Myeloperoxidase-mediated iodination in granulocytes

Myeloperoxidase and elastase are only expressed by neutrophils in normal and in inflamed liver

Myeloperoxidase (MPO) is involved in acute and chronic inflammatory diseases. The source of MPO in acute liver diseases is still a matter of debate. Therefore, we analysed MPO-gene expression on sections from normal and acutely damaged [carbon tetrachloride-(CCl₄) or whole liver γ-Irradiation] rat liver by immunohistochemistry, real time PCR and Western blot analysis of total RNA and protein. Also total RNA and protein from isolated Kupffer cells, hepatic stellate cells, Hepatocytes, endothelial cells and neutrophil granulocytes (NG) was analysed by real time PCR and Western blot, respectively. Sections of acutely injured human liver were prepared for MPO and CD68 immunofluorescence double staining. In normal rat liver MPO was detected immunohistochemically and by immunofluorescence double staining only in single NG. No MPO was detected in isolated parenchymal and non-parenchymal cell populations of the normal rat liver. In acutely damaged rat liver mRNA of MPO increased 2.8-fold at 24 h after administration of CCl₄ and 3.3-fold at 3 h after γ-Irradiation and MPO was detected by immunofluorescence double staining only in elastase (NE) positive NGs but not in macrophages (ED1 or CD68 positive cells). Our results demonstrate that, increased expression of MPO in damaged rat and human liver is due to recruited elastase positive NGs.

The tetraspanin CD63 is involved in granule targeting of neutrophil elastase

Targeting mechanisms of neutrophil elastase (NE) and other luminal proteins stored in myeloperoxidase (MPO)–positive secretory lysosomes/primary granules of neutrophils are unknown. These granules contain an integral membrane protein, CD63, with an adaptor protein-3–dependent granule delivery system. Therefore, we hypothesized that CD63 cooperates in granule delivery of the precursor of NE (proNE). Supporting this hypothesis, an association was demonstrated between CD63 and proNE upon coexpression in COS cells. This also involved augmented cellular retention of proNE requiring intact large extracellular loop of CD63. Furthermore, depletion of CD63 in promyelocytic HL-60 cells with RNA interference or a CD63 mutant caused reduction of cellular NE. However, the proNE steady-state level was similar to wild type in CD63-depleted clones, making it feasible to examine possible effects of CD63 on NE trafficking. Thus, depletion of CD63 led to reduced processing of proNE into mature NE and reduced constitutive secretion. Furthermore, CD63-depleted cells showed a lack of morphologically normal granules, but contained MPO-positive cytoplasmic vacuoles with a lack of proNE and NE. Collectively, our data suggest that granule proteins may cooperate in targeting; CD63 can be involved in ER or Golgi export, cellular retention, and granule targeting of proNE before storage as mature NE.

Isolation of bacteria-containing phagosomes by magnetic selection

Background

There is a growing awareness of the importance of intracellular events in determining the outcome of infectious disease. To improve the understanding of such events, like phagosome maturation, we set out to develop a versatile technique for phagosome isolation that is rapid and widely applicable to different pathogens.

Results

We developed two different protocols to isolate phagosomes containing dead or live bacteria modified with small magnetic particles, in conjunction with a synchronized phagocytosis protocol and nitrogen cavitation. For dead bacteria, we performed analysis of the phagosome samples by microscopy and immunoblot, and demonstrated the appearance of maturation markers on isolated phagosomes.

Conclusion

We have presented detailed protocols for phagosome isolation, which can be adapted for use with different cell types and prey. The versatility and simplicity of the approach allow better control of phagosome isolation, the parameters of which are critical in studies of host-bacteria interaction and phagosome maturation.

Analysis of neutrophil membrane traffic during phagocytosis

In this chapter, we describe methods to study membrane traffic during phagosome formation and maturation. Although it is convenient to define events as occurring either before (i.e., during formation) or after (during maturation) the creation of a sealed phagosome, it might not be correct to assume that this is reflected by a sudden change in the membrane traffic events involved. Nevertheless, formation events are studied by approaches different from those of maturation events. Before closure of a phagosome, methods relying on immunochemistry and fluorescent markers are employed. Once phagosomes have formed, these can be isolated and additional methods can be used for their characterization. Here, we describe (1) methods to study membrane traffic during phagosome formation and (2) magnetic purification of bacteria-containing phagosomes for maturation studies.

A new method for the quantification of neutrophil and eosinophil cationic proteins in feces: establishment of normal levels and clinical application in patients with inflammatory bowel disease

OBJECTIVES

The aims of this study were 1) to develop a valid method for the measurement of the eosinophil proteins eosinophil cationic protein (ECP) and eosinophil protein X (EPX) and neutrophil proteins myeloperoxidase and human neutrophil lipocalin (HNL) in feces and 2) to investigate their potential role as disease activity markers in inflammatory bowel disease (IBD).

METHODS

Feces samples were obtained from 44 apparently healthy individuals (HIs), 18 patients with IBD (11 with ulcerative colitis [UC] and seven with Crohn's disease [CD]), and three with collagen colitis. The granulocyte markers were measured using immunoassays in supernatants from processed feces.

RESULTS

ECP, myeloperoxidase, and, to a lesser degree, EPX and HNL were bound to the solid part of feces. However, feces homogenized in an extraction buffer containing the cationic detergent N-cetyl-N,N,N-trimethylammonium bromide allowed an efficient recovery of the proteins (i.e., up to 100-fold increased levels compared to homogenization in saline). All four proteins were stable for at least 7 days at +6 degrees C and at least 3 days at +22 degrees C. The normal fecal geometric mean (95th percentile) levels of ECP, EPX, myeloperoxidase, and HNL were estimated to be, respectively, 1.69 microg/g (6.41), 0.57 microg/g (1.72), 3.54 microg/g (8.77), and 1.97 microg/g (4.91). Markedly increased feces levels of all markers (p < 0.0002), compared to HIs and CD patients, were observed in UC. However, the marker levels in CD patients were significantly increased relative to HIs (p < 0.05 to p < 0.0002). Increased levels of HNL and myeloperoxidase were also observed in the three collagen colitis patients. The discriminative capability between UC patients and HIs was somewhat superior for EPX and myeloperoxidase.

