Mice lacking neutrophil elastase reveal impaired host defense against gram negative bacterial sepsis

Protection against acute lung injury by intravenous or intratracheal pretreatment with EPI-HNE-4, a new potent neutrophil elastase inhibitor

Excessive accumulation of active neutrophil elastase (NE) in pulmonary fluids and tissues of patients with cystic fibrosis (CF) is thought to act on the lungs, compromising their structure and function. The aim of this study was to investigate the in vitro and in vivo protective effect of a new, rapidly acting, potent (Ki = 5.45 x 10(-12) M and Kon = 8 x 10(6) M(-1) s(-1)) and specific human NE inhibitor, EPI-HNE-4, engineered from the Kunitz domain. The results demonstrated that this inhibitor was able to (i) effectively inhibit in vitro the high levels of active NE present in a medium as complex as sputum from children with CF, with a measured IC(50) equal or close to the calculated IC(50) in 60% of cases, and (ii) almost completely block (91%) the N-formyl-methionine-leucine-phenylalanine-induced migration of purified human neutrophils across a Matrigel basement membrane. Intratracheal administration (250, 175, or 100 microg per rat) of the inhibitor 5 min before instillation of pure human NE (HNE) (150 microg per rat) to rats induced effective, dose-dependent protection of the lungs, 4 h later, from hemorrhage, serum albumin leakage, residual active NE, and discrete neutrophil influx in air spaces induced by instillation of pure HNE. Intravenous administration (3 mg per rat) of EPI-HNE-4, 15 min before instillation of the soluble fraction of pooled sputum (delivering 120 microg of active NE per rat) from children with CF, effectively reduced (64%), 4 h later, the massive neutrophil influx induced by sputum instillation. Overall, these data strongly suggest that associated aerosol and systemic administration of EPI-HNE-4 would be beneficial in the treatment of CF.

Dipeptidyl peptidase I activates neutrophil-derived serine proteases and regulates the development of acute experimental arthritis

Leukocyte recruitment in inflammation is critical for host defense, but excessive accumulation of inflammatory cells can lead to tissue damage. Neutrophil-derived serine proteases (cathepsin G [CG], neutrophil elastase [NE], and proteinase 3 [PR3]) are expressed specifically in mature neutrophils and are thought to play an important role in inflammation. To investigate the role of these proteases in inflammation, we generated a mouse deficient in dipeptidyl peptidase I (DPPI) and established that DPPI is required for the full activation of CG, NE, and PR3. Although DPPI(-/-) mice have normal in vitro neutrophil chemotaxis and in vivo neutrophil accumulation during sterile peritonitis, they are protected against acute arthritis induced by passive transfer of monoclonal antibodies against type II collagen. Specifically, there is no accumulation of neutrophils in the joints of DPPI(-/-) mice. This protective effect correlates with the inactivation of neutrophil-derived serine proteases, since NE(-/-) x CG(-/-) mice are equally resistant to arthritis induction by anti-collagen antibodies. In addition, protease-deficient mice have decreased response to zymosan- and immune complex-mediated inflammation in the subcutaneous air pouch. This defect is accompanied by a decrease in local production of TNF-alpha and IL-1 beta. These results implicate DPPI and polymorphonuclear neutrophil-derived serine proteases in the regulation of cytokine production at sites of inflammation.

Mutations in the ELA2 gene encoding neutrophil elastase are present in most patients with sporadic severe congenital neutropenia but only in some patients with the familial form of the disease

Severe congenital neutropenia (SCN) was originally described as an autosomal recessive disorder. Subsequently, autosomal dominant and sporadic forms of the disease have been recognized. All forms are manifest by persistent severe neutropenia and recurrent bacterial infection. In contrast, cyclical hematopoiesis is characterized by periodic neutropenia inter-spaced with (near) normal neutrophil counts. Recently, linkage analysis on 13 affected pedigrees identified chromosome 19p13.3 as the likely position for mutations in cyclical hematopoiesis. Heterozygous mutations in the ELA2 gene encoding neutrophil elastase were detected in all families studied. Further work also demonstrated mutations in ELA2 in sporadic and autosomal dominant SCN. However, all mutations described to date are heterozygous and thus appear to act in a dominant fashion, which is inconsistent with an autosomal recessive disease. Therefore, the current study investigated whether mutations in ELA2 could account for the disease phenotype in classical autosomal recessive SCN and in the sporadic and autosomal dominant types. All 5 exons of ELA2 and their flanking introns were studied in 18 patients (3 autosomal recessive, 5 autosomal dominant [from 3 kindreds], and 10 sporadic) using direct automated sequencing. No mutations were found in the autosomal recessive families. A point mutation was identified in 1 of 3 autosomal dominant families, and a base substitution was identified in 8 of 10 patients with the sporadic form, though 1 was subsequently shown to be a low-frequency polymorphism. These results suggest that mutations in ELA2 are not responsible for classical autosomal recessive Kostmann syndrome but provide further evidence for the role of ELA2 in SCN.

Neutrophils employ the myeloperoxidase system to generate antimicrobial brominating and chlorinating oxidants during sepsis

The myeloperoxidase system of neutrophils uses hydrogen peroxide and chloride to generate hypochlorous acid, a potent bactericidal oxidant in vitro. In a mouse model of polymicrobial sepsis, we observed that mice deficient in myeloperoxidase were more likely than wild-type mice to die from infection. Mass spectrometric analysis of peritoneal inflammatory fluid from septic wild-type mice detected elevated concentrations of 3-chlorotyrosine, a characteristic end product of the myeloperoxidase system. Levels of 3-chlorotyrosine did not rise in the septic myeloperoxidase-deficient mice. Thus, myeloperoxidase seems to protect against sepsis in vivo by producing halogenating species. Surprisingly, levels of 3-bromotyrosine also were elevated in peritoneal fluid from septic wild-type mice and were markedly reduced in peritoneal fluid from septic myeloperoxidase-deficient mice. Furthermore, physiologic concentrations of bromide modulated the bactericidal effects of myeloperoxidase in vitro. It seems, therefore, that myeloperoxidase can use bromide as well as chloride to produce oxidants in vivo, even though the extracellular concentration of bromide is at least 1,000-fold lower than that of chloride. Thus, myeloperoxidase plays an important role in host defense against bacterial pathogens, and bromide might be a previously unsuspected component of this system.

