Distribution of the granulocyte serine proteinases proteinase 3 and elastase in human glomerulonephritis

Immune complexome analysis reveals the presence of immune complexes and identifies disease-specific immune complex antigens in saliva samples from patients with Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease that mainly damages the salivary and lacrimal glands. Immune complex (IC) formation triggers local inflammation through IC deposition and decreased antigen function. Some ICs can leak from the lesion and into the saliva, but no salivary ICs have been reported to date. We used immune complexome analysis to comprehensively identify antigens incorporated into IC (IC-antigens) in saliva samples from patients with SS (n = 9) or with xerostomia (n = 7). Neutrophil defensin 1 (67%), small proline-rich protein 2D (67%), myeloperoxidase (44%), neutrophil elastase (44%), cathepsin G (33%), nuclear mitotic apparatus 1 (33%) and phosphatidylinositol 4-phosphate 3-kinase C2 domain-containing subunit gamma (33%) were identified as new IC-antigens specifically and frequently detected in the saliva of SS patients. Of these, neutrophil defensin 1, myeloperoxidase, neutrophil elastase and cathepsin G are neutrophil intracellular proteins, which suggests that repeated destruction of neutrophils due to abnormal autoimmunity may be involved in the pathogenesis of SS. We also analyzed serum samples from three SS patients. There was little overlap of IC-antigens between two of the samples (fewer than 30% of the IC-antigens in the saliva samples), suggesting that many ICs are formed locally and independently of the circulation. In addition, we found that four SS-specific salivary antigens show sequence homology with several proteins of oral microbiomes but no antigen has homology with Epstein-Barr virus proteins. The homology between some IC-antigens and oral microbiome proteins may indicate the impact of oral infection on local autoimmunity through molecular mimicry theory.

THEORY OF MECHANICAL IMMUNOLOGY

Numerous autoimmune illnesses are not only caused by defects of the immune system but may also be caused by defects in anatomical barriers. Morphologically, most of these barriers consist of basal membranes combined with epithelial cells or, more precisely, their cell membranes. In many organs, these barriers are associated with specialized, phagocytizing cells (e.g. histiocytes, macrophages, microglial cells A and B cells in joints). A collapse of these anatomical barriers caused either by mechanical effects (invasion by micro-organisms) or destructive tumor growth, leads to contact between macrophages and the CD4 lymphocytes, with protein structures of the cell interior. In principle, many intracellular structures should be able to function, on this basis, as potential antigens via MHC II. Contact between intracellular structures and the immune system first leads to a restricted local immune reaction and then to local autoantibody production. In order that a systemic immune reaction can take place, the contact between macrophages, CD4 cells and intracellular structures must occur over a long period and with high intensity. As a desirable, remote target, new clinical therapeutic strategies can be developed from this theory, for example, for patients with cell damage. Examples of such illnesses are, amongst others, cardiac infarcts and strokes as well as accident traumas. An immunosuppressive therapy should reduce the immune reply in all the patients mentioned and thus reduce the volume of the cell damage, giving the patient an advantage.

Mechanistic connection between inflammation and fibrosis

Fibrosis of the kidney is caused by the prolonged injury and deregulation of normal wound healing and repair processes, and by an excess deposition of extracellular matrices. Despite intensive research, our current understanding of the precise mechanism of fibrosis is limited. There is a connection between fibrotic events involving inflammatory and non-inflammatory glomerulonephritis, inflammatory cell infiltration, and podocyte loss. The current review will discuss the inflammatory response after renal injury that leads to fibrosis in relation to non-inflammatory mechanisms.

Identification and validation of urinary biomarkers for differential diagnosis and evaluation of therapeutic intervention in anti-neutrophil cytoplasmic antibody-associated vasculitis

Renal activity and smoldering disease is difficult to assess in anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) because of renal scarring. Even repeated biopsies suffer from sampling errors in this focal disease especially in patients with chronic renal insufficiency. We applied capillary electrophoresis coupled to mass spectrometry toward urine samples from patients with active renal AAV to identify and validate urinary biomarkers that enable differential diagnosis of disease and assessment of disease activity. The data were compared with healthy individuals, patients with other renal and non-renal diseases, and patients with AAV in remission. 113 potential biomarkers were identified that differed significantly between active renal AAV and healthy individuals and patients with other chronic renal diseases. Of these, 58 could be sequenced. Sensitivity and specificity of models based on 18 sequenced biomarkers were validated using blinded urine samples of 40 patients with different renal diseases. Discrimination of AAV from other renal diseases in blinded samples was possible with 90% sensitivity and 86.7-90% specificity depending on the model. 10 patients with active AAV were followed for 6 months after initiation of treatment. Immunosuppressive therapy led to a change of the proteome toward "remission." 47 biomarkers could be sequenced that underwent significant changes during therapy together with regression of clinical symptoms, normalization of C-reactive protein, and improvement of renal function. Proteomics analysis with capillary electrophoresis-MS represents a promising tool for fast identification of patients with active AAV, indication of renal relapses, and monitoring for ongoing active renal disease and remission without renal biopsy.

