophils’ ability to efficiently enter the site of infection, Ly6G contributes to the early engagement of intracellular pathogens by the immune system.

Neutrophils in respiratory viral infections

Viral respiratory infections are a common cause of severe disease, especially in infants, people who are immunocompromised, and in the elderly. Neutrophils, an important innate immune cell, infiltrate the lungs rapidly after an inflammatory insult. The most well-characterized effector mechanisms by which neutrophils contribute to host defense are largely extracellular and the involvement of neutrophils in protection from numerous bacterial and fungal infections is well established. However, the role of neutrophils in responses to viruses, which replicate intracellularly, has been less studied. It remains unclear whether and, by which underlying immunological mechanisms, neutrophils contribute to viral control or confer protection against an intracellular pathogen. Furthermore, neutrophils need to be tightly regulated to avoid bystander damage to host tissues. This is especially relevant in the lung where damage to delicate alveolar structures can compromise gas exchange with life-threatening consequences. It is inherently less clear how neutrophils can contribute to host immunity to viruses without causing immunopathology and/or exacerbating disease severity. In this review, we summarize and discuss the current understanding of how neutrophils in the lung direct immune responses to viruses, control viral replication and spread, and cause pathology during respiratory viral infections.

Retinoblastoma tumor cell proliferation is negatively associated with an immune gene expression signature and increased immune cells

This study focuses on gene expression differences between early retinal states that ultimately lead to normal development, late onset retinoblastoma, or rapid bilateral retinoblastoma tumors. The late-onset and early-onset retinoblastoma tumor cells are remarkably similar to normally proliferating retinal progenitor cells, but they fail to properly express differentiation markers associated with normal development. Further, early-onset retinoblastoma tumor cells express a robust immune gene expression signature followed by accumulation of dendritic, monocyte, macrophage, and T-lymphocyte cells in the retinoblastoma tumors. This characteristic was not shared by either normal retinae or late-onset retinoblastomas. Comparison of our data with other human and mouse retinoblastoma tumor gene expression significantly confirmed, that the immune signature is present in tumors from each species. Strikingly, we observed that the immune signature in both mouse and human tumors was most highly evident in those with the lowest proliferative capacity. We directly assessed this relationship in human retinoblastoma tumors by co-analyzing proliferation and immune cell recruitment by immunohistochemistry, uncovering a significant inverse relationship between increased immune-cell infiltration in tumors and reduced tumor cell proliferation. Directly inhibiting proliferation with a PI3K/mTOR inhibitor significantly increased the number of CD45+ immune cells in the retina. This work establishes an in vivo model for the rapid recruitment of immune cells to tumorigenic neural tissue.

Visualizing the In Vivo Dynamics of Anti-Leishmania Immunity: Discoveries and Challenges

Intravital microscopy, such as 2-photon microscopy, is now a mainstay in immunological research to visually characterize immune cell dynamics during homeostasis and pathogen infections. This approach has been especially beneficial in describing the complex process of host immune responses to parasitic infections in vivo, such as Leishmania. Human-parasite co-evolution has endowed parasites with multiple strategies to subvert host immunity in order to establish chronic infections and ensure human-to-human transmission. While much focus has been placed on viral and bacterial infections, intravital microscopy studies during parasitic infections have been comparatively sparse. In this review, we will discuss how in vivo microscopy has provided important insights into the generation of innate and adaptive immunity in various organs during parasitic infections, with a primary focus on Leishmania. We highlight how microscopy-based approaches may be key to providing mechanistic insights into Leishmania persistence in vivo and to devise strategies for better parasite control.

Unraveling the Role of Immune Checkpoints in Leishmaniasis

Leishmaniasis are Neglected Tropical Diseases affecting millions of people every year in at least 98 countries and is one of the major unsolved world health issues. Leishmania is a parasitic protozoa which are transmitted by infected sandflies and in the host they mainly infect macrophages. Immunity elicited against those parasites is complex and immune checkpoints play a key role regulating its function. T cell receptors and their respective ligands, such as PD-1, CTLA-4, CD200, CD40, OX40, HVEM, LIGHT, 2B4 and TIM-3 have been characterized for their role in regulating adaptive immunity against different pathogens. However, the exact role those receptors perform during Leishmania infections remains to be better determined. This article addresses the key role immune checkpoints play during Leishmania infections, the limiting factors and translational implications.

