Pietro Dri

The Croton oil ear test revisited

Introduction Among the few tests available to detect the activity of topical antiinflammatory drugs, the Croton oil (CO) ear test is one of the most commonly used [1 3]. In this test the inflammatory response (IR) is usually quantified by measuring the increase in ear plug weight (EPW) at a single time-interval after CO application, when the IR is maximal. In this paper this experimental model of inflammation has been reevaluated in terms of time-course, contribution of granulocyte infiltration (GI) to the IR and response to both steroidal and non steroidal antiinflammatory drugs.

Killing by neutrophil extracellular traps: fact or folklore?

Neutrophil extracellular traps (NETs) are DNA structures released by dying neutrophils and claimed to constitute a new microbicidal mechanism. Killing by NET-forming cells is ascribed to these structures because it is prevented by preincubation with DNase, which has been shown to dismantle NETs, before addition of the target microorganisms. Curiously, the possibility that the microorganisms ensnared in NETs are alive has not been considered. Using Staphylococcus aureus and Candida albicans blastospores, we demonstrate that the microorganisms captured by NETs and thought to be killed are alive because they are released and recovered in cell medium by incubation with DNase. It is concluded that NETs entrap but do not kill microbes.

Studies on the mechanism of metabolic stimulation in polymorphonuclear leucocytes during phagocytosis I. Evidence for superoxide anion involvement in the oxidation of NADPH2

1. The oxidation of NADPH2 by leucocyte granules, as measured at acid pH in the presence of Mn-2+, was found to be inhibited by superoxide dismutase. 2. Omission of Mn-2+ markedly lowered the oxidase activity at acid pH, which was still inhibited by superoxide dismutase. 3. At alkaline pH the oxidase activity was lower than at acid pH. 4. During oxidation of NADPH2 by leucocyte granules, reduction of cytochrome c occurred which was partially inhibited by superoxide dismutase. 5. It was concluded that NADPH2 oxidation occurs through an enzymatic reaction and a nonenzymatic chain reaction. Superoxide anion (O-minus-2 and NADPH- free radical would be involved in the chain reaction. The differential sensitivity of NADPH2 oxidation to superoxide dismutase in different experimental conditions (see above 1, 2 and 3) was explained on the basis of changes in the properties of the chain reaction.

TNF-Induced Shedding of TNF Receptors in Human Polymorphonuclear Leukocytes: Role of the 55-kDa TNF Receptor and Involvement of a Membrane-Bound and Non-Matrix Metalloproteinase

A down-modulation of both the 55-kDa (TNF-R55) and the 75-kDa (TNF-R75) TNF receptors is observed in neutrophils exposed to a variety of stimuli. Proteolytic cleavage of the extracellular region of both receptors (shedding) and, with TNF, internalization of TNF-R55 and shedding of TNF-R75 are the proposed mechanisms. We have characterized the TNF-induced shedding of TNF receptors in neutrophils and determined the nature of the involved proteinase. Neutrophils exposed to TNF release both TNF receptors. A release of TNF receptors comparable to that observed with TNF was induced with TNF-R55-specific reagents (mAbs and a mutant of TNF) but not with the corresponding TNF-R75-specific reagents. A hydroxamic acid compound (KB8301) almost completely inhibited shedding of TNF-R55 and to a lesser degree shedding of TNF-R75. KB8301 also inhibited FMLP-induced shedding to a similar extent. Shedding was also inhibited by 1,10-phenanthroline, but this effect was considered nonspecific as the compound, at variance with KB8301, almost completely inhibited TNF and FMLP-induced PMN activation. Diisopropylfluorophosphate partially inhibited shedding of TNF-R75, suggesting the contribution of a serine proteinase to the release of this receptor. Shedding activity was not affected by matrix metalloproteinases inhibitors nor was it released in the supernatants of FMLP-stimulated neutrophils. These results suggest that TNF induces release of its receptors, that such a release is mediated via TNF-R55, and that a membrane-bound and non-matrix metalloproteinase is involved in the process. The possibility that ADAM-17, which we show to be expressed in neutrophils, might be the involved proteinase is discussed.