Mutations in the neutrophil elastase gene in cyclic and congenital neutropenia

Severe neutropenia disorders are characterized by extremely low levels of peripheral blood neutrophils, a maturation block of bone marrow progenitor cells and recurring severe bacterial and fungal infections. Recent reports indicated that severe neutropenia is a consequence of an impaired survival and abnormal cell cycle progression of myeloid progenitor cells in both cyclic and severe congenital neutropenia. Mutations in the neutrophil elastase gene were identified in all patients with cyclic neutropenia and most of the patients with severe congenital neutropenia. We hypothesize that expression of mutant neutrophil elastase protein results in deregulation of intracellular activity and premature cell death of myeloid-committed progenitor cells in these disorders, resulting in the lack of peripheral blood neutrophils. The potential molecular mechanisms of mutant-protein-mediated neutropenia is discussed.

Involvement of a serine protease, but not of neutrophil elastase, in tumor necrosis factor-induced lethal hepatitis and induction of platelet-activating factor

BACKGROUND/AIMS

Tumor necrosis factor (TNF) plays an essential role in several types of acute and chronic hepatitis. Our aims in the present study were to elucidate the mechanism by which TNF leads to acute lethal hepatitis, thereby focusing on the role of serine proteases and platelet-activating factor (PAF).

METHODS

All experiments were performed in a model of acute hepatitis, induced by TNF in combination with D-(+)-galactosamine (GalN). Neutrophil elastase (NE)-deficient mice, generated by gene targeting were used in the studies.

RESULTS

We found that a serine protease plays an essential mediating role in the in vivo TNF effect as alpha1-antitrypsin (alpha1-AT), soybean trypsin inhibitor (STI) and turkey trypsin inhibitor (TTI), confer complete protection. alpha1-AT and TTI, but not STI, reduce PAF blood levels, induced by TNF/GalN, which is compatible with an elastase-like serine protease involvement in PAF synthesis. In our search for relevant serine proteases we believed that NE was an excellent candidate protease. However, we found that TNF/GalN-induced lethality is not attenuated in mice deficient in NE.

CONCLUSIONS

The data suggest that TNF-induced lethal hepatitis is accompanied by increases in circulating PAF and plasma clotting time, and mediated by a serine protease, but not by NE.

Host-bacterial interactions in the initiation of inflammation

The respiratory epithelium provides both a physical and an immunological barrier to inhaled pathogens. In the normal host, innate defences prevent bacteria from activating inflammation by providing efficient muco-ciliary clearance and antimicrobial activity. Bacteria that persist in the airway lumen, as in cystic fibrosis, activate both the professional immune cells in the respiratory mucosa as well as the more abundant airway epithelial cells. As most of the bacteria become entrapped in airway mucin, shed bacterial products such as pili, flagella, peptidoglycan and lipopolysaccharide from lysed bacteria are likely to be the stimuli most important in activating epithelial signalling. The airway cells respond briskly to bacterial components through several signalling systems which activate epithelial expression of pro-inflammatory cytokines and chemokines. These signals recruit neutrophils to the airways where they eliminate the contaminating bacteria causing inflammation and the ensuing clinical signs of infection.

Adenoviral augmentation of elafin protects the lung against acute injury mediated by activated neutrophils and bacterial infection

During acute pulmonary infection, tissue injury may be secondary to the effects of bacterial products or to the effects of the host inflammatory response. An attractive strategy for tissue protection in this setting would combine antimicrobial activity with inhibition of human neutrophil elastase (HNE), a key effector of neutrophil-mediated tissue injury. We postulated that genetic augmentation of elafin (an endogenous inhibitor of HNE with intrinsic antimicrobial activity) could protect the lung against acute inflammatory injury without detriment to host defense. A replication-deficient adenovirus encoding elafin cDNA significantly protected A549 cells against the injurious effects of both HNE and whole activated human neutrophils in vitro. Intratracheal replication-deficient adenovirus encoding elafin cDNA significantly protected murine lungs against injury mediated by Pseudomonas aeruginosa in vivo. Genetic augmentation of elafin therefore has the capacity to protect the lung against the injurious effects of both bacterial pathogens resistant to conventional antibiotics and activated neutrophils.

Dipeptidyl peptidase I is essential for activation of mast cell chymases, but not tryptases, in mice

Dipeptidyl peptidase I (DPPI) is the sole activator in vivo of several granule-associated serine proteases of cytotoxic lymphocytes. In vitro, DPPI also activates mast cell chymases and tryptases. To determine whether DPPI is essential for their activation in vivo, we used enzyme histochemical and immunohistochemical approaches and solution-based activity assays to study these enzymes in tissues and bone marrow-derived mast cells (BMMCs) from DPPI +/+ and DPPI -/- mice. We find that DPPI -/- mast cells contain normal amounts of immunoreactive chymases but no chymase activity, indicating that DPPI is essential for chymase activation and suggesting that DPPI -/- mice are functional chymase knockouts. The absence of DPPI and chymase activity does not affect the growth, granularity, or staining characteristics of BMMCs and, despite prior predictions, does not alter IgE-mediated exocytosis of histamine. In contrast, the level of active tryptase (mMCP-6) in DPPI -/- BMMCs is 25% that of DPPI +/- BMMCs. These findings indicate that DPPI is not essential for mMCP-6 activation but does influence the total amount of active mMCP-6 in mast cells and therefore may be an important, but not exclusive mechanism for tryptase activation.

Exploitation of syndecan-1 shedding by Pseudomonas aeruginosa enhances virulence

Cell-surface heparan sulphate proteoglycans (HSPGs) are ubiquitous and abundant receptors/co-receptors of extracellular ligands, including many microbes. Their role in microbial infections is poorly defined, however, because no cell-surface HSPG has been clearly connected to the pathogenesis of a particular microbe. We have previously shown that Pseudomonas aeruginosa, through its virulence factor LasA, enhances the in vitro shedding of syndecan-1-the predominant cell-surface HSPG of epithelia. Here we show that shedding of syndecan-1 is also activated by P. aeruginosa in vivo, and that the resulting syndecan-1 ectodomains enhance bacterial virulence in newborn mice. Newborn mice deficient in syndecan-1 resist P. aeruginosa lung infection but become susceptible when given purified syndecan-1 ectodomains or heparin, but not when given ectodomain core protein, indicating that the ectodomain's heparan sulphate chains are the effectors. In wild-type newborn mice, inhibition of syndecan-1 shedding or inactivation of the shed ectodomain's heparan sulphate chains prevents lung infection. Our findings uncover a pathogenetic mechanism in which a host response to tissue injury-syndecan-1 shedding-is exploited to enhance microbial virulence apparently by modulating host defences.

