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

Ectosomes Released by Human Neutrophils Are Specialized Functional Units

Here we show that human polymorphonuclear leukocytes (PMN) release ectosomes independently of complement attack during their activation both in vitro and at the site of inflammation in vivo. Patterns of biotinylated proteins on the surface of PMN and on PMN-derived ectosomes indicated a specific sorting of cell surface proteins into and out of ectosomes. Ectosomes expressed clusters of complement receptor 1 (CR1), which allowed them to bind efficiently to opsonized bacteria. Myeloperoxidase and human leukocyte elastase, both stored within the azurophilic granules of PMN, were found to colocalize on ectosomes with CR1. Furthermore, myeloperoxidase colocalized with human leukocyte elastase. In contrast, not present on CR1-expressing ectosomes were CD63, a selective marker for the azurophilic granules, and CD14, which is located within the same granules and the secretory vesicles as CR1. Of the other complement regulatory proteins expressed by PMN, only CD59 colocalized with CR1, while CD55 and CD46 were almost absent. Ectosomes released by activated PMN at the site of inflammation may function as a well organized element (ecto-organelle), designed to focus antimicrobial activity onto opsonized surfaces.

Aerosolized prolastin suppresses bacterial proliferation in a model of chronic Pseudomonas aeruginosa lung infection

High levels of active neutrophil elastase (HNE) are present in the respiratory secretions of patients with cystic fibrosis (CF). We hypothesized that aerosolized Prolastin (alpha(1)-protease inhibitor or alpha(1)PI, purified from human blood) could suppress airway neutrophil inflammation and accelerate bacterial clearance from the lung in a model of chronic Pseudomonas aeruginosa lung infection. Because human alpha(1)PI effectively inhibits rat as well as human neutrophil elastase (NE) activity in vitro, we choose to test this hypothesis using a rat agar bead model of chronic P. aeruginosa lung infection. In this model, aerosolized Prolastin significantly decreased elastase activity (p < 0.01), lung neutrophil counts (p < 0.01), and bacterial colony counts (p < 0.01). Prolastin had no direct bactericidal effect on P. aeruginosa in vitro. Lung tissue histopathology revealed a marked decrease in lung inflammation in animals treated with Prolastin. These studies indicate that Prolastin can significantly decrease the elastase burden in the chronically infected lung. In addition, not only does Prolastin suppress lung inflammation, but it also markedly decreases P. aeruginosa density in a rat model of chronic P. aeruginosa lung infection. These data suggest that aerosolized alpha(1)PI may represent a useful nonantibiotic adjunct in the treatment and control of infection and inflammation associated with CF lung disease.

Oxygen-independent microbicidal mechanisms of phagocytes

The principal biological function of phagocytic cells is the destruction of invading microorganisms. Following phagocytosis, microbes are exposed to multiple antimicrobial substances ranging in complexity from simple oxygen radicals to large proteins. These substances disrupt various microbial structures and eventually kill and digest most of the invaders. This review is focused on oxygen-independent microbicidal mechanisms in granulocytes and macrophages.

A Novel Serpin Expressed by Blood-Borne Microfilariae of the Parasitic Nematode Brugia malayi Inhibits Human Neutrophil Serine Proteinases

Serine proteinase inhibitors (serpins) play a vital regulatory role in a wide range of biological processes, and serpins from viruses have been implicated in pathogen evasion of the host defence system. For the first time, we report a functional serpin gene from nematodes that may function in this manner. This gene, named Bm-spn-2, has been isolated from the filarial nematode Brugia malayi, a causative agent of human lymphatic filariasis. Polymerase chain reaction (PCR) and Western blot experiments indicate that Bm-spn-2 is expressed only by microfilariae (Mf), which are the long-lived blood-dwelling larval stage. A survey of the greater than 14,000 expressed sequence tags (ESTs) from B malayi deposited in dbEST shows that greater than 2% of the ESTs sequenced from Mf cDNA libraries correspond to Bm-spn-2. Despite its abundance in the microfilarial stage, Bm-spn-2 has not been found in any other point in the life cycle. The predicted protein encoded byBm-spn-2 contains 428 amino acids with a putative signal peptide. Antibodies to recombinant Bm-SPN-2 protein react specifically with a 47.5-kD native protein in Mf extract. Bm-SPN-2 is one of the largest of the 93 known serpins, due to a 22 amino acid carboxy-terminal extension, and contains the conserved serpin signature sequence. Outside these regions, levels of homology are low, and only a distant relationship can been seen to a Caenorhabditis elegansserpin. The Bm-spn-2 gene contains 6 introns, 2 of which appear to be shared by both nematode species. The B malayi introns have an extended and conserved 3′ splice site and are relatively large compared with C elegans. A panel of mammalian serine proteinases were screened and Bm-SPN-2 protein was found to specifically inhibit enzymatic activity of human neutrophil cathepsin G and human neutrophil elastase, but not a range of other serine proteinases. It is possible that Bm-SPN-2 could function as a stage-specific serpin in the blood environment of the microfilarial parasite in protection from human immunity and thus may be a good candidate for protective vaccine.