Clinical and immunological characteristics of tegumentary leishmaniasis cases in Bolivia

BACKGROUND

Tegumentary leishmaniasis (TL) is a parasitic disease that can present a cutaneous or mucocutaneous clinical form (CL and MCL, respectively). The disease is caused by different Leishmania species and transmitted by phlebotomine sand flies. Bolivia has one of the highest incidences of the disease in South America and the diagnosis is done by parasitological techniques. Our aim was to describe the clinical and immunological characteristics of CL and MCL patients attending the leishmaniasis reference center in Cochabamba, Bolivia, in order to gain updated clinical and epidemiological information, to evaluate the diagnostic methods used and to identify biomarkers related to clinical disease and its evolution.

METHODOLOGY/PRINCIPAL FINDINGS

The study was conducted from September 2014 to November 2015 and 135 patients with lesions compatible with CL or MCL were included. Epidemiological and clinical data were collected using a semi-structured questionnaire. Two parasitological diagnostic methods were used: Giemsa-stained smears and culture of lesion aspirates. Blood samples obtained from participants were used to measure the concentrations of different cytokines. 59.2% (80/135) were leishmaniasis confirmed cases (CL: 71.3%; MCL: 28.7%). Sixty percent of the confirmed cases were positive by smears and 90.6% were positive by culture. 53.8% were primo-infections. Eotaxin and monokine induced by IFN-γ presented higher serum concentrations in the MCL clinical presentation compared to CL cases and no-cases. None of the cytokines presented different concentrations between primo-infections and secondary infections due to treatment failure.

CONCLUSIONS/SIGNIFICANCE

In Bolivia, parasitological diagnosis remains the reference standard in diagnosis of leishmaniasis because of its high specificity, whereas the sensitivity varies over a wide range leading to loss of cases. Until more accurate tools are implemented, all patients should be tested by both smears and culture of lesion aspirates to minimize the risk of false negatives. Our results showed higher concentrations of several cytokines in MCL compared to CL, but no differences were observed between CL and no-cases. In addition, none of the cytokines differed between primary and secondary infections. These results highlight the need of further research to identify biomarkers of susceptibility and disease progression, in addition to looking at the local cellular immune responses in the lesions.

The Impact of Neutrophil Recruitment to the Skin on the Pathology Induced by Leishmania Infection

Leishmania (L.) are obligate intracellular protozoan parasites that cause the leishmaniases, a spectrum of neglected infectious vector-borne diseases with a broad range of clinical manifestations ranging from local cutaneous, to visceral forms of the diseases. The parasites are deposited in the mammalian skin during the blood meal of an infected female phlebotomine sand fly. The skin is a complex organ acting as the first line of physical and immune defense against pathogens. Insults to skin integrity, such as that occurring during insect feeding, induces the local secretion of pro-inflammatory molecules generating the rapid recruitment of neutrophils. At the site of infection, skin keratinocytes play a first role in host defense contributing to the recruitment of inflammatory cells to the infected dermis, of which neutrophils are the first recruited cells. Although neutrophils efficiently kill various pathogens including Leishmania, several Leishmania species have developed mechanisms to survive in these cells. In addition, through their rapid release of cytokines, neutrophils modulate the skin microenvironment at the site of infection, a process shaping the subsequent development of the adaptive immune response. Neutrophils may also be recruited later on in unhealing forms of cutaneous leishmaniasis and to the spleen and liver in visceral forms of the disease. Here, we will review the mechanisms involved in neutrophil recruitment to the skin following Leishmania infection focusing on the role of keratinocytes in this process. We will also discuss the distinct involvement of neutrophils in the outcome of leishmaniasis.

