NADPH oxidase is not essential for low density lipoprotein oxidation by human monocyte-derived macrophages

NADPH oxidase has been reported to be involved in low density lipoprotein (LDL) oxidation by monocytes. We have investigated the ability of monocyte-derived macrophages from four chronic granulomatous disease patients, which lack NADPH oxidase, to oxidise LDL. All the cells oxidised LDL to significantly increase its uptake by mouse macrophages. We conclude therefore that NADPH oxidase is not essential for LDL oxidation by macrophages.

Interaction of Rac with p67phox and regulation of phagocytic NADPH oxidase activity

Rho and Rac, two members of the Ras superfamily of guanosine triphosphate (GTP)-binding proteins, regulate a variety of signal transduction pathways in eukaryotic cells. Upon stimulation of phagocytic cells, Rac enhances the activity of the enzyme nicotinamide adenine dinucleotide phosphate (reduced) (NADPH) oxidase, resulting in the production of superoxide radicals. Activation of the NADPH oxidase requires the assembly of a multimolecular complex at the plasma membrane consisting of two integral membrane proteins, gp91phox and p21phox, and two cytosolic proteins, p67phox and p47phox. Rac1 interacted directly with p67phox in a GTP-dependent manner. Modified forms of Rac with mutations in the effector site did not stimulate oxidase activity or bind to p67phox. Thus, p67phox appears to be the Rac effector protein in the NADPH oxidase complex.

Activation of NADPH oxidase involves the dissociation of p21rac from its inhibitory GDP/GTP exchange protein (rhoGDI) followed by its translocation to the plasma membrane

Activation of the NADPH oxidase of phagocytes involves the small GTP-binding protein p21rac. In this paper we report that neutrophil cytosol contains predominantly p21rac2 rather than p21rac1, and that the P21rac2 is almost entirely complexed with rhoGDI (GDP dissociation inhibitor) to form a heterodimer with a molecular mass of 45-50 kDa. Activation of superoxide production by phorbol 12-myristate 13-acetate or formylmethionyl-leucyl-phenylalanine in whole cells, and by SDS in the cell-free assay, led to the dissociation of some of the p21rac2 from rhoGDI and its movement to the plasma membrane together with p47phox and p67phox. The appearance of these proteins at the plasma membrane was related to the dose of the agonist and to the rate of superoxide generation. The nucleotide bound to p21rac2 in this complex following isolation was almost exclusively GDP, with less than 2% GTP, and the complex was active in the cell-free assay. Although the rac/GDI complex could activate the NADPH oxidase in the absence of exogenous GTP, the rate of superoxide production was increased 3-fold by the addition of GTP and was almost completely inhibited by GDP. Our findings confirm that rhoGDI serves as GDP dissociation inhibitor and that the release of p21rac2 from this inhibitor is an important step in activation of the NADPH oxidase.

p40phox, a third cytosolic component of the activation complex of the NADPH oxidase to contain src homology 3 domains

The NADPH oxidase generates superoxide in phagocytic cells. It is important for immunity and its deficiency leads to chronic granulomatous disease (CGD). It consists of a membrane-bound flavocytochrome b that lies dormant until activated by the translocation to the plasma membrane of cytosolic proteins, p47phox (phox for phagocyte oxidase), p67phox and p21rac, a small GTP-binding protein. We show here that a novel component, p40phox, forms an activation complex with p47phox and p67phox with which it translocates to the membrane to associate with the flavocytochrome b. cDNA cloning and amino acid analysis revealed that p40phox has an src homology 3 (SH3) domain and a large region of sequence similarity with the N-terminus of p47phox. The primary association of p40phox appears to be with p67phox, and it is present in reduced amounts in patients with CGD lacking p67phox.

The management of chronic granulomatous disease

Chronic granulomatous disease (CGD) is a primary immunodeficiency disease which results from absence of the NADPH oxidase in the professional phagocytic cells neutrophils, monocytes, macrophages and eosinophils. Deficiency of this oxidase renders the patient liable to infection by bacteria and fungi, and, as the name of the disease suggests, to chronic granulomatous inflammation. These patients present with a great variety of infections and other complications of their disease, which often tax the clinical and therapeutic skill of the doctors responsible for their care. Collectively we look after, or advise on the management of, over 100 of these subjects, and have developed experience in the diagnosis and management of the infections and other clinical problems they present. We thought that it might be timely to provide guidelines for their management based upon this experience. The numbers of patients are still relatively small, and the clinical presentations very varied, so it is impossible to provide clear statistical proof of the veracity of this advice. It does, however, reflect the working practise of the physicians caring for many of these patients in Europe.

