Bactericidal activity of human eosinophilic granulocytes against Escherichia coli

Bordetella spp. block eosinophil recruitment to suppress the generation of early mucosal protection

Bordetella spp. are respiratory pathogens equipped with immune evasion mechanisms. We previously characterized a Bordetella bronchiseptica mutant (RB50ΔbtrS) that fails to suppress host responses, leading to rapid clearance and long-lasting immunity against reinfection. This work revealed eosinophils as an exclusive requirement for RB50ΔbtrS clearance. We also show that RB50ΔbtrS promotes eosinophil-mediated B/T cell recruitment and inducible bronchus-associated lymphoid tissue (iBALT) formation, with eosinophils being present throughout iBALT for Th17 and immunoglobulin A (IgA) responses. Finally, we provide evidence that XCL1 is critical for iBALT formation but not maintenance, proposing a novel role for eosinophils as facilitators of adaptive immunity against B. bronchiseptica. RB50ΔbtrS being incapable of suppressing eosinophil effector functions illuminates active, bacterial targeting of eosinophils to achieve successful persistence and reinfection. Overall, our discoveries contribute to understanding cellular mechanisms for use in future vaccines and therapies against Bordetella spp. and extension to other mucosal pathogens.

Impact of gold nanoparticles (AuNPs) on eosinophils isolated from male and female individuals

It is well established that some differences exist between the male and female immune systems. Despites this, a sex-based analysis is not frequently performed in most scientific published reports. Knowing that inflammation is a common undesired effect observed resulting from nanoparticle (NP) exposure, we investigate here how in vitro treatment of gold NPs with a primary size of 20 and 70 nm (AuNP20 and AuNP70, respectively) will alter the biology of human eosinophils isolated from men and women blood. We found that treatment of AuNP70, but not AuNP20, significantly delay apoptosis only in eosinophils isolated from women. AuNPs were found to decrease eosinophil phagocytosis, however, significance was only observed in AuNP20-induced eosinophils isolated from women. The production of IL-8 was significantly increased in response to both AuNPs but only in eosinophils isolated from men and the production of IL-1β was increased in AuNPs-induced eosinophils, although significance was observed only in AuNP70-induced eosinophils isolated from women. We conclude that future studies investigating the toxicity of AuNPs (or other NPs) should include a sex-based analysis, especially if the tested NPs have potential medical applications knowing the increased interest in the development of personalized precision medicine.

Experimental infection of post-weaned pigs with F18-encoding enterotoxigenic and enterotoxigenic/shigatoxigenic Escherichia coli strain isolated from the diarrheic feces in Korea

Background

In the porcine industry, Escherichia coli (E. coli) infections have been causing post-weaning diarrhea (PWD) and edema disease (ED) for many years. It is classified into pathotypes and serotypes in animals according to virulence factors. Serotyping is performed for O, K, H, and F antigens, essential for discriminating pathogenicity and epidemiology. Furthermore, E. coli strains that produce F18 fimbriae are major sources of ED and PWD associated with Shiga-toxin producing E. coli (STEC) expressing F18ab and enterotoxigenic E. coli (ETEC) expressing F18ac, respectively.

Aim

To investigate the pathogenicity potential and infection characteristics of experimental infection and confirm the pathological features of the Korean STEC/ETEC strains F18ab and F18ac in piglets.

Methods

Three-week-old pigs were randomized into three experimental groups: infected G1 (F18ab), infected G2 (F18ac), and G3 (control). General health status was monitored daily, and pathological changes were evaluated.

Results

Diarrhea occurred in all infected piglets. Pathological changes were only observed in the small intestine and regional lymph nodes. In G1, mucosal necrosis, inflammatory cell infiltration with hemorrhagic lesions, and apoptotic cell death in the tunica media of arterioles in the small intestine were observed. In contrast, the mucosa and epithelium appeared almost intact, with no abnormal vessel lesions in G2.

Conclusion

Both strains, isolated from pigs in Korea, could be infected and did not spread from the alimentary tract to other organs. The pathological features were quite different among the F18 subtypes. The F18ab strain was more virulent than F18ac, and the virulence characteristics of the F18ac strain were more similar to ETEC than STEC.

Clinical features and three-year prognosis of AECOPD patients with different levels of blood eosinophils

BACKGROUND

Eosinophils are thought to be associated with the frequency and severity of acute exacerbations of chronic obstructive pulmonary disease (AECOPD); however, the role of eosinophilic inflammation in AECOPD is still incompletely understood.

OBJECTIVES

To investigate the relationship between different levels of blood eosinophils and clinical features, including comorbidities, therapy, and prognosis, and to further explore the optimal eosinophilic cutoff.

METHODS

We retrospectively collected and analyzed medical data, laboratory findings, chest CT images, treatment, and three-year follow-up data from 984 AECOPD patients with different blood eosinophil (EOS) levels: EOS%<2%, ≥2%; EOS%<3%, ≥3%; eosinophil counts<100 cells/L, ≥100 cells/L.

RESULTS

The prevalence of eosinophilia was 36.48% of EOS≥2% (359 cases), 22.87% of EOS≥3% (225 cases), and 48.48% with eosinophil counts≥100 cells/µl (477 cases). EOS was associated with comorbidities, including pulmonary heart disease, arrhythmia (atrial fibrillation), laboratory testing and clinical treatment, including respiratory failure, airway limitation, infectious inflammation, rate of antibiotic use, systemic glucocorticoids, and three mortality rates. The ROC curve showed that the indicators of AUC≥0.5 included chest CT imaging (emphysema 1.8% or ≥100/µl, bronchitis, 1.7% or ≥100/µl), osteoporosis (2.4% or ≥140/µl), mental illness 6.1% (or ≥400/µl), dust exposure (2.2% or ≥240/µl) and ex-smoker (1.3% or ≥100/µl).

CONCLUSIONS

The relatively higher EOS group (≥2% or ≥100/µl) was associated with fewer complications, mild airflow limitation, a tendency of noninfectious inflammation, and lower 3-year mortality. Eosinophils can not only guide clinical treatment but also be an indicator of predicting clinical outcome and prognosis in AECOPD patients.

