Cellular inflammatory response to persistent localized Staphylococcus aureus infection: phenotypical and functional characterization of polymorphonuclear neutrophils (PMN)

High-dimensional analysis reveals an immune atlas and novel neutrophil clusters in the lungs of model animals with Actinobacillus pleuropneumoniae-induced pneumonia

Due to the increase in bacterial resistance, improving the anti-infectious immunity of the host is rapidly becoming a new strategy for the prevention and treatment of bacterial pneumonia. However, the specific lung immune responses and key immune cell subsets involved in bacterial infection are obscure. Actinobacillus pleuropneumoniae (APP) can cause porcine pleuropneumonia, a highly contagious respiratory disease that has caused severe economic losses in the swine industry. Here, using high-dimensional mass cytometry, the major immune cell repertoire in the lungs of mice with APP infection was profiled. Various phenotypically distinct neutrophil subsets and Ly-6C+ inflammatory monocytes/macrophages accumulated post-infection. Moreover, a linear differentiation trajectory from inactivated to activated to apoptotic neutrophils corresponded with the stages of uninfected, onset, and recovery of APP infection. CD14+ neutrophils, which mainly increased in number during the recovery stage of infection, were revealed to have a stronger ability to produce cytokines, especially IL-10 and IL-21, than their CD14- counterparts. Importantly, MHC-II+ neutrophils with antigen-presenting cell features were identified, and their numbers increased in the lung after APP infection. Similar results were further confirmed in the lungs of piglets infected with APP and Klebsiella pneumoniae infection by using a single-cell RNA-seq technique. Additionally, a correlation analysis between cluster composition and the infection process yielded a dynamic and temporally associated immune landscape where key immune clusters, including previously unrecognized ones, marked various stages of infection. Thus, these results reveal the characteristics of key neutrophil clusters and provide a detailed understanding of the immune response to bacterial pneumonia.

The effect of Staphylococcus aureus on innate and adaptive immunity and potential immunotherapy for S. aureus-induced osteomyelitis

Osteomyelitis is a chronic inflammatory bone disease caused by infection of open fractures or post-operative implants. Particularly in patients with open fractures, the risk of osteomyelitis is greatly increased as the soft tissue damage and bacterial infection are often more severe. Staphylococcus aureus, one of the most common pathogens of osteomyelitis, disrupts the immune response through multiple mechanisms, such as biofilm formation, virulence factor secretion, and metabolic pattern alteration, which attenuates the effectiveness of antibiotics and surgical debridement toward osteomyelitis. In osteomyelitis, immune cells such as neutrophils, macrophages and T cells are activated in response to pathogenic bacteria invasion with excessive inflammatory factor secretion, immune checkpoint overexpression, and downregulation of immune pathway transcription factors, which enhances osteoclastogenesis and results in bone destruction. Therefore, the study of the mechanisms of abnormal immunity will be a new breakthrough in the treatment of osteomyelitis.

Immunomodulatory biomaterials for implant-associated infections: from conventional to advanced therapeutic strategies

Implant-associated infection (IAI) is increasingly emerging as a serious threat with the massive application of biomaterials. Bacteria attached to the surface of implants are often difficult to remove and exhibit high resistance to bactericides. In the quest for novel antimicrobial strategies, conventional antimicrobial materials often fail to exert their function because they tend to focus on direct bactericidal activity while neglecting the modulation of immune systems. The inflammatory response induced by host immune cells was thought to be a detrimental force impeding wound healing. However, the immune system has recently received increasing attention as a vital player in the host's defense against infection. Anti-infective strategies based on the modulation of host immune defenses are emerging as a field of interest. This review explains the importance of the immune system in combating infections and describes current advanced immune-enhanced anti-infection strategies. First, the characteristics of traditional/conventional implant biomaterials and the reasons for the difficulty of bacterial clearance in IAI were reviewed. Second, the importance of immune cells in the battle against bacteria is elucidated. Then, we discuss how to design biomaterials that activate the defense function of immune cells to enhance the antimicrobial potential. Based on the key premise of restoring proper host-protective immunity, varying advanced immune-enhanced antimicrobial strategies were discussed. Finally, current issues and perspectives in this field were offered. This review will provide scientific guidance to enhance the development of advanced anti-infective biomaterials.

Crosstalk between the Intestinal Virome and Other Components of the Microbiota, and Its Effect on Intestinal Mucosal Response and Diseases

In recent years, there has been ample evidence illustrating the effect of microbiota on gut immunity, homeostasis, and disease. Most of these studies have engaged more efforts in understanding the role of the bacteriome in gut mucosal immunity and disease. However, studies on the virome and its influence on gut mucosal immunity and pathology are still at infancy owing to limited metagenomic tools. Nonetheless, the existing studies on the virome have largely been focused on the bacteriophages as these represent the main component of the virome with little information on endogenous retroviruses (ERVs) and eukaryotic viruses. In this review, we describe the gut virome, and its role in gut mucosal response and disease progression. We also explore the crosstalk between the virome and other microorganisms in the gut mucosa and elaborate on how these interactions shape the gut mucosal immunity going from bacteriophages through ERVs to eukaryotic viruses. Finally, we elucidate the potential contribution of this crosstalk in the pathogenesis of inflammatory bowel diseases and colon cancer.