A structural model for the nucleotide binding domains of the flavocytochrome b-245 beta-chain

NADPH is a system in phagocytic cells that generates O2- and hydrogen peroxide in the endocytic vacuole, both of which are important for killing of the engulfed microbe. Dysfunction of this oxidase results in the syndrome of chronic granulomatous disease, characterized by a profound predisposition to bacterial and fungal infections. A flavocytochrome b is the site of most of the mutations causing this syndrome. The FAD and NADPH binding sites have been located on the beta subunit of this molecule, the C-terminal half of which showed weak sequence similarity to other reductases, including the ferredoxin-NADP reductase (FNR) of known structure. This enabled us to build a model of the nucleotide binding domains of the flavocytochrome using this structure as a template. The model was built initially using a novel automatic modeling method based on distance-matrix projection and then refined using energy minimization with appropriate side-chain torsional constraints. The resulting model rationalized much of the observed sequence conservation and identified a large insertion as a potential regulatory domain. It confirms the inclusion of the neutrophil flavocytochrome b-245 (Cb-245) as a member of the FNR family of reductases and strongly supports its function as the proximal electron transporting component of the NADPH oxidase.

Alpha-enolase: a novel cytosolic autoantigen in ANCA positive vasculitis

Anti-neutrophil cytoplasmic antibodies (ANCA) in sera from patients with clinically proven vasculitis have been described as reacting with proteins present in the granules of human neutrophils. We have studied sera from 59 ANCA positive patients to further characterize the antibody response. In addition to the antigens previously identified in the vasculitic syndromes (myeloperoxidase and serine proteinase 3) the majority of these sera contained antibodies that reacted with a cytosolic extract of neutrophils on Western blots. Nearly 40% of these sera had antibodies directed against a cytosolic protein(s) of molecular mass 48 kD. This protein was purified from neutrophil cytosol by ammonium sulphate fractionation, anion exchange and reverse phase chromatography. Amino acid sequence analysis of a proteolytic fragment of this protein identified it as alpha enolase. The anti-enolase antibodies only recognized the alpha isoform and were present in sera giving either a pANCA or cANCA staining pattern by indirect immunofluorescence. Antibodies to alpha enolase were also found in sera from patients with systemic lupus erythematosus, particularly those with renal disease. We conclude that the antibody response in ANCA positive vasculitis is not restricted to neutrophil granule proteins.

The biochemical basis of the NADPH oxidase of phagocytes

The NADPH oxidase is an electron transport chain found in lymphocytes and in the wall of the endocytic vacuole of 'professional' phagocytic cells. It is so called because NADPH is used as an electron donor to reduce oxygen to superoxide and hydrogen peroxide. The redox components are provided by a very unusual flavocytochrome b from the membrane, which is dependent upon cytosolic factors (including two specialized proteins, p47phox and p67phox) for activation. The small GTP-binding protein, p21rac, is also implicated in this system, possibly as the switch that triggers electron transport. This system provides a key to our understanding of the way in which these GTP-binding proteins function.

Okadaic acid produces changes in phosphorylation and translocation of proteins and in intracellular calcium in human neutrophils. Relationship with the activation of the NADPH oxidase by different stimuli

Okadaic acid, a potent inhibitor of protein phosphatases 1 and 2A, profoundly influenced the activity of the NADPH oxidase of human neutrophils. It strongly inhibited stimulation of superoxide generation by phorbol 12-myristate 13-acetate (PMA) and impaired translocation of protein kinase activity and of the two cytosolic components p47-phox and p67-phox to the plasma membrane. The increase in the phosphorylation of the cytochrome b-245 subunits p22-phox and gp91-phox after stimulation was also blocked. Inhibition of activity was associated with a decrease in cytosolic free Ca2+ and was reversed by the Ca2+ ionophore A23187, which also restored protein translocation and phosphorylation of the cytochrome. This effect of A23187 was itself blocked by preincubation with cyclosporin A, suggesting that calcineurin might be involved in the re-activation process. In contrast with PMA, the response to the bacterial peptide fMet-Leu-Phe was greatly prolonged after an initial decrease in the rate of onset of NADPH oxidase activity.

Isolation and characterization of grancalcin, a novel 28 kDa EF-hand calcium-binding protein from human neutrophils

A novel 28 kDa protein, which we have named 'grancalcin', has been identified in human neutrophils. The protein was isolated from the cytosol and found to be a homodimer, with an apparent molecular mass of 55 kDa on gel filtration. Polyclonal antibodies were raised to the native protein. N-Terminal sequence analysis and tryptic-peptide sequence analysis was performed. The protein exhibits sequence similarity to sorcin, a 24 kDa calcium-binding protein over-expressed in certain multi-drug-resistant cell lines. It appears to be a member of the EF-hand family of calcium-binding proteins. The association of a high proportion of this protein with the membranes and granules in the presence of physiological concentrations of calcium may indicate a role in granule-membrane fusion and degranulation.