Migration of human granulocytes through reconstituted basement membrane is not dependent on matrix metalloproteinase-9 (MMP-9)

Transmigration of human granulocytes across a basal lamina equivalent was studied in vitro. Transwell inserts were coated with Matrigel, a reconstituted basement membrane. Granulocytes (2x10(6)) were applied to the upper chamber. As chemoattractant interleukin-8 (IL-8; 25 ng/ml) was added to the lower chamber. After 1 h of migration, cells were counted in the lower chamber. Specific hydroxamate inhibitors of MMPs (BB-3103, Ro 31-9790) or of serine proteases (Pefabloc, leupeptin) were added at various concentrations to both chambers before the start of migration. Additional experiments were performed with alpha(2)-macroglobulin, a natural inhibitor of MMPs and a monoclonal antibody which specifically blocks the activity of MMP-9. Migration of granulocytes through Matrigel could not be reduced significantly by any of the MMP inhibitors. A dose-dependent impairment of transmigration was only found with Pefabloc, however, this substance also induced severe morphological changes of the cells. The other inhibitor of serine proteases, leupeptin, did not influence migration at all.

Characterization of mutant neutrophil elastase in severe congenital neutropenia

Severe congenital neutropenia is a heritable human disorder characterized by neutropenia and acute myelogenous leukemia. We recently determined that the majority of cases result from de novo or autosomal dominantly inherited heterozygous mutations in ELA2, encoding neutrophil elastase. Neutrophil elastase is a chymotryptic serine protease localized in granules of neutrophils and monocytes and is the major target of inhibition of the serpin alpha(1)-antitrypsin. The mutations causing severe congenital neutropenia consist of amino acid missense substitutions, in-frame deletion, splice donor mutation producing a deletion, splice acceptor mutation causing insertion of novel residues, and protein truncating mutations of the carboxyl terminus resulting from nonsense substitutions and deletions leading to frameshifts. We have expressed 14 mutant forms of neutrophil elastase in vitro and have characterized their biochemical properties. The mutations have variable effects on proteolytic activity, eliminating the possibility that the disease results from haploinsufficiency. There is no evidence that the mutant enzymes are cytotoxic. The mutant enzymes retain vulnerability to inhibition by alpha(1)-antitrypsin, but demonstrate variable avidity for interaction with this serpin. Somewhat surprisingly, the mutant enzymes inhibit the wild type enzyme when both are coexpressed within the same cell, suggesting the potential to interfere with normal subcellular trafficking or post-translational processing.

The neutrophil: function and regulation in innate and humoral immunity

The neutrophil is a critical effector cell in humoral and innate immunity and plays vital roles in phagocytosis and bacterial killing. Discussed here are the neutrophil components necessary for these processes and the diseases in which these components are either lacking or dysfunctional, illustrating that normal neutrophil function is vital for health.

Accelerated calcium influx and hyperactivation of neutrophils in chronic granulomatous disease

The relationship between activation of NADPH-oxidase, alterations in membrane potential and triggering of Ca2+ fluxes in human phagocytes has been investigated using neutrophils from four subjects with chronic granulomatous disease (CGD). Cytosolic Ca2+ and membrane potential were measured by spectrofluorimetry, and net efflux and influx of Ca2+ by radiometric procedures. Exposure of normal neutrophils to the chemotactic tripeptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP; 1 microM) was accompanied by an abrupt increase in cytosolic Ca2+ coincident with membrane depolarization and efflux of the cation. These events terminated at around 30 s after the addition of FMLP and were followed by membrane repolarization and store-operated influx of Ca2+, both of which were superimposable and complete after about 5 min. Activation of CGD neutrophils was also accompanied by an increase in cytosolic Ca2+, which, in spite of an efficient efflux response, was prolonged in relation to that observed in normal cells. This prolonged increase in cytosolic Ca2+ in activated CGD neutrophils occurred in the setting of trivial membrane depolarization and accelerated influx of Ca2+, and was associated with hyperactivity of the cells according to excessive release of elastase and increased activity of phospholipase A2. Treatment of CGD neutrophils with the type 4 phosphodiesterase inhibitor, rolipram (1 microM) restored Ca2+ homeostasis and attenuated the increase in elastase release. These findings support the involvement of NADPH-oxidase in regulating membrane potential and Ca2+ influx in activated neutrophils, and may explain the disordered inflammatory responses and granuloma formation which are characteristic of CGD.

Neutrophil activation and acute lung injury

Neutrophils are considered to be central to the pathogenesis of most forms of acute lung injury (ALI). For the sake of clarity, neutrophil involvement in ALI can be conceptualized as consisting of sequential stages, beginning with their sequestration in the pulmonary microvasculature, followed by adhesion and activation, and culminating in the production of a microbicidal or "effector" response, such as the generation of reactive oxygen species or release of proteolytic enzymes. Great strides have been made in elucidating these various stages of neutrophil involvement. Recent studies have focused on the intracellular signaling pathways that govern neutrophil activation and have elucidated complex cascades of kinases and other intracellular signaling molecules that allow for amplication of the neutrophil response, yet simultaneously confer specificity of a response. We believe that the inflammatory response in ALI may initially be adaptive, such as the pivotal role played by neutrophils in a bacterial or fungal infection. Ultimately, it is the persistence or the dysregulation of neutrophil activation that may lead to ALI. An increased understanding of how neutrophils function will facilitate the design of therapeutic strategies that retain the beneficial aspects of the inflammatory response, while avoiding unnecessary tissue damage.

The restricted expression of granzyme M in human lymphocytes

We have analyzed the expression of human granzyme M (Gzm M) in various human leukocyte subsets using the specific mAb 4H10. Using FACS and Western blotting analysis we compared the expression of Gzm M with that of other granzymes (Gzm A and Gzm B) and the lytic protein perforin. Human Gzm M was constitutively highly expressed in NK cells as was perforin and Gzm A. Surprisingly, freshly isolated NK cells had very low (sometimes undetectable) levels of Gzm B. In contrast to Gzm B and perforin, Gzm M was not detected in highly purified CD4(+) and CD8(+) T cells either constitutively or after short term activation in vitro. However, low levels of Gzm M were observed in some T cell clones on prolonged passage in vitro. Gzm M was not detected in highly purified neutrophils, monocytes, or tumor cells of the myelomonocytic lineage. Examination of minor T cell subsets from human peripheral blood showed detectable Gzm M in CD3(+), CD56(+) T cells and gammadelta T cells. A histological staining procedure was developed that demonstrated a granular staining pattern for Gzm M and a cellular distribution similar to that observed by Western blotting. These data indicate that the expression of Gzm M does not always correlate with the lytic activity of cytotoxic cells. However, expression of Gzm M in NK cells, CD3(+), CD56(+) T cells, and gammadelta T cells suggests that this enzyme may play some role in innate immune responses.