Therapeutic evaluation of immunomodulators in reducing surgical wound infection

Despite many advances in infection control practices, including prophylactic antibiotics, surgical site infections (SSIs) remain a significant cause of morbidity, prolonged hospitalization, and death worldwide. Our innate immune system possesses a multitude of powerful antimicrobial strategies which make it highly effective in combating bacterial, fungal, and viral infections. However, pathogens use various stealth mechanisms to avoid the innate immune system, which in turn buy them time to colonize wounds and damage tissues at surgical sites. We hypothesized that immunomodulators that can jumpstart and activate innate immune responses at surgical sites, would likely reduce infection at surgical sites. We used three immunomodulators; fMLP (formyl-Methionine-Lysine-Proline), CCL3 (MIP-1α), and LPS (Lipopolysaccharide), based on their documented ability to elicit strong inflammatory responses; in a surgical wound infection model with Pseudomonas aeruginosa to evaluate our hypothesis. Our data indicate that one-time topical treatment with these immunomodulators at low doses significantly increased proinflammatory responses in infected and uninfected surgical wounds and were as effective, (or even better), than a potent prophylactic antibiotic (Tobramycin) in reducing P. aeruginosa infection in wounds. Our data further show that immunomodulators did not have adverse effects on tissue repair and wound healing processes. Rather, they enhanced healing in both infected and uninfected wounds. Collectively, our data demonstrate that harnessing the power of the innate immune system by immunomodulators can significantly boost infection control and potentially stimulate healing. We propose that topical treatment with these immunomodulators at the time of surgery may have therapeutic potential in combating SSI, alone or in combination with prophylactic antibiotics.

CEBPE-Mutant Specific Granule Deficiency Correlates With Aberrant Granule Organization and Substantial Proteome Alterations in Neutrophils

Specific granule deficiency (SGD) is a rare disorder characterized by abnormal neutrophils evidenced by reduced granules, absence of granule proteins, and atypical bilobed nuclei. Mutations in CCAAT/enhancer-binding protein-ε (CEBPE) are one molecular etiology of the disease. Although C/EBPε has been studied extensively, the impact of CEBPE mutations on neutrophil biology remains elusive. Here, we identified two SGD patients bearing a previously described heterozygous mutation (p.Val218Ala) in CEBPE. We took this rare opportunity to characterize SGD neutrophils in terms of granule distribution and protein content. Granules of patient neutrophils were clustered and polarized, suggesting that not only absence of specific granules but also defects affecting other granules contribute to the phenotype. Our analysis showed that remaining granules displayed mixed protein content and lacked several glycoepitopes. To further elucidate the impact of mutant CEBPE, we performed detailed proteomic analysis of SGD neutrophils. Beside an absence of several granule proteins in patient cells, we observed increased expression of members of the linker of nucleoskeleton and cytoskeleton complex (nesprin-2, vimentin, and lamin-B2), which control nuclear shape. This suggests that absence of these proteins in healthy individuals might be responsible for segmented shapes of neutrophilic nuclei. We further show that the heterozygous mutation p.Val218Ala in CEBPE causes SGD through prevention of nuclear localization of the protein product. In conclusion, we uncover that absence of nuclear C/EBPε impacts on spatiotemporal expression and subsequent distribution of several granule proteins and further on expression of proteins controlling nuclear shape.

Combating Implant Infections. Remarks by a Women's Team

Research on implant infections requires cooperative efforts and integration between basic and clinical expertises. An international group of women scientists is acting together in this field. The main research topics of the participants of this group are described. Formation of bacterial biofilms, antibiotic resistance and production of virulence factors like adhesins and toxins are investigated. New biomaterials, coatings and drugs designed to inhibit microbial adhesion are evaluated, and infection-resistant biomaterials are under study, such as a novel heparinizable polycarbonate-urethane (Bionate) or incorporation of diamino-diamide-diol (PIME) to reduce bacterial attachment. The correlation between biofilm production and the accessory-gene-regulator (agr) is investigated in Staphylococcus aureus. The ability to form biofilm has also been shown to be one of the important virulence factors of Enterococcus faecalis, favouring colonization of inert and biological surfaces. The study of quorum sensing has led to the discovery of a quorum sensing inhibitor termed RIP that suppresses staphylococcal biofilm and infections. The immune response and the local defence mechanisms of the host against implant-associated infections, activation and infiltration of immunocompetent cells into the sites of infection have been studied in patients with implant-associated osteomyelitis. Production of monoclonal antibodies (mAbs) as possible vaccines against the staphylococcal collagen-binding MSCRAMMs is in progress. (Int J Artif Organs 2008; 31: 858–64)

Behavior of Neutrophil Granulocytes during Toxoplasma gondii Infection in the Central Nervous System

Cerebral toxoplasmosis is characterized by activation of brain resident cells and recruitment of specific immune cell subsets from the periphery to the central nervous system (CNS). Our studies revealed that the rapidly invaded Ly6G⁺ neutrophil granulocytes are an early non-lymphoid source of interferon-gamma (IFN-γ), the cytokine known to be the major mediator of host resistance to Toxoplasma gondii (T. gondii). Upon selective depletion of Ly6G⁺ neutrophils, we detected reduced IFN-γ production and increased parasite burden in the CNS. Ablation of Ly6G⁺ cells resulted in diminished recruitment of Ly6C^hi monocytes into the CNS, indicating a pronounced interplay. Additionally, we identified infiltrated Ly6G⁺ neutrophils to be a heterogeneous population. The Ly6G⁺CD62-L^hiCXCR4⁺ subset released cathelicidin-related antimicrobial peptide (CRAMP), which can promote monocyte dynamics. On the other hand, the Ly6G⁺CD62-L^loCXCR4⁺ subset produced IFN-γ to establish early inflammatory response. Collectively, our findings revealed that the recruited Ly6G⁺CXCR4⁺ neutrophil granulocytes display a heterogeneity in the CNS with a repertoire of effector functions crucial in parasite control and immune regulation upon experimental cerebral toxoplasmosis.