A Novel Serpin Expressed by Blood-Borne Microfilariae of the Parasitic Nematode Brugia malayi Inhibits Human Neutrophil Serine Proteinases

Serine proteinase inhibitors (serpins) play a vital regulatory role in a wide range of biological processes, and serpins from viruses have been implicated in pathogen evasion of the host defence system. For the first time, we report a functional serpin gene from nematodes that may function in this manner. This gene, named Bm-spn-2, has been isolated from the filarial nematode Brugia malayi, a causative agent of human lymphatic filariasis. Polymerase chain reaction (PCR) and Western blot experiments indicate that Bm-spn-2 is expressed only by microfilariae (Mf), which are the long-lived blood-dwelling larval stage. A survey of the greater than 14,000 expressed sequence tags (ESTs) from B malayi deposited in dbEST shows that greater than 2% of the ESTs sequenced from Mf cDNA libraries correspond to Bm-spn-2. Despite its abundance in the microfilarial stage, Bm-spn-2 has not been found in any other point in the life cycle. The predicted protein encoded byBm-spn-2 contains 428 amino acids with a putative signal peptide. Antibodies to recombinant Bm-SPN-2 protein react specifically with a 47.5-kD native protein in Mf extract. Bm-SPN-2 is one of the largest of the 93 known serpins, due to a 22 amino acid carboxy-terminal extension, and contains the conserved serpin signature sequence. Outside these regions, levels of homology are low, and only a distant relationship can been seen to a Caenorhabditis elegansserpin. The Bm-spn-2 gene contains 6 introns, 2 of which appear to be shared by both nematode species. The B malayi introns have an extended and conserved 3′ splice site and are relatively large compared with C elegans. A panel of mammalian serine proteinases were screened and Bm-SPN-2 protein was found to specifically inhibit enzymatic activity of human neutrophil cathepsin G and human neutrophil elastase, but not a range of other serine proteinases. It is possible that Bm-SPN-2 could function as a stage-specific serpin in the blood environment of the microfilarial parasite in protection from human immunity and thus may be a good candidate for protective vaccine.

Dipeptidyl peptidase I is required for the processing and activation of granzymes A and B in vivo

Dipeptidyl peptidase I (DPPI) is a lysosomal cysteine protease that has been implicated in the processing of granzymes, which are neutral serine proteases exclusively expressed in the granules of activated cytotoxic lymphocytes. In this report, we show that cytotoxic lymphocytes derived from DPPI-/- mice contain normal amounts of granzymes A and B, but these molecules retain their prodipeptide domains and are inactive. Cytotoxic assays with DPPI-/- effector cells reveal severe defects in the induction of target cell apoptosis (as measured by [(125)I]UdR release) at both early and late time points; this defect is comparable to that detected in perforin-/- or granzyme A-/- x B-/- cytotoxic lymphocytes. DPPI therefore plays an essential role in the in vivo processing and activation of granzymes A and B, which are required for cytotoxic lymphocyte granule-mediated apoptosis.