Ligation of the adhesion-GPCR EMR2 regulates human neutrophil function

At present, ~150 different members of the adhesion‐G protein‐coupled receptor (GPCR) family have been identified in metazoans. Surprisingly, very little is known about their function, although they all possess large extracellular domains coupled to a seven‐transmembrane domain, suggesting a potential role in cell adhesion and signaling. Here, we demonstrate how the human‐restricted adhesion‐GPCR, EMR2 (epidermal growth factor‐like module‐containing mucin‐like hormone receptor), regulates neutrophil responses by potentiating the effects of a number of proinflamma‐tory mediators and show that the transmembrane region is critical for adhesion‐GPCR function. Using an anti‐EMR2 antibody, ligation of EMR2 increases neu‐trophil adhesion and migration, and augments superoxide production and proteolytic enzyme degranulation. On neutrophil activation, EMR2 is rapidly translocated to membrane ruffles and the leading edge of the cell. Further supporting the role in neutrophil activation, EMR2 expression on circulating neutrophils is significantly increased in patients with systemic inflammation. These data illustrate a definitive function for a human adhesion‐GPCR within the innate immune system and suggest an important role in potentiating the inflammatory response. Ligation of the adhesion‐GPCR EMR2 regulates human neutrophil function.—Yona S., Lin, H.‐H., Dri, P., Davies, J. Q., Hayhoe, R. P. G., Lewis, S. M., Heinsbroek, S. E. M., Brown, K. A., Perretti, M., Hamann, J., Treacher, D. F., Gordon S., Stacey M. Ligation of the adhesion‐GPCR EMR2 regulates human neutrophil function. FASEB J. 22, 741–751 (2008)

Common methodology is inadequate for studies on the microbicidal activity of neutrophils

Microbicidal activity of neutrophils is usually measured by colony‐counting techniques after cell lysis in distilled water. While studying the effect of the reduced nicotinamide adenine dinucleotide phosphate‐oxidase inhibitor diphenyleneiodonium (DPI) on the staphylocidal activity of neutrophils, we obtained inconsistent results: various degrees of inhibition in some experiments and no effect in others. The lysis step, i.e., dilution of neutrophils in distilled water, was the source of error. Cell‐associated microorganisms were not dispersed effectively by this tretment. We overcame this problem by using water at pH 11 for cell lysis. Under these conditions, killing was inhibited completely and reproducibly by DPI. Here, we show that cell lysis in distilled water is incomplete and leads to an overestimate of microbial killing. This hinders identification of partial defects and makes complete defects appear as partial. We found that DPI‐treated neutrophils and chronic granulomatous disease neutrophils were completely defective in killing of Staphylococcus aureus and Candida albicans and partially defective in killing of Escherichia coli after lysis with water pH 11, whereas after lysis in distilled water, killing of S. aureus and C. albicans was ∼60% and ∼70% of control killing, respectively, and killing of E. coli was normal. Likewise, killing of S. aureus by myeloperoxidase‐deficient neutrophils was severely impaired after lysis in water pH 11 but appeared normal after lysis in distilled water. As most studies about neutrophil microbicidal activity have been performed using distilled water, our findings indicate that previous data about killing defects and the effects of agents that modulate microbicidal activity of neutrophils should be re‐evaluated.