Phenotypic and functional characteristics of HLA-DR+ neutrophils in Brazilians with cutaneous leishmaniasis

The protozoan Leishmania braziliensis causes cutaneous leishmaniasis (CL) in endemic regions. In murine models, neutrophils (PMNs) are recruited to the site of infection soon after parasite inoculation. However, the roles of neutrophils during chronic infection and in human disease remain undefined. We hypothesized that neutrophils help maintain a systemic inflammatory state in subjects with CL. Lesion biopsies from all patients with CL tested contained neutrophils expressing HLA-DR, a molecule thought to be restricted to professional antigen-presenting cells. Although CL is a localized disease, a subset of patients with CL also had circulating neutrophils expressing HLA-DR and the costimulatory molecules CD80, CD86, and CD40. PMNs isolated from a low-density leukocyte blood fraction (LD-PMNs) contained a higher percentage of HLA-DR⁺ PMNs than did normal-density PMNs. In vitro coculture experiments suggested LD-PMNs do not suppress T cell responses, differentiating them from MDSCs. Flow-sorted HLA-DR⁺ PMNs morphologically resembled conventional PMNs, and they exhibited functional properties of PMNs. Compared with conventional PMNs, HLA-DR⁺ PMNs showed increased activation, degranulation, DHR123 oxidation, and phagocytic capacity. A few HLA-DR⁺ PMNs were observed in healthy subjects, and that proportion could be increased by incubation in either inflammatory cytokines or in plasma from a patient with CL. This was accompanied by an increase in PMN hladrb1 mRNA, suggesting a possible connection between neutrophil "priming" and up-regulation of HLA-DR. These data suggest that PMNs that are primed for activation and that also express surface markers of antigen-presenting cells emerge in the circulation and infected tissue lesions of patients with CL.

Origin and Role of a Subset of Tumor-Associated Neutrophils with Antigen-Presenting Cell Features in Early-Stage Human Lung Cancer

Based on studies in mouse tumor models, granulocytes appear to play a tumor-promoting role. However, there are limited data about the phenotype and function of tumor-associated neutrophils (TANs) in humans. Here, we identify a subset of TANs that exhibited characteristics of both neutrophils and antigen-presenting cells (APCs) in early-stage human lung cancer. These APC-like "hybrid neutrophils," which originate from CD11b(+)CD15(hi)CD10(-)CD16(low) immature progenitors, are able to cross-present antigens, as well as trigger and augment anti-tumor T cell responses. Interferon-γ and granulocyte-macrophage colony-stimulating factor are requisite factors in the tumor that, working through the Ikaros transcription factor, synergistically exert their APC-promoting effects on the progenitors. Overall, these data demonstrate the existence of a specialized TAN subset with anti-tumor capabilities in human cancer.

Herpes Simplex Virus (HSV) Modulation of Staphylococcus aureus and Candida albicans Initiation of HeLa 299 Cell-Associated Biofilm

Although herpes simplex virus type-1 (HSV-1), and type-2 (HSV-2), Staphylococcus aureus and Candida albicans co-habit the oral and genital mucosa, their interaction is poorly understood. We determined the effect HSV has on bacterial and/or fungal adherence, the initial step in biofilm formation. HeLa229 cells were infected with HSV-1 (KOS) gL86 or HSV-2 (KOS) 333gJ⁻ at a multiplicity of infection (MOI) of 50 and 10. S. aureus (ATCC 25923) and/or C. albicans (yeast forms or germ tube forms) were co-incubated for 30 min (37 °C; 5 % CO₂; 5:1 organism: HeLa cell ratio; n = 16) with virus-infected HeLa cells or uninfected HeLa cell controls. Post-incubation, the monolayers were washed (3x; PBS), lysed (RIPA), and the lysate plated onto Fungisel and/or mannitol salts agar for standard colony count. The level of HeLa-associated S. aureus was significantly decreased (P < 0.05) for both HSV-1- and HSV-2-infected cells, as compared to virus-free HeLa cell controls (38 and 59 % of control, respectively). In contrast, HSV-1 and HSV-2 significantly (P < 0.05) enhanced HeLa cell association of C. albicans yeast forms and germ tube approximately two-fold, respectively. The effect of S. aureus on germ tube and yeast form adherence to HSV-1- and HSV-2-infected cells was specific for the Candida phenotype tested. Our study suggests that HSV, while antagonist towards S. aureus adherence enhances Candida adherence. Furthermore, the combination of the three pathogens results in S. aureus adherence that is either unaffected, or partially restored depending on both the herpes viral species and the fungal phenotype present.

How Neutrophils Shape Adaptive Immune Responses

Neutrophils are classically considered as cells pivotal for the first line of defense against invading pathogens. In recent years, evidence has accumulated that they are also important in the orchestration of adaptive immunity. Neutrophils rapidly migrate in high numbers to sites of inflammation (e.g., infection, tissue damage, and cancer) and are subsequently able to migrate to draining lymph nodes (LNs). Both at the site of inflammation as well as in the LNs, neutrophils can engage with lymphocytes and antigen-presenting cells. This crosstalk occurs either directly via cell–cell contact or via mediators, such as proteases, cytokines, and radical oxygen species. In this review, we will discuss the current knowledge regarding locations and mechanisms of interaction between neutrophils and lymphocytes in the context of homeostasis and various pathological conditions. In addition, we will highlight the complexity of the microenvironment that is involved in the generation of suppressive or stimulatory neutrophil phenotypes.