Human Polymorphonuclear Leukocytes Produce IL-12, TNF-α, and the Chemokines Macrophage-Inflammatory Protein-1α and -1β in Response to Toxoplasma gondii Antigens

The induction of a type 1 inflammatory cytokine response is a key event in the initiation of immunity to Toxoplasma gondii. Because polymorphonuclear leukocytes rapidly respond to infection by exiting the peripheral blood and accumulating at a site of infection, we sought to determine whether these cells produce cytokines in response to T. gondii. When human peripheral blood neutrophils were stimulated with parasite Ag, they produced both IL-12 (p70) and TNF-α. Similarly, up-regulated expression of macrophage-inflammatory protein-1α (MIP-1α) and MIP-1β gene transcripts was induced. Kinetic analysis of IL-12 and TNF-α production revealed distinct patterns following stimulation by T. gondii or LPS. Exogenous TNF-α alone also provided a potent stimulus of MIP-1α and MIP-1β expression, and when neutralizing anti-TNF-α antiserum was included in cultures of parasite-stimulated cells, expression of these CC-family chemokines was partially blocked. These results establish that T. gondii possesses the ability of driving neutrophil proinflammatory cytokine production, and they suggest that parasite-induced MIP-1α and MIP-1β partly results from autocrine stimulation through TNF-α.

Migration of neutrophils across human pulmonary endothelial cells is not blocked by matrix metalloproteinase or serine protease inhibitors

It has long been speculated that neutrophils deploy proteases to digest subendothelial matrix as they migrate from the bloodstream. Direct evidence for the involvement of proteases in neutrophil transendothelial migration is, however, lacking. To address this issue we used transmission electron microscopy to verify the presence of continuous basal lamina beneath pulmonary endothelial cells grown on microporous filters, and then examined the effects of protease inhibitors on neutrophil migration through the endothelial cells and their associated subcellular matrix. Inhibitors of the two major matrix-degrading protease groups present in neutrophils, the matrix metalloproteinases (MMPs) and serine proteases, were assessed for their ability to modulate neutrophil transendothelial migration in response to the chemoattractant n-formylmethionyl leucylphenylalanine (FMLP). Neither the naturally occurring MMP inhibitor, tissue inhibitor of metalloproteinase-1, nor the hydroxamic acid-based inhibitors GM-6001, BB-3103, or Ro 31-9790 had any significant effect on FMLP-stimulated neutrophil migration across endothelial cells and associated basal lamina, with >/= 80% of neutrophils migrating through the system, even in the presence of inhibitors, at concentrations that totally inhibited all the gelatinase B (MMP-9) released upon stimulation with FMLP. Similarly, with serine protease inhibitors no significant inhibition of neutrophil migration was observed with a naturally occurring inhibitor, secretory leukocyte protease inhibitor, or a low molecular-weight synthetic inhibitor, Pefabloc SC. These results indicate that neither MMP nor serine protease digestion of sub-endothelial matrix is required for successful neutrophil transendothelial migration.

Neutrophil emigration in the lungs, peritoneum, and skin does not require gelatinase B

Polymorphonuclear leukocytes (PMN) release gelatinase B in response to variable stimuli. Gelatinase B degrades basement membrane components in vitro, and inhibition of matrix metalloproteinase activity blunts PMN migration through a prototype basement membrane (Matrigel) and amnionic membranes. Accordingly, it has been speculated that gelatinase B is necessary for PMN emigration. To test this hypothesis we induced acute inflammation in the lungs, peritoneum, and skin in mice with a null mutation of the gelatinase B gene (gelatinase B-/-) and littermate controls (gelatinase B+/+). At 3, 6, 12, and 24 h after intratracheal instillation of LPS, the emigration of PMN in the lung, as determined by PMN in bronchoalveolar lavage fluid, was similar in gelatinase B-/- and gelatinase B+/+ mice. The number of PMN in the peritoneal cavity 4 h after thioglycollate-induced peritonitis was also comparable in gelatinase B-/- and gelatinase B+/+ mice. At 4 h after an intradermal injection of interleukin-8, numerous PMN were present extravascularly in the dermis in both gelatinase B-/- and gelatinase B+/+ mice and the myeloperoxidase activities of the skin at the injection sites were indistinguishable between the two types of mice. PMN from gelatinase B-/- mice migrated through Matrigel in response to zymosan-activated serum with the same efficiency as did PMN from gelatinase B+/+ mice. In vitro, gelatinase B-/- PMN killed Staphylococcus aureus and Klebsiella pneumoniae as effectively as did PMN from gelatinase B+/+ mice. These findings indicate that gelatinase B is not required for PMN emigration, and suggest that the antibacterial function of PMN is preserved despite gelatinase B deficiency.