CONCLUSIONS

The method described here takes into account the molecular properties of the granule proteins and the heterogeneity in feces consistency, which is a prerequisite for a valid and reproducible measurement of cationic granule proteins. We suggest that EPX and myeloperoxidase, when applied in IBD, are the best eosinophil and neutrophil markers for studying GI inflammation.

Prevalence and clinical significance of antikeratin antibodies and other serological markers in Lithuanian patients with rheumatoid arthritis

OBJECTIVES

To assess the clinical value of several serological markers in Lithuanian patients with rheumatoid arthritis (RA) compared with control patients with rheumatic disease and age matched healthy controls.

METHODS

Serum samples from 96 patients with RA of approximately 8 years' duration, 90 rheumatic disease controls, and 37 healthy subjects were tested. Antikeratin antibody (AKA), antineutrophil cytoplasmic antibody (ANCA), and antinuclear antibody (ANA) titres were estimated by indirect immunofluorescence (IIF) and serum samples positive for ANA and ANCA were further studied by enzyme linked immunosorbent assay (ELISA). IgA and IgM rheumatoid factors (RF) were measured by ELISA.

RESULTS

A positive AKA test was highly specific for RA (diagnostic specificity 97%), being found in 44% of the patients. Although both RF tests had a higher sensitivity, they were less specific for RA. ANCA was detected in 33% of patients with RA but lacked diagnostic specificity. AKA and ANCA were associated with more erosive disease and the presence of extra-articular manifestations. Positivity for AKA, IgA RF, and ANCA was significantly associated with disease activity and worse functional capacity. However, in multiple regression analysis only positivity for AKA was significantly correlated with functional disability (p=0.0001), evaluated by the Steinbrocker functional classification, and no single marker had any relation with radiological damage.

CONCLUSION

Although AKA showed the highest disease specificity, all serological markers studied except ANA exhibited interesting associations with important clinical and paraclinical parameters of RA.

Myeloperoxidase exerts microbicidal activity against Mycobacterium tuberculosis

We investigated the antimycobacterial role of myeloperoxidase (MPO), one of the most abundant granule proteins in human neutrophils. Our data indicate that purified MPO, in the presence of hydrogen peroxide, exerts a consistent killing activity against Mycobacterium tuberculosis H37Rv and against a clinical isolate. The activity is time and dose dependent and requires the presence of chloride ions in the assay medium.

Clinical evaluation of a capture ELISA for detection of proteinase-3 antineutrophil cytoplasmic antibody

Detection of antineutrophil cytoplasmic antibodies (ANCA) has become a useful tool in the diagnosis of Wegener's granulomatosis and microscopic polyangiitis. However, the results obtained with indirect immunofluorescence (IIF) and by ELISA for ANCA demonstration do not always correlate. A possible explanation for this finding could be that proteins are denatured during the process of antigen purification or during coating onto the solid phase. To avoid this possibility, a monoclonal antibody to PR3 that is precoated on the plate can be used. In the present study we have used the monoclonal antibody (MoAb) 4A3 for the capture of PR3 in an ELISA, and a clinical evaluation of the diagnostic properties of the new capture ELISA has been made. The sensitivity of the capture PR3-ANCA ELISA was 85% in a material of c-ANCA positive sera. A specificity of 90% was obtained in analyses from patients having various forms of glomerulonephritis. There was a significantly higher diagnostic sensitivity of the capture PR3-ANCA ELISA (85%) compared to c-ANCA by IIF (58%) in patients with Wegener's granulomatosis with renal involvement. Capture PR3-ANCA and direct ELISA for MPO-ANCA together gave a diagnostic sensitivity of 98%, versus 75% using IIF. In conclusion, the capture PR3-ANCA ELISA seems to be a valuable tool in the diagnosis of Wegener's granulomatosis with renal involvement. Preliminary data suggest that the technique may have an advantage over direct ELISA for PR3-ANCA, as well as in the follow-up of c-/PR3-ANCA associated vasculitides. However, further prospective studies are needed to clarify this premise.

The role of the propeptide for processing and sorting of human myeloperoxidase

Myeloperoxidase (MPO), stored in azurophil granules of neutrophils, is critical for an optimal oxygen-dependent microbicidal activity of these cells. Pro-MPO goes through a stepwise proteolytic trimming with elimination of an amino-terminal propeptide to yield one heavy and one light polypeptide chain. The propeptide of MPO may have a role in retention and folding of the nascent protein into its tertiary structure or in targeting of pro-MPO for processing and storage in granules. A propeptide-deleted pro-MPO mutant (MPODeltapro) was constructed to determine if deletion of the propeptide interferes with processing and targeting after transfection to the myeloid 32D cell line. Transfection of full-length cDNA for human MPO results in normal processing and targeting of MPO to cytoplasmic dense organelles. Although the efficiency of incorporation was lower for MPODeltapro, both pro-MPO and MPODeltapro showed heme incorporation indicating that the propeptide is not critical for this process. Deletion of the propeptide results in synthesis of a protein that lacks processing into mature two-chain forms but rather is degraded intracellularly or secreted. The finding of continued degradation of MPODeltapro in the presence of lysosomotrophic agents or brefeldin A rules out that the observed degradation takes place after transfer to granules. Intracellular pro-MPO has high mannose oligosaccharide side chains, whereas stored mature MPO was found to have both high mannose and complex oligosaccharide side chains as judged by only partial sensitivity to endoglycosidase H. The propeptide may normally interfere with the generation of certain complex oligosaccharide chain(s) supported by the finding of high mannose side chains in secreted pro-MPO and lack of them in MPODeltapro that contained complex oligosaccharide side chains only. In conclusion, elimination of the propeptide of pro-MPO blocks the maturation process and abolishes accumulation of the final product in granules suggesting a critical role of the propeptide for late processing of pro-MPO and targeting for storage in granules.