Neutrophils and Visceral Leishmaniasis: Impact on innate immune response and cross-talks with macrophages and dendritic cells

Neutrophils with their array of microbicidal activities are the first innate immune cells to guard against infection. They are also most crucial for the host's initial defense against Leishmania parasites which cause clinically diverse diseases ranging from self-healing cutaneous leishmaniasis (CL) to a more severe visceral form, visceral leishmaniasis (VL). Neutrophils are recruited in large numbers at the infection site after bite of sandfly, which is the vector for the disease. The initial interaction of neutrophils with the parasites may modulate the subsequent innate and adaptive immune responses and hence affect the disease outcome. The purpose of this review is to comprehensively appraise the role of neutrophils during the early stages of Leishmania infection with a focus on the visceral form of the disease. In the past decade, new insights regarding the role of neutrophils in VL have surfaced which have been extensively elaborated in the present review. In addition, since much of the information regarding neutrophil-Leishmania early interaction has accumulated through studies on mouse models of CL, these studies are also revisited. We begin by reviewing the factors which drive the recruitment of neutrophils at the site of injection by the sandfly. We then discuss the studies delineating the molecular mechanisms involved in the uptake of the Leishmania parasite by neutrophils and how the parasite subverts their microbicidal functions. In the end, the interaction of infected neutrophils with macrophages and dendritic cells is summarized.

Neutrophils in respiratory syncytial virus infection: From harmful effects to therapeutic opportunities

Respiratory syncytial virus (RSV) is an important infectious agent in infants and young children. In most cases, RSV infection only causes mild disease, but in some, it requires invasive ventilation. Although antiviral drugs are obvious candidates to treat viral illness, and some have shown antiviral effects in humans, antivirals such as GS-5806, ALX-0171 and ALS-8176 have not yet met their expectations. Since the inappropriate or dysregulated immune response against RSV leads to harmful immune pathology, a robust immune cascade is probably underway by the time patients reach the hospital. RSV infection is associated with a strong neutrophil influx into the airway. It not clear if these cells contribute to antiviral defence or to lung pathology. This article discusses the protective and harmful roles of neutrophils during RSV infection and provides an overview of mechanisms by which neutrophil function could be targeted to prevent tissue injury and preserve homeostasis.

Essential Role of Neutrophils in the Protective Immune Response Induced by a Live Attenuated Leishmania Vaccine

No licensed vaccine exists against visceral leishmaniasis (VL), a disease caused by the Leishmania donovani parasite. We have previously reported both macrophages and dendritic cells play important role in the protection induced by a live attenuated centrin gene-deleted L. donovani (LdCen^-/- ) parasite vaccine. The role of neutrophils in orchestrating the initial innate response to pathogens is widely recognized. To investigate the early interaction of LdCen^-/- with neutrophils, we immunized mice intradermally in the ear pinna with LdCen^-/- Compared with LdWT infection, LdCen^-/- parasites induced higher recruitment of neutrophils to the ear dermis and ear draining lymph nodes (dLN) as early as 6-18 h after immunization, which were predominantly proinflammatory in nature. Neutrophils from ear dLN of LdCen^-/- -immunized mice exhibited heightened expression of costimulatory molecules and attenuated expression of coinhibitory molecules necessary for higher T cell activation. Further phenotypic characterization revealed heterogeneous neutrophil populations containing Nα and Nβ subtypes in the ear dLN. Of the two, the parasitized Nα subset from LdCen^-/- -immunized mice exhibited much stronger Ag-specific CD4⁺ T cell proliferation ex vivo. Adoptive transfer of neutrophils bearing LdCen^-/- parasites induced an increased Th1 response in naive mice. Importantly, neutrophil depletion significantly abrogated Ag-specific CD4⁺ T cell proliferation in LdCen^-/- -immunized mice and impaired protection against virulent challenge. Conversely, replenishing of neutrophils significantly restored the LdCen^-/- -induced host-protective response. These results suggest that neutrophils are indispensable for protective immunity induced by LdCen^-/- parasite vaccine.