First report of eosinophil peroxidase in starry flounder (Platichthys stellatus): Gene identification and gene expression profiling

Eosinophils are granular leukocytes that are evolutionarily preserved in the innate immune system of some invertebrates and vertebrates, and these cells can directly remove invading microorganisms and secrete various cytokines, and are also involved in homeostasis. These eosinophils are made up of specific granular proteins that can be differentiated from other cells, and eosinophil peroxidase (EPX) is a peroxidase released only from eosinophils that plays an important role in maintaining the main function and homeostasis of eosinophils. We obtained the sequence information of EPX for the first time from the starry flounder (Platichthys stellatus), and predicted it by amino acid sequencing to confirm sequence alignment and phylogenetic characteristics with other species. Based on analysis of the expression characteristics of PsEPX mRNA in healthy P. stellatus, it was expressed at the highest level in peripheral blood lymphocytes (PBLs) and was also expressed at a relatively high level in the head kidney and intestine, which are immune-related tissues. After artificial infection with Streptococcus parauberis and viral haemorrhagic septicaemia virus, which are the causes of major pathogenic diseases, the expression level of PsEPX was significantly regulated, which showed specific characteristics of pathogens or tissues. These results suggest that PsEPX is an important component of the immune system of P. stellatus and is considered a basic research case for the study of the immunological function of eosinophils in fish.

Eosinophils and Bacteria, the Beginning of a Story

Eosinophils are granulocytes primarily associated with TH2 responses to parasites or immune hyper-reactive states, such as asthma, allergies, or eosinophilic esophagitis. However, it does not make sense from an evolutionary standpoint to maintain a cell type that is only specific for parasitic infections and that otherwise is somehow harmful to the host. In recent years, there has been a shift in the perception of these cells. Eosinophils have recently been recognized as regulators of immune homeostasis and suppressors of over-reactive pro-inflammatory responses by secreting specific molecules that dampen the immune response. Their role during parasitic infections has been well investigated, and their versatility during immune responses to helminths includes antigen presentation as well as modulation of T cell responses. Although it is known that eosinophils can present antigens during viral infections, there are still many mechanistic aspects of the involvement of eosinophils during viral infections that remain to be elucidated. However, are eosinophils able to respond to bacterial infections? Recent literature indicates that Helicobacter pylori triggers TH2 responses mediated by eosinophils; this promotes anti-inflammatory responses that might be involved in the long-term persistent infection caused by this pathogen. Apparently and on the contrary, in the respiratory tract, eosinophils promote TH17 pro-inflammatory responses during Bordetella bronchiseptica infection, and they are, in fact, critical for early clearance of bacteria from the respiratory tract. However, eosinophils are also intertwined with microbiota, and up to now, it is not clear if microbiota regulates eosinophils or vice versa, or how this connection influences immune responses. In this review, we highlight the current knowledge of eosinophils as regulators of pro and anti-inflammatory responses in the context of both infection and naïve conditions. We propose questions and future directions that might open novel research avenues in the future.

The Host Cellular Immune Response to Infection by Campylobacter Spp. and Its Role in Disease

Campylobacter spp. are the leading cause of bacterium-derived gastroenteritis worldwide, impacting 96 million individuals annually. Unlike other bacterial pathogens of the gastrointestinal tract, Campylobacter spp. lack many of the classical virulence factors that are often associated with the ability to induce disease in humans, including an array of canonical secretion systems and toxins. Consequently, the clinical manifestations of human campylobacteriosis and its resulting gastrointestinal pathology are believed to be primarily due to the host immune response toward the bacterium. Further, while gastrointestinal infection is usually self-limiting, numerous postinfectious disorders can occur, including the development of Guillain-Barré syndrome, reactive arthritis, and irritable bowel syndrome. Because gastrointestinal disease likely results from the host immune response, the development of these postinfectious disorders may be due to dysregulation or misdirection of the same inflammatory response. As a result, it is becoming increasingly important to the Campylobacter field, and human health, that the cellular immune responses toward Campylobacter be better understood, including which immunological events are critical to the development of disease and the postinfectious disorders mentioned above. In this review, we collectively cover the cellular immune responses across susceptible hosts to Campylobacter jejuni infection, along with the tissue pathology and postinfectious disorders which may develop.

Eosinophils as Major Player in Type 2 Inflammation: Autoimmunity and Beyond

Eosinophils are a subset of differentiated granulocytes which circulate in peripheral blood and home in several body tissues. Along with their traditional relevance in helminth immunity and allergy, eosinophils have been progressively attributed important roles in a number of homeostatic and pathologic situations. This review aims at summarizing available evidence about eosinophils functions in homeostasis, infections, allergic and autoimmune disorders, and solid and hematological cancers.Their structural and biological features have been described, along with their physiological behavior. This includes their chemokines, cytokines, granular contents, and extracellular traps. Besides, pathogenic- and eosinophilic-mediated disorders have also been addressed, with the aim of highlighting their role in Th2-driven inflammation. In allergy, eosinophils are implicated in the pathogenesis of atopic dermatitis, allergic rhinitis, and asthma. They are also fundamentally involved in autoimmune disorders such as eosinophilic esophagitis, eosinophilic gastroenteritis, acute and chronic eosinophilic pneumonia, and eosinophilic granulomatosis with polyangiitis. In infections, eosinophils are involved in protection not only from parasites but also from fungi, viruses, and bacteria. In solid cancers, local eosinophilic infiltration is variably associated with an improved or worsened prognosis, depending on the histotype. In hematologic neoplasms, eosinophilia can be the consequence of a dysregulated cytokine production or the result of mutations affecting the myeloid lineage.Recent experimental evidence was thoroughly reviewed, with findings which elicit a complex role for eosinophils, in a tight balance between host defense and tissue damage. Eventually, emerging evidence about eosinophils in COVID-19 infection was also discussed.

Intestinal eosinophils, homeostasis and response to bacterial intrusion

Eosinophils are traditionally considered as end-stage effector cells involved in the pathogenesis of Th2 immune-mediated disorders as well as in the protection against parasite infection. However, this restricted view has recently been challenged by a series of studies revealing the highly plastic nature of these cells and implication in various homeostatic processes. Large numbers of eosinophils reside in the lamina propria of the gastrointestinal tract, at the front line of host defence, where they contribute to maintain the intestinal epithelial barrier function in the face of inflammation-associated epithelial cell damage. Eosinophils confer active protection against bacterial pathogens capable of penetrating the mucosal barrier through the release of cytotoxic compounds and the generation of extracellular DNA traps. Eosinophils also integrate tissue-specific cytokine signals such as IFN-γ, which synergise with bacterial recognition pathways to enforce different context-dependent functional responses, thereby ensuring a rapid adaptation to the ever-changing intestinal environment. The ability of eosinophils to regulate local immune responses and respond to microbial stimuli further supports the pivotal role of these cells in the maintenance of tissue homeostasis at the intestinal interface.

Molecular Pathogenesis and Treatment Perspectives for Hypereosinophilia and Hypereosinophilic Syndromes

Hypereosinophilia (HE) is a heterogeneous condition with a persistent elevated eosinophil count of >350/mm³, which is reported in various (inflammatory, allergic, infectious, or neoplastic) diseases with distinct pathophysiological pathways. HE may be associated with tissue or organ damage and, in this case, the disorder is classified as hypereosinophilic syndrome (HES). Different studies have allowed for the discovery of two major pathogenetic variants known as myeloid or lymphocytic HES. With the advent of molecular genetic analyses, such as T-cell receptor gene rearrangement assays and Next Generation Sequencing, it is possible to better characterize these syndromes and establish which patients will benefit from pharmacological targeted therapy. In this review, we highlight the molecular alterations that are involved in the pathogenesis of eosinophil disorders and revise possible therapeutic approaches, either implemented in clinical practice or currently under investigation in clinical trials.