Development and standardization of solid phase assays for the detection of anti-neutrophil cytoplasmic antibodies (ANCA). A report on the second phase of an international cooperative study on the standardization of ANCA assays

Anti-neutrophil cytoplasmic antibodies (ANCA) are diagnostic markers for systemic vasculitis. They are classically detected by an indirect immunofluorescence test using normal donor neutrophils as substrate. This assay lacks antigenic specificity and is not quantitative. The 'EC/BCR Project for ANCA Assay Standardization' is an international collaboration study with the aim to develop and standardize solid phase assays for ANCA detection. In this part of the study the isolation and characterization of proteinase-3 and myeloperoxidase, the two main target molecules for ANCA, and the development and standardization of ELISAs with these antigens are described. Six laboratories successfully isolated purified proteinase-3 preparations that could be used. Three of these preparations, together with one myeloperoxidase preparation, were subsequently used for ANCA testing by ELISA. The ELISA technique was standardized in two rounds of testing in the 14 participating laboratories. The coefficient of variation of these new assays decreased from values of approx. 50% in the first round to approx. 20% in the second round. We conclude that purified proteinase-3 and myeloperoxidase can be used in standardized ELISAs for ANCA detection. Whether such procedures offer advantages over the IIF test will be determined in a prospective clinical study.

Granulocytic protein p25 is a DNA-binding subunit of protein M(r) = 50,000: subcellular localization, cell and species specificity

We have previously reported the presence and isolation of the novel protein M(r) = 25,000 (p25) from human granulocytes. In this study, the protein p25 was characterized by its: (a) ability to bind DNA, (b) subunit association, (c) partial protein sequencing, (d) subcellular localization, (e) cellular and species specificity and (f) stability in the presence of released granulocytic proteinases. For the detection of p25 in various extracts, fractions and types of human or animal hematopoietic cells, SDS-PAGE/Western blotting and immunohistochemical staining were used. The protein p25 was subjected to N-terminal amino acid sequence analysis. Protein p25-DNA interactions were monitored using Southwestern blotting. Selective inhibition of granulocytic proteinases was performed. Granulocytic protein p25 was found to be a product of oxidative cleavage of disulfide bridges in the p50 dimer. It was shown that neither protein p50 nor the p25 subunit is a degradation product of a protein of higher molecular weight. The N-terminal amino acid sequence of p25 was: RLNYNKPHAA. Binding capacity for double stranded DNA without significant sequence specificity was revealed and nuclear localization of some fraction of p50 dimer was established. The data concerning the cell and species specificity demonstrated that the protein is expressed only in normal human granulocytes. In summary, protein p25 originates from splitting of the p50 dimer. This subunit shows no identity with proteins already sequenced. DNA-binding of p25 is not sequence specific. It is concluded that the protein p50 is localized in the nuclei and cytoplasmic granules of mature human polymorphonuclear leukocytes or granulocytes of species high on the evolutionary tree. The functions of this protein remain to be determined.

Clinical correlates and substrate specificities of antibodies exhibiting neutrophil nuclear reactivity--a methodological study

In a serological laboratory with a routine service for determining autoantibodies to human neutrophils, antibodies giving a selective or preferential reaction with the nucleus or perinuclear area of neutrophils are not uncommon. The aim of this study was to look for clinical correlates with the presence of such neutrophil-reactive autoantibodies. The specificity of such antibodies for nuclear or cytoplasmic antigens was studied in 65 consecutive sera displaying nuclear/perinuclear reactivity at a titre of at least 80 using the indirect immunofluorescence technique (IIF) on ethanol-fixed leucocytes. The sera were also investigated by IIF on formalin-acetone fixed leucocytes and on HEp-2 cells. ELISA techniques were used to measure antibodies to azurophil granule constituents (ANCA), purified myeloperoxidase (MPO-ANCA), and lactoferrin (LF-ANCA). Furthermore a qualitative spot immunoassay was used for the detection of antibodies to alpha, beta, and gamma fractions, and the nuclear fraction of neutrophils, purified proteinase 3 (PR3), MPO, enolase, lysozyme, elastase, lactoferrin, and cathepsin G. The diagnoses linked to such GS-ANA/pANCA positivity were arthritides, vasculitides, inflammatory bowel disease and chronic hepatic conditions. MPO was the main antigen recognized in the vasculitis group, but apart from that, rather limited antigen reactivity was demonstrable by these techniques, lysozyme being the most frequently recognized autoantigen in patients with arthritides. Human lymphocytes served as a suitable control substrate when distinguishing between GS-ANA/pANCA and ANA, whereas HEp-2 cells usually could not be used if both classes of antibodies were present in a sample. Furthermore, formalin-acetone fixation is not recommended for routine use.

Circulating autoantibodies as serological markers in the differential diagnosis of pulmonary renal syndrome

OBJECTIVES

Pulmonary renal syndrome (lung haemorrhage and glomerulonephritis) is a fulminant condition that warrants a rapid diagnosis and treatment to prevent mortality and preserve renal functions. However, the patients frequently present with non-specific pulmonary symptoms in the early phase of the syndrome and the diagnosis is often missed. Recently, several autoantibodies have been described in association with various forms of glomerulonephritis. We evaluated the association as well as the diagnostic and the prognostic significance of these antibodies in pulmonary renal syndrome.

DESIGN

Retrospective clinical study.

SETTING

University Hospital.

SUBJECTS

Forty consecutive patients with biopsy verified glomerulonephritis and overt haemoptysis or pulmonary infiltrates compatible with lung haemorrhage.

INTERVENTIONS

Analysis of proteinase 3 antineutrophil cytoplasm antibodies (PR3-ANCA), myeloperoxidase (MPO)-ANCA, antiglomerular basement membrane (GBM) and anti-entactin antibodies.

RESULTS

Thirty-six (90%) patients possessed one or more autoantibodies. Twenty-seven (70%) patients had ANCA (PR3-ANCA, MPO-ANCA or both). The remaining positive patients (n = 9) had anti-GBM antibodies. Only two patients had anti-entactin antibodies, suggesting a poor association of these antibodies with PRS. The majority of patients with anti-GBM antibodies had a very poor clinical outcome (five irreversible renal failure; three deaths). On the other hand, despite no significant difference in clinical features or renal morphology from patients with anti-GBM antibodies, 19 patients (70%) with ANCA recovered completely following treatment.

CONCLUSIONS

Our study demonstrated that the presence of autoantibodies is a predominant feature of PRS and that the type of immunologic injury is of paramount importance in determining the course of illness in this syndrome. Analysis of the aforementioned antibodies can help in an early differential diagnosis and thus, in better management of PRS.