Elastase deposits in the kidney and urinary elastase excretion in patients with glomerulonephritis--evidence for neutrophil involvement in renal injury

OBJECTIVE

Elastase is a key proteolytic enzyme released during polymorphonuclear leukocyte degranulation. There are abundant data of elastase involvement in the development of injury in experimental models of glomerulonephritis (GN), but scant direct evidence of its involvement in human primary GN. The aims of this study were to determine the immunolocalization of elastase deposits in kidney biopsy specimens from patients with primary idiopathic GN, to attempt to correlate the distribution and intensity of deposits with urinary elastase excretion, and to determine clinical markers of renal injury in several types of primary idiopathic GN.

MATERIAL AND METHODS

The immunohistochemical localization and intensity of elastase deposits in kidney biopsies, the urinary excretion of leukocyte elastase, and proteinuria and serum creatinine levels were evaluated in 23 patients with primary GN and the associations between these factors were sought.

RESULTS

Patients with crescentic proliferative GN had the highest intensity of elastase deposits. In this group of patients, elastase was present in the glomerular endothelium, as well as in the tubular epithelium and interstitium. Patients with a high intensity of elastase deposits within the glomerular endothelium and Bowman's capsule had significantly higher urinary excretion of elastase. Patients with interstitial, mesangial and perivascular elastase deposits had significantly higher serum creatinine than those without. Patients with elastase deposits in the glomerular endothelium and in the interstitium had insignificantly higher proteinuria than those without.

CONCLUSION

Our data provide morphological evidence of leukocyte elastase involvement in renal injury occurring in the course of primary idiopathic GN, in particular in the proliferative types.

Wegener autoantigen induces maturation of dendritic cells and licenses them for Th1 priming via the protease-activated receptor-2 pathway

Autoantibodies to proteinase 3 (PR3) are involved in the pathogenesis of autoimmune-mediated vasculitis in Wegener granulomatosis (WG). To address the question how the autoantigen PR3 becomes a target of adaptive immunity, we investigated the effect of PR3 on immature dendritic cells (iDCs) in patients with WG, healthy blood donors, and patients with Crohn disease (CD), another granulomatous disease. PR3 induces phenotypic and functional maturation of a fraction of blood monocyte-derived iDCs. PR3-treated DCs express high levels of CD83, a DC-restricted marker of maturation, CD80 and CD86, and HLA-DR. Furthermore, the DCs become fully competent antigen-presenting cells and can induce stimulation of PR3-specific CD4+ T cells, which produce IFN-γ. PR3-maturated DCs derived from WG patients induce a higher IFN-γ response of PR3-specific CD4+ T cells compared with patients with CD and healthy controls. The maturation of DCs mediated through PR3 was inhibited by a serine protease inhibitor, by antibodies directed against the protease-activated receptor-2 (PAR-2), and by inhibition of phospholipase C, suggesting that the interactions of PR3 with PAR-2 are involved in the induction of DC maturation. Wegener autoantigen interacts with a “gateway” receptor (PAR-2) on iDCs in vitro triggering their maturation and licenses them for a T helper 1 (Th1)–type response potentially favoring granuloma formation in WG.

Proinflammatory Cytokines Induce Proteinase 3 as Membrane-Bound and Secretory Forms in Human Oral Epithelial Cells and Antibodies to Proteinase 3 Activate the Cells through Protease-Activated Receptor-2

Anti-neutrophil cytoplasmic Abs targeting proteinase 3 (PR3) have been detected in relation to a wide range of inflammatory conditions such as periodontitis, and interaction of anti-PR3 Abs with endothelial and epithelial cells provokes cell activation, although the underlying mechanism has been unclear. The present study showed that human oral epithelial cells expressed PR3 mRNA after treatment with proinflammatory cytokines such as IL-1alpha, TNF-alpha, IFN-alpha, IFN-beta, and IFN-gamma. A 29-kDa PR3 was expressed on the cell surface and released into culture supernatants by the cells upon stimulation with these cytokines. The membrane and supernatant fractions of oral epithelial cells exhibited enzymatic activity, which was inhibited by serine proteinase inhibitors, but not by a cysteine proteinase inhibitor or secretory leukocyte protease inhibitor. Addition of anti-PR3 Abs to cytokine-primed oral epithelial cells in culture induced remarkable secretion of IL-8 and monocyte chemoattractant protein 1 and aggregation of PR3 on the cells. RNA interference targeted to protease-activated receptor-2 mRNA and intracellular Ca2+ mobilization assays revealed that anti-PR3 Abs activated the epithelial cells through protease-activated receptor-2, a family of G protein-coupled receptors. The anti-PR3 Ab-mediated cell activation was completely abolished by RNA interference targeted to PR3 mRNA and by inhibition of phospholipase C and NF-kappaB. Immunohistochemistry showed that inflamed oral epithelium actually expresses PR3 protein. These results suggest that oral epithelial cells express functional PR3 in the inflamed sites and respond to anti-PR3 Abs detected in diseased sera, and that these mechanisms may actively participate in the inflammatory process, including periodontitis.