Mechanisms of toxicity mediated by neutrophil and eosinophil granule proteins

Neutrophils and eosinophils are granulocytes which are characterized by the presence of granules in the cytoplasm. Granules provide a safe storage site for granule proteins that play important roles in the immune function of granulocytes. Upon granulocytes activation, diverse proteins are released from the granules into the extracellular space and contribute to the fight against infections. In this article, we describe granule proteins of both neutrophils and eosinophils able to kill pathogens and review their anticipated mechanism of antimicrobial toxicity. It should be noted that an excess of granules protein release can lead to tissue damage of the host resulting in chronic inflammation and organ dysfunction.

Eosinophils in transbronchial biopsies: a predictor of chronic lung allograft dysfunction and reduced survival after lung transplantation - a retrospective single-center cohort study

Long-term outcomes after lung transplantation remain inferior to those of other solid organ groups. The significance of eosinophils detected on transbronchial biopsies (TBBx) after lung transplantation and their relationship to long-term outcomes remain unknown. A retrospective single-center cohort study was performed of patients transplanted between January 01, 2001, and July 31, 2018, who had at least 1 TBBx with evaluable parenchymal tissue. Multivariable Cox proportional hazard models were used to assess the associations between eosinophil detection and: all-cause mortality and Chronic Lung Allograft Dysfunction (CLAD). 8887 TBBx reports from 1440 patients were reviewed for the mention of eosinophils in the pathology report. 112 (7.8%) patients were identified with eosinophils on at least one TBBx. The median (95% CI) survival time for all patients was 8.28 (7.32-9.31) years. Multivariable analysis, adjusted for clinical variables known to affect post-transplant outcomes, showed that the detection of eosinophils was independently associated with an increased risk of death (HR 1.51, 95% CI 1.24-1.85, p < 0.01) and CLAD (HR 1.35, 95% CI 1.07-1.70, P = 0.01). Eosinophils detected in TBBx are associated with an increased risk of CLAD and death. There may be benefit in specifically reporting the presence of eosinophils in TBBx reports and incorporating their presence in clinical decision-making.

Eosinophils and Neutrophils-Molecular Differences Revealed by Spontaneous Raman, CARS and Fluorescence Microscopy

Leukocytes are a part of the immune system that plays an important role in the host’s defense against viral, bacterial, and fungal infections. Among the human leukocytes, two granulocytes, neutrophils (Ne) and eosinophils (EOS) play an important role in the innate immune system. For that purpose, eosinophils and neutrophils contain specific granules containing protoporphyrin-type proteins such as eosinophil peroxidase (EPO) and myeloperoxidase (MPO), respectively, which contribute directly to their anti-infection activity. Since both proteins are structurally and functionally different, they could potentially be a marker of both cells’ types. To prove this hypothesis, UV−Vis absorption spectroscopy and Raman imaging were applied to analyze EPO and MPO and their content in leukocytes isolated from the whole blood. Moreover, leukocytes can contain lipidic structures, called lipid bodies (LBs), which are linked to the regulation of immune responses and are considered to be a marker of cell inflammation. In this work, we showed how to determine the number of LBs in two types of granulocytes, EOS and Ne, using fluorescence and coherent anti-Stokes Raman scattering (CARS) microscopy. Spectroscopic differences of EPO and MPO can be used to identify these cells in blood samples, while the detection of LBs can indicate the cell inflammation process.

Eosinopenia is a predictive factor for the severity of acute ischemic stroke

Previous data have revealed an association between eosinopenia and mortality of acute ischemic stroke. However, the relationship of eosinopenia with infarct volume, infection rate, and poor outcome of acute ischemic stroke is still unknown. The retrospective study included 421 patients (273 males, 65%; mean age, 68.0 ± 13.0 years) with first acute ischemic stroke who were hospitalized in the Second Affiliated Hospital of Soochow University, China, from January 2017 to February 2018. Laboratory data, neuroimaging results, and modified Rankin Scale scores were collected. Patients were divided into four groups according to their eosinophil percentage level (< 0.4%, 0.4–1.1%, 1.1–2.3%, ≥ 2.3%). Spearman’s correlation analysis showed that the percentage of eosinophils was negatively correlated with infarct volume (r_s = −0.514, P < 0.001). Receiver operating characteristic analysis demonstrated that eosinopenia predicted a large infarct volume more accurately than neutrophilia; the area under curve was 0.906 and 0.876, respectively; a large infarct was considered as that with a diameter larger than 3 cm and involving more than two major arterial blood supply areas. Logistic regression analysis revealed that eosinophil percentage was an independent risk factor for acute ischemic stroke (P = 0.002). Moreover, eosinophil percentage was significantly associated with large infarct volume, high infection rate (pulmonary and urinary tract infections), and poor outcome (modified Rankin Scale score > 3) after adjusting for potential confounding factors (P-trend < 0.001). These findings suggest that eosinopenia has the potential to predict the severity of acute ischemic stroke. This study was approved by the Ethics Committee of the Second Affiliated Hospital of Soochow University, China (approval number: K10) on November 10, 2015.

[Eosinopenia in 2018]

Since 1893, eosinopenia is a biological test to help a diagnosis of bacterial infection. Several publications have confirmed this hypothesis, particularly in the intensive care, pneumology and pediatric units. The value of this marker has been identified in vascular cerebral diseases and coronary bypass. Its contribution seems as relevant as procalcitonin, without extra cost. The diagnostic performance of this test was reinforced by a composite score (CIBLE score) that may improve its value in daily routine. Finally, monitoring eosinopenia appears to be a reliable mortality marker.

The Eosinophil in Infection

First described by Paul Ehrlich in 1879, who noted its characteristic staining by acidophilic dyes, for many years, the eosinophil was considered to be an end-effector cell associated with helminth infections and a cause of tissue damage. Over the past 30 years, research has helped to elucidate the complexity of the eosinophil's function and establish its role in host defense and immunity. Eosinophils express an array of ligand receptors which play a role in cell growth, adhesion, chemotaxis, degranulation, and cell-to-cell interactions. They play a role in activation of complement via both classical and alternative pathways. Eosinophils synthesize, store and secrete cytokines, chemokines, and growth factors. They can process antigen, stimulate T cells, and promote humoral responses by interacting with B cells. Eosinophils can function as antigen presenting cells and can regulate processes associated with both T1 and T2 immunity. Although long known to play a role in defense against helminth organisms, the interactions of eosinophils with these parasites are now recognized to be much more complex. In addition, their interaction with other pathogens continues to be investigated. In this paper, we review the eosinophil's unique biology and structure, including its characteristic granules and the effects of its proteins, our developing understanding of its role in innate and adaptive immunity and importance in immunomodulation, and the part it plays in defense against parasitic, viral, fungal and bacterial infections. Rather than our worst enemy, the eosinophil may, in fact, be one of the most essential components in host defense and immunity.