Inhibition of neutrophil elastase prevents cathelicidin activation and impairs clearance of bacteria from wounds

The host defense roles of neutrophil elastase in a porcine skin wound chamber model were explored. Analysis of wound fluid by acid-urea polyacrylamide gel electrophoresis, Western blot, and bacterial overlay confirmed that the neutrophil-derived protegrins constituted the major stable antimicrobial polypeptide in the wound fluid. The application to the wound of 0.10 and 0.25 mM N-methoxysuccinyl-alanine-alanine-proline-valine (AAPV) chloromethyl ketone, a specific neutrophil elastase inhibitor (NEI), blocked the proteolytic activation of protegrins and diminished the associated antimicrobial activity as detected by radial diffusion assay against Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans or by bacterial gel overlay against S epidermidis and E coli. The application of the related cathepsin G inhibitor (CGI), benzyloxycarbonyl-glycine-leucine-phenylalanine (ZGLF) chloromethyl ketone, had no effect. In wound chambers that received 10(6) colony-forming unit (CFU)/mL of S epidermidis, the presence of NEI significantly decreased the 24-hour clearance of bacteria from the wound compared to wounds treated with CGI or solvent only. Neither inhibitor, at 0.10 or 0.25 mM concentration, affected leukocyte accumulation or degranulation in the wound chambers. The in vitro microbicidal decrement due to NEI was restored by an amount of the specific protegrin (PG-1), which was equivalent to the measured difference of protegrin between control and inhibited chambers. Administration of 1 microg/mL exogenous PG-1 4 hours after chamber preparation was sufficient to normalize in vivo antimicrobial activity. Although pharmacologic NEIs are promising candidates as anti-inflammatory drugs, they may impair host defense in part by inhibiting the activation of cathelicidins by neutrophil elastase.

Evolving concepts in the pathogenesis of chronic obstructive pulmonary disease

It is arguable that more biologic insight has been gained from the study of COPD than from any other pulmonary disorder. A vast knowledge of the biology of extracellular matrix proteins, proteinases, and proteinase inhibitors has largely stemmed from the elastase:anti-elastase hypothesis for the pathogenesis of emphysema. An equally compelling case could be made that interest in, and funding for, COPD research has been woeful, and investigators have made no significant medical breakthroughs in the treatment of this disorder, which, unfortunately, is becoming epidemic worldwide. Indeed, it cannot be argued that physicians have very little treatment to offer to the many patients with COPD. Humankind is rapidly approaching a time when all human genes will be sequenced, and genetic engineering will allow determination of the function of these proteins in vivo. Expression profiling and bioinformatics will allow clinicians to assess the spectrum of genes and proteins regulated in biologic processes, no longer limiting study to naïve candidate genes. These advances will allow investigators to decipher precise pathways of complex diseases, identify genetic and environmental interactions, and ultimately lead to specific (pre)diagnoses and rational treatment. Answers to the question as to why only a subset of smokers develop COPD will enhance the understanding of the disease process. Fortunately, there has been a resurgence of interest in COPD, led largely by the pharmaceutical industry, which has discovered the potential of this unmet need. Consequently, these state-of-the-art scientific techniques are being directly applied to COPD, lending hope for the future. Of even greater importance, the tide seems to be turning on the cigarette industry. Although difficult to imagine, perhaps cigarettes will disappear in this lifetime or at least the next generation won't be fooled by this deadly habit! Well ... the rational therapy thing could work.

Cleavage of CD14 on human gingival fibroblasts cocultured with activated neutrophils is mediated by human leukocyte elastase resulting in down-regulation of lipopolysaccharide-induced IL-8 production

Activated polymorphonuclear leukocytes (PMNs) release various types of proteases and express them on the cell surface. The proteases play important roles in PMN-mediated events. In the present study, flow cytometric analysis revealed that CD14 expression on human gingival fibroblasts (HGF) was markedly reduced by PMA-activated PMNs in a coculture system. We found that this reduction was caused by both secreted and cell surface proteases produced by activated PMNs. A protease responsible for the reduction was found to be human leukocyte elastase (HLE) secreted from the activated PMNs by use of various protease inhibitors, although HLE was only partially involved in CD14 reduction caused by cell-bound molecule(s) on fixed PMNs. Analysis with purified HLE revealed a time- and dose-dependent reduction of CD14 on HGF, and complete reduction was observed by 20 microg/ml HLE treatment for 30-60 min, but the other molecules such as CD26, CD59, CD157, and MHC class I on HGF were only slightly reduced. This reduction of CD14 resulted from direct proteolysis by HLE on the cell surface, because HLE reduced CD14 on fixed HGF and also on purified cell membranes. As a result of CD14 proteolysis, IL-8 production by HGF was suppressed when triggered by 10 ng/ml LPS, but not by IL-1alpha, indicating that HLE inhibited a CD14-dependent cell activation. These findings suggested that activated PMNs have a potential negative feedback mechanism for HGF function at the inflammatory site, particularly in periodontal tissues.

Structural features and biological activities of the cathelicidin-derived antimicrobial peptides

Cathelicidins are a numerous group of mammalian proteins that carry diverse antimicrobial peptides at the C-terminus of a highly conserved preproregion. These peptides, which become active when released from the proregion, display a remarkable variety of sizes, sequences, and structures, and in fact comprise representatives of all the structural groups in which the known antimicrobial peptides have been classified. Most of the cathelicidin-derived peptides exert a broad spectrum and potent antimicrobial activity and also bind to lipopolysaccharide and neutralize its effects. In addition, some of them have recently been shown to exert other activities and might participate in host defense also by virtue of their ability to induce expression of molecules involved in a variety of biological processes. This review is aimed at providing a general overview of the cathelicidins and of the peptides derived therefrom, with emphasis on aspects such as structure, biological activities in vitro and in vivo, and structure/activity relationship studies.

Antimicrobial proteins and peptides of blood: templates for novel antimicrobial agents

The innate immune system provides rapid and effective host defense against microbial invasion in a manner that is independent of prior exposure to a given pathogen.1 It has long been appreciated that the blood contains important elements that mediate rapid responses to infection. Thus, anatomic compartments with ample blood supply are less frequently infected and recover more readily once infected, whereas regions with poor perfusion are prone to severe infection and may require surgical débridement. Blood-borne innate immune mediators are either carried in circulating blood cells (ie, leukocytes and platelets) or in plasma after release from blood cells or on secretion by the liver.

