Chronic granulomatous disease

The vacuolar anti-Pseudomonal activity of neutrophil primary granule peptidyl-arginine deiminase enzymes

The role of neutrophils in host defense involves several cell processes including phagocytosis, degranulation of antimicrobial proteins, and the release of neutrophil extracellular traps (NETs). In turn, dysregulated cell activity is associated with the pathogenesis of airway and rheumatic diseases, in which neutrophil-derived enzymes including peptidyl-arginine deiminases (PADs) play a role. Known physiological functions of PADs in neutrophils are limited to the activity of PAD isotype 4 in histone citrullination in NET formation. The aim of this study was to extend our knowledge on the role of PADs in neutrophils and, specifically, bacterial killing within the confines of the phagocytic vacuole. Human neutrophils were fractionated by sucrose gradient ultracentrifuge and PADs localized in subcellular compartments by Western blot analysis. Direct interaction of PADs with Pseudomonas aeruginosa (P. aeruginosa) was assessed by flow cytometry and Western blot overlay. The participation of neutrophil PAD2 and PAD4 in killing of P. aeruginosa was assessed by inclusion of PAD-specific inhibitors. In vitro, bactericidal activity of recombinant human PAD2 or PAD4 enzymes against P. aeruginosa was determined by enumeration of colony-forming units (CFU). Together with neutrophil elastase (NE), PAD2 and PAD4 were localized to primary granules and, following activation with particulate stimuli, were degranulated in to the phagocytic vacuole. In vitro, PAD2 and PAD4 bound P. aeruginosa (p = 0.04) and significantly reduced bacterial survival to 49.1 ± 17.0 (p < 0.0001) and 48.5 ± 13.9% (p < 0.0001), respectively. Higher antibacterial activity was observed at neutral pH levels with the maximum toxicity at pH 6.5 and pH 7.5, comparable to the effects of neutrophil bactericidal permeability increasing protein. In phagosomal killing assays, inclusion of the PAD2 inhibitor, AFM-30a, or PAD4 inhibitor, GSK484, significantly increased survival of P. aeruginosa (AFM-30a, p = 0.05; and GSK484, p = 0.0079). Results indicate that PAD2 and PAD4 possess antimicrobial activity and are directly involved in the neutrophil antimicrobial processes. This study supports further research into the development of PAD-based antimicrobials.

The multi-faceted role of NADPH in regulating inflammation in activated myeloid cells

Recent advances in the immunometabolism field have demonstrated the importance of metabolites in fine-tuning the inflammatory responses in myeloid cells. Cofactors, which are metabolites comprised of inorganic ions and organic molecules, may tightly or loosely bind to distinct sites of enzymes to catalyze a specific reaction. Since many enzymes that mediate inflammatory and anti-inflammatory processes require the same cofactors to function, this raises the possibility that under conditions where the abundance of these cofactors is limited, inflammatory and anti-inflammatory enzymes must compete with each other for the consumption of cofactors. Thus, this competition may reflect a naturally evolved mechanism to efficiently co-regulate inflammatory versus anti-inflammatory pathways, fine-tuning the extent of an inflammatory response. The role of NADPH, the reduced form of nicotinamide adenine dinucleotide phosphate (NADP+), in mediating inflammatory and anti-inflammatory responses in activated myeloid cells has been well-established in the past decades. However, how the dynamic of NADPH consumption mediates the co-regulation between individual inflammatory and anti-inflammatory pathways is only beginning to be appreciated. In this review, we will summarize the established roles of NADPH in supporting inflammatory and anti-inflammatory pathways, as well as highlight how the competition for NADPH consumption by these opposing pathways fine-tunes the inflammatory response in activated myeloid cells.

Immunonutrition: facilitating mucosal immune response in teleost intestine with amino acids through oxidant-antioxidant balance

Comparative animal models generate fundamental scientific knowledge of immune responses. However, these studies typically are conducted in mammals because of their biochemical and physiological similarity to humans. Presently, there has been an interest in using teleost fish models to study intestinal immunology, particularly intestinal mucosa immune response. Instead of targeting the pathogen itself, a preferred approach for managing fish health is through nutrient supplementation, as it is noninvasive and less labor intensive than vaccine administrations while still modulating immune properties. Amino acids (AAs) regulate metabolic processes, oxidant-antioxidant balance, and physiological requirements to improve immune response. Thus, nutritionists can develop sustainable aquafeeds through AA supplementation to promote specific immune responses, including the intestinal mucosa immune system. We propose the use of dietary supplementation with functional AAs to improve immune response by discussing teleost fish immunology within the intestine and explore how oxidative burst is used as an immune defense mechanism. We evaluate immune components and immune responses in the intestine that use oxidant-antioxidant balance through potential selection of AAs and their metabolites to improve mucosal immune capacity and gut integrity. AAs are effective modulators of teleost gut immunity through oxidant-antioxidant balance. To incorporate nutrition as an immunoregulatory means in teleost, we must obtain more tools including genomic, proteomic, nutrition, immunology, and macrobiotic and metabonomic analyses, so that future studies can provide a more holistic understanding of the mucosal immune system in fish.

The Dual Role of Myeloperoxidase in Immune Response

The heme protein myeloperoxidase (MPO) is a major constituent of neutrophils. As a key mediator of the innate immune system, neutrophils are rapidly recruited to inflammatory sites, where they recognize, phagocytose, and inactivate foreign microorganisms. In the newly formed phagosomes, MPO is involved in the creation and maintenance of an alkaline milieu, which is optimal in combatting microbes. Myeloperoxidase is also a key component in neutrophil extracellular traps. These helpful properties are contrasted by the release of MPO and other neutrophil constituents from necrotic cells or as a result of frustrated phagocytosis. Although MPO is inactivated by the plasma protein ceruloplasmin, it can interact with negatively charged components of serum and the extracellular matrix. In cardiovascular diseases and many other disease scenarios, active MPO and MPO-modified targets are present in atherosclerotic lesions and other disease-specific locations. This implies an involvement of neutrophils, MPO, and other neutrophil products in pathogenesis mechanisms. This review critically reflects on the beneficial and harmful functions of MPO against the background of immune response.

Downregulation of endothelial nitric oxide synthase (eNOS) and endothelin-1 (ET-1) in a co-culture system with human stimulated X-linked CGD neutrophils

Phagocytes in patients with chronic granulomatous disease (CGD) do not generate reactive oxidative species (ROS), whereas nitric oxide (NO) production is increased in response to the calcium ionophore A23187 in CGD phagocytes compared with healthy phagocytes. Recently, patients with X-linked CGD (X-CGD) have been reported to show higher flow-mediated dilation, suggesting that endothelial cell function is affected by NO production from phagocytes. We studied NOS3 and EDN1 mRNA and protein expression in human umbilical vein endothelial cells (HUVECs) in a co-culture system with neutrophils from X-CGD patients. HUVECs were co-cultured for 30 minutes with human neutrophils from X-CGD or healthy participants in response to A23187 without cell-to-cell contact. The expression of NOS3 and EDN1 mRNA in HUVECs was quantified by real-time polymerase chain reaction. Moreover, we demonstrated the protein expression of eNOS, ET-1, and NFκB p65, including phosphorylation at Ser1177 of eNOS and Ser536 of NFκB p65. Neutrophils from X-CGD patients showed significantly higher NO and lower H₂O₂ production in response to A23187 than healthy neutrophils in vitro. Compared with healthy neutrophils, X-CGD neutrophils under A23187 stimulation exhibited significantly increased NO and decreased H₂O₂, and promoted downregulated NOS3 and EDN1 expression in HUVECs. The total expression and phosphorylation at Ser1177 of eNOS and ET-1 expression were significantly decreased in HUVECs co-cultures with stimulated X-CGD neutrophils. Also, phosphorylation at Ser536 of NFκB p65 were significantly decreased. In conclusions, eNOS and ET-1 significantly down-regulated in co-culture with stimulated X-CGD neutrophils through their excessive NO and the lack of ROS production. These findings suggest that ROS generated from neutrophils may mediate arterial tone affecting eNOS and ET-1 expression via their NO and ROS production.