Abundance of RNase4 and RNase5 mRNA and protein in host defence related tissues and secretions in cattle

Members of the RNaseA family are present in various tissues and secretions but their function is not well understood. Some of the RNases are proposed to participate in host defence. RNase4 and RNase5 are present in cows' milk and have antimicrobial activity. However, their presence in many tissues and secretions has not been characterised. We hypothesised that these two RNases are present in a range of tissues and secretions where they could contribute to host defence. We therefore, determined the relative abundance of RNase4 and RNase5 mRNA as well as protein levels in a range of host defence related and other tissues as well as a range of secretions in cattle, using real time PCR and western blotting. The two RNases were found to be expressed in liver, lung, pancreas, mammary gland, placenta, endometrium, small intestine, seminal vesicle, salivary gland, kidney, spleen, lymph node, skin as well as testes. Corresponding proteins were also detected in many of the above tissues, as well as in seminal fluid, mammary secretions and saliva. This study provides evidence for the presence of RNase4 and RNase5 in a range of tissues and secretions, as well as some major organs in cattle. The data are consistent with the idea that these proteins could contribute to host defence in these locations. This work contributes to growing body of data suggesting that these proteins contribute to the physiology of the organism in a more complex way than acting merely as digestive enzymes.

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RNase4 and RNase5 are present in several tissues and secretions in cattle.

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mRNA and protein levels of the RNases correlate in various tissues analysed.

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The RNases could contribute to host defence in these tissues and secretions.

Eosinophils in mucosal immune responses

Eosinophils, multifunctional cells that contribute to both innate and adaptive immunity, are involved in the initiation, propagation, and resolution of immune responses, including tissue repair. They achieve this multifunctionality by expression of a diverse set of activation receptors, including those that directly recognize pathogens and opsonized targets, and by their ability to store and release preformed cytotoxic mediators that participate in host defense, to produce a variety of de novo pleotropic mediators and cytokines, and to interact directly and indirectly with diverse cell types, including adaptive and innate immunocytes and structural cells. Herein, we review the basic biology of eosinophils and then focus on new emerging concepts about their role in mucosal immune homeostasis, particularly maintenance of intestinal IgA. We review emerging data about their development and regulation and describe new concepts concerning mucosal eosinophilic diseases. We describe recently developed therapeutic strategies to modify eosinophil levels and function and provide collective insight about the beneficial and detrimental functions of these enigmatic cells.

Schistosoma haematobium infection and asymptomatic bacteriuria in young South African females

Schistosoma haematobium eggs can induce lesions in the urinary and genital tract epithelia, as eggs pass through or get trapped in the tissue. Local inflammatory reactions induced by S. haematobium eggs might affect the ability of bacteria to establish mucosal super-infection foci. S. haematobium infection and asymptomatic bacteriuria can both portray haematuria, proteinuria and leukocyturia. This shared set of proxy diagnostic markers could fuel routine misdiagnosis in S. haematobium endemic areas. Furthermore, S. haematobium infected individuals might be at a higher risk of contracting bacterial urinary tract infections, which could manifest either as symptomatic or asymptomatic bacteriuria. The aim of the current study was to explore whether schistosomal lesions are susceptible to super-infection by bacteria measured as asymptomatic bacteriuria. S. haematobium infection was determined by microscopy of urine samples. Furthermore, urine samples were tested with dipslides for asymptomatic bacteriuria and with dipsticks for haematuria, proteinuria and leukocytes. We found no association between asymptomatic bacteriuria and S. haematobium infection in a sample of 1040 female primary and high school students from a schistosomiasis endemic area in KwaZulu-Natal, South Africa. Furthermore, it was demonstrated that asymptomatic bacteriuria is not a bias for use of micro-haematuria as a proxy diagnostic measure for S. haematobium infection in this population.

Eosinophil secretion of granule-derived cytokines

Eosinophils are tissue-dwelling leukocytes, present in the thymus, and gastrointestinal and genitourinary tracts of healthy individuals at baseline, and recruited, often in large numbers, to allergic inflammatory foci and sites of active tissue repair. The biological significance of eosinophils is vast and varied. In health, eosinophils support uterine and mammary gland development, and maintain bone marrow plasma cells and adipose tissue alternatively activated macrophages, while in response to tissue insult eosinophils function as inflammatory effector cells, and, in the wake of an inflammatory response, promote tissue regeneration, and wound healing. One common mechanism driving many of the diverse eosinophil functions is the regulated and differential secretion of a vast array of eosinophil-derived cytokines. Eosinophils are distinguished from most other leukocytes in that many, if not all, of the over three dozen eosinophil-derived cytokines are pre-synthesized and stored within intracellular granules, poised for very rapid, stimulus-induced secretion. Eosinophils engaged in cytokine secretion in situ utilize distinct pathways of cytokine release that include classical exocytosis, whereby granules themselves fuse with the plasma membrane and release their entire contents extracellularly; piecemeal degranulation, whereby granule-derived cytokines are selectively mobilized into vesicles that emerge from granules, traverse the cytoplasm and fuse with the plasma membrane to release discrete packets of cytokines; and eosinophil cytolysis, whereby intact granules are extruded from eosinophils, and deposited within tissues. In this latter scenario, extracellular granules can themselves function as stimulus-responsive secretory-competent organelles within the tissue. Here, we review the distinctive processes of differential secretion of eosinophil granule-derived cytokines.

Eosinophils as a pharmacological target for the treatment of allergic diseases

Eosinophils are innate immune cells and active players in inflammatory responses. Their activation and increased levels in the blood and at specific sites are associated with parasitic infections and several inflammatory conditions, notably allergic diseases in which eosinophils are considered to be damaging cells. Intervention targeting eosinophils is thought to prevent and/or limit irreversible organ damage and other eosinophil-associated disorders like hypereosinophilic syndromes, some cancers and autoimmune diseases. Several eosinophil-targeted therapeutic agents which block specific steps in eosinophil differentiation, migration and activation have recently been developed, showing encouraging results and new insights into their specific role in allergy. Here, we review some potentially effective drug compounds, their drawbacks and future prospective focusing on allergic diseases.