Antimicrobial proteins and peptides of blood: templates for novel antimicrobial agents

The innate immune system provides rapid and effective host defense against microbial invasion in a manner that is independent of prior exposure to a given pathogen.1 It has long been appreciated that the blood contains important elements that mediate rapid responses to infection. Thus, anatomic compartments with ample blood supply are less frequently infected and recover more readily once infected, whereas regions with poor perfusion are prone to severe infection and may require surgical débridement. Blood-borne innate immune mediators are either carried in circulating blood cells (ie, leukocytes and platelets) or in plasma after release from blood cells or on secretion by the liver.

Mutations in the gene encoding neutrophil elastase in congenital and cyclic neutropenia

Congenital neutropenia and cyclic neutropenia are disorders of neutrophil production predisposing patients to recurrent bacterial infections. Recently the locus for autosomal dominant cyclic neutropenia was mapped to chromosome 19p13.3, and this disease is now attributable to mutations of the gene encoding neutrophil elastase (the ELA2 gene). The authors hypothesized that congenital neutropenia is also due to mutations of neutrophil elastase. Patients with congenital neutropenia, cyclic neutropenia, or Shwachman-Diamond syndrome were referred to the Severe Chronic Neutropenia International Registry. Referring physicians provided hematologic and clinical data. Mutational analysis was performed by sequencing polymerase chain reaction (PCR)-amplified genomic DNA for each of the 5 exons of the neutrophil ELA2 gene and 20 bases of the flanking regions. RNA from bone marrow mononuclear cells was used to determine if the affected patients expressed both the normal and the abnormal transcript. Twenty-two of 25 patients with congenital neutropenia had 18 different heterozygous mutations. Four of 4 patients with cyclic neutropenia and 0 of 3 patients with Shwachman-Diamond syndrome had mutations. For 5 patients with congenital neutropenia having mutations predicted to alter RNA splicing or transcript structure, reverse transcriptase-PCR showed expression of both normal and abnormal transcripts. In cyclic neutropenia, the mutations appeared to cluster near the active site of the molecule, whereas the opposite face was predominantly affected by the mutations found in congenital neutropenia. This study indicates that mutations of the gene encoding neutrophil elastase are probably the most common cause for severe congenital neutropenia as well as the cause for sporadic and autosomal dominant cyclic neutropenia.

Mutations in the gene encoding neutrophil elastase in congenital and cyclic neutropenia

Congenital neutropenia and cyclic neutropenia are disorders of neutrophil production predisposing patients to recurrent bacterial infections. Recently the locus for autosomal dominant cyclic neutropenia was mapped to chromosome 19p13.3, and this disease is now attributable to mutations of the gene encoding neutrophil elastase (the ELA2 gene). The authors hypothesized that congenital neutropenia is also due to mutations of neutrophil elastase. Patients with congenital neutropenia, cyclic neutropenia, or Shwachman-Diamond syndrome were referred to the Severe Chronic Neutropenia International Registry. Referring physicians provided hematologic and clinical data. Mutational analysis was performed by sequencing polymerase chain reaction (PCR)-amplified genomic DNA for each of the 5 exons of the neutrophil ELA2 gene and 20 bases of the flanking regions. RNA from bone marrow mononuclear cells was used to determine if the affected patients expressed both the normal and the abnormal transcript. Twenty-two of 25 patients with congenital neutropenia had 18 different heterozygous mutations. Four of 4 patients with cyclic neutropenia and 0 of 3 patients with Shwachman-Diamond syndrome had mutations. For 5 patients with congenital neutropenia having mutations predicted to alter RNA splicing or transcript structure, reverse transcriptase-PCR showed expression of both normal and abnormal transcripts. In cyclic neutropenia, the mutations appeared to cluster near the active site of the molecule, whereas the opposite face was predominantly affected by the mutations found in congenital neutropenia. This study indicates that mutations of the gene encoding neutrophil elastase are probably the most common cause for severe congenital neutropenia as well as the cause for sporadic and autosomal dominant cyclic neutropenia.

The serpin alpha1-proteinase inhibitor is a critical substrate for gelatinase B/MMP-9 in vivo

We have identified the key protein substrate of gelatinase B/MMP-9 (GB) that is cleaved in vivo during dermal-epidermal separation triggered by antibodies to the hemidesmosomal protein BP180 (collagen XVII, BPAG2). Mice deficient in either GB or neutrophil elastase (NE) are resistant to blister formation in response to these antibodies in a mouse model of the autoimmune disease bullous pemphigoid. Disease develops upon complementation of GB -/- mice with NE -/- neutrophils or NE -/- mice with GB -/- neutrophils. Only NE degrades BP180 and produces dermal-epidermal separation in vivo and in culture. Instead, GB acts upstream to regulates NE activity by inactivating alpha1-proteinase inhibitor (alpha1-PI). Excess NE produces lesions in GB -/- mice without cleaving alpha1-PI. Excess alpha1-PI phenocopies GB and NE deficiency in wild-type mice.

Degradation of outer membrane protein A in Escherichia coli killing by neutrophil elastase

In determining the mechanism of neutrophil elastase (NE)-mediated killing of Escherichia coli, we found that NE degraded outer membrane protein A (OmpA), localized on the surface of Gram-negative bacteria. NE killed wild-type, but not OmpA-deficient, E. coli. Also, whereas NE-deficient mice had impaired survival in response to E. coli sepsis, as compared to wild-type mice, the presence or absence of NE had no influence on survival in response to sepsis that had been induced with OmpA-deficient E. coli. These findings define a mechanism of nonoxidative bacterial killing by NE and point to OmpA as a bacterial target in host defense.

Discrimination of sepsis and systemic inflammatory response syndrome by determination of circulating plasma concentrations of procalcitonin, protein complement 3a, and interleukin-6

OBJECTIVE

To evaluate whether plasma concentrations of procalcitonin (PCT), interleukin-6 (IL-6), protein complement 3a (C3a), leukocyte elastase (elastase), and the C-reactive protein (CRP) determined directly after the clinical onset of sepsis or systemic inflammatory response syndrome (SIRS) discriminate between patients suffering from sepsis or SIRS and predict the outcome of these patients.

DESIGN

Prospective study.

SETTING

Medical intensive care unit at a university hospital.

PATIENTS

Twenty-two patients with sepsis and 11 patients with SIRS.