Modulation of α-adrenoceptor signalling protects photoreceptors after retinal detachment by inhibiting oxidative stress and inflammation

BACKGROUND AND PURPOSE

Currently available treatments do not halt progression of photoreceptor death and subsequent visual impairment related to retinal detachment (RD) which is observed in various retinal disorders. This study investigated the neuroprotective effects of two adrenoceptor ligands, the α₁ -adrenoceptor antagonist doxazosin and the α₂ -adrenoceptor agonist guanabenz, against photoreceptor cell death in RD.

EXPERIMENTAL APPROACH

We used a model of experimental RD in Brown-Norway rats induced by subretinal injection of sodium hyaluronate. Oxidative stress biomarkers and cytokine production were quantified with elisa. Protein expression levels and immunofluorescent labelling were determined in rats with RD and controls for mechanistic elucidation. The effects of systemic (i.p.) administration of doxazosin or guanabenz on photoreceptor apoptosis, retinal histology and electroretinography were evaluated in rats with RD and compared to the effects in vehicle controls.

KEY RESULTS

Photoreceptors were the major source of RD-induced ROS overproduction in the rat retina through the regulation of NADPH oxidase. Systemic administration of doxazosin or guanabenz decreased the RD-induced production of ROS and proinflammatory cytokines, including IL-1β and the chemokine CCL2, and suppressed retinal gliosis, resulting in attenuation of photoreceptor death and preservation of retinal structures and functions in RD.

CONCLUSIONS AND IMPLICATIONS

Our findings point to α-adrenoceptors as novel therapeutic targets to provide photoreceptor protection and suggest that both doxazosin and guanabenz, two FDA-approved drugs, could be further explored to treat retinal diseases.

NADPH Oxidase Contributes to Photoreceptor Degeneration in Constitutively Active RAC1 Mice

Purpose

The active form of small GTPase RAC1 is required for activation of NADPH oxidase (NOX), which in turn generates reactive oxygen species (ROS) in nonphagocytic cells. We explored whether NOX-induced oxidative stress contributes to rod degeneration in retinas expressing constitutively active (CA) RAC1.

Methods

Transgenic (Tg)–CA-RAC1 mice were given apocynin (10 mg/kg, intraperitoneal), a NOX inhibitor, or vehicle daily for up to 13 weeks. Superoxide production and oxidative damage were assessed by dihydroethidium staining and by protein carbonyls and malondialdehyde levels, respectively. Outer nuclear layer (ONL) cells were counted and electroretinogram (ERG) amplitudes measured in Tg-CA-RAC1 mice. Outer nuclear layer cells were counted in wild-type (WT) mice after transfer of CA-Rac1 gene by subretinal injection of AAV8-pOpsin-CA Rac1-GFP.

Results

Transgenic-CA-RAC1 retinas had significantly fewer photoreceptor cells and more apoptotic ONL cells than WT controls from postnatal week (Pw) 3 to Pw13. Superoxide accumulation and protein and lipid oxidation were increased in Tg-CA-RAC1 retinas and were reduced in mice treated with apocynin. Apocynin reduced the loss of photoreceptors and increased the rod ERG a- and b-wave amplitudes when compared with vehicle-injected transgenic controls. Photoreceptor loss was also observed in regions of adult WT retina transduced with AAV8-pOpsin-CA Rac1-GFP but not in neighboring regions that were not transduced or in AAV8-pOpsin-GFP–transduced retinas.

Conclusions

Constitutively active RAC1 promotes photoreceptor cell death by oxidative damage that occurs, at least partially, through NOX-induced ROS. Reactive oxygen species are likely involved in multiple forms of retinal degenerations, and our results support investigating RAC1 inhibition as a therapeutic approach that targets this disease pathway.

Vitamin C: the known and the unknown and Goldilocks

Vitamin C (Ascorbic Acid), the antiscorbutic vitamin, cannot be synthesized by humans and other primates, and has to be obtained from diet. Ascorbic acid is an electron donor and acts as a cofactor for fifteen mammalian enzymes. Two sodium-dependent transporters are specific for ascorbic acid, and its oxidation product dehydroascorbic acid is transported by glucose transporters. Ascorbic acid is differentially accumulated by most tissues and body fluids. Plasma and tissue vitamin C concentrations are dependent on amount consumed, bioavailability, renal excretion, and utilization. To be biologically meaningful or to be clinically relevant, in vitro and in vivo studies of vitamin C actions have to take into account physiologic concentrations of the vitamin. In this paper, we review vitamin C physiology; the many phenomena involving vitamin C where new knowledge has accrued or where understanding remains limited; raise questions about the vitamin that remain to be answered; and explore lines of investigations that are likely to be fruitful.

The impact of age-related dysregulation of the angiotensin system on mitochondrial redox balance

Aging is associated with the accumulation of various deleterious changes in cells. According to the free radical and mitochondrial theory of aging, mitochondria initiate most of the deleterious changes in aging and govern life span. The failure of mitochondrial reduction-oxidation (redox) homeostasis and the formation of excessive free radicals are tightly linked to dysregulation in the Renin Angiotensin System (RAS). A main rate-controlling step in RAS is renin, an enzyme that hydrolyzes angiotensinogen to generate angiotensin I. Angiotensin I is further converted to Angiotensin II (Ang II) by angiotensin-converting enzyme (ACE). Ang II binds with equal affinity to two main angiotensin receptors—type 1 (AT₁R) and type 2 (AT₂R). The binding of Ang II to AT₁R activates NADPH oxidase, which leads to increased generation of cytoplasmic reactive oxygen species (ROS). This Ang II-AT₁R–NADPH-ROS signal triggers the opening of mitochondrial K_ATP channels and mitochondrial ROS production in a positive feedback loop. Furthermore, RAS has been implicated in the decrease of many of ROS scavenging enzymes, thereby leading to detrimental levels of free radicals in the cell. AT₂R is less understood, but evidence supports an anti-oxidative and mitochondria-protective function for AT₂R. The overlap between age related changes in RAS and mitochondria, and the consequences of this overlap on age-related diseases are quite complex. RAS dysregulation has been implicated in many pathological conditions due to its contribution to mitochondrial dysfunction. Decreased age-related, renal and cardiac mitochondrial dysfunction was seen in patients treated with angiotensin receptor blockers. The aim of this review is to: (a) report the most recent information elucidating the role of RAS in mitochondrial redox hemostasis and (b) discuss the effect of age-related activation of RAS on generation of free radicals.

What is wrong with granulocytes in inflammatory bowel diseases?