Restoration of superoxide generation to a chronic granulomatous disease-derived B-cell line by retrovirus mediated gene transfer

Failure of a superoxide generating system, the NADPH oxidase, present in neutrophils and other phagocytes gives rise to chronic granulomatous disease (CGD), a group of single-gene inherited disorders all characterized by an extreme susceptibility to pyogenic infection, with potentially fatal consequences. About 30% of CGD cases are caused by an autosomally inherited deficiency of a 47-Kd cytoplasmic component of the oxidase (p47-phox). Epstein-Barr virus (EBV) immortalized B-lymphocyte lines established from these CGD patients also express this NADPH oxidase defect and consequently are rendered incapable of generating superoxide on stimulation. We have used a p47-phox-deficient EBV-transformed B-cell line as a recipient for retroviral transfer of a functional p47-phox cDNA. The presence and activity of the retrovirally encoded p47-phox in the transduced cells is demonstrated and we show that this restores their capacity to generate superoxide.

Reconstitution of neutrophil NADPH oxidase activity in the cell-free system by four components: p67-phox, p47-phox, p21rac1, and cytochrome b-245

Activation of the NADPH oxidase of phagocytes in the cell-free system requires the association of several cytosolic components with membrane-bound cytochrome b. In this study we were able to fully reconstitute NADPH oxidase activity in the cell-free system with three recombinant proteins: p67-phox, p47-phox, p21rac1, and pure cytochrome b-245. Activity was dependent upon the concentration of the proteins, with maximal activity observed with roughly equimolar ratios of the cytochrome b and p67-phox (133 and 163 mol/s/mol, respectively) and concentrations of the other two proteins approximately 1 order of magnitude greater. No activity was observed in the absence of any one of these components. In addition, activation was dependent upon p21rac1 being preloaded with GTP, the cytochrome b being reconstituted with lipid, and the presence of FAD during activation. Half-maximal activity was observed at a concentration of NADPH of approximately 50 microM. These findings confirm our recent description of the membrane-bound cytochrome b as a FAD-containing flavocytochrome b containing the NADPH binding site, and implicate the three cytosolic proteins in its activation.

Cytochrome b-245 is a flavocytochrome containing FAD and the NADPH-binding site of the microbicidal oxidase of phagocytes

The NADPH oxidase of phagocytic cells is important for the efficient killing and digestion of ingested microbes. A very unusual low-potential cytochrome b (b-245) is the only redox molecule to have been identified in this system. The FAD-containing flavoprotein that binds NADPH and transfers electrons to the cytochrome has eluded identification for three decades. We show here that the haem/FAD ratio in the membranes does not change significantly on activation of this oxidase, indicating that the FAD is present in the membranes from the outset and not recruited from the cytosol. The FAD content of membranes from cells of patients with X-linked chronic granulomatous disease (CGD) lacking the cytochrome b was roughly one-quarter of that in normal subjects and in autosomal recessive CGD patients lacking the cytosolic protein p47-phox. Similar low amounts of FAD were present in uninduced promyelocytic (HL60) cells, suggesting that the low amount of FAD in cells from X-CGD patients was probably unrelated to this oxidase system. Cytochrome b-245 appears to bind both the haem and FAD, in a molar ratio of 2:1. The e.p.r. signal of the purified cytochrome was weak and had an asymmetric g(z) peak at g = 3.31. The purified cytochrome could be partially reflavinated (about 20%) in the presence of lipid. Amino acid sequence homology was detected between the beta-subunit of this cytochrome b and the ferredoxin-NADP+ reductase (FNR) family of reductases in the putative NADPH- and FAD-binding sites. 32P-labelled 2-azido-NADP was used as a photoaffinity label for the NADPH-binding site. Labelling that was competed off with NADP was observed in the region of the beta-subunit of the cytochrome. No labelling was seen in this region in X-CGD in three subjects in whom this cytochrome was missing and in a third in whom it was present but bore a Pro-His transposition in the putative NADPH-binding site. These studies indicate that cytochrome b-245 is a flavocytochrome, the first described in higher eukaryotic cells, bearing the complete electron-transporting apparatus of the NADPH oxidase.

Identification of the defective NADPH-oxidase component in chronic granulomatous disease: a study of 57 European families

Chronic Granulomatous Disease (CGD) manifests as a predisposition to infection as a result of defective function of the NADPH oxidase of phagocytic cells. Proteins identified as part of this system include two subunits of a cytochrome b (cytochrome b-245) and two cytosolic factors. The affected oxidase component was determined in 63 CGD patients from 57 families, by Western blotting of extracts of their neutrophils with antibodies to those proteins. 38 (67%) of the families were X-linked with a defect of the beta subunit of the cytochrome. 13 (23%) lacked p47-phox, 3 (5%) p67-phox, and 3 (5%) the alpha subunit of the cytochrome.