Human Vγ9/Vδ2 T cells: Innate adaptors of the immune system

Unconventional T cells are gaining center stage as important effector and regulatory cells that orchestrate innate and adaptive immune responses. Human Vγ9/Vδ2 T cells are amongst the best understood unconventional T cells, as they are easily accessible in peripheral blood, can readily be expanded and manipulated in vitro, respond to microbial infections in vivo and can be exploited for novel tumor immunotherapies. We here review findings that suggest that Vγ9/Vδ2 T cells, and possibly other unconventional human T cells, play an important role in bridging innate and adaptive immunity by promoting the activation and differentiation of various types of antigen-presenting cells (APCs) and even turning into APCs themselves, and thereby pave the way for antigen-specific effector responses and long-term immunological memory. Although the direct physiological relevance for most of these mechanisms still needs to be demonstrated in vivo, these findings may have implications for novel therapies, diagnostic tests and vaccines.

Cytokine-mediated induction of MHC class II in human neutrophils is dependent on NADPH oxidase activity

In response to selected cytokines, neutrophils are induced to express MHC class II and acquire properties of antigen-presenting cells. Here we show that (a) GM-CSF- and IFN-γ-mediated induction of MHC class II in human neutrophils is associated with intracellular ROS up-regulation, (b) cell-permeable ROS scavengers MnTMPyP and polyethylene glycol-conjugated superoxide dismutase and NADPH oxidase inhibitors diphenylene iodonium and apocynin abrogate both the cytokine-mediated ROS elevation and the induction of MHC class II and (c) neutrophils from chronic granulomatous disease patients which lack NADPH oxidase activity fail to express MHC class II in response to the cytokines. Thus, NADPH oxidase activity is required for the cytokine-mediated induction of MHC class II expression in neutrophils.

Microbe-specific unconventional T cells induce human neutrophil differentiation into antigen cross-presenting cells

The early immune response to microbes is dominated by the recruitment of neutrophils whose primary function is to clear invading pathogens. However, there is emerging evidence that neutrophils play additional effector and regulatory roles. The present study demonstrates that human neutrophils assume Ag cross-presenting functions and suggests a plausible scenario for the local generation of APC-like neutrophils through the mobilization of unconventional T cells in response to microbial metabolites. Vγ9/Vδ2 T cells and mucosal-associated invariant T cells are abundant in blood, inflamed tissues, and mucosal barriers. In this study, both human cell types responded rapidly to neutrophils after phagocytosis of Gram-positive and Gram-negative bacteria producing the corresponding ligands, and in turn mediated the differentiation of neutrophils into APCs for both CD4(+) and CD8(+) T cells through secretion of GM-CSF, IFN-γ, and TNF-α. In patients with acute sepsis, circulating neutrophils displayed a similar APC-like phenotype and readily processed soluble proteins for cross-presentation of antigenic peptides to CD8(+) T cells, at a time when peripheral Vγ9/Vδ2 T cells were highly activated. Our findings indicate that unconventional T cells represent key controllers of neutrophil-driven innate and adaptive responses to a broad range of pathogens.

Granulocyte functions are independent of arginine availability

Arginine depletion via myeloid cell arginase is critically involved in suppression of the adaptive immune system during cancer or chronic inflammation. On the other hand, arginine depletion is being developed as a novel anti-tumor metabolic strategy to deprive arginine-auxotrophic cancer cells of this amino acid. In human immune cells, arginase is mainly expressed constitutively in PMNs. We therefore purified human primary PMNs from healthy donors and analyzed PMN function as the main innate effector cell and arginase producer in the context of arginine deficiency. We demonstrate that human PMN viability, activation-induced IL-8 synthesis, chemotaxis, phagocytosis, generation of ROS, and fungicidal activity are not impaired by the absence of arginine in vitro. Also, profound pharmacological arginine depletion in vivo via ADI-PEG20 did not inhibit PMN functions in a mouse model of pulmonary invasive aspergillosis; PMN invasion into the lung, activation, and successful PMN-dependent clearance of Aspergillus fumigatus and survival of mice were not impaired. These novel findings add to a better understanding of immunity during inflammation-associated arginine depletion and are also important for the development of therapeutic arginine depletion as anti-metabolic tumor therapy.

Polymorphonuclear Neutrophils in Osteomyelitis: Link to Osteoclast Generation and Bone Resorption

Chronic and persistent inflammatory processes in bones may lead to severe erosions with consequent functional impairment sometimes requiring amputation of the limb. To explore the relationship between inflammation and bone erosion, biopsies of patients with osteomyelitis due to arterial occlusive disease or to diabetes mellitus were examined (n=31). Histologically, inflammation and bone erosion were confirmed. In the eroded bones the number of osteoclasts correlated with the abundance of infiltrated polymorphonuclear neutrophils (PMN), which were highly activated as shown by expression of MHC class II. For functional characterisation of the infiltrating PMN, patients with implant-associated osteomyelitis, a condition associated with persistent bacterial infection and bone destruction, were recruited. The cells were recovered from infected sites and examined ex vivo. These PMN expressed MHC class II and produced interleukin (IL)-8, a further indication of PMN activation. To assess a possible link between infiltrating PMN and bone erosion, we tested the effect of IL-8 on osteoclast generation in vitro. CD14+ monocytes derived from the peripheral blood of healthy individuals were cultivated with monocyte colony stimulating factor (M-CSF) and IL-8. Within 3 days, a translocation of the transcription factor NFATcl into the nucleus was seen, and by 10 to 20 days multinucleated cells with typical osteoclast morphology appeared that expressed tartrate-resistant acid phosphatase (TRAP) and cathepsin K. Moreover, the cells were able to resorb bone, proving that IL-8 was able to induce the differentiation of monocytes to osteoclasts. Because IL-8 is a major cytokine produced by activated PMN, we propose that in the course of persistent infection infiltrating PMN contribute to induction of osteoclast formation, thus providing a link between inflammation and bone erosion.