The neutrophil plays a central role in the acute inflammatory response, a crucial mechanism required for the efficient clearance of invading microorganisms and antigenic material. Patients with primary immunodeficiencies of neutrophil function, particularly chronic granulomatous disease, are predisposed to develop bowel inflammation that is indistinguishable from Crohn's disease (CD) on the basis of clinical, endoscopic and histopathological features. The intrinsic function of the neutrophil is normal in the vast majority of patients with CD; however, there is clear evidence of an impairment of neutrophil recruitment to sites of trauma and bacterial infection. This is associated with an inability to adequately clear bacteria that have penetrated the tissues, resulting in the formation of granulomata, the histological hallmark of the disease, and the subsequent initiation of a chronic adaptive immune response. The reduced secretion of proinflammatory cytokines by macrophages, most notably TNF-α, may account for the attenuated neutrophil recruitment observed in CD. Stimulation of the innate immune system in CD, particularly in patients in remission, may be an alternative therapeutic strategy that could reduce the risk of future disease relapses.

C-terminal truncation of Noxa1 greatly enhances its ability to activate Nox2 in a pure reconstitution system

Noxa1 activates Nox2 together with Noxo1 and Rac in a pure reconstitution system, but the resulting activity is considerably lower than that induced by p67(phox) and p47(phox). In this study, we found that C-terminal-truncated forms of Noxa1 exhibited higher activities than full-length Noxa1. Of the truncations examined, Noxa1(1-225) showed the highest ability for activation. Kinetic studies revealed that Noxa1(1-225) had a threefold higher Vmax value than full-length Noxa1 with a similar EC50 value. The affinities of Noxo1 and RacQ61L were not much altered by the truncation. Conversely, the affinity of FAD for the Nox2 complex was enhanced after the truncation. In the absence of Noxo1, Noxa1(1-225) showed much higher activity with a lower EC50 than full-length Noxa1. Noxa1(1-225) showed comparable activity to that of p67(phox) with either Noxo1 or p47(phox), although the stability was lower than that with p67(phox) and p47(phox). These findings indicate that the role of the C-terminal half of Noxa1 is autoinhibition. The data suggest a two-step autoinhibition mechanism, comprising self-masking to interrupt the binding to the oxidase, and holding of the activation domain in a suboptimal position to the oxidase. This study reveals that when both types of inhibition are released, Noxa1 achieves high-level superoxide production.

Senecio scandens Buch.-Ham.: a review on its ethnopharmacology, phytochemistry, pharmacology, and toxicity

ETHNOPHARMACOLOGICAL RELEVANCE

The aerial parts of Senecio scandens Buch.-Ham. (family Asteraceae) have a long history in traditional Chinese medicine as a treatment for various ailments, such as bacterial diarrhea, enteritis, conjunctivitis, and respiratory tract infections.

MATERIALS AND METHODS

A bibliographic investigation of Senecio scandens was accomplished by analyzing secondary sources, including the Chinese Medicinal plantal Classics, the Internet (Google Scholar and Baidu Scholar), and scientific databases accepted worldwide (Pubmed, Scopus, Web of Science, SciFinder, and CNKI). These sources were scrutinized for available information about the uses of Senecio scandens in traditional Chinese medicine, phytochemistry, pharmacology, and toxicology.

RESULTS

Senecio scandens is a medicinal plant with a climbing woody stem. Phytochemical studies have shown the presence of numerous valuable compounds, such as flavonoids, alkaloids, phenolic acids, terpenes, volatile oils, carotenoids, and trace elements. Among them, PAs are the characteristic constituents, adonifoline is one of the index ingredients of Senecio scandens. Studies in modern pharmacology have demonstrated that extracts and compounds isolated from Senecio scandens show a wide spectrum of pharmacological activities, including anti-inflammatory, antimicrobial, anti-leptospirosis, hepatoprotective, anti-infusorial, antioxidant, antiviral, antitumoral, analgesic, mutagenic, and toxicological activities.

CONCLUSIONS

Phytochemical and pharmacological studies have demonstrated that the extracts of the plant possess various pharmacological activities that can be attributed to the presence of various flavonoids, phenolic acids, and alkaloids. Newer technologies for qualitative and quantitative methods of PAs need to be developed to obtain better accuracy and sensitivity. Due to the toxicity of PAs present in this medicinal plant, the regulations on PAs of Senecio scandens were varied among different countries and regions. In China, the PAs toxicity of Senecio scandens ranking criteria is not well defined in the Chinese Pharmacopoeia 2010, and there is no strict uniform requirement on the PAs in western countries. We propose that the use of Senecio scandens should be reevaluated based on a set of criteria, which includes risk-benefit analysis and severity of the toxic effects, clinical and preclinical data to ensure safe use while continuing to satisfy the need for access to the medicinal plant.

Regulation of innate immunity by NADPH oxidase

NADPH oxidase is a critical regulator of both antimicrobial host defense and inflammation. Activated in nature by microbes and microbial-derived products, the phagocyte NADPH oxidase is rapidly assembled, and generates reactive oxidant intermediates (ROIs) in response to infectious threat. Chronic granulomatous disease (CGD) is an inherited disorder of the NADPH oxidase characterized by recurrent and severe bacterial and fungal infections, and pathology related to excessive inflammation. Studies in CGD patients and CGD mouse models indicate that NADPH oxidase plays a key role in modulating inflammation and injury that is distinct from its antimicrobial function. The mechanisms by which NADPH oxidase mediates killing of pathogens and regulation of inflammation have broad relevance to our understanding of normal physiological immune responses and pathological states, such as acute lung injury and bacterial or fungal infections.

Glutathione reductase facilitates host defense by sustaining phagocytic oxidative burst and promoting the development of neutrophil extracellular traps

Glutathione reductase (Gsr) catalyzes the reduction of glutathione disulfide to glutathione, which plays an important role in the bactericidal function of phagocytes. Because Gsr has been implicated in the oxidative burst in human neutrophils and is abundantly expressed in the lymphoid system, we hypothesized that Gsr-deficient mice would exhibit marked defects during the immune response against bacterial challenge. We report in this study that Gsr-null mice exhibited enhanced susceptibility to Escherichia coli challenge, indicated by dramatically increased bacterial burden, cytokine storm, striking histological abnormalities, and substantially elevated mortality. Additionally, Gsr-null mice exhibited elevated sensitivity to Staphylococcus aureus. Examination of the bactericidal functions of the neutrophils from Gsr-deficient mice in vitro revealed impaired phagocytosis and defective bacterial killing activities. Although Gsr catalyzes the regeneration of glutathione, a major cellular antioxidant, Gsr-deficient neutrophils paradoxically produced far less reactive oxygen species upon activation both ex vivo and in vivo. Unlike wild-type neutrophils that exhibited a sustained oxidative burst upon stimulation with phorbol ester and fMLP, Gsr-deficient neutrophils displayed a very transient oxidative burst that abruptly ceased shortly after stimulation. Likewise, Gsr-deficient neutrophils also exhibited an attenuated oxidative burst upon encountering E. coli. Biochemical analysis revealed that the hexose monophosphate shunt was compromised in Gsr-deficient neutrophils. Moreover, Gsr-deficient neutrophils displayed a marked impairment in the formation of neutrophil extracellular traps, a bactericidal mechanism that operates after neutrophil death. Thus, Gsr-mediated redox regulation is crucial for bacterial clearance during host defense against massive bacterial challenge.