Anti-neutrophil cytoplasmic antibodies in chronic inflammatory bowel disease. Prevalence and diagnostic role

BACKGROUND

Anti-neutrophil cytoplasmic antibodies (ANCA), originally found to be associated with vasculitis, have been reported to be present in chronic inflammatory bowel disease. Most often the ANCA staining pattern is of the perinuclear type (p-ANCA), although nuclear and cytoplasmic stainings are seen. Single studies have shown some of the antibodies to react with lactoferrin or cathepsin G; however, most studies have not been able to determine a main antigenic specificity. We studied the prevalence of ANCA in sera from 155 patients with ulcerative colitis, 128 patients with Crohn's disease, and 51 patients with coeliac disease. The presence of ANCA was correlated to disease activity, extent, and age of onset of the diseases. Furthermore, we tried to characterize the antigen specificity by enzyme-linked immunosorbent assay (ELISA), using elastase, lactoferrin, myeloperoxidase, proteinase 3, and cathepsin G as antigens.

METHODS

The sera were screened for ANCA by indirect immunofluorescence. Anti-nuclear antibodies (ANA) were analysed on HEp2 cells, and ELISA for specific ANCA was performed using the antigens mentioned.

RESULTS

Most of the sera with positive immunofluorescence had the p-ANCA type of pattern. Seventy-eight of 155 (50.3%) of the patients with ulcerative colitis were ANCA-positive, compared with 31 of 128 (24.2%) of patients with Crohn's disease (p < 0.001). However, in the subgroup with Crohn's colitis, 16 of 44 (36.4%) were ANCA-positive. Only 4 of 51 patients (7.7%) with coeliac disease showed positive immunofluorescence (p < 0.001 compared with ulcerative colitis). Less than 10% of the samples were positive in the specific ELISA assays; thus other than the most well known granule proteins can be the target for ANCA in ulcerative colitis.

CONCLUSION

ANCA occur significantly more often in ulcerative colitis than in Crohn's disease. However, the prevalence of ANCA is rather high in Crohn's colitis. ANCA are thus of limited value in differentiating Crohn's colitis from ulcerative colitis. ANCA found in inflammatory bowel disease are different from those associated with vasculitis. The antigen(s) responsible remain to be determined.

Circulating granulocyte antibodies in first attacks of colitis

BACKGROUND

Antineutrophil cytoplasmic antibodies (ANCA) have recently been demonstrated in the sera of patients with inflammatory bowel disease (IBD).

METHODS

The presence of ANCA was studied in 107 sera obtained during 1 year from 48 patients with a first attack of IBD and in 33 such sera from 19 patients with infectious or infectious-type colitis (non-relapsing colitis (NRC)).

RESULTS

In 65% (31 of 48) of the IBD patients positive immunofluorescence reactivity against granulocytes was observed, compared with in 5% of the NRC patients. No significant difference in granulocyte reactivity was found either between patients with colonic Crohn's disease and those with ulcerative colitis or between active and inactive phases of the disease. Most of the sera showed a perinuclear immunofluorescence staining pattern (68%), in contrast to the classical cytoplasmic staining pattern seen in Wegener's granulomatosis. In sera obtained at the first visit from the 31 IBD patients with positive granulocyte reactivity a hitherto unknown antibody against beta-glucuronidase was found in 42%, whereas in 45% the specificity was not identified. Other antibodies, rarely seen, were directed against myeloperoxidase, lactoferrin, elastase, and cathepsin G. No antibody directed against lysozyme was detected.

CONCLUSIONS

Positive granulocyte reactivity practically excluded NRC and was seen in more than half of IBD patients. Antibodies against beta-glucuronidase were common, but still almost half of the antibodies remained unknown.

Some patients with anti-myeloperoxidase autoantibodies have a C-ANCA pattern

Rapidly progressive glomerulonephritis with or without other signs of systemic vasculitis is often accompanied by antibodies to myeloperoxidase. Such antibodies normally produce a perinuclear pattern on ethanol-fixed neutrophils (perinuclear anti-neutrophil cytoplasm antibodies (P-ANCA)) at indirect immunofluorescence. We report here sera from three patients that are anti-myeloperoxidase-positive in ELISA that instead produce a cytoplasmic pattern (classical anti-neutrophil cytoplasmic antibodies (C-ANCA)), a pattern normally seen in conjunction with antibodies to proteinase 3. These sera did not react with proteinase 3. For two of the sera the specificity of the anti-myeloperoxidase reaction was confirmed with inhibition-ELISA experiments and with immunoblotting. A mouse anti-myeloperoxidase MoAb that produces a cytoplasmic pattern is also described. Competition ELISA experiments show that this antibody and anti-myeloperoxidase sera with cytoplasmic pattern recognize epitopes that are separate from epitopes recognized by another perinuclear pattern producing anti-myeloperoxidase MoAb. 'Cytoplasmic pattern' epitopes as well as 'perinuclear pattern' epitopes can be found on all three major myeloperoxidase isoforms, after separation by ion exchange chromatography. Affinity chromatography, using the cytoplasmic pattern producing anti-myeloperoxidase monoclonal antibody, shows that the epitope recognized by this MoAb is present on all myeloperoxidase molecules. This epitope is not confined to any special subpopulation. These findings indicate that all myeloperoxidase do not relocate after ethanol fixation, and that C-ANCA and P-ANCA epitopes exist simultaneously on the same myeloperoxidase molecule. We propose that the two immunofluorescence patterns arise due to different availabilities of the epitopes in the microenvironment where myeloperoxidase is present.

The development of an assay for human neutrophil lipocalin (HNL)--to be used as a specific marker of neutrophil activity in vivo and vitro

Human neutrophil lipocalin (HNL) is a newly discovered protein from human neutrophil secretory granules. A double-antibody radioimmunoassay (RIA) was developed for the measurement of HNL in various body fluids and its high specificity was confirmed by the absence of cross-reaction with other granulocyte granule proteins. The RIA measures HNL within the range of 4-256 micrograms/l. The intra- and interassay coefficients of variation were less than 6% and 10%, respectively. When HNL was added to serum samples full recovery was obtained. Sera and plasma from 100 apparently healthy individuals revealed a mean level of 78.40 micrograms/l (range 37.95-190.87 micrograms/l) in serum and a mean level of 50.65 micrograms/l (range 30.51-105.8 micrograms/l) in EDTA-plasma. The distribution of HNL after gel filtration indicated that HNL exists mainly in two major forms, dimer and monomer. This, in addition to the excellent recovery, suggests that these major forms of HNL do not bind to compounds in serum or plasma that would interfere with the assay. The high specificity, sensitivity, reproducibility and accuracy of the present assay should facilitate the measurement of HNL in blood and other body fluids.

