Peptidoglycan induces mobilization of the surface marker for activation marker CD66b in human neutrophils but not in eosinophils

The chemorepellent, SLIT2, bolsters innate immunity against Staphylococcus aureus

Neutrophils are essential for host defense against Staphylococcus aureus (S. aureus). The neuro-repellent, SLIT2, potently inhibits neutrophil chemotaxis, and might, therefore, be expected to impair antibacterial responses. We report here that, unexpectedly, neutrophils exposed to the N-terminal SLIT2 (N-SLIT2) fragment kill extracellular S. aureus more efficiently. N-SLIT2 amplifies reactive oxygen species production in response to the bacteria by activating p38 mitogen-activated protein kinase that in turn phosphorylates NCF1, an essential subunit of the NADPH oxidase complex. N-SLIT2 also enhances the exocytosis of neutrophil secondary granules. In a murine model of S. aureus skin and soft tissue infection (SSTI), local SLIT2 levels fall initially but increase subsequently, peaking at 3 days after infection. Of note, the neutralization of endogenous SLIT2 worsens SSTI. Temporal fluctuations in local SLIT2 levels may promote neutrophil recruitment and retention at the infection site and hasten bacterial clearance by augmenting neutrophil oxidative burst and degranulation. Collectively, these actions of SLIT2 coordinate innate immune responses to limit susceptibility to S. aureus.

The Effects of Indoor Pollutants Exposure on Allergy and Lung Inflammation: An Activation State of Neutrophils and Eosinophils in Sputum

BACKGROUND

To explore the inflammation phenotypes following indoor pollutants exposure based on marker expression on eosinophils and neutrophils with the application of chemometric analysis approaches.

METHODS

A cross-sectional study was undertaken among secondary school students in eight suburban and urban schools in the district of Hulu Langat, Selangor, Malaysia. The survey was completed by 96 students at the age of 14 by using the International Study of Asthma and Allergies in Children (ISAAC) and European Community Respiratory Health Survey (ECRHS) questionnaires. The fractional exhaled nitric oxide (FeNO) was measured, and an allergic skin prick test and sputum induction were performed for all students. Induced sputum samples were analysed for the expression of CD11b, CD35, CD63, and CD66b on eosinophils and neutrophils by flow cytometry. The particulate matter (PM2.5 and PM10), NO2, CO2, and formaldehyde were measured inside the classrooms.

RESULTS

Chemometric and regression results have clustered the expression of CD63 with PM2.5, CD11b with NO2, CD66b with FeNO levels, and CO2 with eosinophils, with the prediction accuracy of the models being 71.88%, 76.04%, and 76.04%, respectively. Meanwhile, for neutrophils, the CD63 and CD66b clustering with PM2.5 and CD11b with FeNO levels showed a model prediction accuracy of 72.92% and 71.88%, respectively.

CONCLUSION

The findings indicated that the exposure to PM2.5 and NO2 was likely associated with the degranulation of eosinophils and neutrophils, following the activation mechanisms that led to the inflammatory reactions.

Determinants of eosinophil survival and apoptotic cell death

Eosinophils (Eos) are potent inflammatory cells and abundantly present in the sputum and lung of patients with allergic asthma. During both transit to and residence in the lung, Eos contact prosurvival cytokines, particularly IL-3, IL-5 and GM-CSF, that attenuate cell death. Cytokine signaling modulates the expression and function of a number of intracellular pro- and anti-apoptotic molecules. Both intrinsic mitochondrial and extrinsic receptor-mediated pathways are affected. This article discusses the fundamental role of the extracellular and intracellular molecules that initiate and control survival decisions by human Eos and highlights the role of the cis-trans isomerase, Pin1 in controlling these processes.

Homology in systemic neutrophil response induced by human experimental endotoxemia and by trauma