Noxa1 as a moderate activator of Nox2-based NADPH oxidase

Noxa1 was discovered as an activating factor for Nox1, an O(2)(-)-generating enzyme. Subsequent studies have shown that Noxa1 is colocalized with Nox2 in several cell types, including vascular cells. Nox2 activation by Noxa1 has been examined in reconstituted model cells. However, little is known about the kinetic properties of Noxa1 in Nox2 activation. In the present study, we used purified cyt.b(558) (Nox2 plus p22(phox)), Rac(Q61L), and Noxo1 to examine the ability of Noxa1 to activate Nox2. In the pure reconstitution system, Noxa1 activated Nox2 with lower efficiency than p67(phox), a canonical activator of Nox2. The EC(50) value of Noxa1 was considerably higher than that of p67(phox). The V(max) value with Noxa1 and Noxo1 was one-third of that with p67(phox) and p47(phox). The EC(50) value of Noxo1 or Rac(Q61L) was also higher when Noxa1 was used. The affinity of FAD for the oxidase and the stability of the active complex were remarkably low when Noxa1 and Noxo1 were used compared with p67(phox) and p47(phox). The stability was not improved by fusion of Noxa1 with Rac(Q61L). These findings show that Noxa1 has quite different kinetic properties from p67(phox) and suggest that Noxa1 may function as a moderate activator of Nox2.

Inflammatory bowel disease: is it a primary immunodeficiency?

Inflammatory bowel diseases (IBD) such as ulcerative colitis and Crohn's disease are chronic and relapsing conditions, characterized by abdominal pain, diarrhea, bleeding and malabsorption. IBD has been considered a hyperinflammatory state due to disturbed interactions between the immune system and the commensal bacterial flora of the gut. However, there is evidence that Crohn's disease might be the consequence of a reduced release of pro-inflammatory cytokines and an impaired acute inflammatory response, thereby suggesting that IBD might be an immunodeficiency rather than an excessive inflammatory reaction. This theory has been supported by observations in patients with primary immunodeficiencies such as the Wiskott-Aldrich syndrome and IPEX (immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome). In contrary, defects in the anti-inflammatory down-regulation of the immune response as they are seen in patients with Mendelian defects in the IL10 signaling pathway support the hyper-inflammatory theory. In this review, we describe and discuss primary immunodeficiencies associated with IBD and show that the bowel is a highly sensitive indicator of dysregulations, making IBD a model disease to study and identify key regulators required to balance the human mucosal immune system.

Role of NADPH oxidase versus neutrophil proteases in antimicrobial host defense

NADPH oxidase is a crucial enzyme in mediating antimicrobial host defense and in regulating inflammation. Patients with chronic granulomatous disease, an inherited disorder of NADPH oxidase in which phagocytes are defective in generation of reactive oxidant intermediates (ROIs), suffer from life-threatening bacterial and fungal infections. The mechanisms by which NADPH oxidase mediate host defense are unclear. In addition to ROI generation, neutrophil NADPH oxidase activation is linked to the release of sequestered proteases that are posited to be critical effectors of host defense. To definitively determine the contribution of NADPH oxidase versus neutrophil serine proteases, we evaluated susceptibility to fungal and bacterial infection in mice with engineered disruptions of these pathways. NADPH oxidase-deficient mice (p47^phox−/−) were highly susceptible to pulmonary infection with Aspergillus fumigatus. In contrast, double knockout neutrophil elastase (NE)^−/−×cathepsin G (CG)^−/− mice and lysosomal cysteine protease cathepsin C/dipeptidyl peptidase I (DPPI)-deficient mice that are defective in neutrophil serine protease activation demonstrated no impairment in antifungal host defense. In separate studies of systemic Burkholderia cepacia infection, uniform fatality occurred in p47^phox−/− mice, whereas NE^−/−×CG^−/− mice cleared infection. Together, these results show a critical role for NADPH oxidase in antimicrobial host defense against A. fumigatus and B. cepacia, whereas the proteases we evaluated were dispensable. Our results indicate that NADPH oxidase dependent pathways separate from neutrophil serine protease activation are required for host defense against specific pathogens.

Lipopolysaccharide primes the respiratory burst of Atlantic salmon SHK-1 cells through protein kinase C-mediated phosphorylation of p47phox

The superoxide-producing NADPH oxidase complex of phagocytes plays a crucial role in host defenses against microbial infection. NADPH oxidase consists of a membrane heterodimeric protein, composed of gp91phox and p22phox, and the cytosolic proteins, p40phox, p47phox and p67phox. In the present study, we clone and sequence the full-length cDNAs coding for the Atlantic salmon (Salmo salar) phagocyte NADPH oxidase components, p47phox, p67phox and gp91phox, using a homology cloning approach. The sequences of these cDNAs showed that the S. salar p47phox, p67phox and gp91phox genes contained single open reading frames, which encoded predicted proteins of 413, 504 and 565 amino acids, respectively. Comparison of the deduced amino acid sequences showed that the S. salar p47phox, p67phox and gp91phox sequences shared 51, 45 and 68% identity with those of human components, respectively. Despite this relatively low homology between salmon and mammalian NADPH oxidase subunits, their functional domains are highly conserved. We also found that the mRNA levels of p47phox, p67phox and gp91phox expression were higher in immune-related tissues, such as kidney, spleen and gill. In addition, infection of the salmon macrophage cell line SHK-1 with Piscirickettsia salmonis induced the expression of p47phox, but had no effect on p67phox and gp91phox expression. Finally, we show for the first time in fish that activation of macrophages with lipopolysaccharide promotes the activation of protein kinase C, which in turn phosphorylates p47phox, leading to NADPH oxidase activation and reactive oxygen species generation. Collectively, these results suggest that the mechanisms of activation of phagocyte NADPH oxidase are well conserved from fish to mammals.

Hematologically important mutations: X-linked chronic granulomatous disease (third update)

Chronic granulomatous disease (CGD) is an immunodeficiency disorder affecting about 1 in 250,000 individuals. The disease is caused by a lack of superoxide production by the leukocyte enzyme NADPH oxidase. Superoxide is used to kill phagocytosed micro-organisms in neutrophils, eosinophils, monocytes and macrophages. The leukocyte NADPH oxidase is composed of five subunits, of which the enzymatic component is gp91-phox, also called Nox2. This protein is encoded by the CYBB gene on the X chromosome. Mutations in this gene are found in about 70% of all CGD patients. This article lists all mutations identified in CYBB in the X-linked form of CGD. Moreover, apparently benign polymorphisms in CYBB are also given, which should facilitate the recognition of future disease-causing mutations.

Multiple mechanisms of NADPH oxidase inhibition by type A and type B Francisella tularensis

Ft is a facultative intracellular pathogen that infects many cell types, including neutrophils. In previous work, we demonstrated that the type B Ft strain LVS disrupts NADPH oxidase activity throughout human neutrophils, but how this is achieved is incompletely defined. Here, we used several type A and type B strains to demonstrate that Ft-mediated NADPH oxidase inhibition is more complex than appreciated previously. We confirm that phagosomes containing Ft opsonized with AS exclude flavocytochrome b(558) and extend previous results to show that soluble phox proteins were also affected, as indicated by diminished phosphorylation of p47(phox) and other PKC substrates. However, a different mechanism accounts for the ability of Ft to inhibit neutrophil activation by formyl peptides, Staphylococcus aureus, OpZ, and phorbol esters. In this case, enzyme targeting and assembly were normal, and impaired superoxide production was characterized by sustained membrane accumulation of dysfunctional NADPH oxidase complexes. A similar post-assembly inhibition mechanism also diminished the ability of anti-Ft IS to confer neutrophil activation and bacterial killing, consistent with the limited role for antibodies in host defense during tularemia. Studies of mutants that we generated in the type A Ft strain Schu S4 demonstrate that the regulatory factor fevR is essential for NADPH oxidase inhibition, whereas iglI and iglJ, candidate secretion system effectors, and the acid phosphatase acpA are not. As Ft uses multiple mechanisms to block neutrophil NADPH oxidase activity, our data strongly suggest that this is a central aspect of virulence.