A rapid and semi-quantitative method for the detection of autoantibodies by multiple spot immunoassay

A method for rapid simultaneous determination of multiple autoantibodies in sera has been developed. 42 different antigens were coated onto a nitrocellulose membrane in a miniblotter apparatus with 42 lanes. The membrane was also coated with different concentrations of human IgG to create a standard curve. The blotting apparatus after coating, blocking and washing was turned 90 degrees so that all lanes crossed the antigen coated lanes. Thereafter, 42 sera were incubated with the antigens. After this stage the membrane was treated as in the usual dot-blot procedure. After incubation with alkaline phosphatase labelled anti-human IgG, staining and drying of the membrane, the staining intensity of individual lanes was scanned into a data file and analyzed by computer. By this method it was possible in 4 h to examine 42 sera for autoantibodies against 42 antigens, i.e., more than 1600 tests. Furthermore, the amount of antibody could be semi-quantified, using the IgG standards. The method should be useful for rapid screening of autoantibodies in a routine laboratory.

Interaction of myeloperoxidase and elastase enzyme activity with the antihypertensive agents hydralazine and dihydralazine

Autoantibodies directed against myeloperoxidase and elastase have been found in patients developing hydralazine-induced lupus and hydralazine-induced isolated glomerulonephritis. The aim of this study was to investigate influence of hydralazine and dihydralazine upon myeloperoxidase and elastase enzyme activity. Using a 4-aminoantipyrin in vitro system, dihydralazine was 2.5 times as potent in inhibiting myeloperoxidase activity as compared to hydralazine. The corresponding Ki-values were 4 microns M for dihydralazine and 25 microM for hydralazine. When using 2.2'-azino-bis-3-ethyl-benzothiazoline-6-sulphonic acid system inhibition was found at lower concentrations. Furthermore, the difference between the compounds was not so pronounced as seen for 4-aminoantipyrin. The Ki-values for hydralazine and dihydralazine were 1.2 and 1.4 microM respectively. Complete inhibition was seen for both compounds at concentrations above 7.5 microM. Hydralazine binds to elastase, but neither hydralazine nor dihydralazine inhibited elastase enzyme activity.

The value of indirect immunofluorescence and solid phase techniques for ANCA detection. A report on the first phase of an international cooperative study on the standardization of ANCA assays. EEC/BCR Group for ANCA Assay Standardization

This study describes the results of phase I of an international effort to develop and standardize assays for the detection of anti-neutrophil cytoplasmic antibodies (ANCA). 12 sera, four of which were selected for their potential to cause problems in the detection of various ANCA specificities, were analyzed in the standard indirect immunofluorescence (IIF) test and in ELISAs for ANCA routinely performed in the seven participating laboratories. The IIF methodology differed with respect to the dilution of the serum being screened and the concentration of the conjugate used. Results from sera with high ANCA titers were similar, although the quantitative values could not be compared. In sera containing rheumatoid factor and anti-nuclear antibodies (ANA), ANCA-unrelated staining patterns were observed. Six antigen preparations were used in ELISA for the detection of cANCA. In ELISA with purified proteinase-3 all three cANCA sera were positive, but not anti-myeloperoxidase (MPO) or anti-lactoferrin (LF) positive sera. The other assays were less sensitive or gave inconsistent results. Various preparations of purified MPO and LF used in ELISA were readily recognized by anti-MPO and anti-LF positive sera. From this study it can be concluded that the IIF test, although performed with different methods, shows comparable results using strongly positive sera. In general solid phase assays for cANCA detection are not well standardized and need improvement although the purified proteinase-3 ELISA is possibly an exception. MPO and LF can be used in ELISA procedures for the detection of pANCA-related antibodies.

Interaction between myeloperoxidase and antibodies against myeloperoxidase measured by chemiluminescence

We investigated interaction between antibodies directed against myeloperoxidase (anti-MPO) and myeloperoxidase (MPO) with chemiluminescence. Whole serum diluted 1/10 containing circulating anti-MPO antibodies as well as serum from normal blood donors inhibited myeloperoxidase (MPO) enzyme activity when incubated with 1.42 micrograms MPO. When further diluted the inhibitory effect was abolished. Incubation with purified human IgG fraction of anti-MPO, did not cause any inhibition when diluted 1/10 and incubated with 1.42 micrograms MPO. When adding MPO to normal sera a rapid increase of the enzyme activity was seen above 5 micrograms, and the inhibitory effect was completely abolished when 10 micrograms was added. Both sera from healthy individuals, as well as sera from patients with circulating anti-MPO inhibited MPO activity. The inability of pure IgG fractions from anti-MPO sera to inhibit MPO enzyme activity, clearly indicates the presence of an inhibitory factor, unspecific or specific, in serum.

Anti-neutrophil cytoplasm antibodies, anti-GBM antibodies and anti-dsDNA antibodies in glomerulonephritis

The diagnostic potential of assays detecting anti-neutrophil cytoplasm antibodies (ANCA), anti-GBM antibodies and anti-dsDNA antibodies was evaluated by examining sera from time of admission in a consecutive series of 455 patients with biopsy verified primary or secondary glomerulonephritis (GN). ANCA were classified into c- and p-ANCA by indirect immunofluorescence (IIF) and ELISAs using alfa-granule extract, proteinase-3, myeloperoxidase (MPO), elastase and lactoferrin. C-ANCA was virtually confined to 64 patients with systemic small vessel vasculitis, 66-74% being c-ANCA positive. P-ANCA against MPO, seen in 47 patients, segregated through many diagnostic categories of primary and secondary severe GN. ANCA against lactoferrin and elastase were rare. Anti-dsDNA positive patients constituted 57% of the 44 ANA-positive patients with systemic lupus erythematosus. It is concluded that the IIF and ELISAs for anti-proteinase-3, anti-MPO, anti-dsDNA and anti-GBM have an acceptable performance and are useful in the primary diagnostic work-up of patients suspected for secondary GN as the majority of such patients will be classified by these assays.