Cytokine saga in visceral leishmaniasis

In humans, infection with Leishmania manifests into a spectrum of diseases. The manifestation of the diseases depend on the resultant evasion of the parasite to immune responses namely by macrophages, which is an exclusive host of Leishmania. The B cells valiantly mount antibody responses, however, to no avail as the Leishmania parasites occupy the intracellular niches of the macrophages and subvert the immune response. Extensive studies have been documented on the role of cell-mediated immunity (CMI) in protection and counter survival strategies of the parasites leading to downregulation of CMI. The present review attempts to discuss the cytokines in progression or resolution of visceral form of leishmaniasis or kala-azar, predominantly affecting the Indian subcontinent. The components/cytokine(s) responsible for the regulation of the critical balance of T helper cells and their subsets have been discussed in the perspective. Therefore, any strategy involving the treatment of visceral leishmania (VL) needs to consider the balance and regulation of T cell function.

Reconstituting NK Cells After Allogeneic Stem Cell Transplantation Show Impaired Response to the Fungal Pathogen Aspergillus fumigatus

Delayed natural killer (NK) cell reconstitution after allogeneic stem cell transplantation (alloSCT) is associated with a higher risk of developing invasive aspergillosis. The interaction of NK cells with the human pathogen Aspergillus (A.) fumigatus is mediated by the fungal recognition receptor CD56, which is relocated to the fungal interface after contact. Blocking of CD56 signaling inhibits the fungal mediated chemokine secretion of MIP-1α, MIP-1β, and RANTES and reduces cell activation, indicating a functional role of CD56 in fungal recognition. We collected peripheral blood from recipients of an allograft at defined time points after alloSCT (day 60, 90, 120, 180). NK cells were isolated, directly challenged with live A. fumigatus germ tubes, and cell function was analyzed and compared to healthy age and gender-matched individuals. After alloSCT, NK cells displayed a higher percentage of CD56^brightCD16^dim cells throughout the time of blood collection. However, CD56 binding and relocalization to the fungal contact side were decreased. We were able to correlate this deficiency to the administration of corticosteroid therapy that further negatively influenced the secretion of MIP-1α, MIP-1β, and RANTES. As a consequence, the treatment of healthy NK cells ex vivo with corticosteroids abrogated chemokine secretion measured by multiplex immunoassay. Furthermore, we analyzed NK cells regarding their actin cytoskeleton by Structured Illumination Microscopy (SIM) and flow cytometry and demonstrate an actin dysfunction of NK cells shown by reduced F-actin content after fungal co-cultivation early after alloSCT. This dysfunction remains until 180 days post-alloSCT, concluding that further actin-dependent cellular processes may be negatively influenced after alloSCT. To investigate the molecular pathomechansism, we compared CD56 receptor mobility on the plasma membrane of healthy and alloSCT primary NK cells by single-molecule tracking. The results were very robust and reproducible between tested conditions which point to a different molecular mechanism and emphasize the importance of proper CD56 mobility.

The Contribution of Neutrophils to the Pathogenesis of RSV Bronchiolitis

Acute viral bronchiolitis causes significant mortality in the developing world, is the number one cause of infant hospitalisation in the developed world, and is associated with the later development of chronic lung diseases such as asthma. A vaccine against respiratory syncytial virus (RSV), the leading cause of viral bronchiolitis in infancy, remains elusive, and hence new therapeutic modalities are needed to limit disease severity. However, much remains unknown about the underlying pathogenic mechanisms. Neutrophilic inflammation is the predominant phenotype observed in infants with both mild and severe disease, however, a clear understanding of the beneficial and deleterious effects of neutrophils is lacking. In this review, we describe the multifaceted roles of neutrophils in host defence and antiviral immunity, consider their contribution to bronchiolitis pathogenesis, and discuss whether new approaches that target neutrophil effector functions will be suitable for treating severe RSV bronchiolitis.