Crohn's disease: an immune deficiency state

Crohn's disease is a chronic inflammatory disorder primarily affecting the gastrointestinal tract. Its clinical manifestations arise from a substantial infiltration of the intestinal mucosa by activated leukocytes and the downstream consequences of chronic inflammation. The underlying cause driving this immunological reaction remains poorly understood. A number of hypotheses have been proposed, most of which postulate a primary over-activation of the immune response, based on the pathological appearances of active Crohn's lesions. Interestingly, none of these theories have been mechanistically proven. It is possible that the immunological events responsible for disease initiation are quite different from those contributing to its persistence and propagation. A substantial body of data has emerged in recent years to suggest that the primary defect in Crohn's disease is actually one of relative immunodeficiency. This review considers the evidence for such a phenomenon in contrast to alternative prevailing hypotheses and attempts to address some of the potential paradoxes that it generates.

Inhibition of neutrophil function following exposure to the Aspergillus fumigatus toxin fumagillin

The filamentous fungus Aspergillus fumigatus produces a variety of enzymes and toxins that may facilitate fungal colonization of tissue and evasion of the host immune response. One such toxin, fumagillin, was investigated for its ability to inhibit the action of neutrophils, which are a central component of the innate immune response to microbial infection. Neutrophils exposed to 2 microg fumagillin ml(-1) for 25 min showed a significantly reduced ability to kill yeast cells (P<0.02), to phagocytose conidia of A. fumigatus (P<0.023) and to consume oxygen (P<0.032). The ability of neutrophils to generate superoxide is dependent upon the action of a functional NADPH oxidase complex which is composed of cytosolic (p40phox, p47phox, p67phox, Rac2) and membrane (gp91phox) proteins. Exposure of neutrophils to fumagillin inhibited the formation of the NADPH oxidase complex by blocking the translocation of p47phox from the cytosolic to the membrane fraction (P=0.02). In addition to the production of superoxide, neutrophils also undergo degranulation, which leads to the release of proteolytic enzymes that contribute to the microbicidal activity of the cell. Fumagillin-treated neutrophils showed reduced degranulation as evidenced by lower myeloperoxidase activity (P<0.019). Fumagillin-treated cells demonstrated reduced levels of F-actin, thus indicating that retarding the formation of F-actin may contribute to the inhibition of the structural rearrangements required in the activated neutrophil. This work indicates that fumagillin may contribute to reducing the local immune response by altering the activity of neutrophils and thus facilitate the continued persistence and growth of A. fumigatus in the host.

Impaired macrophage function following bacterial stimulation in chronic granulomatous disease

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is critical for phagocyte anti-microbial activity and plays a major role in innate immunity. Defects in genes coding for components of the NADPH oxidase enzyme system are responsible for chronic granulomatous disease (CGD), a rare primary neutrophil immunodeficiency associated with recurrent, life-threatening bacterial and fungal infections. Microbial killing and digestion within the neutrophil phagosomal compartment are defective in these patients. NADPH oxidase activity is also crucial for optimal macrophage and dendritic cell function and has recently been implicated in both cross-presentation and T-cell priming. We present evidence of impaired macrophage function in CGD, with attenuated pro-inflammatory cytokine and increased interleukin-10 secretion following bacterial stimulation. These results highlight additional abnormalities in macrophage function associated with CGD and the importance of NADPH oxidase activity in immunity.

Effects of polychlorinated biphenyls on the neutrophil NADPH oxidase system

Polychlorinated biphenyls (PCBs) are reported to induce the formation of reactive oxygen species (ROS) in human neutrophil granulocytes through the activation of the NADPH oxidase. The purpose of the present study is to elucidate the cellular mechanisms responsible for the activation of the NADPH oxidase after exposure to PCB. We have previously shown that PCB activates human neutrophil granulocytes through a calcium dependent activation of phospholipase D and/or phospholipase C, followed by the activation of protein kinase C. In the present study, pharmacological characterization of Aroclor (A) 1242-induced respiratory burst in human neutrophils was conducted by the use of enzymatic inhibitors. Pre-incubation with U0126, SB203580, SP600125, cyclosporin A and FK506 attenuated the A 1242-induced respiratory burst, measured by DCF-fluorescence, and luminol-amplified chemiluminescence. Our results show that the Erk1/2 kinases and p38MAPK/JNK are involved in ROS formation in neutrophils exposed to A 1242.

Inflammatory bowel disease in CGD reproduces the clinicopathological features of Crohn's disease

OBJECTIVES

Patients with chronic granulomatous disease (CGD), a rare congenital disorder characterized by defective neutrophil function, frequently develop an inflammatory bowel disease similar to Crohn's disease. The clinical presentations and concordance between the features of the bowel disease in these two conditions have never been formally evaluated.

METHODS

Retrospective case note analysis of all adult patients with CGD treated at a tertiary care hospital.

RESULTS

A total of 25 eligible patients were identified. Of these, 14 (56%) had experienced gastrointestinal symptoms in the preceding 3 years; and 11 (44%) had documented gastrointestinal inflammation not secondary to infection, manifesting throughout the alimentary canal including the upper gastrointestinal tract (45%), small intestine (27%), colon (73%), and rectum (73%). All had discontinuous inflammation and perianal involvement, and approximately half (55%) demonstrated epithelioid granulomata on histology. All patients fulfilled the Lennard-Jones criteria for the diagnosis of Crohn's disease. Therapeutic responses were observed in five patients to 5-aminosalicylates, and in individual patients to thalidomide, interferon-gamma, azathioprine, infliximab, and intestinal resection.

CONCLUSIONS

There are striking clinical and pathological resemblances between the bowel diseases observed in CGD and Crohn's disease, supporting the possibility of mechanistic similarities in their pathogenesis. Patients with CGD appear particularly prone to developing perianal disease.

Phagocyte dysfunction and inflammatory bowel disease

Inflammatory bowel diseases are common chronic inflammatory disorders. The majority are idiopathic and can be broadly divided into Crohn's disease and ulcerative colitis. Their cause is unknown, but most hypotheses focus on a primary role for T-cell dysfunction. Conversely, there is a collection of congenital disorders of phagocyte function that result not only in immunodeficiency but also in noninfectious inflammatory bowel disease. In all cases, the latter is strikingly reminiscent of the clinical and pathological features of Crohn's disease. This coincides with recent work demonstrating that despite previous emphasis on adaptive immune dysfunction, patients with Crohn's disease actually possess an unusually weak acute innate inflammatory response. This review consolidates the literature on inflammatory bowel disease in congenital immunodeficiencies and considers the role of phagocyte dysfunction in Crohn's disease. Concepts about pathogenesis and treatment that can be carried across these disorders are also discussed.

Innate immunity in inflammatory bowel disease: a disease hypothesis

Crohn's disease arises from a defective interaction between the highly concentrated mass of bacteria in the gastrointestinal tract and the underlying tissues. It has generally been believed to result from an excessively exuberant inflammatory response or from 'autoimmunity'. Recent evidence has emerged that the problem is instead a failure of the way in which the body responds to the penetration of bacteria and other bowel contents through the intestinal mucosal barrier. Rather than Crohn's disease being caused by excessive inflammation, the primary mechanism is actually that of an immunodeficiency. Failure of inflammatory mediator production leads to insufficient recruitment of neutrophils, resulting in inadequate removal of bacteria and other debris. This impairment of acute inflammation can be compensated in some circumstances by signalling through NOD2. If not cleared, the foreign material in the bowel wall is taken up within macrophages, eliciting a granulomatous reaction and the local and systemic sequelae so characteristic of Crohn's disease.