Self-labeling of human polymorphonuclear leucocyte myeloperoxidase with 125iodine

In order to obtain a radioimmunoassay (RIA) technique for the measurement of human plasma myeloperoxidase (MPO), we purified the enzyme from polymorphonuclear granulocytes (neutrophils), and compared three methods of labeling it with 125Iodine:chloramine T, lactoperoxidase, and an original technique of 'self labeling' based on the ability of the enzyme to oxidize and bind 125I in the presence of H2O2. The chloramine T technique produced a degraded protein, as well shown by a high non-specific binding of tracer to antibody. The lactoperoxidase technique did not succeed in labeling MPO with an adequate specific activity. In contrast, the self-labeling method gave a stable tracer with a specific activity of 23 microCi/micrograms MPO (85 MBq), a satisfactory level of immunoreactivity, and a low-specific binding (less than or equal to 3%). After labeling, purification of tracer was achieved by gel filtration chromatography in phosphate buffer (0.05 M; pH7) to which 0.1% poly-L-lysine was added. The labeled molecule remained stable for 40 days and could be used for RIA with a polyclonal antibody raised in rabbits.

Structural and biological properties of human recombinant myeloperoxidase produced by Chinese hamster ovary cell lines

The cDNA encoding human myeloperoxidase carries three ATG codons in frame; 144, 111 and 66 bp upstream from the proprotein DNA sequence. In order to determine the most efficient signal sequence, three cDNA modules starting at each of the ATG were cloned into an eucaryotic expression vector and stably expressed in Chinese hamster ovary cell lines. In all three cases, recombinant human myeloperoxidase (recMPO) was secreted into the culture medium of transfected cells, indicating that each of the signal peptides functions efficiently. One of the recombinant cell lines, which was amplified using methotrexate, overexpresses enzymatically active recMPO up to 6 micrograms.ml-1.day-1. The recombinant product was purified by a combination of ion-exchange and metal-chelate chromatography, and characterized in terms of molecular mass, amino-terminal amino acid analysis, glycosylation, physicochemical properties and biological activity. The data show that recMPO is secreted essentially as a monomeric, heme-containing, single-chain precursor of 84 kDa which exhibits peroxidase activity. Amino-terminal analysis indicated that cleavage of the signal peptide occurs between amino acids 48 and 49. In addition, recMPO appeared to be glycosylated up to the last stage of sialylation, to an extent similar to that of the natural enzyme. Specific activity measurements as well as stability data, in various pH, temperature, ionic strength and reducing conditions, indicated that the recombinant single-chain enzyme behaves essentially in the same way as the natural two-chain molecule. Finally, recMPO was shown to exert potent cytotoxicity towards Escherichia coli when provided with its physiological substrates, i.e. hydrogen peroxide and chloride ions.

Antibodies to neutrophil granulocyte myeloperoxidase and elastase: autoimmune responses in glomerulonephritis due to hydralazine treatment

Autoantibodies against myeloperoxidase and elastase were found in a study of nine patients who had developed glomerulonephritis after treatment with hydralazine, but not in patients who were treated with hydralazine without side-effects. Circulating IgM isotype antibodies against myeloperoxidase, and IgM and IgG anti-elastase, were mainly present during the initial months after withdrawal of the drug. By contrast, IgG isotype antibodies against myeloperoxidase, initially found in seven patients, had increased in concentration and were present in all patients at follow-up after 4-12 years.

Autoantibodies against neutrophil cytoplasm components in systemic lupus erythematosus and in hydralazine-induced lupus

Anti-neutrophil cytoplasm antibody (ANCA) has been shown to be no marker of systemic lupus erythematosus (SLE) including lupus nephritis or of progressive systemic sclerosis (PSS). Antibodies against myeloperoxidase (anti-MPO) and elastase, two granulocyte lysosomal enzymes, were found in patients with SLE but not in those with PSS, except for one patient who had anti-MPO. Anti-MPO was present in 21% of patients with SLE, and at low concentrations in about 80% of these cases. Anti-elastase was found in four patients with SLE. In another group of six patients with a SLE-like syndrome induced by anti-hypertensive treatment with the anti-hypertensive hydralazine, anti-MPO antibodies occurred in all six, and anti-elastase antibodies in five. Monitored during a 2-year follow-up period, anti-MPO antibodies were found to persist, whereas anti-elastase antibodies were rapidly eliminated, after withdrawal of the drug.

Myeloperoxidase oxidation states involved in myeloperoxidase-oxidase oxidation of thiols

The changes in the oxidation state of the leucocyte enzyme myeloperoxidase, induced by buffer and thiols, were studied with visible-light-absorption spectroscopy. It was concluded that phosphate buffer contains small amounts of H2O2 and that thiols, when added to buffer, induce the generation of minute amounts of superoxide radical anion. These minute amounts of reduced oxygen species are suggested to account for the initiation of myeloperoxidase-oxidase oxidation of thiols. Myeloperoxidase was found to be in its Compound III oxidation state during myeloperoxidase-oxidase oxidation of thiols. However, myeloperoxidase-mediated oxidation of thiols with concomitant O2 consumption can also occur with myeloperoxidase in its Compound II oxidation state. These studies indicate that the ferro and Compound III oxidation states may not be essential intermediates in myeloperoxidase-oxidase oxidation of thiols, but rather that the formation of the Compound III oxidation state retards the reaction.

Membrane peroxidases

It is well known that the partial reduction of oxygen can result in the formation of highly reactive oxygen products. Hydrogen peroxide is one of these metabolites of oxygen. Peroxidases utilize this metabolite for a variety of functions. It is the purpose of this treatise to review the nature and function of various membrane peroxidases in the body.