Activity of abundant antimicrobials of the human airway

Human airways produce several antimicrobial factors; the most abundant are lysozyme and lactoferrin. Despite their likely importance in preventing infection, and their possible key role in the pathogenesis of cystic fibrosis (CF), we know little about their antibacterial activity in the context of the CF airway. We found that abundant airway antimicrobial factors kill common CF pathogens, although Burkholderia was relatively resistant. To study the antibacterial activity, we developed a rapid, sensitive, and quantitative in vitro luminescence assay. Because NaCl concentrations may be elevated in CF airway surface liquid, we tested the effect of salt on antibacterial activity. Activity of individual factors and of airway lavage fluid was inhibited by high ionic strength, and it was particularly sensitive to divalent cations. However, it was not inhibited by nonionic osmolytes and thus did not require hypotonic liquid. The inhibition by ionic strength could be partially compensated by increased concentrations of antibacterial factors, thus there was no one unique salt concentration for inhibition. CF airway secretions also contain abundant mucin and elastase; however, these had no effect on antibacterial activity of lysozyme, lactoferrin, or airway lavage fluids. When studied at low NaCl concentrations, CF and non-CF airway lavage fluids contained similar levels of antibacterial activity. These results suggest approaches toward developing treatments aimed at preventing or reducing airway infections in individuals with CF.

Macrophage metalloelastase, MMP-12, cleaves human apolipoprotein(a) in the linker region between kringles IV-4 and IV-5. Potential relevance to lipoprotein(a) biology

In this study we found that macrophage metalloelastase, MMP-12 cleaves, in vitro, apolipoprotein(a) (apo(a)) in the Asn3518-Val3519 bond located in the linker region between kringles IV-4 and IV-5, a bond immediately upstream of the Ile3520-Leu3521 bond, shown previously to be the site of action by neutrophil elastase (NE). We have also shown that human apo(a) injected into the tail vein of control mice undergoes degradation as reflected by the appearance of immunoreactive fragments in the plasma and in the urine of these animals. To define whether either or both of these enzymes may be responsible for the in vivo apo(a) cleavage, we injected intravenously MMP-12(-/-), NE -/- mice and litter mates, all of the same strain, with either lipoprotein(a) (Lp(a)), full-length free apo(a), or its N-terminal fragment, F1, obtained by the in vitro cleavage of apo(a) by NE. In the plasma of Lp(a)/apo(a)-injected mice, F1 was detected in control and NE -/- mice but was virtually absent in the MMP-12(-/-) mice. Moreover, fragments of the F1 type were present in the urine of the animals except for the MMP-12(-/-) mice. These fragments were significantly smaller in size than those observed in the plasma. All of the animals injected with F1 exhibited small sized fragments in their urine. These observations provide evidence that, in the mouse strain used, MMP-12 plays an important role in the generation of F1 from injected human Lp(a)/apo(a) and that this fragment undergoes further cleavage during renal transit via a mechanism that is neither NE- nor MMP-12-dependent. Thus, factors influencing the expression of MMP-12 may have a modulating action on the biology of Lp(a).

Severe impairment in early host defense against Candida albicans in mice deficient in myeloperoxidase

Myeloperoxidase (MPO) catalyzes the reaction of hydrogen peroxide with chloride ion to produce hypochlorous acid (HOCl), which is used for microbial killing by phagocytic cells. Despite the important role of MPO in host defense, however, MPO deficiency is relatively common in humans, and most of these individuals are in good health. To define the in vivo role of MPO, we have generated by gene targeting mice having no MPO activity in their neutrophils and monocytes. The mice without MPO developed normally, were fertile, and showed normal clearance of intraperitoneal Staphylococcus aureus. However, they showed increased susceptibility to pneumonia and death following intratracheal infection with Candida albicans. Furthermore, the lack of MPO significantly enhanced the dissemination of intraperitoneally injected C. albicans into various organs during the first 7 days. Thus, MPO is important for early host defense against fungal infection, and the inability to generate HOCl cannot be compensated for by other oxygen-dependent systems in vivo in mice. The mutant mice serve as a model for studying pulmonary and systemic candidiasis.