Primary Immunodeficiencies

Primary immunodeficiencies (PIDs), once considered to be very rare, are now increasingly recognized because of growing knowledge in the immunological field and the availability of more sophisticated diagnostic techniques and therapeutic modalities [161]. However in a database of >120,000 inpatients of a general hospital for conditions suggestive of ID 59 patients were tested, and an undiagnosed PID was found in 17 (29%) of the subjects tested [107]. The publication of the first case of agammaglobulinemia by Bruton in 1952 [60] demonstrated that the PID diagnosis is first done in the laboratory. However, PIDs require specialized immunological centers for diagnosis and management [33]. A large body of epidemiological evidence supports the hypothesis of the existence of a close etiopathogenetic relation between PID and atopy [73]. In particular, an elevated frequency of asthma, food allergy (FA), atopic dermatitis and enteric pathologies can be found in various PIDs. In addition we will discuss another subject that is certainly of interest: the pseudo-immunodepressed child with recurrent respiratory infections (RRIs), an event that often requires medical intervention and that very often leads to the suspicion that it involves antibody deficiencies [149].

Differential Regulation of NADPH Oxidase in Sympathetic and Sensory Ganglia in Deoxycorticosterone Acetate–Salt Hypertension

We demonstrated recently that superoxide anion levels are elevated in prevertebral sympathetic ganglia of deoxycorticosterone acetate–salt hypertensive rats and that this superoxide anion is generated by reduced nicotinamide-adenine dinucleotide phosphate oxidase. In this study we compared the reduced nicotinamide-adenine dinucleotide phosphate oxidase enzyme system of dorsal root ganglion (DRG) and sympathetic celiac ganglion (CG) and its regulation in hypertension. The reduced nicotinamide-adenine dinucleotide phosphate oxidase activity of ganglion extracts was measured using fluorescence spectrometry of dihydroethidine; the activity in hypertensive dorsal root ganglion was 34% lower than in normotensive DRG. In contrast, activity was 79% higher in hypertensive CG than normotensive CG. mRNA for the oxidase subunits NOX1, NOX2, NOX4, p47 phox , and p22 phox were present in both CG and DRG; mRNA for NOX4 was significantly higher in CG than in DRG. The levels of mRNA and protein expression of the membrane-bound catalytic subunit p22 phox and of the regulatory subunits p47 phox and Rac-1 were measured in CG and DRG in normotensive and hypertensive rats. p22 phox mRNA and protein expression was greater in CG of hypertensive rats but not in DRG. Compared with normotensive controls, p47 phox mRNA and protein, as well as Rac-1 protein, were significantly decreased in hypertensive DRG but not in CG. Immunohistochemical staining of p47 phox showed translocation from cytoplasm to membrane in hypertensive CG but not in hypertensive DRG. This suggests that reduced nicotinamide-adenine dinucleotide phosphate oxidase activation in sympathetic neurons and sensory neurons is regulated in opposite directions in hypertension. This differential regulation may contribute to unbalanced vasomotor control and enhanced vasoconstriction in the splanchnic circulation.

p40phox as an alternative organizer to p47phox in Nox2 activation: A new mechanism involving an interaction with p22phox

p40(phox) activated phagocyte NADPH oxidase without p47(phox) in a cell-free system consisting of p67(phox), Rac and cytochrome b(558) relipidated with phosphatidylinositol 3-phosphate. The activation reached to 70% of that by p47(phox). Addition of p47(phox) slightly increased the activation, but not additively. p40(phox) improved the efficiency of p67(phox) in the activation. The C-terminus-truncated p67(phox), p40(phox)(D289A), p40(phox)(R58A), or p40(phox)(W207R) showed an impaired activation. A peptide corresponding to the p22(phox) Pro-rich region suppressed the activation, and far-western blotting revealed its interaction with p40(phox) SH3 domain. Thus, p40(phox) can substitute for p47(phox) in the activation, interacting with p22(phox) and p67(phox) through their specific regions.

SK channels mediate NADPH oxidase-independent reactive oxygen species production and apoptosis in granulocytes

Neutrophils are immune cells that bind to, engulf, and destroy bacterial and fungal pathogens in infected tissue, and their clearance by apoptosis is essential for the resolution of inflammation. Killing involves both oxidative and nonoxidative processes, the oxidative pathway requiring electrogenic production of superoxide by the membrane-bound NADPH oxidase complex. A variety of stimuli, from bacterial chemotactic peptides to complement- or IgG-opsonized microbes, can induce the production of reactive oxygen species (ROS) by neutrophils, presumably by means of NADPH oxidase. We report here that 1-ethyl-2-benzimidazolinone (1-EBIO), an activator of Ca2+-activated potassium channels of small conductance (SK) and intermediate conductance (IK), causes production of superoxide and hydrogen peroxide by neutrophils and granulocyte-differentiated PLB-985 cells. This response can be partially inhibited by the SK blocker apamin, which inhibits a Ca2+-activated K+ current in these cells. Analysis of RNA transcripts indicates that channels encoded by the SK3 gene carry this current. The effects of 1-EBIO and apamin are independent of the NADPH oxidase pathway, as demonstrated by using a PLB-985 cell line lacking the gp91phox subunit. Rather, 1-EBIO and apamin modulate mitochondrial ROS production. Consistent with the enhanced ROS production and K+ efflux mediated by 1-EBIO, we found that this SK opener increased apoptosis of PLB-985 cells. Together, these findings suggest a previously uncharacterized mechanism for the regulation of neutrophil ROS production and programmed cell death.

Leu505 of Nox2 is crucial for optimal p67phox-dependent activation of the flavocytochrome b558 during phagocytic NADPH oxidase assembly

The role of Leu505 of Nox2 on the NADPH oxidase activation process was investigated. An X-CGD PLB-985 cell line expressing the Leu505Arg Nox2 mutant was obtained, exactly mimicking the phenotype of a previously published X91+-CGD case. In a reconstituted cell-free system (CFS), NADPH oxidase and iodonitrotetrazolium (INT) reductase activities were partially maintained concomitantly with a partial cytosolic factors translocation to the plasma membrane. This suggests that assembly and electron transfer from NADPH occurred partially in the Leu505Arg Nox2 mutant. Moreover, in a simplified CFS using purified mutant cytochrome b558 and recombinant p67phox, p47phox, and Rac1proteins, we found that the Km for NADPH and for NADH was about three times higher than those of purified WT cytochrome b558, indicating that the Leu505Arg mutation induces a slight decrease of the affinity for NADPH and NADH. In addition, oxidase activity can be extended by increasing the amount of p67phox in the simplified CFS assay. However, the maximal reconstituted oxidase activity using WT purified cytochrome b558 could not be reached using mutant cytochrome b558. In a three-dimensional model of the C-terminal tail of Nox2, Leu505 appears to have a strategic position just at the entry of the NADPH binding site and at the end of the alpha-helical loop (residues 484-504), a potential cytosolic factor binding region. The Leu505Arg mutation seems to affect the oxidase complex activation process through alteration of cytosolic factors binding and more particularly the p67phox interaction with cytochrome b558, thus affecting NADPH access to its binding site.

Gastrointestinal manifestations of chronic granulomatous disease

OBJECTIVE

Chronic granulomatous disease is a rare clinical entity characterized by recurrent infective and inflammatory complications. Patients are usually assigned to specialist centres, but nonspecialist clinicians may be required to treat these patients in the emergency setting. This review serves as a management guide to those clinicians who are faced with patients presenting with gastrointestinal manifestations of chronic granulomatous disease.