Synergistic cytolysis mediated by hydrogen peroxide combined with peptide defensins

Possible cytolytic interactions between hydrogen peroxide (H2O2) and neutrophil granule proteins were studied. Preliminary experiments demonstrated synergistic cytolysis when erythro-leukemia targets were exposed to H2O2 combined with a low molecular weight (approximately 3900) granule extract that was predominantly composed of peptide defensins. The synergistic interaction was confirmed when sublytic concentrations of H2O2 were combined with defensin preparations that had been purified to homogeneity. Synergy was concentration dependent in regard to both molecules and could not be explained by trace contamination of defensin preparations with myeloperoxidase. Sequential addition experiments suggested that synergistic lysis required a simultaneous exposure to both cytotoxins. In the presence of sublytic concentrations of H2O2, the binding of iodinated defensin to targets was significantly increased, providing a possible explanation for the observed synergy. Since both molecules are concurrently secreted by activated neutrophils, this interaction may be important during leukocyte-mediated anti-tumor effects or inflammatory tissue injury.

Purification and characterization of eosinophil cationic protein from normal human eosinophils

ECP (eosinophil cationic protein) was purified in high yield from the granules of human buffy coat eosinophils obtained from healthy individuals. The separation procedure included gel filtration on Sephadex G-75, ion-exchange chromatography on Bio Rex 70, and chelating chromatography on zinc-chelate Sepharose 6B. The normal ECP is a single-chain, highly cationic glycoprotein which separates on SDS-polyacrylamide gel electrophoresis into at least 3 molecular weight forms, with molecular weights of 18.5, 20 and 22 kDa. A heterogeneity in charge was also observed, with the 18.5 kDa form being the most cationic one. The various molecular species of ECP exhibited antigenic identity, identical amino acid compositions, and identical amino-terminal amino acid sequences. The molecular heterogeneity was shown to be caused by differences in glycosylation of the protein.

Biosynthesis and processing of myeloperoxidase--a marker for myeloid cell differentiation

Myeloperoxidase (MPO), a heme protein, is a major component of azurophilic granules of neutrophils. Optimal oxygen-dependent microbicidal activity depends on MPO as the critical enzyme for the generation of hypochlorous acid and other toxic oxygen products. MPO is synthesized during the promyelocytic stage of myeloid differentiation, the stage at which azurophilic granules are formed. Like other lysosomal enzymes, MPO is synthesized as a larger precursor which is subsequently processed and transported intracellularly to the lysosomes. The primary translation product is a single 80-kDa protein which undergoes cotranslational N-linked glycosylation to produce a 92-kDa glycoprotein. Glucosidases in the endoplasmic reticulum or early cis Golgi convert the proMPO to a 90-kDa form which is sorted into a prelysosomal compartment that undergoes final proteolytic maturation to native MPO, a pair of heavy-light protomers with subunits of 60 kDa and a 12 kDa. These events contrast with similar processes seen with other lysosomal enzymes in two ways. First, alkalinization of lysosomes with NH4+ does not alter processing or transport, in contrast to the pH dependence of these processes for other lysosomal enzymes. However, some studies indicate retardation of processing in the presence of the proton ionophore monensin. Second, intracellular transport of MPO is not apparently mediated by the mannose-6-phosphate receptor system. The gene for MPO is on the long arm of chromosome 17 (17q22, 23) near the breakpoint of the 15, 17 translocation of acute promyelocytic leukemia. The gene spans approximately 14 kb and contains 11 irons and 12 exons. The cloned full-length cDNA is approximately 2.2 kb and both normal bone marrow and cultured promyelocytic leukemia cells express two species of mRNA. Inherited MPO deficiency, a relatively common disorder, is associated with the absence of mature MPO but the presence of proMPO, consistent with a post-translational defect. Studies at the molecular level aimed at identifying the underlying genetic defect are thus far consistent with that hypothesis. In addition, the basis for the observed association between acquired MPO deficiency and some myeloid leukemias can now be studied at the molecular level using these probes.

Myeloperoxidase-oxidase oxidation of cysteamine

Cysteamine oxidation was shown to be catalysed by nanomolar concentrations of myeloperoxidase in a peroxidase-oxidase reaction, i.e. an O2-consuming oxidation of a compound catalysed by peroxidase without H2O2 addition. When auto-oxidation of the thiol was prevented by the metal-ion chelator diethylenetriaminepenta-acetic acid, native, but not heat-inactivated, myeloperoxidase induced changes in the u.v.-light-absorption spectrum of cysteamine. These changes were consistent with disulphide (cystamine) formation. Concomitantly, O2 was consumed and superoxide radical anion formation could be detected by Nitro Blue Tetrazolium reduction. Both superoxide dismutase and catalase inhibited the reaction, whereas the hydroxyl-radical scavengers mannitol and ethanol did not. O2 consumption increased with increasing pH (between pH 6.0 and 8.0), and 50% inhibition was exhibited by about 3 mM-NaCl at pH 7.0 and by about 100 mM-NaCl at pH 8.0. Cysteamine was about 5 times as active (in terms of increased O2 consumption at pH 7.5) as the previously reported peroxidase-oxidase substrates NADPH, dihydroxyfumaric acid and indol-3-ylacetic acid. A possible reaction pathway for the myeloperoxidase-oxidase oxidation of cysteamine is discussed. These results indicate that cysteamine is a very useful substrate for studies on myeloperoxidase-oxidase activity.

Peroxidase and peroxidase-oxidase activities of isolated human myeloperoxidases

Isolated neutrophils from healthy donors were used for the isolation of four highly purified forms of myeloperoxidase as determined by spectral (A430/A280 ratio 0.80-0.87) and enzyme-activity measurements. Although the myeloperoxidases exhibited different elution profiles on cation-exchange chromatography, gel filtration indicated similar relative molecular masses. When these forms were assayed for peroxidase and peroxidase-oxidase activities with several substrates, they all exhibited virtually the same specific activities. These results suggest that possible functional differences between the enzymes may be related to differences in their sites of action rather than to differences in enzyme activity. Myeloperoxidase from a patient with chronic myeloid leukaemia also revealed a similar heterogeneity on cation-exchange chromatography. However, this myeloperoxidase contained in addition one form with a lower and one form with a higher relative molecular mass, as indicated by gel-filtration chromatography.