Molecular cloning and characterization of grancalcin, a novel EF-hand calcium-binding protein abundant in neutrophils and monocytes

A novel EF-hand Ca(2+)-binding protein we have called grancalcin has been identified and characterized. This protein is particularly abundant in neutrophils and monocytes, with relatively small amounts in lymphocytes. The cDNA for this protein has been cloned and sequenced. The sequence predicts that the protein is composed of 217 amino acids, with a molecular mass of 24,010 daltons. It contains four EF-hand calcium-binding motifs and exhibits strong homology to sorcin, one of two proteins overexpressed in multidrug-resistant cells whose function is unknown. There are potentially one phosphorylation and two glycosylation sites. The 1.65-kilobase mRNA is detected in bone marrow and is present in neutrophils, monocytes, macrophages, B and T lymphocytes, and the promyelocytic cell line HL60s. The protein displays a Ca(2+)-dependent translocation to the granules and plasma membrane of neutrophils, suggesting that it might play an effector role in the specialized functions of these cells.

Biochemistry and molecular biology of chronic granulomatous disease

The NADPH oxidase of phagocytic cells is an electron transport chain in the wall of the endocytic vacuole that is activated upon engulfment of the microbe, and is important for its efficient killing and digestion. The oxidase consists of a heterodimeric cytochrome b in the membrane, which is the site of the haem and FAD groups, and two cystolic factors p47-phox and p67-phox that appear to activate the system. Absence of this oxidase as a result of defects in each of these specialized proteins causes the syndrome of chronic granulomatous disease (CGD), that is characterized by a profound predisposition to pyogenic infection.

Activation of the NADPH oxidase involves the small GTP-binding protein p21rac1

Professional phagocytes, such as neutrophils and monocytes, have an NADPH oxidase that generates superoxide and other reduced oxygen species important in killing microorganisms. Several components of the oxidase complex have been identified as targets of genetic defects causing chronic granulomatous disease. The complex consists of an electron transport chain that has as its substrate cytosolic NADPH and which discharges superoxide into the cavity of the intracellular phagocytic vacuole. The only electron transport component identified so far is a low-potential cytochrome b, apparently the only membrane component required. At least three cytosolic factors are also necessary, two of which, p67phOx and p47phOx, have been identified by their absence in patients with chronic granulomatous disease. A third component, sigma 1, is required for stimulation of oxidase activity in a cell-free system. The active components of purified sigma 1 are two proteins that associate as heterodimers, and here we report that these are the small GTP-binding protein p21rac1 and the GDP-dissociation inhibitor rhoGDI.

Autosomal recessive chronic granulomatous disease caused by deletion at a dinucleotide repeat

Chronic granulomatous disease (CGD) is a rare inherited condition rendering neutrophils incapable of killing invading pathogens. This condition is due to the failure of a multicomponent microbicidal oxidase that normally yields a low-midpoint-potential b cytochrome (cytochrome b245). Although defects in the X chromosome-linked cytochrome account for the majority of CGD patients, as many as 30% of CGD cases are due to an autosomal recessive disease. Of these, greater than 90% have been shown to be defective in the synthesis of a 47-kDa cytosolic component of the oxidase. We demonstrate here in three unrelated cases of autosomal recessive CGD that the identical underlying molecular lesion is a dinucleotide deletion at a GTGT tandem repeat, corresponding to the acceptor site of the first intron-exon junction. Slippage of the DNA duplex at this site may contribute to the high frequency of defects in this gene.

Killing of pathogens associated with chronic granulomatous disease by the non-oxidative microbicidal mechanisms of human neutrophils

The susceptibility of opportunist pathogens associated with chronic granulomatous disease (CGD) to the non-oxidative killing mechanisms of neutrophils has been assessed by incubation in human neutrophil primary granule lysate. The dose and pH-dependency of killing of Aspergillus fumigatus, Candida albicans, Escherichia coli, Nocardia asteroides, Serratia marcescens and Staphylococcus aureus differed markedly and may partly explain their virulence in CGD, in which oxygen-dependent killing mechanisms are defective. At the acid pH in CGD neutrophil phagosomes S. aureus, Ser. marcescens, N. asteroides and A. fumigatus spores were highly resistant but C. albicans, a less frequent pathogen in patients with CGD, was much more susceptible.