METHODS

This review is based on a literature search (Medline and NLM PubMed) with manual cross-referencing of all articles related to gastrointestinal chronic granulomatous disease.

RESULTS

Gastrointestinal tract involvement is present in most affected patients. Clinical presentation can mimic common surgical complications such as colitis, perianal sepsis, gastric outlet obstruction and liver abscess. A history of recurrent infections during childhood is common. Management involves haematological, microbiological, endoscopic and radiological investigations. Treatment modalities include early aggressive empirical antimicrobial therapy for sepsis, immunomodulation for inflammatory complications and surgical drainage of abscesses.

CONCLUSION

Early involvement of a centre with immunological expertise combined with aggressive management of complications significantly improves morbidity and mortality from this rare condition.

Physiology and pathophysiology of the DUOXes

The dual oxidases (DUOXes) 1 and 2 are named based on their having both a domain homologous to the NADPH-oxidase of the phagocyte NADPH-oxidase gp91( phox )/NOX2 and a domain homologous to thyroid peroxidase. The DUOX1 and DUOX2 mRNAs were originally cloned from thyroid tissue, and the corresponding proteins were recognized as intricate components of the thyroid hormone synthesis process, providing hydrogen peroxide essential for the organification of iodide. The function of DUOX2 in thyroid hormonogenesis has been firmly established by linking the congenital hypothyroid phenotype "total iodide organification defect" to biallelic inactivating DUOX2 mutations. Based on the expression of both DUOXes in combination with a peroxidase in a range of different tissues and functional studies; the concept evolves that DUOX is important not only for thyroid hormonogenesis but also as an integral part of the host defense system of mucosal surfaces, participates in the control of epithelial infection, augments surface B-cell receptor signaling in lymphocytes, and is involved in generating a respiratory burst at fertilization.

Transmembrane topology of FRO2, a ferric chelate reductase from Arabidopsis thaliana

Iron uptake in Arabidopsis thaliana is mediated by ferric chelate reductase FRO2, a transmembrane protein belonging to the flavocytochrome b family. There is no high resolution structural information available for any member of this family. We have determined the transmembrane topology of FRO2 experimentally using the alkaline phosphatase fusion method. The resulting topology is different from that obtained by theoretical predictions and contains 8 transmembrane helices, 4 of which build up the highly conserved core of the protein. This core is present in the entire flavocytochrome b family. The large water soluble domain of FRO2, which contains NADPH, FAD and oxidoreductase sequence motifs, was located on the inside of the membrane.

The sodium/hydrogen exchanger: a possible mediator of immunity

Immune cells such as macrophages and neutrophils provide the first line of defence of the immune system using phagocytosis, cytokine and chemokine synthesis and release, as well as Reactive Oxygen Species (ROS) generation. Many of these functions are positively coupled with cytoplasmic pH (pHi) and/or phagosomal pH (pHp) modification; an increase in pHi represents an important signal for cytokine and chemokine release, whereas a decrease in pHp can induce an efficient antigen presentation. However, the relationship between pHi and ROS generation is not well understood. In immune cells two main transport systems have been shown to regulate pHi: the Na+/H+ Exchanger (NHE) and the plasmalemmal V-type H+ ATPase. NHE is a family of proteins which exchange Na+ for H+ according to their concentration gradients in an electroneutral manner. The exchanger also plays a key role in several other cellular functions including proliferation, differentiation, apoptosis, migration, and cytoskeletal organization. Since not much is known on the relationship between NHE and immunity, this review outlines the contribution of NHE to different aspects of innate and adaptive immune responses such as phagosomal acidification, NADPH oxidase activation and ROS generation, cytokine and chemokine release as well as T cell apoptosis. The possibility that several pro-inflammatory diseases may be modulated by NHE activity is evaluated.

Impaired neutrophil chemotaxis in Crohn's disease relates to reduced production of chemokines and can be augmented by granulocyte-colony stimulating factor

BACKGROUND

Defective neutrophil recruitment has been described as a primary pathogenic abnormality in Crohn's disease. Cantharidin-induced blisters provide a novel investigative tool to assess cellular influx and inflammatory mediator production during acute inflammation and allows the effects of therapy on these parameters to be measured.

AIMS

To determine whether reduced neutrophil tissue penetration in Crohn's disease relates to impaired production of inflammatory mediators, and whether it can be reversed by granulocyte-colony stimulating factor (G-CSF).

METHODS

Neutrophil and monocyte/macrophage populations and inflammatory mediators were measured in cantharidin blisters at 24 h. Neutrophil chemotaxis was assessed in vitro using blister fluid as the chemoattractant. The effect of s.c. G-CSF on blister phenotype was determined.

RESULTS

Significantly fewer neutrophils migrated into blisters in Crohn's patients. The production of neutrophil chemokines, but not other inflammatory mediators, was reduced. This significantly correlated with reduced chemotaxis in vitro. Differences were unrelated to caspase-recruitment domain 15 genotype. G-CSF significantly increased blister neutrophil concentrations in control subjects and Crohn's patients.

CONCLUSIONS

Reduced neutrophil migration during acute inflammation in Crohn's disease is associated with impaired production of appropriate chemoattractants. G-CSF therapy increases neutrophil tissue migration, which may partially account for its observed therapeutic effect.

Molecular dynamics study on the ligand recognition by tandem SH3 domains of p47phox, regulating NADPH oxidase activity

The phagocyte NADPH oxidase complex plays a crucial role in host defense against microbial infection through the production of superoxides. Chronic granulomatous disease (CGD) is an inherited immune deficiency caused by the absence of certain components of the NADPH oxidase. Key to the activation of the NADPH oxidase is the cytoplasmic subunit p47phox, which includes the tandem SH3 domains (N-SH3 and C-SH3). In active phagocytes, p47phox forms a stable complex with the cytoplasmic region of membrane subunit p22phox that forms a left-handed polyproline type-II (PPII) helix conformation. In this report, we have analyzed the conformational changes of p47phox-p22phox complexes of wild-type and three mutants, which have been detected in CGD patients, using molecular dynamics simulations. We have found that in the wild-type, two basal planes of PPII prism in cytoplasmic region of p22phox interacted with N-SH3 and C-SH3. In contrast, in the modeled mutants, the residue at the ape of PPII helix, which interacts simultaneously with both of the tandem SH3 domains in the wild-type, moved toward C-SH3. Furthermore, interaction energies of the cytoplasmic region of p22phox with C-SH3 tend to decrease in these mutants. All these findings led us to conclude that interactions between N-SH3 of p47phox and PPII helix, which is formed by cytoplasmic region of p22phox, may play a significant role in the activation of the NADPH oxidase.

Can unresolved infection precipitate autoimmune disease?

Autoimmune diseases are frequently postulated to arise as post-infectious phenomena. Here we survey the evidence supporting these theories, with particular emphasis on Crohn's disease and ankylosing spondylitis. Direct proof that infection establishes persistent autoimmunity remains lacking, although it may provoke a prolonged inflammatory response when occurring on a susceptible immunological background. The argument of infective causality is by no means trivial, since it carries important consequences for the safety of vaccine development.