Innate immune dysfunctions in aged mice facilitate the systemic dissemination of methicillin-resistant S. aureus

Elderly humans show increased susceptibility to invasive staphylococcal disease after skin and soft tissue infection. However, it is not understood how host immunity changes with aging, and how that predisposes to invasive disease. In a model of severe skin infection, we showed that aged mice (16- to 20-month-old) exhibit dramatic bacterial dissemination compared with young adult mice (2-month-old). Bacterial dissemination was associated with significant reductions of CXCL1 (KC), polymorphonuclear cells (PMNs), and extracellular DNA traps (NETs) at the infection site. PMNs and primary skin fibroblasts isolated from aged mice showed decreased secretion of CXCL2 (MIP-2) and KC in response to MRSA, and in vitro analyses of mitochondrial functions revealed that the mitochondrial electron transport chain complex I plays a significant role in induction of chemokines in the cells isolated from young but not old mice. Additionally, PMNs isolated from aged mice have reduced ability to form NETs and to kill MRSA. Expression of nuclease by S. aureus led to increased bacterial systemic dissemination in young but not old mice, suggesting that defective NETs formation in elderly mice permitted nuclease and non-nuclease expressing S. aureus to disseminate equally well. Overall, these findings suggest that gross impairment of both skin barrier function and innate immunity contributes to the propensity for MRSA to disseminate in aged mice. Furthermore, the study indicates that contribution of bacterial factors to pathogenicity may vary with host age.

First human model of in vitro Candida albicans persistence within granuloma for the reliable study of host-fungi interactions

Backgound

The balance between human innate immune system and Candida albicans virulence signaling mechanisms ultimately dictates the outcome of fungal invasiveness and its pathology. To better understand the pathophysiology and to identify fungal virulence-associated factors in the context of persistence in humans, complex models are indispensable. Although fungal virulence factors have been extensively studied in vitro and in vivo using different immune cell subsets and cell lines, it is unclear how C. albicans survives inside complex tissue granulomas.

Methodology/Principal Finding

We developed an original model of in vitro human granuloma, reproducing the natural granulomatous response to C. albicans. Persistent granulomas were obtained when the ratio of phagocytes to fungi was high. This in vitro fungal granuloma mimics natural granulomas, with infected macrophages surrounded by helper and cytotoxic T lymphocytes. A small proportion of granulomas exhibited C. albicans hyphae. Histological and time-lapse analysis showed that C. albicans blastoconidia were located within the granulomas before hyphae formation. Using staining techniques, fungal load calculations, as well as confocal and scanning electron microscopy, we describe the kinetics of fungal granuloma formation. We provide the first direct evidence that C. albicans are not eliminated by immunocompetent cells inside in vitro human granulomas. In fact, after an initial candicidal period, the remaining yeast proliferate and persist under very complex immune responses.

Conclusions/Significance

Using an original in vitro model of human fungal granuloma, we herein present the evidence that C. albicans persist and grow into immunocompetent granulomatous structures. These results will guide us towards a better understanding of fungal invasiveness and, henceforth, will also help in the development of better strategies for its control in human physiological conditions.

Human polymorphonuclear neutrophils express RANK and are activated by its ligand, RANKL

The receptor activator of NF-κB (RANK) is especially well studied in the context of bone remodeling, and RANK and its ligand, RANKL, are key molecules in the induction of bone resorbing osteoclasts. We now report that polymorphonuclear neutrophils (PMNs) contain preformed RANK, stored in secretory vesicles and in specific granules. Upon stimulation of PMNs in vitro, RANK was translocated to the cell membrane. In patients with persistent bacterial infections, RANK surface expression was enhanced compared with that of healthy individuals. The functional activity of RANK was assessed by determining migration of PMNs toward RANKL. A time- and dose-dependent migration was seen, leading to the conclusion that RANK on PMNs is functional. We presume that regulated RANK expression contributes to the fine tuning of PMN migration, for example, on and through inflamed endothelium that is known to express RANKL.

Acquisition of antigen-presenting functions by neutrophils isolated from mice with chronic colitis

Active episodes of the inflammatory bowel diseases are associated with the infiltration of large numbers of myeloid cells including neutrophils, monocytes, and macrophages. The objective of this study was to systematically characterize and define the different populations of myeloid cells generated in a mouse model of chronic gut inflammation. Using the T cell transfer model of chronic colitis, we found that induction of disease was associated with enhanced production of myelopoietic cytokines (IL-17 and G-CSF), increased production of neutrophils and monocytes, and infiltration of large numbers of myeloid cells into the mesenteric lymph nodes (MLNs) and colon. Detailed characterization of these myeloid cells revealed three major populations including Mac-1(+)Ly6C(high)Gr-1(low/neg) cells (monocytes), Mac-1(+)Ly6C(int)Gr-1(+) cells (neutrophils), and Mac-1(+)Ly6C(low/neg)Gr-1(low/neg) leukocytes (macrophages, dendritic cells, and eosinophils). In addition, we observed enhanced surface expression of MHC class II and CD86 on neutrophils isolated from the inflamed colon when compared with neutrophils obtained from the blood, the MLNs, and the spleen of colitic mice. Furthermore, we found that colonic neutrophils had acquired APC function that enabled these granulocytes to induce proliferation of OVA-specific CD4(+) T cells in an Ag- and MHC class II-dependent manner. Finally, we observed a synergistic increase in proinflammatory cytokine and chemokine production following coculture of T cells with neutrophils in vitro. Taken together, our data suggest that extravasated neutrophils acquire APC function within the inflamed bowel where they may perpetuate chronic gut inflammation by inducing T cell activation and proliferation as well as by enhancing production of proinflammatory mediators.