Regulation of pro-apoptotic leucocyte granule serine proteinases by intracellular serpins

Caspase activation and apoptosis can be initiated by the introduction of serine proteinases into the cytoplasm of a cell. Cytotoxic lymphocytes have evolved at least one serine proteinase with specific pro-apoptotic activity (granzyme B), as well as the mechanisms to deliver it into a target cell, and recent evidence suggests that other leucocyte granule proteinases may also have the capacity to kill if released into the interior of cells. For example, the monocyte/granulocyte proteinase cathepsin G can activate caspases in vitro, and will induce apoptosis if its entry into cells is mediated by a bacterial pore-forming protein. The potent pro-apoptotic activity of granzyme B and cathepsin G suggests that cells producing these (or other) proteinases would be at risk from self-induced death if the systems involved in packaging, degranulation or targeting fail and allow proteinases to enter the host cell cytoplasm. The purpose of the present review is to describe recent work on a group of intracellular serine proteinase inhibitors (serpins) which may function in leucocytes to prevent autolysis induced by the granule serine proteinases.

Alpha-1 antitrypsin deficiency alleles and severe cystic fibrosis lung disease

BACKGROUND

Alpha-1 antitrypsin (alpha 1-AT) is the most abundant proteinase inhibitor within the lung. We have recently reported the surprising observation that cystic fibrosis patients with mild to moderate deficiency of alpha 1-antitrypsin have significantly better pulmonary function than non-deficient patients. This study may have been biased as it did not include the most severely affected patients who have died in childhood or those who have undergone orthotopic lung transplantation. The prevalence of alpha 1-antitrypsin deficiency alleles in this most severely affected group of patients with cystic fibrosis was therefore assessed.

METHODS

DNA was obtained from neonatal blood spots from children with cystic fibrosis who had died from pulmonary disease and from formalin fixed lung tissue from transplanted cystic fibrosis patients. The common S and Z deficiency alleles of alpha 1-AT were sought by amplification mutagenesis of the appropriate region of the alpha 1-AT gene followed by restriction enzyme digestion with Xmn I and Taq I, respectively.

RESULTS

Seventy-nine patients were identified (seven dead, 72 transplanted). Two patients (2.5%) were heterozygous for the Z allele of alpha 1-AT and four (5.1%) were heterozygous for the S allele. This is not significantly different from the incidence in the normal population of 4% and 8% for the S and Z alleles, respectively.

CONCLUSIONS

These data support previous findings that deficiency of alpha 1-AT is not associated with more severe pulmonary disease in cystic fibrosis and may be associated with milder lung disease. Further work is needed to clarify the mechanisms underlying the progressive lung damage in cystic fibrosis.

Response of serum interleukin-6 in patients undergoing elective surgery of varying severity

1. Recent studies have suggested that interleukin-6 is a major mediator of the acute-phase protein response in man. The aim of the present study was to investigate the relationships between the response of serum interleukin-6 to surgery, the type of surgical procedure performed and the response of serum C-reactive protein. 2. Timed venous blood samples were taken from 26 patients in five broad surgical categories (minor surgery, cholecystectomy, hip replacement, colorectal surgery and major vascular surgery). C-reactive protein and interleukin-6 were measured in each sample. 3. Serum interleukin-6 rose within 2-4 h of incision in all patients and the magnitude of the response differed among the various surgical groups. The response of interleukin-6 correlated (r = 0.80, P less than 0.001) with the duration of surgery. In contrast, serum C-reactive protein was not detectable after minor surgery (less than 10 mg/l) and the response of C-reactive protein did not differ among the more major surgical groups. The response of interleukin-6 showed a weak, but significant, correlation with the response of C-reactive protein (r = 0.67, P less than 0.001). 4. We conclude that serum interleukin-6 is a sensitive, early marker of tissue damage. In general, the greater the surgical trauma, the greater the response of serum interleukin-6 and the greater the peak serum concentration of interleukin-6. Our results are consistent with a role for interleukin-6 in the induction of C-reactive protein synthesis.