NADPH oxidases in cardiovascular health and disease

Increased oxidative stress plays an important role in the pathophysiology of cardiovascular diseases such as hypertension, atherosclerosis, diabetes, cardiac hypertrophy, heart failure, and ischemia-reperfusion. Although several sources of reactive oxygen species (ROS) may be involved, a family of NADPH oxidases appears to be especially important for redox signaling and may be amenable to specific therapeutic targeting. These include the prototypic Nox2 isoform-based NADPH oxidase, which was first characterized in neutrophils, as well as other NADPH oxidases such as Nox1 and Nox4. These Nox isoforms are expressed in a cell- and tissue-specific fashion, are subject to independent activation and regulation, and may subserve distinct functions. This article reviews the potential roles of NADPH oxidases in both cardiovascular physiological processes (such as the regulation of vascular tone and oxygen sensing) and pathophysiological processes such as endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, angiogenesis, and vascular and cardiac remodeling. The complexity of regulation of NADPH oxidases in these conditions may provide the possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the disease process.

Identification of an actin-binding site in p47phoxan organizer protein of NADPH oxidase

Actin has been reported to enhance the superoxide-generating activity of neutrophil NADPH oxidase in a cell-free system and to interact with p47phox, a regulatory subunit of the oxidase. In the present study, we searched for an actin-binding site in p47phox by far-western blotting and blot-binding assays using truncated forms of p47phox. The amino-acid sequence 319-337 was identified as an actin-binding site, and a synthetic peptide of this sequence bound to actin. The sequence shows no homology to other known actin-binding motifs. It is located in the autoinhibitory region of p47phox and includes Ser-328, a phosphorylation site essential for unmasking. Although a phosphorylation-mimetic p47phox mutant bound to actin with a lower affinity than the wild type, the same mutant interacted with filamentous actin more efficiently than the wild type. A mutant peptide p47phox (319-337, Ser328Glu) bound to filamentous actin more tightly than to monomer actin. These results suggest that p47phox moves to cortical actin when it becomes unmasked in the cells.

A new type of O2−-generating tool for oxidative stress studies by remodeling neutrophil NADPH oxidase

The effects of reactive oxygen species on cells have attracted much attention in relation to redox regulation and oxidative stress-related diseases. Superoxide (O(2)(-)) is the reactive oxygen species primarily formed in biological systems. However, no convenient O(2)(-)-generating device has been available for use in cell or tissue culture. The neutrophil NADPH oxidase, a professional enzyme for killing bacteria, has a high ability to produce O(2)(-). However, the cell-free activation process requires several protein factors and an anionic amphiphile, and moreover, the activation is transient. To utilize the enzyme as an O(2)(-) generator, we improved the cell-free activation method by remodeling regulatory components, optimizing lipid composition, and modifying the mixing conditions. We established a new method to produce an active enzyme that is stable, efficient, and preservable. As an application, we examined the effect of the device on cultured HEK293 cells and observed that it caused cell death. This system has several advantages over the xanthine oxidase system often used. The new device will be useful for studies of oxidative stress and related diseases.

Virulence comparisons of Aspergillus nidulans mutants are confounded by the inflammatory response of p47phox-/- mice

While investigating the requirement for phagosomal alkalinization in the host defense against pulmonary aspergillosis, we observed high morbidity of p47(phox)(-/-) mice infected with pH-insensitive Aspergillus nidulans mutants despite a paucity of fungal growth. Fatal infection also resulted from a normally avirulent p-aminobenzoate auxotroph. This demonstrates that p47(phox)(-/-) murine immunity contributes significantly to A. nidulans lethality. These data have wider implications for microbial virulence studies with p47(phox)(-/-) mice.

How neutrophils kill microbes

Neutrophils provide the first line of defense of the innate immune system by phagocytosing, killing, and digesting bacteria and fungi. Killing was previously believed to be accomplished by oxygen free radicals and other reactive oxygen species generated by the NADPH oxidase, and by oxidized halides produced by myeloperoxidase. We now know this is incorrect. The oxidase pumps electrons into the phagocytic vacuole, thereby inducing a charge across the membrane that must be compensated. The movement of compensating ions produces conditions in the vacuole conducive to microbial killing and digestion by enzymes released into the vacuole from the cytoplasmic granules.

Activation and assembly of the NADPH oxidase: a structural perspective

The NADPH oxidase of professional phagocytes is a crucial component of the innate immune response due to its fundamental role in the production of reactive oxygen species that act as powerful microbicidal agents. The activity of this multi-protein enzyme is dependent on the regulated assembly of the six enzyme subunits at the membrane where oxygen is reduced to superoxide anions. In the resting state, four of the enzyme subunits are maintained in the cytosol, either through auto-inhibitory interactions or through complex formation with accessory proteins that are not part of the active enzyme complex. Multiple inputs are required to disrupt these inhibitory interactions and allow translocation to the membrane and association with the integral membrane components. Protein interaction modules are key regulators of NADPH oxidase assembly, and the protein-protein interactions mediated via these domains have been the target of numerous studies. Many models have been put forward to describe the intricate network of reversible protein interactions that regulate the activity of this enzyme, but an all-encompassing model has so far been elusive. An important step towards an understanding of the molecular basis of NADPH oxidase assembly and activity has been the recent solution of the three-dimensional structures of some of the oxidase components. We will discuss these structures in the present review and attempt to reconcile some of the conflicting models on the basis of the structural information available.

Effect of sulfur amino acids on stimulus-induced superoxide generation and translocation of p47phox and p67phox to cell membrane in human neutrophils and the scavenging of free radical

BACKGROUND

Various cystathionine metabolites are in the urine of the patients with cystathioninuria. Among these metabolites, cystathionine ketimine significantly enhanced N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide generation in parallel with tyrosyl phosphorylation of 45 kDa protein in human neutrophils.

METHODS

We investigated the effect of various sulfur amino acids on fMLP-, phorbol-12-myristate-13-acetate (PMA)- and arachidonic acid (AA)-induced superoxide generation in human neutrophils. In addition, the effects of these sulfur amino acids on the membrane translocation of cytosolic compounds p47(phox) and p67(phox) and on the scavenging of superoxide anions were investigated.

RESULTS

When the cells were preincubated with various sulfur amino acids, fMLP-induced superoxide generation was enhanced by D,L-homocysteine and D,L-homocysteine-thiolactone but was inhibited by other sulfur amino acids in a concentration-dependent manner. The AA-induced superoxide was enhanced by L-cysteine, N-acetyl-L-cysteine and D,L-homocysteine. The strength of enhancing effect was: L-cysteine>>N-acetyl-L-cysteine>D,L-homocysteine. On the other hand, the superoxide generation was weakly inhibited by L-cystathionine. The superoxide generation induced by PMA was weakly inhibited by L-cysteine, N-acetyl-L-cysteine and L-cystathionine. Homocysteine and D,L-homocysteine-thiolactone had no effect. In addition, D,L-homocysteine also enhanced translocation to the cell membrane of cytosolic compounds p47(phox) and p67(phox). Conversely, L-cystathionine and N-acetyl-L-cysteine inhibited the translocation to membrane of p47(phox) and p67(phox) in a concentration-dependent manner. N-acetyl-L-cysteine and L-cysteine revealed scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. The sulfur amino acids tested also indicated radical scavenging activity on superoxide anion generated by phenazine methoxysulfate (PMS)-NADH system.

CONCLUSION

D,L-homocysteine and D,L-homocysteine-thiolactone enhanced fMLP-induced superoxide generation by the increment of translocation to membrane of p47(phox) and p67(phox). L-cystathionine and N-acetyl-L-cysteine suppressed fMLP- and PMA-induced superoxide generation by the inhibition of translocation to membrane of p47(phox) and p67(phox). N-acetyl-L-cysteine also had scavenging activity against DPPH radicals and superoxide anion.