Experimental sepsis impairs humoral memory in mice

Patients with sepsis are often immune suppressed, and experimental mouse models of sepsis also display this feature. However, acute sepsis in mice is also characterized by a generalized B cell activation and plasma cell differentiation, resulting in a marked increase in serum antibody concentration. Its effects on humoral memory are not clearly defined. We measured the effects of experimental sepsis on long-term immunological memory for a defined antigen: we induced colon ascendens stent peritonitis (CASP) 8 weeks after 2 rounds of immunization with ovalbumin. Four weeks later, the antigen-specific bone marrow plasma cell count had doubled in immunized non-septic animals, but remained unchanged in immunized septic animals. Sepsis also caused a decrease in antigen-specific serum antibody concentration. We conclude that sepsis weakens humoral memory by impeding the antigen-specific plasma cell pool's development, which is not complete 8 weeks after secondary immunization.

Inhibition of human platelet aggregation by eosinophils

AIMS

The relationship between the activity of eosinophils and platelets has been observed in recent decades by many scientists. These observations include increased numbers of eosinophils associated with platelet disorders, including changes in the coagulation cascade and platelet aggregation. Based on these observations, the interaction between eosinophils and platelets in platelet aggregation was analyze.

MAIN METHODS

Human platelets were incubated with eosinophil cytosolic fraction, promyelocytic human HL-60 clone 15 cell lineage, and eosinophil cationic protein (ECP). Platelet rich plasma (PRP) aggregation was induced by adenosine diphosphate, platelet activating factor, arachidonic acid, and collagen, and washed platelets (WP) were activated by thrombin.

KEY FINDINGS

Aggregation induced by all agonists was dose dependently inhibited by eosinophil cytosolic fraction. This inhibition was only partially reversed by previous incubation of the eosinophils with l-Nitro-Arginine-Methyl-Ester (l-NAME). Previous incubation with indomethacin did not prevent the cytosolic fraction induced inhibition. The separation of eosinophil cytosolic fraction by gel filtration on Sephadex G-75 showed that the inhibitory activity was concentrated in the lower molecular weight fraction. HL-60 clone 15 cells differentiated into eosinophils for 5 and 7 day were able to inhibit platelet aggregation. The ECP protein inhibited the platelet aggregation on PRP and WP. This inhibition was more evident in WP, and the citotoxicity MTT assay proved the viability of tested platelets, showing that the observed inhibition by the ECP protein does not occur simply by cell death.

SIGNIFICANCE

Our results indicate that eosinophils play a fundamental role in platelet aggregation inhibition.

Eosinophils in infection and intestinal immunity

PURPOSE OF REVIEW

Inflammatory bowel diseases (IBDs, e.g., Crohn's disease and ulcerative colitis) are thought to be a consequence of an uncontrolled inflammatory response against luminal antigens, including commensal bacteria. The observed link between eosinophil levels and severity and remission rates in IBD has led to speculation that eosinophils may contribute to the antimicrobial inflammatory response in IBD.

RECENT FINDINGS

Eosinophils express the necessary cellular machinery (innate immune receptors, proinflammatory cytokines, antibacterial proteins, and DNA traps) to mount an efficient antibacterial response; however, the rapid decline in eosinophil numbers following acute systemic bacterial infection suggests a very limited role for eosinophils in bacterial responses.

SUMMARY

We describe the clinical evidence of eosinophil involvement in IBD, summarize the in-vitro and in-vivo evidence of eosinophil antibacterial activity and the biology of eosinophils focusing on eosinophil-mediated bactericidal mechanisms and the involvement of eosinophil-derived granule proteins in this response, and conceptualize the contribution of eosinophils to a response against commensal bacteria in IBD.

The presence of eosinophil leucocytes in cervicovaginal smears with Actinomyces-like organisms: Light microscopic examination

BACKGROUND

Actinomyces species are part of mucosal surfaces of oral cavity, gastrointestinal and genital tracts. When these mucosal surfaces disrupt, Actinomyces become pathogen and cause infection. Eosinophil leucocytes participate in host defense against helminthic infestation and they generally play a role in asthma and allergy. However, the role of eosinophil leucocytes in host defense against bacteria is conflicting.

AIM

To determine whether there is a relationship between Actinomyces-like organisms (ALOs) and eosinophil leucocytes at light microscopic level.

MATERIALS AND METHODS

Cervicovaginal samples obtained from 200 patients were examined by both Pap smear microscopy and anaerobic culturing. Since the results obtained by these methods were not concordant for diagnosis of genital Actinomyces, 6 of 200 patients (3%) diagnosed with ALOs by Pap smear microscopy became the study group. Patients without any infectious agents (n=134) were the control group. Statistical analyses were conducted with χ(2) test using SPSS program.

RESULTS

The study and control groups were compared statistically in view of the presence of eosinophil leucocytes and it was found that there was a significant correlation between the presence of ALOs and eosinophil leucocytes (P<0.05). Abundant polymorphonuclear leucocytes (PMNLs) and macrophages were also detected in the study group.

CONCLUSION

This study implies that eosinophil leucocytes might have a role in host defense against Actinomyces in addition to PMNLs and macrophages.

Sialoadhesin promotes rapid proinflammatory and type I IFN responses to a sialylated pathogen, Campylobacter jejuni

Sialoadhesin (Sn) is a macrophage (Mφ)-restricted receptor that recognizes sialylated ligands on host cells and pathogens. Although Sn is thought to be important in cellular interactions of Mφs with cells of the immune system, the functional consequences of pathogen engagement by Sn are unclear. As a model system, we have investigated the role of Sn in Mφ interactions with heat-killed Campylobacter jejuni expressing a GD1a-like, sialylated glycan. Compared to Sn-expressing bone marrow-derived macrophages (BMDM) from wild-type mice, BMDM from mice either deficient in Sn or expressing a non-glycan-binding form of Sn showed greatly reduced phagocytosis of sialylated C. jejuni. This was accompanied by a strong reduction in MyD88-dependent secretion of TNF-α, IL-6, IL-12, and IL-10. In vivo studies demonstrated that functional Sn was required for rapid TNF-α and IFN-β responses to i.v.-injected sialylated C. jejuni. Bacteria were captured within minutes after i.v. injection and were associated with Mφs in both liver and spleen. In the spleen, IFN-β-reactive cells were localized to Sn⁺ Mφs and other cells in the red pulp and marginal zone. Together, these studies demonstrate that Sn plays a key role in capturing sialylated pathogens and promoting rapid proinflammatory cytokine and type I IFN responses.