Incidence of myeloperoxidase deficiency in an area of northern Italy: histochemical, biochemical and functional studies

Forty‐five subjects with a complete deficiency of myeloperoxidase were identified in an area of the region Friuli‐Venezia Giulia in north‐eastern Italy using the Hemalog D system as the screening technique. Histochemical and biochemical tests performed on the leucocytes of some of these subjects confirmed the defects shown by the Hemalog D system. The defect was of genetic origin in seven subjects. The genetic origin could be suspected in another eight subjects since more than two affected members were present in a given family. Eosinophil peroxidase, which is present in MPO deficient subjects, interfered with the guaiacol assay of MPO, and in several cases masked the genetic transmission. An assay was developed using o‐dianisidine as the electron donor which considerably reduced the interference by EPO. With this assay an autosomal recessive pattern of inheritance was found. The MPO deficient leucocytes had a higher respiratory burst than control cells and an impaired bactericidal activity, at early post‐phagocytic periods, which became comparable to that of control cells at later stages. Particle ingestion by the MPO‐deficient cells was normal.

Human MICL (CLEC12A) is differentially glycosylated and is down-regulated following cellular activation.

C‐type lectins are the most diverse and prevalent lectin family in immunity. Particular interest has recently been attracted by the C‐type lectin‐like receptors on NK cells, which appear to regulate the activation/inhibitory balance of these cells, controlling cytotoxicity and cytokine production. We previously identified a human C‐type lectin‐like receptor, closely related to both the beta‐glucan receptor and the lectin‐like receptor for oxidized‐LDL, named MICL (myeloid inhibitory C‐type lectin‐like receptor), which we had shown using chimeric analysis to function as an inhibitory receptor. Using a novel MICL‐specific monoclonal antibody, we show here that human MICL is expressed primarily on myeloid cells, including granulocytes, monocytes, macrophages, and dendritic cells. Although MICL was highly N‐glycosylated in primary cells, the level of glycosylation was found to vary between cell types. MICL surface expression was down‐regulated during inflammatory/activation conditions in vitro, as well as during an in vivo model of acute inflammation, which we characterize here. This suggests that human MICL may be involved in the control of myeloid cell activation during inflammation.

A simple reliable assay for myeloperoxidase activity in mixed neutrophil-eosinophil cell suspensions: Application to detection of myeloperoxidase deficiency

Quantitation of myeloperoxidase (MPO) activity by guaiacol peroxidation (GP) assay is profoundly affected by the peroxidase present in eosinophils (EPO) that contaminate the granulocyte suspensions. Inclusion of 3-amino-1,2,4-triazole (AMT) in the GP assay permits quantitation of MPO activity in mixed neutrophil-eosinophil suspension because of the differential inhibition of EPO and MPO by AMT. Results show that: (1) the peroxidase activity of eosinophil-free granulocyte suspensions is not appreciably affected by AMT; (2) in the presence of AMT the peroxidase activities of granulocyte preparations containing different numbers of eosinophils are similar on a neutrophil basis, regardless of the number of eosinophils and correspond with the activity of eosinophil-free granulocyte suspensions; (3) AMT almost completely inhibits the activity of partially purified EPO, only slightly affecting the catalytic activity of partially purified MPO; (4) AMT completely inhibits the residual peroxidase activity of granulocyte suspensions from MPO-deficient subjects contributed by contaminating eosinophils. The GP assay in the presence of AMT was used to study the pattern of hereditary transmission of MPO deficiency. The genealogy derived on the basis of this assay was compatible with an autosomal recessive inheritance, in agreement with previously reported results, while no definite pattern of inheritance could be established by use of the GP assay without AMT. We suggest that the GP assay supplemented with AMT is the method of choice for detection of MPO deficiency, particularly partial deficiency.

NADPH oxidizing activity in rabbit polymorphonuclear leukocytes: Localization in azurophilic granules

Abstract Rabbit polymorphonuclear leukocyte granules were submitted to zonal fractionation through a discontinuous sucrose gradient. Distribution of azurophilic and specific granules, enzymatically characterized by peroxidase and alkaline phosphatase respectively, was as reported by others. NADPH oxidizing activity was associated with azurophilic granules. 3-Amino-1H-1, 2,4-triazole stimulated NADPH oxidation by azurophilic granules and inhibited peroxidase. Relationships between peroxidase and NADPH oxidizing activity are discussed.