Mouse neutrophils are professional antigen-presenting cells programmed to instruct Th1 and Th17 T-cell differentiation

Neutrophils play a major role in the innate immune system and are normally considered to be short-lived effector cells that exert anti-microbial activity and sometimes immunopathology. Here, we show that these cells possess an additional function as professional antigen-presenting cells capable of priming a T(h)1- and T(h)17-acquired immune response. Using flow cytometry, fluorescence microscopy and western blotting, we show that mouse neutrophils express MHC class II and co-stimulatory molecules CD80 and CD86 after T-cell co-incubation. Neutrophils pulsed with ovalbumin (OVA) process and present peptide antigen to OVA-specific T cells in an MHC class II-dependent manner. Importantly, we demonstrate that neutrophils can prime antigen-specific T(h)1 and T(h)17 immune responses even without the addition of exogenous cytokines to cell cultures.

Vaccine adjuvants alum and MF59 induce rapid recruitment of neutrophils and monocytes that participate in antigen transport to draining lymph nodes

Vaccine adjuvants such as alum and the oil-in-water emulsion MF59 are used to enhance immune responses towards pure soluble antigens, but their mechanism of action is still largely unclear. Since most adjuvanted vaccines are administered intramuscularly, we studied immune responses in the mouse muscle and found that both adjuvants were potent inducers of chemokine production and promoted rapid recruitment of CD11b(+) cells. The earliest and most abundantly recruited cell type are neutrophils, followed by monocytes, eosinophils and later dendritic cells (DCs) and macrophages. Using fluorescent forms of MF59 and ovalbumin (OVA) antigen, we show that all recruited cell types take up both adjuvant and antigen to transport them to the draining lymph nodes (LNs). There, we found antigen-positive neutrophils and monocytes within hours of injection, later followed by B cells and DCs. Compared to alum, MF59-injection lead to a more prominent neutrophil recruitment and a more efficient antigen re-localization from the injection site to the LN. As antigen-transporting neutrophils were observed in draining LNs, we asked whether these cells play an essential role in MF59-mediated adjuvanticity. However, antibody-mediated neutrophil ablation left MF59-adjuvanticity unaltered. Further studies will reveal whether other single cell types are crucial or whether the different recruited cell populations are redundant with overlapping functions.

Nitric oxide production disorders in leukocytes of patients with recurrent furunculosis

AIM

The propensity for certain individuals to develop staphylococcal recurrent furunculosis (RF) is not fully understood. But among the reasons of its development the immune system dysfunctions are described. As in the staphylococcus elimination the main role is played by neutrophils, the objective of this study was to determine nitric oxide (NO) and reactive oxygen species (ROS) production by polymo rphonuclear leukocytes (PMNs) of patients with RF and to compare them with the response of normal cells to stimulation.

MATERIALS AND METHODS

The spontaneous and pyrogenal-stimulated nitric oxide production was evaluated in leukocyte cell cultures by Griess reaction, and ROS generation was determined in the stimulated and unstimulated NBT-test.

RESULTS

In this study we have demonstrated that leukocytes of healthy subjects respond on stimulation by the increase of both NO and ROS production. In contrast, leukocytes of patients with RF react by depression of NO formation at stimulation, and are characterized by decrease of ROS production reserve with the increasing of spontaneous ROS generation. Described disorders are revealed in the remission period as well as at exacerbation of furunculosis.

CONCLUSION

The present study suggests that leukocytes of patients with RF have stable defect of stimulated NO production increase, which can be the reason for recurrent and severe course of furunculosis.

The usefulness of neutrophil CD64 expression in the diagnosis of local infection in patients with rheumatoid arthritis in daily practice

BACKGROUND

The diagnosis of local infection in patients with rheumatoid arthritis (RA) is frequently difficult because clinical signs and symptoms and laboratory test results of local infection are also observed in arthritis of active RA. The need for a specific marker of infection is high in RA patients. The usefulness of neutrophil CD64 expression (CD64) to diagnose local musculoskeletal infection (local infection) and discriminate local infection from RA-related inflammation in RA patients was examined.

METHODS

CD64 was measured by a quantitative method using flow cytometry in 61 RA patients in whom local infection was suspected, and the usefulness of CD64 was examined by comparing the findings with clinical results.

RESULTS

There were 25 patients with local infection and 36 patients without infection. The median CD64 value the patients with local infection was 3148 molecules/cell (interquartile range [IQR], 2140-6231) and that of the patients without infection was 1106 molecules/cell (IQR, 804-1464) with a statistically significant difference (P < 0.0001). In contrast, no significant difference between the groups was observed in C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and white blood cell (WBC) count. The area under the curve of CD64 calculated by receiver operating characteristic curve analysis was larger than that of CRP, ESR, or WBC count, suggesting that CD64 has superior ability to discriminate of infection compared to these other markers. When the cutoff value of CD64 was set at 2000 molecules/cell, the sensitivity and specificity of CD64 for the detection of local infection in RA patients were 76.0% and 94.4%, respectively.

CONCLUSIONS

CD64 is a useful marker in RA patients to discriminate local infection from RA-related inflammation.

Activation of T Lymphocytes in Response to Persistent Bacterial Infection: Induction of CD11b and of Toll-Like Receptors on T Cells

T cell activation is invariably associated with virus infections, but activation of T cells is also noted, for example, in patients with persistent bacterial infections with intracellular pathogens or localised bacterial biofilms. The latter is characterised by a destructive inflammatory process. Massive infiltration of leukocytes, predominantly of polymorphonuclear neutrophils (PMNs) and of T lymphocytes, is seen. While PMN influx into sites of bacterial infection is in line with their role as "first-line defence" a role of T cells in bacterial infection has not yet been delineated. We now found evidence for activation and expansion of peripheral blood T cells and an upregulation of Toll-like receptors 1, 2, and 4 on small portions of T cells. T cells recovered from the infected site were terminally differentiated and produced interferon gamma, a cytokine known to enhance functions of phagocytic cells, leading to the conclusion that infiltrated T cells support the local immuner defence.