Pattern-recognition receptors in human eosinophils

The pattern-recognition receptor (PRR) family includes Toll-like receptors (TLRs), nucleotide-binding oligomerization domain (NOD) -like receptors (NLRs), RIG-I-like receptors (RLRs), C-type lectin receptors (CLRs) and the receptor for advanced glycation end products (RAGE). They recognize various microbial signatures or host-derived danger signals and trigger an immune response. Eosinophils are multifunctional leucocytes involved in the pathogenesis of several inflammatory processes, including parasitic helminth infection, allergic diseases, tissue injury and tumour immunity. Human eosinophils express several PRRs, including TLR1-5, TLR7, TLR9, NOD1, NOD2, Dectin-1 and RAGE. Receptor stimulation induces survival, oxidative burst, activation of the adhesion system and release of cytokines (interleukin-1β, interleukin-6, tumour necrosis factor-α and granulocyte-macrophage colony-stimulating factor), chemokines (interleukin-8 and growth-related oncogene-α) and cytotoxic granule proteins (eosinophil cationic protein, eosinophil-derived neurotoxin, eosinophil peroxidase and major basic protein). It is also evident that eosinophils play an immunomodulatory role by interacting with surrounding cells. The presence of a broad range of PRRs in eosinophils indicates that they are not only involved in defence against parasitic helminths, but also against bacteria, viruses and fungi. From a clinical perspective, eosinophilic PRRs seem to be involved in both allergic and malignant diseases by causing exacerbations and affecting tumour growth, respectively.

Surfactant protein-A suppresses eosinophil-mediated killing of Mycoplasma pneumoniae in allergic lungs

Surfactant protein-A (SP-A) has well-established functions in reducing bacterial and viral infections but its role in chronic lung diseases such as asthma is unclear. Mycoplasma pneumoniae (Mp) frequently colonizes the airways of chronic asthmatics and is thought to contribute to exacerbations of asthma. Our lab has previously reported that during Mp infection of non-allergic airways, SP-A aides in maintaining airway homeostasis by inhibiting an overzealous TNF-alpha mediated response and, in allergic mice, SP-A regulates eosinophilic infiltration and inflammation of the airway. In the current study, we used an in vivo model with wild type (WT) and SP-A^−/− allergic mice challenged with the model antigen ovalbumin (Ova) that were concurrently infected with Mp (Ova+Mp) to test the hypothesis that SP-A ameliorates Mp-induced stimulation of eosinophils. Thus, SP-A could protect allergic airways from injury due to release of eosinophil inflammatory products. SP-A deficient mice exhibit significant increases in inflammatory cells, mucus production and lung damage during concurrent allergic airway disease and infection (Ova+Mp) as compared to the WT mice of the same treatment group. In contrast, SP-A deficient mice have significantly decreased Mp burden compared to WT mice. The eosinophil specific factor, eosinophil peroxidase (EPO), which has been implicated in pathogen killing and also in epithelial dysfunction due to oxidative damage of resident lung proteins, is enhanced in samples from allergic/infected SP-A^−/− mice as compared to WT mice. In vitro experiments using purified eosinophils and human SP-A suggest that SP-A limits the release of EPO from Mp-stimulated eosinophils thereby reducing their killing capacity. These findings are the first to demonstrate that although SP-A interferes with eosinophil-mediated biologic clearance of Mp by mediating the interaction of Mp with eosinophils, SP-A simultaneously benefits the airway by limiting inflammation and damage.

Antimicrobial activity of human eosinophil granule proteins: involvement in host defence against pathogens

Eosinophils have been associated with the pathophysiology of various allergic diseases and asthma. Eosinophils secrete a number of granule proteins that have been identified as effector molecules responsible for many of the actions of eosinophils. The four major eosinophil granule proteins, major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil derived neurotoxin (EDN) and eosinophil peroxidase have been shown to be involved in a number of eosinophil associated functions. EDN possesses antiviral activity against single stranded RNA viruses like respiratory syncytial virus, Hepatitis and HIV, whereas ECP and MBP have antibacterial and antiparasitic properties. This review summarizes the studies on antipathogenic activities of eosinophil granule proteins against bacteria, viruses, protozoans and helminths.

Eosinophils in innate immunity: an evolving story

Eosinophils are innate immune leukocytes found in relatively low numbers within the blood. Terminal effector functions of eosinophils, deriving from their capacity to release their content of tissue-destructive cationic proteins, have historically been considered primary effector mechanisms against specific parasites, and are likewise implicated in tissue damage accompanying allergic responses such as asthma. However, the past decade has seen dramatic advancements in the field of eosinophil immunobiology, revealing eosinophils to also be key participants in many other facets of innate immunity, from bridging innate and adaptive immune responses to orchestrating tissue remodeling events. Here, we review the multifaceted functions of eosinophils in innate immunity that are currently known, and discuss new avenues in this evolving story.

[Eosinophil: a new effector of innate immunity?]

The eosinophil leukocyte has long been considered as a second class cell. It appears now that its functions extend far beyond solely the release of cytotoxic mediators involved in a protective role in some parasitic infections or in pathological manifestations during allergic diseases. The recent demonstration that eosinophils express innate immune receptors (TLR, gdTCR) and mediators (a-defensins), in addition to the numerous receptors involved in adaptive immunity, confers to eosinophils the potential to directly recognize danger signals including pathogens. Thus, both such a functional plasticity together with its strategic tissue localization indicate that eosinophils likely play a previously unsuspected role in anti-infectious response.

Gastrointestinal eosinophils in health, disease and functional disorders

Eosinophils are potent innate immune cells that home to the gastrointestinal tract where they participate in host immunity to luminal pathogens, and help to maintain intestinal epithelial homeostasis. However, these cells are now recognized to have key functions in the pathogenesis of numerous other disorders of the gastrointestinal tract, including primary eosinophilic gastrointestinal disease, common functional conditions, such as dyspepsia, and also in gastrointestinal disorders in patients with allergic disease. We are just beginning to understand the potential pathological role of eosinophils in gastrointestinal disease, and it is increasingly likely that gastroenterologists and histopathologists will need to account for the presence of gastrointestinal eosinophils and relate their presence to gastrointestinal symptoms. This Review discusses the role of gastrointestinal eosinophils in health and disease, including their associations with functional and allergic disorders.

Mouse eosinophils possess potent antibacterial properties in vivo

Eosinophils are best known as the predominant cellular infiltrate associated with asthma and parasitic infections. Recently, numerous studies have documented the presence of Toll-like receptors (TLRs) on the surfaces of eosinophils, suggesting that these leukocytes may participate in the recognition and killing of viruses and bacteria. However, the significance of this role in the innate immune response to bacterial infection is largely unknown. Here we report a novel role for eosinophils as antibacterial defenders in the host response. Isolated mouse eosinophils possessed antipseudomonal properties in vitro. In vivo, interleukin-5 transgenic mice, which have profound eosinophilia, demonstrated improved clearance of Pseudomonas aeruginosa introduced into the peritoneal cavity. The findings of improved bacterial clearance following adoptive transfer of eosinophils, and impaired bacterial clearance in mice with a congenital eosinophil deficiency, established that this effect was eosinophil specific. The data presented also demonstrate that eosinophils mediate this antibacterial effect in part through the release of cationic secondary granule proteins. Specifically, isolated eosinophil granules had antibacterial properties in vitro, and administration of eosinophil granule extracts significantly improved bacterial clearance in vivo. These data suggest a potent yet underappreciated antibacterial role for eosinophils in vivo, specifically for eosinophil granules. Moreover, the data suggest that the administration of eosinophil-derived products may represent a viable adjuvant therapy for septic or bacteremic patients in the intensive care unit.