The investigation of the trauma-induced innate immune responses is hampered by the wide variability in patients, type of trauma, and environmental factors. To circumvent this heterogeneity, we examined whether the systemic innate immune response toward human experimental endotoxemia is similar to the response during systemic inflammatory response syndrome after trauma. We tested the hypothesis that the innate immune response to pathogen-associated molecular pattern (e.g., lipopolysaccharides [LPSs]) and danger-associated molecular pattern (as induced by injury) leads to a comparable in vivo activation of human neutrophils. Escherichia coli LPS (2 ng/kg) was injected intravenously in nine healthy volunteers to induce a controlled systemic inflammatory response. Indices of systemic inflammation in this human inflammation model were compared with those of 12 trauma patients with a mean injury severity score of 19. Blood samples were withdrawn at 3 and 24 h after LPS-challenge or injury. Blood samples of nine healthy volunteers were used as control. Receptor expression was measured as readout for neutrophil activation by flow cytometry. Endotoxemia and injury resulted in a comparable activation phenotype of circulating neutrophils. This phenotype was characterized by downregulation of chemokine receptors CXCR1 and CXCR2 and of Fcγ receptors II and III. A significant difference between both conditions was seen in CD66b expression and for endotoxin resulted in an increased CD66b expression, whereas injury did not. Neutrophil activation was present 3 h after onset of inflammation, both during experimental endotoxemia as well as in trauma patients. Endotoxin and trauma appear to induce a similar neutrophil activation phenotype.

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.

Malaria and bacterial sepsis: similar mechanisms of endothelial apoptosis and its prevention in vitro

OBJECTIVE AND DESIGN

Apoptotic endothelial damage contributes to multiorgan failure in Plasmodium falciparum malaria and in sepsis. In malaria, endothelial apoptosis is amplified by neutrophils and their secretory products, and reduced by inhibitors of neutrophil-derived substances in vitro. We compared the mechanisms of endothelial apoptosis in malaria and in sepsis, using the human umbilical vein endothelial cell as a model.

INTERVENTIONS

Endothelial cells were incubated with patient sera (P. falciparum malaria, Escherichia coli sepsis, Staphylococcus aureus sepsis) or culture supernatants of the respective organisms, with or without neutrophils. Ascorbic acid or ulinastatin was used to neutralize reactive oxygen species or elastase secreted by neutrophils. Transwell sieve inserts or antibodies against leukocyte function antigen 1 or intercellular adhesion molecule 1 was used to study the effect of direct interaction between neutrophils and endothelial cells. The rate of apoptotic endothelial cells was determined by TUNEL and annexin staining.

MEASUREMENTS AND MAIN RESULTS

Incubation of endothelial cells with patient sera or culture supernatants (P. falciparum, E. coli, S. aureus) lead to higher apoptosis rates, compared with incubation with control sera or control supernatants. Addition of neutrophils augmented the apoptosis rate further. Addition of ascorbic acid or ulinastatin reduced endothelial apoptosis in the presence of neutrophils. Separation of neutrophils from endothelial cells with Transwell sieve inserts, or addition of anti-leukocyte function antigen-1 antibodies also reduced endothelial cell apoptosis. However, addition of anti-intercellular adhesion molecule-1 antibodies restored high apoptosis rates that had been reduced by Transwell inserts.

CONCLUSIONS

These in vitro results show how neutrophils can contribute to endothelial damage in malaria and in sepsis, both by their secretory products and by binding to intercellular adhesion molecule-1 on endothelial cells. The presence of similar pathomechanisms suggests that similar antiapoptotic strategies may offer potential benefit in malaria and in sepsis.

Accumulation, activation, and survival of neutrophils in ulcerative colitis: regulation by locally produced factors in the colon and impact of steroid treatment

BACKGROUND AND AIMS

Neutrophil granulocytes infiltrate the intestinal mucosa in active ulcerative colitis (UC), and may contribute to tissue damage and inflammation. The aim of this investigation was to study the importance of locally produced factors and the impact of steroid treatment on neutrophil functions in UC.

PATIENTS AND METHODS

Intestinal perfusion fluids from 11 patients with active distal UC before and after seven and 28 days of treatment with prednisolone and from seven control patients were used in the study. Neutrophil migration towards perfusion fluid was measured in a microchemotaxis chamber. The effect of perfusion fluids on neutrophil activation was assessed as the surface expression of CD66b by flow cytometry. Neutrophil survival was evaluated by staining with propidium iodide, annexin V, and fluorescein di-acetate. We also assessed the viability of freshly isolated tissue neutrophils from rectal biopsy samples.

RESULTS

Perfusion fluids from untreated patients caused increased migration, activation, and survival of neutrophils. Perfusion fluids collected after treatment had no effect on neutrophil migration, but some of the activation and anti-apoptotic effects remained after 7 days. Anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) inhibited the anti-apoptotic effect of perfusion fluids. Rectal tissue neutrophils from patients with active proctitis had increased viability compared to patients with inactive proctitis and control subjects.