MEASUREMENTS AND MAIN RESULTS

The plasma concentrations of PCT, C3a, and IL-6 obtained < or =8 hrs after clinical onset of sepsis or SIRS but not those of elastase or CRP were significantly higher in septic patients (PCT: median, 16.8 ng/mL, range, 0.9-351.2 ng/mL, p = .003; C3a: median, 807 ng/mL, range, 422-4788 ng/mL, p < .001; IL-6: median, 382 pg/mL, range, 5-1004 pg/mL, p = .009, all Mann-Whitney rank sum test) compared with patients suffering from SIRS (PCT: median, 3.0 ng/mL, range, 0.7-29.5 ng/mL; C3a: median, 409 ng/mL, range, 279566 ng/mL; IL-6: median, 98 pg/mL, range, 23-586 pg/mL). The power of PCT, C3a, and IL-6 to discriminate between septic and SIRS patients was determined in a receiver operating characteristic analysis. C3a was the best variable to differentiate between both populations with a maximal sensitivity of 86% and a specificity of 80%. An even better discrimination (i.e., a maximal sensitivity of 91% and a specificity of 80%) was achieved when PCT and C3a were combined in a "sepsis score." C3a concentrations also helped to predict the outcome of patients. Based on the sepsis score, a logistic regression model was developed that allows a convenient and reliable determination of the probability of an individual patient to suffer from sepsis or SIRS.

CONCLUSIONS

Our data show that the determination of PCT, IL-6, and C3a is more reliable to differentiate between septic and SIRS patients than the variables CRP and elastase, routinely used at the intensive care unit. The determination of PCT and C3a plasma concentrations appears to be helpful for an early assessment of septic and SIRS patients in intensive care.

Reactive oxygen and nitrogen intermediates in the relationship between mammalian hosts and microbial pathogens

This review summarizes recent evidence from knock-out mice on the role of reactive oxygen intermediates and reactive nitrogen intermediates (RNI) in mammalian immunity. Reflections on redundancy in immunity help explain an apparent paradox: the phagocyte oxidase and inducible nitric oxide synthase are each nonredundant, and yet also mutually redundant, in host defense. In combination, the contribution of these two enzymes appears to be greater than previously appreciated. The remainder of this review focuses on a relatively new field, the basis of microbial resistance to RNI. Experimental tuberculosis provides an important example of an extended, dynamic balance between host and pathogen in which RNI play a major role. In diseases such as tuberculosis, a molecular understanding of host-pathogen interactions requires characterization of the defenses used by microbes against RNI, analogous to our understanding of defenses against reactive oxygen intermediates. Genetic and biochemical approaches have identified candidates for RNI-resistance genes in Mycobacterium tuberculosis and other pathogens.

Human monocyte/neutrophil elastase inhibitor (MNEI) is regulated by PU.1/Spi-1, Sp1, and NF-kappaB

Human monocyte/neutrophil elastase inhibitor (MNEI) is a specific inhibitor of the neutrophil azurophil granule proteases including elastase. To understand the physiological mechanisms that regulate expression of MNEI, we dissected a 1.0 kb region upstream of exon 1. On transient transfection, promoter activity of MNEI-luciferase constructs was highest in U937 myeloid cells, followed by K562 hematopoietic cells, followed by HeLa cervical carcinoma cells, indicating that the MNEI promoter is most active in myeloid cells and is also active in non-myeloid cells. Three transcription factor binding elements, which confer the majority of activity, are located within the first 180 base pairs of the promoter, one of which, located at -128, was active in U937 and K562 cells but inactive in non-myeloid HeLa cells. The three proximal elements were identified by transient transfection, mutation, gel shift and competition assays as Sp1 at -170, PU.1/Spi-1 at -128, and Sp1 at -66. The trans-acting factors that bind and control these elements were detected, and their identity confirmed by antibody supershift assays. Further upstream at -821, an additional regulatory element was identified controlled by NF-kappaB, which supports the highest levels of MNEI transcriptional activity. In U937 cells, reporter gene expression by the MNEI-luciferase construct that included the NF-kappaB element was two- to three-fold greater than the construct without the element. In addition, treatment of myeloid cells with lipopolysaccharide, a complex glycolipid of gram-negative bacteria, activated NF-kappaB to bind the -821 element, together suggesting that enhancement of expression of the anti-inflammatory MNEI gene is linked to innate immune responses to bacterial infection.

Critical role of neutrophils for the generation of psoriasiform skin lesions in flaky skin mice

Although T cell dysregulation is thought to underlie the pathogenesis of psoriasis, prominent infiltration and microabscess formation by neutrophils is a distinctive hallmark feature of this common disorder. The exact role of neutrophils in the pathogenesis of psoriasiform alterations in vivo, however, is unknown. Similar to human psoriasis, flaky skin mice (fsn/fsn) revealed a prominent infiltrate of neutrophils, and microabscesses within the hyperproliferative epidermis were associated with de novo expression of intercellular adhesion molecule-1. Intraperitoneal injection with the neutrophil-depleting RB6-8C5 monoclonal antibody (anti-Ly-6G) resulted in a dramatic reduction of the epidermal thickness by 58% compared with isotype-treated animals (p < 0.001). In addition, epidermal microabscesses were conspicuously absent (p < 0.001), and cutaneous neutrophils and T cells, but not mast cells or dendritic cells, were markedly reduced in anti-Ly-6G-treated mice. Proinflammatory cytokines, including tumor necrosis factor alpha and interleukin-1, were also downregulated. Therapeutic effects occurred as early as 4 d after beginning of treatment. Wildtype skin was not affected. When the integrin alphaMbeta2 (CD11b/CD18), which mediates neutrophil localization through binding to intercellular adhesion molecule-1, was blocked in vivo with the M1/70 monoclonal antibody, the epidermal thickness was reduced by 31% (p < 0.002), and neutrophil and T cell accumulation was diminished compared with control animals. Likewise, treatment of fsn/fsn mice with the MP1-22E9 monoclonal antibody neutralizing granulocyte macrophage-colony stimulating factor, a cytokine stimulating neutrophils by upregulating alphaMbeta2, resulted in significant reduction of inflammation and acanthosis by 30% (p < 0.003). These results demonstrate a critical pathogenic role of neutrophils for hyperproliferative inflammatory lesions in fsn/fsn mice, suggesting that blocking neutrophil function may have therapeutic benefit in some human skin disorders.

Calcium-dependent secretion in human neutrophils: a proteomic approach

Bactericidal, proteolytic and signal proteins released by activated neutrophils play a major role in infection fighting and inflammatory processes. These proteins are mainly stored in organelles called granules until induction of their controlled exocytosis. The present work deals with the characterization of the proteins which are secreted upon activation of human neutrophils by ionomycin and calcium. Proteins were separated by two-dimensional gel electrophoresis and identified by peptide mass fingerprinting. Almost all the previously described soluble components of neutrophil granules could be identified. Moreover, several additional proteins were shown to be secreted by activated neutrophils, namely calgranulins, human cartilage glycoprotein of 39 kDa (HC gp-39), chitotriosidase, and annexin XI. Their subcellular localization and possible functions are discussed.