Characterization of cDNA clones for human myeloperoxidase: predicted amino acid sequence and evidence for multiple mRNA species

Myeloperoxidase is a component of the microbicidal network of polymorphonuclear leukocytes. The enzyme is a tetramer consisting of two heavy and two light subunits. A large proportion of humans demonstrate genetic deficiencies in the production of myeloperoxidase. As a first step in analyzing these deficiencies in more detail, we have isolated cDNA clones for myeloperoxidase from an expression library of the HL-60 human promyelocytic leukemia cell line. Two overlapping plasmids (pMP02 and pMP062) were identified as myeloperoxidase cDNA clones based on the detection with myeloperoxidase antiserum of 70 kDa protein expressed in pMP02-containing bacteria and a 75 kDa polypeptide produced by hybridization selection and translation using pMP062 and HL-60 RNA. Formal identification of the clones was made by matching the predicted amino acid sequences with the amino terminal sequences of the heavy and light subunits. Both subunits are encoded by one mRNA in the following order: pre-pro-sequences--light subunit--heavy subunit. The molecular weight of the predicted primary translation product is 83.7 kDa. Northern blots reveal two size classes of hybridizing RNAs (approximately 3.0-3.3 and 3.5-4.0 kilobases) whose expression is restricted to cells of the granulocytic lineage and parallels the changes in enzymatic activity observed during differentiation.

Molecular forms of myeloperoxidase in human plasma

A radioimmunoassay for myeloperoxidase was established with the use of affinity-purified anti-(human myeloperoxidase) immunoglobulins. By the use of ion-exchange followed by immunoaffinity chromatography a preparation of immunoreactive, catalytically active myeloperoxidase was obtained from fresh human plasma. In non-denaturing gel electrophoresis, the plasma preparation showed about four catalytically active components of mobility very similar to that of the granulocyte enzyme. SDS/polyacrylamide-gel electrophoresis combined with protein blotting showed that the two polypeptides of strongest antigenicity in the plasma preparation corresponded in Mr to the large and the small subunits of the granulocyte enzyme. In addition, the plasma preparation contained a higher-Mr immunoreactive polypeptide, possibly a precursor form of the enzyme, together with another of Mr similar to that of the large subunit of eosinophil peroxidase.

Evidence for and partial characterization of three major and three minor chromatographic forms of human neutrophil myeloperoxidase

Myeloperoxidase (MPO) is an enzyme found in the azurophil granules of neutrophils. Cation-exchange chromatography on carboxymethyl-cellulose previously has been used to demonstrate the heterogeneity of the peroxidase enzymes isolated from human neutrophils. In this study, fast protein liquid chromatography (FPLC) was used to separate and purify three major (I, II, and III) and three minor (IIa, IIIa, IIIb) forms of MPO from isolated neutrophil granules. Purity was confirmed by polyacrylamide gel electrophoresis in the presence of cetyltrimethylammonium bromide (CETAB-PAGE), by crossed immunoelectrophoresis, and by spectral characteristics. All three major forms were indistinguishable by immunodiffusion against rabbit antiserum, scanning spectrophotometry, and amino acid composition. They differed in their elution from a cation-exchange resin, inhibition by 3-amino-1,2,4-triazole, migration rate in CETAB-PAGE, and subunit molecular weight. Subunit molecular weight was examined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). All three major forms appeared to consist of heavy (H), intermediate (M), and light (L) peptides. The M peptide appeared to be derived from the H subunit. All L subunits exhibited a molecular weight of 14,500. The molecular weights for the H subunits varied, and were 60,000, 59,000, and 57,000 for MPO I, II, and III, respectively. The molecular weights for the M peptides were 44,100, 43,000, and 42,000 for MPO I, II, and III, respectively. The treatment of neutrophils, granules, and extracts with protease inhibitors and sodium azide did not block the appearance of three major forms of MPO. Thus, neither protease activity nor MPO autooxidation during extraction and purification procedures is responsible for the appearance of multiple chromatographic forms of MPO derived from human neutrophils.

Biosynthesis, transport and processing of myeloperoxidase in the human leukaemic promyelocytic cell line HL-60 and normal marrow cells

The processing and intracellular transport of myeloperoxidase were studied in the human promyelocytic leukaemia cell line HL-60 and in normal marrow cells labelled with [35S]methionine or [14C]leucine. Myeloperoxidase was precipitated with antimyeloperoxidase serum; the immunoprecipitates were subjected to sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and radiolabelled myeloperoxidase visualized by fluorography. During a 1 h pulse, myeloperoxidase was labelled in a chain of apparent Mr 90 000. With a subsequent chase, the Mr 90 000 polypeptide disappeared and was replaced by chains of Mr 62 000 and 12 400 corresponding roughly to the size of neutrophil myeloperoxidase subunits. The identification of the radioactive polypeptides as different forms of myeloperoxidase was established also by the similarity in patterns generated by partial proteolysis with V8 proteinase from Staphylococcus aureus. Processing of myeloperoxidase in HL-60 was slow; mature polypeptides were significantly increased only after 6 h. Another myeloperoxidase chain of apparent Mr 82 000 was an intermediate precursor or degradation form. Pulse-chase experiments in combination with sucrose-density-gradient separations of homogenates showed that the Mr 90 000 precursor was located in light density organelles only and not in granule fractions, whereas the Mr 82 000 precursor was located only in intermediate density organelles, suggesting that the latter is a product of the former. Processed mature myeloperoxidase was concentrated in the granule fraction, but some occurred in lower density organelles, which may indicate processing during intracellular transport. Only the Mr 90 000 polypeptide was secreted into the culture medium; this was also the only form found in the cytosol fraction.

Studies on the subunits of human myeloperoxidase

The subunit composition of human myeloperoxidase was studied with the use of sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and gel filtration. The subunit pattern observed depended on the manner in which the enzyme was treated before analysis. Reduction before heat treatment in detergent led to two main protein species (Mr 57 000 and 10 500), whereas reduction during or after heat treatment yielded an additional species of Mr 39 000. Heating without any reductive pretreatment yielded the 39 000-Mr form as the major electrophoretic species. Carbohydrate staining showed large amounts of sugar on the 57 000-Mr species and little on the 10 500-Mr form. Significant amounts of haem were associated with this latter subunit. Haem also seemed to be associated with the 57 000-Mr form but not with the 39 000-Mr one. These three subunit forms were isolated and their amino acid composition analysed. The 57 000-Mr and 39 000-Mr forms had very similar amino acid composition and yielded an apparently identical collection of fragments on incubation with CNBr. Once separated, the subunits could not be interconverted. Generally, minor amounts of other molecular-mass forms were observed. The nature of the various molecular-mass forms originating from myeloperoxidase is discussed.