CONCLUSIONS

These data show that mediators in the colon of patients with active UC stimulate the migration, activation, and survival of neutrophils. The activities were partly neutralized by topical steroid treatment. We also identified GM-CSF as an anti-apoptotic factor for neutrophils in inflamed colon.

Toll-like receptor-expressing cells for antiallergy compound screening

BACKGROUND

Regulation of type 2 helper T cell (TH2) polarization by toll-like receptors (TLRs) has triggered great interest in new antiallergic therapeutics. In addition to being involved in the regulation of co-stimulation by antigen-presenting cells, they are expressed on other immune and non-immune cells.

OBJECTIVE

To review the expression and function of TLRs on these cells and their potential to regulate TH2-associated responses.

METHODS

We focused on human cells that can be used for in vitro testing of TLR agonists.

RESULTS/CONCLUSION

Many cells involved in the allergic reaction have the capacity to respond to TLR agonists. Therefore, one needs to be cautious in extrapolating the antiallergic effect of a TLR agonist from the response analyzed in one cell type. Therefore, it is suggested that several cell types should be studied.

Peptidoglycan--an endotoxin in its own right?

Studies aimed at dissecting the complex pathophysiology of sepsis with multiple organ failure have traditionally focused on lipopolysaccharide of gram-negative bacteria, which is widely regarded as the classical endotoxin. However, gram-positive sepsis now accounts for up to 50% of all cases, calling for a shift of focus. Peptidoglycan (PepG) is the major cell wall component of gram-positive bacteria and has been increasingly recognized as an important proinflammatory molecule. During gram-positive infections, PepG reaches the circulation by bacterial breakdown or translocation from the intestine. Administration of PepG induces all the classical features of infectious illness and endotoxemia and may cause systemic inflammation with organ failure in animal models. Its potency, however, is crucially dependent on various features of its complex structure. PepG interacts with the innate immune system through receptors mainly expressed on monocytes/macrophages but may induce inflammatory changes in other cell types as well. Among the most extensively studied receptor systems are the nucleotide-binding oligomerization domains, the toll-like receptors, and the PepG recognition proteins. Based on the current available literature, we would like to propose that PepG must be regarded as an endotoxin in its own right and to encourage further work in the field of PepG signaling.

Toll-like receptors and corneal innate immunity

The ocular surface is constantly exposed to a wide array of microorganisms. The ability of the cornea to recognize pathogens as foreign and eliminate them is critical to retain its transparency, hence preservation of sight. In the eye, as in other parts of the body, the early response against invading pathogens is provided by innate immunity. Corneal innate immune system uses a series of pattern recognition receptors to detect the presence of pathogens thus allowing for rapid host defense responses to invading microbes. A key component of such receptors is the "Toll-like receptors" (TLRs), which have come to occupy the center stage in innate immunity against invading pathogens. An increasing number of studies have shown that TLRs are expressed by a variety of tissues and cells of the eye and play an important role in ocular defense against microbial infection. Here in this review we summarize the current knowledge about TLR expression in human eye with main emphasis on the cornea, and discuss the future directions of the field.

Human eosinophils selectively recognize and become activated by bacteria belonging to different taxonomic groups

Eosinophils are predominantly found in tissues that have an interface with the external environment and its bacterial flora, such as the gastrointestinal and respiratory tracts. Although it is not the primary function of eosinophils to phagocytose and kill bacteria, we hypothesized that they might be able to recognize and become activated by microorganisms that enter the normally sterile tissues where they reside. The aim of this study was to evaluate whether human eosinophils get universally activated by bacteria or if they discriminate between bacteria derived from different phylogenetic groups. Eleven bacterial species representative of different taxonomic groups were examined. A hierarchy was seen among the bacterial species regarding their capacity to activate eosinophils. Furthermore, several eosinophilic activation patterns were evoked by the different bacterial species. The strongest eosinophil activator, Escherichia coli, elicited chemotaxis, degranulation and respiratory burst. Low numbers of bacteria caused the release of the granule proteins major basic protein and eosinophil peroxidase, whereas high numbers were required for the release of eosinophil cationic protein (ECP). Eosinophils did not seem to discriminate between gram-positive and gram-negative bacteria, unlike monocytes. However, the release of ECP was mainly seen after stimulation with gram-negative species. Blockade of the formyl peptide receptor partially inhibited bacterial activation of eosinophils, implicating its involvement in this activity. We propose that the presence of defined bacterial species in the normally sterile tissues inhabited by eosinophils may constitute danger signals to eosinophils. This may be of importance in the perpetuation of allergic inflammation.