Unique human neutrophil populations are defined by monoclonal antibody ED12F8C10

A mouse IgG1 monoclonal antibody ED12F8C10 (C10) binds a constant percentage of peripheral blood neutrophils in the same individual when studied over time, defining a distinct subset of neutrophils in all normal individuals studied to date. Bone marrow studies confirm that the heterogeneity is present to the same degree at all stages of neutrophil development from the myelocyte to the mature neutrophil. Neither in vivo nor in vitro activation of neutrophils explains or significantly alters the relative percentages of C10-positive and -negative neutrophils in the same individual. With both activation and exudation, however, expression of the C10-defined epitope increases in intensity in the C10 binding subpopulation. Studies of NBT reduction, phagocytosis, adherence, light scattering characteristics, and monoclonal antibody surface binding have failed to demonstrate physical or functional differences between the C10-defined populations. We examined C10 binding in patients with different defects of phagocyte function. In two patients with neutrophil-specific granule deficiency, less than 1% of the neutrophils were found to be C10 positive, while neutrophils from a patient with idiopathic leukemoid reaction and recurrent infections demonstrated greater than 99% C10 binding. Although the present study does not delineate the physiologic significance of C10 binding heterogeneity, it firmly supports the concept of neutrophil heterogeneity at the level of surface antigen expression.

The alpha subunit of cytochrome b-245 mapped to chromosome 16

The chromosomal location of the alpha subunit (23-kDa protein) of human cytochrome b-245 was analyzed by Southern blot hybridization using DNA isolated from a panel of 12 independent human-rodent somatic cell hybrids. The results indicate that this protein is encoded at a single locus on chromosome 16.

Molecular medicine

The enormous advances in the biological sciences are making a dramatic impact upon clinical medicine. The emerging specialty of molecular medicine applies these theoretical and technological advances to understanding the causes, expression and rational treatment of human disease.

Purification of the 47 kDa phosphoprotein associated with the NADPH oxidase of human neutrophils

A 47 kDa protein in the cytosol of phagocytic cells becomes heavily phosphorylated and translocates to the cell membrane upon stimulation. This protein was isolated from the cytosol of human neutrophils by chromatography on ion-exchange and hydroxyapatite resins. Polyclonal antibodies to this protein demonstrated that it was present in the neutrophils of two patients with X-linked chronic granulomatous disease (CGD) but not in those of three patients with the autosomal recessive pattern of inheritance. A sequence of amino acids was determined from a tryptic peptide of this protein: Glu-Met-Phe-Pro-Ile-Glu-Ala-Gly-Ala-Ile-Asn-Xaa-Glu. This served to establish that the phosphoprotein isolated here is the same as a protein of a similar molecular mass identified by other workers. These studies confirm the involvement of this 47 kDa phosphoprotein in the molecular pathology of autosomal recessive CGD and describe a method for the purification of the native protein.

Identification of the haem-binding subunit of cytochrome b-245

Cytochrome b-245 from neutrophil plasma membranes contains two types of subunit with apparent molecular masses from gel electrophoresis in the presence of SDS of 23 kDa and 76-92 kDa. Radiation-inactivation analysis revealed a single-exponential decay process for the visible absorption of the haem chromophore in the membrane, corresponding to a molecular mass of 21 +/- 5 kDa for the haem-containing polypeptide chain. Sedimentation equilibrium of the cytochrome solubilized by the detergent Triton N101 showed that the protein was polydisperse, with a molecular mass of approx. 350 kDa for the smallest detectable species. In another detergent, n-octyl beta-O-glucopyranoside (octyl glucoside), the molecular mass of the haem-containing particle was found to be 20-30 kDa. Thus the quaternary structure of the protein breaks down in this detergent. The haem group is inferred to be attached to the smaller subunit.

The electron transport chain of the microbicidal oxidase of phagocytic cells and its involvement in the molecular pathology of chronic granulomatous disease

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Localization of the 47 kDa phosphoprotein involved in the respiratory-burst NADPH oxidase of phagocytic cells

A 47 kDa phosphoprotein is involved in the respiratory-burst oxidase of phagocytic cells. After stimulation of neutrophils with phorbol myristate acetate, this phosphoprotein was identified in both the cytosol and membranes. Peptide mapping of the two forms resulted in identical patterns of phosphopeptides. Dose-response curves for accumulation of phosphoprotein in the two sites were very similar, whereas the detection of the phosphoprotein in the cytosol preceded that in the membranes. The membrane-associated 47 kDa phosphoprotein was absent from the neutrophils of patients with X-chromosome-linked chronic granulomatous disease, which lack cytochrome b-245, and intermediate levels were detected in the membranes of their heterozygote carrier mothers. Activation of the neutrophil oxidase system appears to be dependent upon phosphorylation of the cytosolic 47 kDa protein and its association with cytochrome b-245 in the membranes. It is probably the cytosolic factor required for reconstitution of the active oxidase in cell-free systems.