Mechanical immunology: every mechanical crushing of a cell in living organisms results in an immunological reaction

Throughout a living organism, the cells are constantly exposed to mechanical stresses. Because of these stresses, cells are continually broken down into various organs and structures. Thus, internal components of the cell that do not appear in the serum or extracellular space under stress-free conditions are released. These components, according to the ideas described here, can lead to an immune reaction and a subsequent inflammatory reaction. For these reasons the organism attempts to prevent the destruction of cells and employs a variety of mechanisms to try and achieve this aim. Apoptosis, i.e. suicide by the damaged cell, is one such mechanism as is the work of phagocytes that appear in the most varied organs. Further protection for the cell consists in the separation of the spaces in which the destruction of cells takes place by means of membranes and basal membranes. A further conclusion, which follows from this concept, is the separation of the CD4 and CD8 T-cell receptor spectra. Whereas CD4 T receptors recognise extracellular antigens the CD8 T-cell receptors recognise intracellular antigens. Conversely, the body's own extracellular structures do not lead to a reaction via the CD4 cells, the corresponding T-cell populations are eliminated and the body's own intracytoplasmic structures do not lead to a reaction via the CD8 cells. Each of the reverse combinations between structures and cell populations should lead, however, to an immune system reaction.

Pathogenesis of diseases associated with antineutrophil cytoplasm autoantibodies

Little is known about the etiologies of diseases associated with circulating antineutrophil cytoplasm autoantibodies (ANCA), such as primary vasculitides and inflammatory bowel diseases. However, the understanding of immune mechanisms supposedly involved in the pathogenesis of these diseases is still growing. In the present review, we first focus on the mechanisms triggering the development of ANCA, including the potential role of microbial superantigens and the possible defect(s) in the progression of apoptosis or in the removal of apoptotic cells. We next concentrate on the contribution of ANCA to the clinical symptoms and on the pathogenic role of ANCA, including the accessibility of ANCA antigens as targets for circulating antibodies and the mode of action of ANCA. Mechanisms of neutrophil activation by ANCA include the engagement of Fcgamma receptors, the possible mechanisms of neutrophil-mediated tissue damage, and the neutrophil-endothelial interaction.

Interaction of antibodies to proteinase 3 (classic anti-neutrophil cytoplasmic antibody) with human renal tubular epithelial cells: impact on signaling events and inflammatory mediator generation

Among the anti-neutrophil cytoplasmic Abs (ANCA), those targeting proteinase 3 (PR3) have a high sensitivity and specificity for Wegener's granulomatosis (WG). A pathogenetic role for these autoantibodies has been proposed due to their capacity of activating neutrophils in vitro. Recently, PR3 was also detected in human renal tubular epithelial cells (TEC). In the present study, the effect of murine monoclonal anti-PR3 Abs (anti-PR3) and purified c-ANCA targeting PR3 from WG serum on isolated human renal tubular cell signaling and inflammatory mediator release was characterized. Priming of TEC with TNF-alpha resulted in surface expression of PR3, as quantified in immunofluorescence studies and by flow cytometry. Moreover, PR3 was immunoprecipitated on surface-labeled TEC. Primed TEC responded to anti-PR3 with a dose- and time-dependent activation of phosphoinositide hydrolysis, resulting in a remarkable accumulation of inositolphosphates. Control IgG was entirely ineffective, whereas PR3-ANCA reproduced the phosphoinositide response. The signaling response was accompanied by a pronounced release of superoxidanion into the cell supernatant. Moreover, large amounts of PGE(2) and, to a lesser extent, of thromboxane B(2), the stable metabolite of TxA(2), were secreted from anti-PR3-stimulated TEC. In parallel, a rise in intracellular cAMP levels was observed, which was blocked by the cyclooxygenase inhibitor indomethacin. We conclude that anti-PR3 Abs directly target renal TECs, thereby provoking pronounced activation of the phosphoinositide-related signal transduction pathway. Associated metabolic events such as the release of reactive oxygen species and lipid mediators may directly contribute to the development of renal lesions and loss of kidney function in WG.