Phagocytosis of heat-killed Staphylococcus aureus by eosinophils: comparison with neutrophils

Eosinophils are characterized by several functional properties, such as chemotaxis, adhesion, superoxide anion production, and degranulation. In this article, we have studied the role of bacterial ingestion by eosinophils in comparison with that by neutrophils. Eosinophils and neutrophils were purified by using the Percoll gradient method followed by selection with CD16-coated immunomagnetic beads and centrifugation through a Ficoll-Hypaque gradient combined with dextran sedimentation, respectively. Both cells were preincubated with anti-FcgammaRIIa mAb (CD32 mAb), anti-FcgammaRIIIb mAb (CD16 mAb), anti-CR3 (CD11b mAb), or anti-CR1 (CD35 mAb) before being examined for phagocytosis of opsonized heat-killed Staphylococcus aureus (S. aureus). Phagocytosis and production of hydrogen peroxide were simultaneously measured by flow cytometry using S. aureus labeled with propidium iodide and stained with 2',7'-dichlorofluorescein diacetate. Eosinophils showed significantly lower activity than neutrophils in both phagocytosis and hydrogen peroxide production. Phagocytosis by both cells was decreased by heat-inactivated serum. Phagocytosis by neutrophils was significantly inhibited by CD16 mAb and CD32 mAb, whereas that by eosinophils was only inhibited by CD35 mAb. Whereas the mechanism of phagocytosis by neutrophils was mediated by CD16 and CD32, that of eosinophils was modulated by complement receptor 1 (CD35).

Mammalian heme peroxidases: from molecular mechanisms to health implications

A marked increase in interest has occurred over the last few years in the role that mammalian heme peroxidase enzymes, primarily myeloperoxidase, eosinophil peroxidase, and lactoperoxidase, may play in both disease prevention and human pathologies. This increased interest has been sparked by developments in our understanding of polymorphisms that control the levels of these enzymes, a greater understanding of the basic chemistry and biochemistry of the oxidants formed by these species, the development of specific biomarkers that can be used in vivo to detect damage induced by these oxidants, the detection of active forms of these peroxidases at most, if not all, sites of inflammation, and a correlation between the levels of these enzymes and a number of major human pathologies. This article reviews recent developments in our understanding of the enzymology, chemistry, biochemistry and biologic roles of mammalian peroxidases and the oxidants that they generate, the potential role of these oxidants in human disease, and the use of the levels of these enzymes in disease prognosis.

The role of the complement anaphylatoxins in the recruitment of eosinophils

Eosinophils are blood and tissue immune cells that participate in a diverse range of activities normally beneficial for the host defense, but in circumstances of untoward inflammatory conditions these cells can be responsible for pathological responses. Accordingly the transit of eosinophils from the blood to tissues is a subject of considerable importance in immunology. In this article we review how the complement anaphylatoxins, C3a and C5a bring about eosinophil extravasation. These mediators do not merely provide a chemotactic or haptotactic gradient but are responsible for orchestrating innumerable responses by other cells types, including of endothelial cells, mast cells, and basophils in order to create an environment that is conducive for eosinophil infiltration. C5a has the capacity to prime the endothelium directly to present P-selectin, and C5a stimulated generation of eosinophil hydrogen peroxide and other oxidants can cause additional upregulation of endothelial P-selectin and ICAM-1. Moreover, the anaphylatoxins have the ability to recruit mast cells and basophils and can stimulate these cells to release IL-4 and IL-13, which by augmenting endothelial VCAM-1, convey some selectivity for eosinophils. The anaphylatoxins also have the capability to evoke the release and activation of eosinophil MMP-9, which is employed by this cell type to digest its way past the subendothelial matrix. Finally, because C3a and C5a can stimulate the generation of nitric oxide along with the secretion of histamine and LTC4 from several cell types, the anaphylatoxins can bring about an increase in vascular permeability that facilitates eosinophil accumulation at sites of allergic inflammation.

Experimental infection of enterotoxemic Escherichia coli associated with porcine edema disease and its pathologic characteristics in the intestine

Edema disease (ED) has become frequent in Japan, but no effective method for experimental infection has been developed. We report here the use of a capsule that resistant against gastric digestion to induce the ED in piglets. Four 21-day-old piglets were used. Shiga toxin 2e-producing Escherichia coli (STEC) cell pellet was encapsulated and administered orally. Two pigs received 1.0x10(10) CFU for two days, and the others received 3.9x10(8) CFU for three days. The high-dose group caused the typical clinical ED signs (palpebral edema or neurologic impairment). Eosinophil infiltration, swollen lymphoid follicles, and edema were observed in the ileum. The kidney had the thrombus in the glomerulus.

[Eosinophils: structure and functions]

Long considered to be secondary cells characterized mainly by their ability to be recruited to inflammation sites, these cells are now known to release a wide array of cytotoxic mediators. Moreover they participate in immune response regulation by producing Th1 and Th2 cytokines as well as regulatory cytokines and chemokines. This review describes recent findings about their expression of surface molecules, eosinophil mediators, and the role of both in these novel eosinophil functions.

Ookinete-induced midgut peroxidases detonate the time bomb in anopheline mosquitoes

Previous analysis of the temporal-spatial relationship between ookinete migration and the cellular localization of genes mediating midgut immune defense responses suggested that, in order to survive, parasites must complete invasion before toxic chemicals ("a bomb") are generated by the invaded cell. Recent studies indicate that ookinete invasion induces tyrosine nitration as a two-step reaction, in which NOS induction is followed by a localized increase in peroxidase activity. Peroxidases utilize nitrite and hydrogen peroxide as substrates, and detonate the time bomb by generating reactive nitrogen intermediates, such as nitrogen dioxide, which mediate nitration. There is evidence that peroxidases also mediate antimicrobial responses to bacteria, fungi and parasites in a broad range of biological systems including humans and plants. Defense reactions that generate toxic chemicals are also potentially harmful to the host mounting the response and often results in apoptosis. The two-step nitration pathway is probably an ancient response, as it has also been described in vertebrate leukocytes and probably evolved as a mechanism to circumscribe the toxic products generated during defense responses involving protein nitration.