The bactericidal effects of the respiratory burst and the myeloperoxidase system isolated in neutrophil cytoplasts

Neutrophil polymorphonuclear leucocytes kill bacteria by oxygen-dependent and oxygen-independent mechanisms. Many potentially toxic mechanisms have been described, but the complexity of the phagosomal environment and the synergy between oxidative and non-oxidative systems hamper the investigation of individual bactericidal mechanism in whole cells. Neutrophil cytoplasts are greatly depleted of granule proteins and permit the investigation of the bactericidal effects of the respiratory burst in isolation. In this study they have been used to examine the role of the respiratory burst and myeloperoxidase in oxygen-dependent killing of Staphylococcus aureus. Cytoplasts generated oxygen radicals at comparable rates to human neutrophils and phagocytosed but did not kill S. aureus. The selective reconstitution of the myeloperoxidase-hydrogen peroxide-halide system by coating bacteria with myeloperoxidase conferred on cytoplasts the ability to kill intracellular bacteria. However, extracellular killing by diffusible bactericidal factors was not detected in this system.

Phosphorylation of the subunits of cytochrome b-245 upon triggering of the respiratory burst of human neutrophils and macrophages

Cytochrome b-245, the only clearly identified component of the microbicidal oxidase system of phagocytes, is a heterodimer consisting of a 23 kDa (alpha) and a 76-92 kDa (beta) subunit. This study was conducted to examine whether, in common with a number of proteins, the subunits of the cytochrome were phosphorylated upon activation of the oxidase. Both subunits were phosphorylated after activation of neutrophils or macrophages with phorbol myristate acetate or a phagocytic stimulus, although the time course of this process did not parallel that of the oxidase. Phosphorylation of these proteins was normal in cells from two patients with autosomal recessive chronic granulomatous disease, in whom phosphorylation of a 47 kDa protein is defective.

Cytochrome b-245 and its involvement in the molecular pathology of chronic granulomatous disease

Cytochrome b-245 is an integral, and probably the terminal, component of the microbicidal oxidase electron transport chain of phagocytic cells. Current knowledge of the biochemistry and cell and molecular biology of this molecule is described. The molecular basis of chronic granulomatous disease, in which defective electron transport down this chain predisposes to infection and impaired digestion by phagocytes, is explained in terms of anomalies of the cytochrome b and related molecules.

The digestion of bacterial macromolecules by phagocytic cells: the effect of mepacrine and ethanol

The digestion of radiolabelled DNA, RNA and protein from two species of bacteria was measured after their ingestion by neutrophils and monocytes. The Escherichia coli (W3110T-) strain was more susceptible to digestion than Staphylococcus aureus. Monocytes solubilized the majority of bacterial DNA to trichloroacetic acid (TCA)-soluble oligonucleotides, which were released rapidly from the cell, whereas neutrophils digested little DNA and retained most as a high molecular weight residue. Both monocytes and neutrophils released about 30% of DNA as large TCA-insoluble fragments. However, neutrophils were more proficient than monocytes at degrading bacterial RNA. Monocytes and neutrophils digested bacterial protein equally well. The drug mepacrine hydrochloride inhibited phagocytosis of bacteria by both neutrophils and monocytes, although monocytes were more sensitive to the drug. Mepacrine specifically inhibited the terminal digestion of DNA by monocytes to TCA-soluble molecules, whereas digestion to large molecular weight fragments apparently was not affected. Ethanol also inhibited the breakdown of DNA by phagocytic cells.

Defective degradation of bacterial DNA by phagocytes from patients with systemic and discoid lupus erythematosus

The digestion of bacterial DNA by peripheral blood monocytes was impaired both in patients with systemic lupus erythematosus (SLE) and discoid lupus erythematosus (DLE). The monocytes of these patients had both a small quantitative defect in the solubilization of DNA and a marked qualitative defect in the extent to which this DNA was degraded. In addition, neutrophils from patients with SLE released significantly less high molecular-weight DNA than control cells. Digestion of bacterial RNA and protein by phagocytes was not defective in either disease. The reduced digestion of DNA by phagocytes resulted in concomitantly larger amounts of high molecular-weight DNA remaining in these cells. Such sequestration of DNA may contribute to the persistence of fairly large DNA fragments in the tissue of patients with lupus erythematosus.