Neutrophils and macrophages work in concert as inducers and effectors of adaptive immunity against extracellular and intracellular microbial pathogens

Emerging data suggest new facets of the concerted participation of neutrophils and macrophages in antimicrobial immunity. The classical view is that DCs and macrophages are the inducers of adaptive antimicrobial immunity, but there is evidence for neutrophil participation in this task as cytokine and chemokine producers and APCs. On the other hand, the concept that the T(H)1 response is only associated with control of infections by intracellular pathogens through activation of macrophages by IFN-gamma, and the T(H)17/IL-17 axis is only involved in protection against extracellular pathogens through mobilization and activation of neutrophils is simplistic: There is evidence suggesting that T(H)1 and T(H)17 responses, separately or in parallel, may use macrophages and neutrophils against infections by extracellular and intracellular microbial pathogens. Opsonization by pathogen-specific Igs enhances the antimicrobial capabilities of neutrophils and macrophages in infections by extracellular and intracellular microbes. The functional partnership between macrophages and neutrophils as inducers and effectors of adaptive antimicrobial immunity conforms to their affiliation with the myeloid phagocyte system and reveals a strategy based on the concurrent use of the two professional phagocytes in the adaptive defense mechanisms. Starting from a common myeloid precursor in the bone marrow, macrophages and neutrophils split during differentiation but come together at the infectious foci for a cooperative strategy that uses modulator and effector activities to attack invading microbial pathogens.

Polymorphonuclear neutrophils and T lymphocytes: strange bedfellows or brothers in arms?

Polymorphonuclear neutrophils (PMN) are linked invariably to the innate immune response, particularly to the defence against bacterial infection. T lymphocytes are studied mainly in virus infections, the defence against tumours, the development and progression of chronic inflammatory processes, in autoimmune phenomena and in materno-fetal tolerance. There is, however, increasing evidence for communication and interactions between PMN and T cells that we discuss here in the context of different physiological and pathological conditions, including acute and chronic inflammatory disease, defence against tumours, and maintenance of pregnancy.

Neutrophil CD64 expression in the diagnosis of local musculoskeletal infection and the impact of antibiotics

We examined the usefulness of neutrophil CD64 expression in detecting local musculoskeletal infection and the impact of antibiotics on its expression. Of 141 patients suspected of musculoskeletal infection, 46 were confirmed by microbiological culture to be infected and 95 had infection excluded. The median CD64 count of patients with localised infection was 2230 molecules per cell (interquartile range (IQR) 918 to 4592) and that of the patients without infection was 937 molecules per cell (IQR 648 to 1309) (p < 0.001). The level of CD64 correlated with the CRP level in patients with infection, but not in those without infection (r = 0.59, p < 0.01). Receiver operator characteristic curve analysis revealed that CD64 was a good predictor of local infection. When the patients were subdivided into two groups based on the administration of antibiotics at the time of CD64 sampling, the sensitivity for detecting infection was better in those who had not received antibiotics.

These results suggest that measurement of CD64 expression is a useful marker for local musculoskeletal infection.

Community-Associated Methicillin-Resistant Staphylococcus aureus Skin and Soft-Tissue Infection in HIV-Infected Patients

Background. Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as the most common cause of skin and soft tissue infections (SSTIs). Methods. Retrospective chart review of 43 adult HIV-infected patients with CA-MRSA SSTI was conducted. Results. Antibiotic susceptibility was as follows: vancomycin (100%), rifampin (100%), gentamicin (97.7%), tetracycline (96.5%), trimethoprim-sulfamethoxazole (95.2%), clindamycin (89.5%), levofloxacin (66.7%), and erythromycin (6.9%). At SSTI presentation, 58.5% of patients had CD4 counts greater than 200 cells/uL, 82.9% had a viral load (VL) below 100 000 log copies/mL, 6 of whom had undetectable VL. All 43 patients received empiric antibiotic therapy. Additionally, 34 patients underwent incision and drainage (I&D). For the 37 patients with follow-up data available at 4 weeks, 30 of the infections were resolved/resolving and 7 had no improvement or worsened. Conclusion. A majority of our patients with CA-MRSA SSTI did not have immunological/virological markers consistent with severe HIV/AIDS disease at time of presentation.

Expression of the CXCR6 on polymorphonuclear neutrophils in pancreatic carcinoma and in acute, localized bacterial infections

The chemokine receptor CXCR6 has been described on lymphoid cells and is thought to participate in the homing of activated T-cells to non-lymphoid tissue. We now provide evidence that the chemokine receptor CXCR6 is also expressed by activated polymorphonuclear neutrophils (PMN) in vivo: Examination of biopsies derived from patients with pancreatic carcinoma by confocal laser scan microscopy revealed a massive infiltration of PMN that expressed CXCR6, while PMN of the peripheral blood of these patients did not. To answer the question whether CXCR6 expression is a property of infiltrated and activated PMN, leucocytes were collected from patients with localized soft tissue infections in the course of the wound debridement. By cytofluorometry, the majority of these cells were identified as PMN. Up to 50% of these PMN were also positive for CXCR6. Again, PMN from the peripheral blood of these patients were nearly negative for CXCR6, as were PMN of healthy donors. In a series of in vitro experiments, up-regulation of CXCR6 on PMN of healthy donors by a variety of cytokines was tested. So far, a minor, although reproducible, effect of tumour necrosis factor (TNFalpha) was seen: brief exposure with low-dose TNFalpha induced expression of CXCR6 on the surface of PMN. Furthermore, we could show an increased migration of PMN induced by the axis CXCL16 and CXCR6. In summary, our data provide evidence that CXCR6 is not constitutively expressed on PMN, but is up-regulated under inflammatory conditions and mediates migration of CXCR6-positive PMN.