Impaired immunity and enhanced resistance to endotoxin in the absence of neutrophil elastase and cathepsin G

While the critical role of reactive oxygen intermediates (ROI) in the microbicidal activity of polymorphonuclear granulocytes is well established, the function of the nonoxidative effector mechanisms in vivo remains unclear. Here we show that mice deficient in the neutrophil granule serine proteases elastase and/or cathepsin G are susceptible to fungal infections, despite normal neutrophil development and recruitment. The protease deficiencies but not the absence of ROI leads to enhanced resistance to the lethal effects of endotoxin LPS, although normal levels of TNFalpha are produced. The data demonstrate a critical role of the nonoxidative effector mechanisms of neutrophils in host immunity and immunopathology and identify elastase and cathepsin G as effectors in the endotoxic shock cascade downstream of TNFalpha.

A critical role for neutrophil elastase in experimental bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune skin disease characterized by subepidermal blisters and autoantibodies against 2 hemidesmosome-associated proteins, BP180 and BP230. The immunopathologic features of BP can be reproduced in mice by passive transfer of anti-BP180 antibodies. Lesion formation in this animal model depends upon complement activation and neutrophil recruitment. In the present study, we investigated the role of neutrophil elastase (NE) in antibody-induced blister formation in experimental BP. Abnormally high levels of caseinolytic activity, consistent with NE, were detected in extracts of lesional skin and blister fluid of mice injected with anti-BP180 IgG. The pathogenic anti-BP180 IgG failed to induce subepidermal blistering in NE-null (NE(-/-)) mutant mice. NE(-/-) mice reconstituted with neutrophils from wild-type mice became susceptible to experimental BP. Wild-type mice given NE inhibitors (alpha1-proteinase inhibitor and Me-O-Suc-Ala-Ala-Pro-Val-CH(2)Cl), but not mice given cathepsin G/chymase inhibitors (alpha1-antichymotrypsin or Z-Gly-Leu-Phe-CH(2)Cl), were resistant to the pathogenic activity of anti-BP180 antibodies. Incubation of murine skin with NE induced BP-like epidermal-dermal detachment. Finally, NE cleaved BP180 in vitro and in vivo. These results implicate NE directly in the dermal-epidermal cleavage induced by anti-BP180 antibodies in the experimental BP model.

Increased elastase and myeloperoxidase activity associated with neutrophil recruitment by IL-17 in airways in vivo

BACKGROUND

A recent study demonstrated that intratracheal administration of the T-lymphocyte cytokine IL-17 recruits neutrophils into airways in vivo by C-X-C chemokine release. It is not known whether IL-17 may also activate airway neutrophils.

OBJECTIVE

Our purpose was to evaluate whether IL-17 activates neutrophils in airways in vivo and, if so, whether the proinflammatory cytokine IL-1beta modulates this action of IL-17.

METHODS

Intratracheal administration of human (h) IL-17 or rat (r) IL-1beta or hIL-17 plus rIL-1beta in anesthetized, spontaneously breathing rats was followed by bronchoalveolar lavage (BAL) 6 hours later. The BAL fluid was characterized in terms of neutrophil count, of the activity for myeloperoxidase (MPO), and in some cases of the activity for elastase (ELA). Isolated rat neutrophils were stimulated with hIL-17 in vitro, followed by characterization of MPO activity in the cell medium.

RESULTS

hIL-17 (1 microg) increased the ELA and the MPO activity, as well as the neutrophil count in BAL fluid, whereas the proinflammatory cytokine rIL-1beta (2.5 ng) did not. Pretreatment with rIL-1beta enhanced IL-17induced ELA and MPO activity, without increasing the neutrophil count. The BAL ELA activity was inhibited by a specific inhibitor of neutrophil serine proteases. Stimulation with hIL-17 in vitro did not increase MPO activity in isolated neutrophils.

CONCLUSION

IL-17 can activate neutrophils in association with their recruitment into the airways in vivo and this effect is probably achieved through induced release of mediators from other airway cells.

Transcriptional induction of stromelysin-3 in mesodermal cells is mediated by an upstream CCAAT/enhancer-binding protein element associated with a DNase I-hypersensitive site

Stromelysin-3 (ST3) is a matrix metalloproteinase whose synthesis is markedly increased in stromal fibroblasts of most invasive human carcinomas. In the present study, we have investigated the molecular mechanisms by which high levels of ST3 expression can be induced. In contrast to the early and transient induction of interstitial collagenase by 12-O-tetradecanoylphorbol-13-acetate (TPA), the fibroblastic induction of ST3 was found to be delayed and to require protein neosynthesis. We demonstrated that this induction is transcriptional and does not result from changes in RNA stability. By looking next to promoter regions accessible to DNase I upon gene induction, we have identified two distal elements and have characterized their role in the transcriptional regulation of ST3. The first one is a TPA-responsive element that controls the base-line ST3 promoter activity but is not required for its activation. We demonstrate that ST3 gene induction is actually mediated by the second element, a C/EBP-binding site, by showing: (i) that this element becomes accessible in cells induced to express ST3, (ii) that endogenous C/EBPbeta binds to the ST3 promoter, and (iii) that this binding leads to ST3 transcriptional activation. Our study provides new insights into the regulation of ST3 and suggests an additional role for C/EBP transcription factors in tissue remodeling processes associated with this MMP.

Normal Neutrophil Function in Cathepsin G-Deficient Mice

Cathepsin G is a neutral serine protease that is highly expressed at the promyelocyte stage of myeloid development. We have developed a homologous recombination strategy to create a loss-of-function mutation for murine cathepsin G. Bone marrow derived from mice homozygous for this mutation had no detectable cathepsin G protein or activity, indicating that no other protease in bone marrow cells has the same specificity. Hematopoiesis in cathepsin G−/− mice is normal, and the mice have no overt abnormalities in blood clotting. Neutrophils derived from cathepsin G−/− mice have normal morphology and azurophil granule composition; these neutrophils also display normal phagocytosis and superoxide production and have normal chemotactic responses to C5a, fMLP, and interleukin-8. Although cathepsin G has previously shown to have broad spectrum antibiotic properties, challenges of mice with Staphylococcus aureus, Klebsiella pneumoniae, or Escherichia coli yielded survivals that were not different from those of wild-type animals. In sum, cathepsin G−/− neutrophils have no obvious defects in function; either cathepsin G is not required for any of these normal neutrophil functions or related azurophil granule proteases with different specificities (ie, neutrophil elastase, proteinase 3, azurocidin, and/or others) can substitute for it in vivo.