The X-linked chronic granulomatous disease gene codes for the beta-chain of cytochrome b-245

Chronic granulomatous disease (CGD) is a rare inherited disorder associated with a profound predisposition to infection due to the lack of a microbicidal oxidase system in the phagocytes of these patients. This syndrome is most commonly inherited through a defect on the X chromosome and the only clearly defined component of the oxidase system, the very unusual cytochrome b (b-245), has been shown to be missing from the cells of these patients. This cytochrome is a heterodimer composed of an alpha-chain of relative molecular mass (Mr) 23,000 (23K) and a 76-92K beta-chain; neither are detectable in neutrophils from X-linked CGD subjects. The defective X-CGD gene has recently been cloned by 'reverse genetics' but the protein predicted from the proposed complementary DNA sequence was not identified. We have purified the beta-chain of the cytochrome and sequenced 43 amino acids from the N terminus. Almost complete homology was obtained between this sequence and that of the complementary nucleotides 19-147 of the sequence of the X-CGD gene, originally designated as a non-coding region.

Absence of both cytochrome b-245 subunits from neutrophils in X-linked chronic granulomatous disease

Phagocytosis by neutrophils and other 'professional' phagocytic cells is accompanied by a microbicidal burst of non-mitochondrial respiration. Cytochrome b-245 is the only clearly defined component of this oxidase system and its absence provides the molecular basis of X-linked chronic granulomatous disease (CGD), in which a profound predisposition to infection results from complete failure of this respiratory burst. Purification of the cytochrome has proved difficult, with uniform disagreement regarding the identity of its apoprotein, descriptions of its relative molecular mass (Mr) on SDS-polyacrylamide gel electrophoresis (PAGE) ranging from 10,000 to 127,000 (10-127K). I report here that it has two subunits, a 23K protein and the previously described 76-92K glycoprotein. These subunits are closely linked and remain associated with the haem of the cytochrome through affinity and gel filtration chromatography and sucrose gradient centrifugation, and exhibit a similar distribution in a pH gradient. Neither protein was detected in the cells of five patients with X-linked CGD whereas both were present in two with the form of this disease with autosomal recessive inheritance.

The development of cytochrome b-245 in maturing human macrophages

Cytochrome b-245, the putative terminal component of the specialized cidal oxidase system of phagocytes, was measured in human monocytes in culture. There was a dramatic synthesis of the cytochrome, which increased by 27.3 +/- 2.0 pmol/day per 10(7) cells. This represents an increase of about 40%/day in the early stages and an overall 7-fold increase after 16 days. The protein content increased 3-fold over the same period, resulting in a doubling of the specific content of the cytochrome b. The newly synthesized cytochrome b was identified as that specifically located in the microbicidal oxidase electron-transport chain, as titration demonstrated that, at day 16 of maturation, 70% of the total membrane cytochrome b had a very low midpoint potential (-260 to -220 mV), characteristic of that found in this oxidase system. This cytochrome distributed with the plasma membrane on analytical subcellular fractionation, and a close relationship was observed between the maturation-induced increase in the concentration of this molecule and the capacity of the cells to produce superoxide.

Further evidence for the involvement of a phosphoprotein in the respiratory burst oxidase of human neutrophils

Phosphorylation of a 47 kDa protein in human neutrophils is induced by phorbol 12-myristate 13-acetate (PMA), opsonized latex beads, fMet-Leu-Phe, calcium ionophore A23187 and fluoride. All of these stimuli activate the specialized microbicidal respiratory burst of neutrophils, and in each case the kinetics of activation correspond with the kinetics of phosphorylation of the 47 kDa protein. Trifluoperazine (50 microM) and chlorpromazine (100 microM), inhibitors of calmodulin and protein kinase C, abolish the increase in oxygen consumption and selectively prevent phosphorylation of the 47 kDa protein after PMA stimulation. Treatment of neutrophils with pertussis toxin totally inhibits both superoxide production and phosphorylation of this protein in response to fMet-Leu-Phe, but not in response to PMA, indicating that a GTP-binding protein modulates the fMet-Leu-Phe receptor signal. Phosphorylation of the 47 kDa protein, a phenomenon absent from the neutrophils of subjects with autosomal recessive chronic granulomatous disease, which lack the respiratory burst, appears to be the common trigger for activation of the burst in normal neutrophils.

Preliminary evidence for gut involvement in the pathogenesis of rheumatoid arthritis?

111Indium leucocyte scans were performed on 26 patients with active rheumatoid arthritis. An abnormal localization of radioactivity was observed in the gut of 12 of these patients, generally in the region of the terminal ileum, caecum and ascending colon. No difference was found in the intake of nonsteroidal anti-inflammatory drugs between those with positive and negative scans. Two patients with positive scans were on no medication. These observations suggest the possibility of a primary role for a gastrointestinal lesion in the aetiology of rheumatoid arthritis, although these abnormalities could be secondary or unrelated.