The pathobiology of eosinophilic gastroenteritis of childhood: is it really the eosinophil, allergic mediated, or something else?

Over the past decade clinicians have witnessed a dramatic rise in the prevalence of eosinophilic gastrointestinal diseases. Diverse symptoms, a broad range of endoscopic findings, and varying histopathologic features pose several questions: Do eosinophils represent an allergic response? What mechanisms drive eosinophils to specific mucosal targets? How do eosinophils affect the gastrointestinal tissues? Recent clinical and basic studies are investigating the pathogenesis of eosinophilic gastrointestinal diseases. This review highlights the literature concerning the mechanisms that govern these diseases, with a specific focus on diseases of gastrointestinal columnar epithelia (eosinophilic gastroenteritis and eosinophilic colitis). The roles of specific chemokines, such as eotaxin, and the data supporting the involvement of eosinophil granule proteins in disease states, are discussed.

Toll Receptor-Mediated Regulation of NADPH Oxidase in Human Dendritic Cells

Activation of NADPH oxidase represents an essential mechanism of defense against pathogens. Dendritic cells (DC) are phagocytic cells specialized in Ag presentation rather than in bacteria killing. Human monocyte-derived DC were found to express the NADPH oxidase components and to release superoxide anions in response to phorbol esters and phagocytic agonists. The NADPH oxidase components p47phox and gp91phox were down-regulated during monocyte differentiation to DC, and maturation of DC with pathogen-derived molecules, known to activate TLRs, increased p47phox and gp91phox expression and enhanced superoxide anions release. Similar results were obtained with plasmacytoid DC following maturation with influenza virus. In contrast, activation of DC by immune stimuli (CD40 ligand) did not regulate NADPH oxidase components or respiratory burst. NADPH oxidase-derived oxygen radicals did not play any role in DC differentiation, maturation, cytokine production, and induction of T cell proliferation, as based on the normal function of DC generated from chronic granulomatous disease patients and the use of an oxygen radical scavenger. However, NADPH oxidase activation was required for DC killing of intracellular Escherichia coli. It is likely that the selective regulation of oxygen radicals production by pathogen-activated DC may function to limit pathogen dissemination during DC trafficking to secondary lymphoid tissues.

Nontypeable Haemophilus influenzae activates human eosinophils through beta-glucan receptors

Eosinophils are a characteristic component of the inflammatory response seen in several diseases, including allergic asthma and chronic obstructive pulmonary disease. After activation, eosinophil-derived products may exert proinflammatory effects and cause considerable tissue damage. In the present study, we investigated innate interactions between the respiratory tract pathogen nontypeable Haemophilus influenzae (NTHi) and human eosinophils. Bacterial binding to eosinophils was dependent on (1-3)-beta-D-glucan receptors, as deduced from blocking experiments using the soluble glucan derivatives laminarin and scleroglucan. In addition, expression of the beta-glucan receptor dectin-1 was shown in eosinophils by reverse transcriptase-polymerase chain reaction. Activation of the beta-glucan receptors by bacteria elicited a time- and dose-dependent respiratory burst in eosinophils. NTHi caused increased expression of the proinflammatory chemokine interleukin-8 as measured by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay. Incubation of eosinophils in the presence of NTHi for 4.5 h revealed upregulation of 245 different genes as detected by microarray. Signal transduction-related transcripts were most strongly upregulated, followed by cytokine mRNAs. Our findings suggest that NTHi can induce an innate inflammatory response in eosinophils that is mainly mediated via beta-glucan receptors. This points to possible pathophysiologic mechanisms involving innate recognition of NTHi by eosinophils during infection of the airways, thus promoting inflammation in chronic pulmonary disease.

Phagocytosis and peroxidase release by seabream (Sparus aurata L.) leucocytes in response to yeast cells

A flow cytometric method was adapted to evaluate phagocytosis by gilthead seabream leucocytes after incubation with yeast cells (Saccharomyces cerevisiae). Head-kidney leucocytes were incubated in vitro for different times in different proportions with heat-killed fluorescein isothiocyanate (FITC)-labeled yeast cells to study the kinetics of phagocytosis. Attached and internalized yeast cells were differentiated by quenching FITC-labeled S. cerevisiae with trypan blue dye. Only internalized cells kept their FITC fluorescence after quenching. Monocyte-macrophages and acidophilic granulocytes showed phagocytic activity, as demonstrated by transmission electron microscopy (TEM). From the ultrastructural features of the phagocytic process, it was observed that cytoplasmic granule membranes fused with the phagocyte membrane at the point where the yeast cell was attached to the phagocyte surface. This observation led us to adapt a colorimetric method to study peroxidase (myeloperoxidase and eosinophil peroxidase) release, since both are considered to be markers of the degranulation that occurs in seabream head-kidney leucocytes in response to yeast cells. Head-kidney leucocytes were incubated with calcium ionophore (CaI), phorbol myristate acetate (PMA), or yeast cells for different periods of time (0-30 min) to study the kinetics of peroxidase release. The results obtained indicate that CaI and yeast cells, but not PMA, stimulate the degranulation (by about 44.51% and 21.04%, respectively, at 30 min) of seabream head-kidney leucocytes.

Persistence of mucosal mast cells and eosinophils in Shigella-infected children

Cells of the innate immune system and their mediators were studied at the single-cell level in the rectums of pediatric and adult patients with Shigella infection to better understand why children are at higher risk for severe infection. Adult patients had increased infiltration of mucosal mast cells (MMC) at the acute stage (3 to 5 days after the onset of diarrhea) and eosinophils in early convalescence (14 to 16 days after onset). Increased expression of stem cell factor and prostaglandin H synthase-1 (PGHS-1) was associated with increased tryptase-K(i)67-double-positive MMC in the acute stage and increased apoptosis of MMC, which led to a rapid decline in early convalescence. The eosinophils demonstrated increased expression of major basic protein (MBP), eotaxin, and CCR3, as well as increased necrotic death. The neutrophils showed enhanced alpha-defensin and lactoferrin expression in the acute phase. In contrast to adults, the pediatric patients demonstrated delayed accumulation of mast cells and eosinophils, while alpha-defensin expression persisted during convalescence. In contrast, neutrophil counts and lactoferrin expression were reduced in children compared to adults. The results suggest that children with shigellosis have a persistent activation of the innate immune response in the convalescent phase, indicating delayed elimination of Shigella antigens compared to adults.

Eosinophils, allergy and parasites

Recently, known eosinophil functions have been extended considerably: previously the cells were thought to have an exclusive role in the release of cytotoxic mediators; now they are known to have roles in antigen presentation and immunoregulation through the release of cytokines. Although questionable, animal models indicate a rather beneficial role of eosinophils in parasitic infections but a detrimental one, together with other cells, in allergy.