Normal Neutrophil Function in Cathepsin G-Deficient Mice

Cathepsin G is a neutral serine protease that is highly expressed at the promyelocyte stage of myeloid development. We have developed a homologous recombination strategy to create a loss-of-function mutation for murine cathepsin G. Bone marrow derived from mice homozygous for this mutation had no detectable cathepsin G protein or activity, indicating that no other protease in bone marrow cells has the same specificity. Hematopoiesis in cathepsin G−/− mice is normal, and the mice have no overt abnormalities in blood clotting. Neutrophils derived from cathepsin G−/− mice have normal morphology and azurophil granule composition; these neutrophils also display normal phagocytosis and superoxide production and have normal chemotactic responses to C5a, fMLP, and interleukin-8. Although cathepsin G has previously shown to have broad spectrum antibiotic properties, challenges of mice with Staphylococcus aureus, Klebsiella pneumoniae, or Escherichia coli yielded survivals that were not different from those of wild-type animals. In sum, cathepsin G−/− neutrophils have no obvious defects in function; either cathepsin G is not required for any of these normal neutrophil functions or related azurophil granule proteases with different specificities (ie, neutrophil elastase, proteinase 3, azurocidin, and/or others) can substitute for it in vivo.

Changes in Chromatin Organization at the Neutrophil Elastase Locus Associated With Myeloid Cell Differentiation

Neutrophil elastase, proteinase-3, and azurocidin are primary components of neutrophil azurophilic granules and are encoded by closely linked genes (gene symbols ELA2, PRTN3, and AZU1, respectively) in a region of approximately 50 kb. These genes are coordinately expressed in a granulocyte-specific fashion, but the mechanisms defining this pattern of expression are unknown. To understand the role of chromatin organization in governing the expression of ELA2, PRTN3, and AZU1, we mapped this region of chromosome 19 and identified the adipsin (complement factor D) gene in proximity to the 3′ end of ELA2. We then examined the changes in chromatin structure at the locus which accompany myeloid cell differentiation and identified 17 DNase I hypersensitive sites (DHS 1 to 17) in U-937 cells, an early myelomonocytic cell line expressing high levels of neutrophil elastase. Chemically induced differentiation and concomitant downregulation of AZU1, PRTN3, and ELA2 transcription in U-937 cells is not accompanied by changes in the DHS-pattern. Mature neutrophils, however, do not carry any of these hypersensitive sites, indicating a large degree of chromatin remodeling at this locus accompanying terminal granulocytic differentiation. Sixteen of the 17 DHS identified in U-937 cells are also present in the HL-60 myelomonocytic cell line. Hematopoietic cell lines representing the early erythroid and lymphocyte lineages, and a nonhematopoietic cell line display a subset of the hypersensitive sites. The altered chromatin structure specific to cells that actively transcribe the AZU1-PRTN3-ELA2 genes suggests that chromatin reorganization is an important mechanism regulating the myeloid-specific transcription of this gene cluster.

Changes in Chromatin Organization at the Neutrophil Elastase Locus Associated With Myeloid Cell Differentiation

Neutrophil elastase, proteinase-3, and azurocidin are primary components of neutrophil azurophilic granules and are encoded by closely linked genes (gene symbols ELA2, PRTN3, and AZU1, respectively) in a region of approximately 50 kb. These genes are coordinately expressed in a granulocyte-specific fashion, but the mechanisms defining this pattern of expression are unknown. To understand the role of chromatin organization in governing the expression of ELA2, PRTN3, and AZU1, we mapped this region of chromosome 19 and identified the adipsin (complement factor D) gene in proximity to the 3′ end of ELA2. We then examined the changes in chromatin structure at the locus which accompany myeloid cell differentiation and identified 17 DNase I hypersensitive sites (DHS 1 to 17) in U-937 cells, an early myelomonocytic cell line expressing high levels of neutrophil elastase. Chemically induced differentiation and concomitant downregulation of AZU1, PRTN3, and ELA2 transcription in U-937 cells is not accompanied by changes in the DHS-pattern. Mature neutrophils, however, do not carry any of these hypersensitive sites, indicating a large degree of chromatin remodeling at this locus accompanying terminal granulocytic differentiation. Sixteen of the 17 DHS identified in U-937 cells are also present in the HL-60 myelomonocytic cell line. Hematopoietic cell lines representing the early erythroid and lymphocyte lineages, and a nonhematopoietic cell line display a subset of the hypersensitive sites. The altered chromatin structure specific to cells that actively transcribe the AZU1-PRTN3-ELA2 genes suggests that chromatin reorganization is an important mechanism regulating the myeloid-specific transcription of this gene cluster.

Mutations in ELA2, encoding neutrophil elastase, define a 21-day biological clock in cyclic haematopoiesis

Human cyclic haematopoiesis (cyclic neutropenia, MIM 162800) is an autosomal dominant disease in which blood-cell production from the bone marrow oscillates with 21-day periodicity. Circulating neutrophils vary between almost normal numbers and zero. During intervals of neutropenia, affected individuals are at risk for opportunistic infection. Monocytes, platelets, lymphocytes and reticulocytes also cycle with the same frequency. Here we use a genome-wide screen and positional cloning to map the locus to chromosome 19p13.3. We identified 7 different single-base substitutions in the gene (ELA2) encoding neutrophil elastase (EC 3. 4.21.37, also known as leukocyte elastase, elastase 2 and medullasin), a serine protease of neutrophil and monocyte granules, on unique haplotypes in 13 of 13 families as well as a new mutation in a sporadic case. Neutrophil elastase (a 240-aa mature protein predominantly found in neutrophil granules) is the target for protease inhibition by alpha1-antitrypsin, and its unopposed release destroys tissue at sites of inflammation. We hypothesize that a perturbed interaction between neutrophil elastase and serpins or other substrates may regulate mechanisms governing the clock-like timing of haematopoiesis.

Leukocyte proteinases in wound healing: roles in physiologic and pathologic processes

Leukocytes express a number of proteinases which play critical roles in physiologic processes during wound healing. However, if the activity of these proteinases is uncontrolled, they can contribute to devastating tissue injury that can affect most organ systems. Until recently, little was known about the mechanisms by which leukocytes retain the activity of their proteinases within the extracellular space which contains highly effective proteinase inhibitors. Studies of the cell biology of leukocyte proteinases have begun to identify the mechanisms by which proteinases can circumvent the effects of physiologic proteinase inhibitors. Herein, we will review the cell biology of leukocyte proteinases, and we will discuss the mechanisms by which leukocyte proteinases can contribute to physiologic processes occurring during wound healing, as well as their roles in pathologic processes.