Elastase in the different primary granules of the human neutrophil

Elastase in the human neutrophil is associated with various subpopulations of primary granules of different density. The proportion of this enzyme that is extracted with acetate pH 4.2 and cetyltrimethylammonium bromide varies in the different subpopulations. Nevertheless, the electrophoretic mobility and relative proportions of elastase isoenzymes is the same in both extracts from the different subpopulations. On stimulation of neutrophils with N-formylmethionylleucylphenylalanine, elastase is not released from the least dense subpopulation, whereas other two subpopulations do undergo degranulation to approximately the same extent. However, the release of elastase from these two denser granules differs after they are isolated and treated with calcium.

Stimulated neutrophils from patients with autosomal recessive chronic granulomatous disease fail to phosphorylate a Mr-44,000 protein

Phagocytosing neutrophils, monocytes, macrophages and eosinophils produce a burst of non-mitochondrial respiration that is important for the killing and digestion of microbes. Much of the information about the oxidase system involved comes from studies on patients with chronic granulomatous disease (CGD), a syndrome in which an undue predisposition to infection results from complete absence of this burst of stimulated respiratory activity. The basis of the oxidase activity is an electron transport chain, the only established component of which is a very unusual b-type cytochrome (b-245) (ref. 2). The molecular defect in the X-linked subgroup of CGD is the absence of this cytochrome b-245, which, however, appears to be normal in those subjects with the autosomal recessive mode of inheritance. In an attempt to identify an abnormality of activation, or an absence or malfunction of a proximal component of the electron transport chain in this latter group, we examined protein phosphorylation in neutrophils after activation of the oxidase with phorbol myristate acetate. All four of the patients studied demonstrated a selective lack of the enhanced phosphorylation of a protein of relative molecular mass (Mr) 44,000 (44K) that was observed in normal subjects and in two CGD patients with an X-linked inheritance. This molecule, therefore, could be an important functional component of the oxidase.

Investigations of host defence in patients with sickle cell disease

Parameters of host defence were investigated in 30 patients with sickle cell disease (SCD). A newly devised perfusion system was used to study the kinetics in whole blood of leucocyte adherence, phagocytosis, killing and solubilization of a mixture of Staph. aureus and Str. pneumoniae, and secretion of lactoferrin. A skin window technique was used to examine the accumulation of leucocytes at inflammatory foci and their subsequent rate of movement through a filter. Serum concentrations of C3, C4, total haemolytic complement and immunoglobulins were also measured. The rate of neutrophil migration into filters was slightly reduced in patients with SCD. The proportion of monocytes that emigrated from the skin windows and their rate of migration were markedly diminished. The adhesion of neutrophils and their ability to kill staphylococci were also reduced, particularly in patients of the haemoglobin (Hb) SS and Hb S-beta-thalassaemia genotypes. Neutrophil function was mostly impaired in patients with the greatest frequency of bacterial infection. The rate of clearance of pneumococci was related to the concentration of type specific immunoglobulin G but not M. Serum concentrations of immunoglobulins and complement were normal. We were unable to define a defect of host defence of sufficient magnitude to explain the susceptibility of these patients to severe infection.

Effect of high-dose methylprednisolone therapy on phagocyte function in systemic lupus erythematosus

Circulating phagocytes play a major role in the defence of the host against microbial infection. In an attempt to identify the reason for the unusual susceptibility to infection of patients with systemic lupus erythematosus (SLE) various parameters of phagocytic cell function were assessed kinetically in whole blood, and the accumulation of cells in areas of inflammation was studied in vivo with the skin window technique. The effect on these parameters of conventional therapy with glucocorticoids and pulse therapy with large doses of methylprednisolone were examined. Patients on conventional doses of steroids had no abnormality of phagocyte function that might have predisposed to infection, apart from a reduced accumulation of monocytes in areas of inflammation and decreased lactoferrin secretion. Pulse therapy with methylprednisolone considerably delayed the secretion of lactoferrin and the adherence of neutrophils in most of the patients, as well as impairing bacterial killing and digestion.

Elemental diet as primary treatment of acute Crohn's disease: a controlled trial

Acute exacerbations of Crohn's disease are usually treated with prednisolone or potentially more toxic immunosuppressive drugs or by surgery. In pilot studies replacing the normal diet by a protein free elemental diet also induced remission. A controlled trial was therefore conducted in which 21 patients acutely ill with exacerbations of Crohn's disease were randomised to receive either prednisolone 0.75 mg/kg/day or an elemental diet (Vivonex) for four weeks. Assessment at four and 12 weeks showed that the patients treated with the elemental diet had improved as much as and by some criteria more than the steroid treated group. Elemental diet is a safe and effective treatment for acute Crohn's disease.