Changes in macrophage inflammatory protein-1 (MIP-1) family members expression induced by traumatic brain injury in mice

A deep knowledge of the profound immunological response induced by traumatic brain injury (TBI) raises the possibility of novel therapeutic interventions. Existing studies have highlighted the important roles of C-C motif ligands in the development of neuroinflammation after brain injury; however, the participation of macrophage inflammatory protein-1 (MIP-1) family members in this phenomenon is still undefined. Therefore, the goal of our study was to evaluate changes in macrophage inflammatory protein-1 (MIP-1) family members (CCL3, CCL4, and CCL9) and their receptors (CCR1 and CCR5) in a mouse model of TBI (induced by controlled cortical impact (CCI)). We also investigated the pattern of activation of immunological cells (such as neutrophils, microglia and astroglia), which on one hand express CCR1/CCR5, and on the other hand might be a source of the tested chemokines in the injured brain. We investigated changes in mRNA (RT-qPCR) and/or protein (ELISA and Western blot) expression in brain structures (the cortex, hippocampus, thalamus, and striatum) at different time points (24 h, 4 days, 7 days, 2 weeks, and/or 5 weeks) after trauma. Our time-course studies revealed the upregulation of the mRNA expression of all members of the MIP-1 family (CCL3, CCL4, and CCL9) in all tested brain structures, mainly in the early stages after injury. A similar pattern of activation was observed at the protein level in the cortex and thalamus, where the strongest activation was observed 1 day after CCI; however, we did not observe any change in CCL3 in the thalamus. Analyses of CCR1 and CCR5 demonstrated the upregulation of the mRNA expression of both receptors in all tested cerebral structures, mainly in the early phases post injury (24 h, 4 days and 7 days). Protein analysis showed the upregulation of CCR1 and CCR5 in the thalamus 24 h after TBI, but we did not detect any change in the cortex. We also observed the upregulation of neutrophil marker (MPO) at the early time points (24 h and 7 days) in the cortex, while the profound activation of microglia (IBA-1) and astroglia (GFAP) was observed mainly on day 7. Our findings highlight for the first time that CCL3, CCL4, CCL9 and their receptors offer promising targets for influencing secondary neuronal injury and improving TBI therapy. The results suggest that the MIP-1 family is an important target for pharmacological intervention for brain injury.

Protective or Detrimental? Understanding the Role of Host Immunity in Leishmaniasis

The intracellular protozoan parasites of the genus Leishmania are the causative agents of leishmaniasis, a vector-borne disease of major public health concern, estimated to affect 12 million people worldwide. The clinical manifestations of leishmaniasis are highly variable and can range from self-healing localized cutaneous lesions to life-threatening disseminated visceral disease. Once introduced into the skin by infected sandflies, Leishmania parasites interact with a variety of immune cells, such as neutrophils, monocytes, dendritic cells (DCs), and macrophages. The resolution of infection requires a finely tuned interplay between innate and adaptive immune cells, culminating with the activation of microbicidal functions and parasite clearance within host cells. However, several factors derived from the host, insect vector, and Leishmania spp., including the presence of a double-stranded RNA virus (LRV), can modulate the host immunity and influence the disease outcome. In this review, we discuss the immune mechanisms underlying the main forms of leishmaniasis, some of the factors involved with the establishment of infection and disease severity, and potential approaches for vaccine and drug development focused on host immunity.

Evasins: Tick Salivary Proteins that Inhibit Mammalian Chemokines

Ticks are hematophagous arachnids that parasitize mammals and other hosts, feeding on their blood. Ticks secrete numerous salivary factors that enhance host blood flow or suppress the host inflammatory response. The recruitment of leukocytes, a hallmark of inflammation, is regulated by chemokines, which activate chemokine receptors on the leukocytes. Ticks target this process by secreting glycoproteins called Evasins, which bind to chemokines and prevent leukocyte recruitment. This review describes the recent discovery of numerous Evasins produced by ticks, their classification into two structural and functional classes, and the efficacy of Evasins in animal models of inflammatory diseases. The review also proposes a standard nomenclature system for Evasins and discusses the potential of repurposing or engineering Evasins as therapeutic anti-inflammatory agents.