Clinical immunology review series: an approach to the patient with recurrent superficial abscesses

Patients may be referred to the immunology clinic for investigation of recurrent superficial abscess formation. In the majority of adult patients this clinical presentation does not equate with an underlying primary immune deficiency. Nevertheless, recurrent mucocutaneous abscesses can be associated with significant morbidity and long-term complications, including scarring and fistula formation, and may be associated with underlying immune-mediated disease. This review sets out an approach to the patient with recurrent superficial abscesses, focusing on the differential diagnoses, investigation and management of both the common causes and those associated with specific immune deficiency.

Murine neutrophils present Class II restricted antigen

Neutrophils were originally described as short lived, terminally differentiated phagocytes that contribute only to the innate immune response. Recent evidence of neutrophil cytokine production and expression of numerous cell surface proteins has suggested that neutrophils are likely to influence adaptive responses and may satisfy the criteria of antigen presenting cells. Under certain inflammatory conditions human neutrophils express major histocompatibilty complex (MHC) Class II and the costimulatory molecules CD80 and CD86. We have employed a murine T cell hybridoma with a transgenic T cell receptor specific for ovalbumin peptide 323–339 (OVA_323–339), and a green fluorescent reporter of T cell receptor ligation, to directly investigate neutrophil-T cell interactions. These cells provide an ideal model system, allowing precise identification of antigen specificity and a clear readout of T cell activation. Additionally, whilst murine neutrophils have previously been shown to stimulate MHC Class I-dependent CD8⁺ T cell activation, CD4⁺ T cells stimulation via MHC Class II-expressing neutrophils has not been investigated. We addressed this by isolating murine neutrophils, loading with OVA_323–339 and co-culturing with T cells specific for the OVA_323–339/MHC Class II complex, and this resulted in T cell activation, as determined by expression of the green-fluorescent protein reporter. Antigen-pulsed neutrophils were also able to prime naïve OVA-specific CD4⁺ T cells in a contact-dependent manner, as shown by proliferation and cytokine production. Activation of lymphocytes was not due to contaminating macrophages. These studies demonstrate that murine neutrophils present MHC Class II-restricted peptides and induce T cell proliferation, confirming findings in human neutrophils, and demonstrate a novel pro inflammatory effect of murine neutrophils.

Neutrophils efficiently cross-prime naive T cells in vivo

Neutrophils are professional phagocytes that migrate early, in high number, to the infection sites. Our study has analyzed how neutrophils cross-present antigens and influence CD8+ T-cell responses. By using highly purified neutrophils from peritoneal exudates and bone marrow, we have shown that neutrophils cross-present ovalbumin to a CD8+ T-cell hybridoma and to naive CD8+ T cells from OT1 transgenic mice. Cross-presentation by neutrophils was TAP and proteasome dependent and was as efficient as in macrophages. Moreover, it actually occurred earlier than in professional antigen-presenting cells. Peritoneal exudate neutrophils from mice injected intraperitoneally with ovalbumin also cross-presented ovalbumin, proving that neutrophils take up and present exogenous antigens into major histocompatibility complex I (MHC I) molecules in vivo. We then evaluated the in vivo influence of antigen cross-presentation by neutrophils on CD8+ T-cell response using beta2-microglobulin-deficient mice transferred with OT1 CD8+ T cells and injected with ovalbumin-pulsed neutrophils. Four days after neutrophil injection, OT1 cells proliferated and expressed effector functions (IFN-gamma production and cytolysis). They also responded efficiently to a rechallenge with ovalbumin-pulsed dendritic cells in CFA. These data are the first demonstration that neutrophils cross-prime CD8+ T cells in vivo and suggest that they may constitute, together with professional antigen-presenting cells, an attractive target to induce cytotoxic T cells in vaccines.

V617F JAK-2 mutation in patients with essential thrombocythemia: relation to platelet, granulocyte, and plasma hemostatic and inflammatory molecules

OBJECTIVE

This article evaluates patients with essential thrombocythemia (ET) to determine whether the V617F mutation in the JAK2 gene affects platelet hemostatic and adhesive molecules, platelet-polymorphonuclear leukocyte (PMN) interactions, and PMN-activation characteristics, as well as plasma hypercoagulation markers.

PATIENTS AND METHODS

Thirty-seven ET patients with V617F JAK2 mutation and 38 wild-type, and 50 healthy controls were studied.

RESULTS

Platelets from overall ET patients, compared to controls, expressed significantly higher membrane tissue factor (TF) and P-selectin (p < 0.01) and lower CD41 and CD42b (p < 0.01). TF appeared significantly higher in the V617F JAK2 carriers compared to wild-type, and total platelet TF antigen levels confirmed the same result. The presence of circulating platelet/PMN aggregates was significantly greater in the JAK2-mutation carriers than in the wild-type and controls (p < 0.05). PMN surface activation and inflammatory markers (i.e., CD14, TF, CD11b, and leukocyte alkaline phosphatase [LAP]) were all significantly higher in ET versus control subjects, with CD14 and LAP being the highest in the JAK2 mutation carriers. Finally, a significant increase in plasma hypercoagulation markers was found in ET patients, and the only difference for the V617F JAK2 carriers was higher plasma thrombomodulin levels (p < 0.01). Differences in white blood cell and PMN count, platelet TF, PMN CD14, and LAP, and plasma thrombomodulin remained significant after multivariate analysis.

CONCLUSIONS

These results show that a correlation exists between the presence of V617F JAK2 mutation and selected hemostatic activation variables.