Endothelial tissue factor stimulation by proteinase 3 and elastase

In ANCA-associated vasculitis the activation of primed leucocytes by autoantibodies with subsequent release of proteases such as myeloperoxidase (MPO), proteinase 3 (PR3) and elastase is thought to play an important pathogenetic role. Whether these proteases contribute to the vascular lesions by stimulating the procoagulant activity of these cells is unknown. Tissue factor (TF) expression and activity were investigated in human umbilical vein endothelial cells after stimulation with MPO, PR3 and elastase. TF activity was measured using a one-stage clotting assay. Polyclonal antibodies to TF were used to prove specificity. TF mRNA was detected by reverse transcriptase-polymerase chain reaction. PR3 and elastase led to a significant increase in TF mRNA expression and increased activity. The stimulation was not mediated by IL-1. The stimulatory effect of PR3 did not depend on its proteolytic activity (no inhibition by alpha-1-antitrypsin), whereas the effect of elastase was blocked by alpha-1-antitrypsin. MPO had no effect on TF activity. These results show that PR3 and elastase stimulate TF expression in human endothelial cells. In ANCA-associated vasculitis the increased release of proteases may contribute to the development of microthrombi and consecutive necrosis.

On the origin of surface proteinase 3 of nonmyeloid cells: evidence favoring an exogenous source

In Wegener's granulomatosis (WG), when the endogenous Proteinase 3 (PR3) of myeloid cells is translocated to the cell surface, a pathologically consequent interaction is believed to occur with classic anti-neutrophil cytoplasmic antibody (cANCA). In contrast, the exact origin of surface PR3 on cells of nonmyeloid origin is still debated. By various methods, PR3 mRNA and protein are easily demonstrated in myeloid cells but not in nonmyeloid cells. Exceptionally, the endothelial ECV304 cell line spontaneously produced PR3 mRNA but no PR3 protein. In the other nonmyeloid cells, we could not show cell surface PR3 either spontaneously or after TNFalpha stimulation. On the other hand, under serum-free conditions and using [(3)H]DFP-labeled HL-60 extract, a rapid, dose-dependent, saturable binding was demonstrated to both myeloid and nonmyeloid cells. That was reproduced with purified [(3)H]DFP-PR3. While we could not demonstrate cell surface PR3 on nonmyeloid cells after incubation with serum-containing supernatants of HL-60 cell cultures, we could do so after an overnight coculture period with HL-60 cell suspensions under the usual serum-containing culture conditions. Overall, our data would suggest that in vivo, the surface PR3 found on nonmyeloid cells is not endogenous but results from adsorption of PR3 extruded in their microenvironment by neighboring myeloid cells coming in close contact with them.

Proteinase-3 mRNA expressed by glomerular epithelial cells correlates with crescent formation in Wegener's granulomatosis

BACKGROUND

Wegener's granulomatosis (WG) is characterized by systemic vasculitis with crescentic glomerulonephritis (CGN) and circulating autoantibodies directed against neutrophil cytoplasmic antigens (ANCA). Proteinase 3 (PR-3), a neutral serine proteinase in neutrophils implicated in the growth control of myeloid cells, has been identified as the target antigen for ANCA in WG. Since the kidneys are frequently involved in WG, we studied the in situ expression of PR-3 by renal parenchymal cells.

METHODS

We assessed the expression of PR-3 in kidney biopsies of 15 patients with WG by immunohistochemistry (IHC) and in situ hybridization (ISH). Normal kidney tissue served as the control.

RESULTS

We detected PR-3 mRNA and PR-3 protein in distal tubular epithelial cells (TECs) and glomerular epithelial cells (GECs) in normal kidney tissue and in CGN. Furthermore, a strong glomerular PR-3mRNA expression restricted to the site of cellular crescents was detected in patients with WG. The analysis of 144 glomeruli with cellular or sclerotic crescents revealed a positive correlation of glomerular PR-3mRNA expression with the percentage of cellular crescents per glomerulus. The capability of human TECs and GECs to synthesize PR-3 was confirmed by Northern blot and ISH on cultured cells.

CONCLUSION

These data provide evidence that nonhematopoetic renal parenchymal cells express PR-3 and that glomerular expression of PR-3 is associated with crescent formation in WG. Our findings suggest that renal parenchymal cells may directly be involved in the pathogenesis of CGN in WG.

Activation of neutrophils, eosinophils, and lymphocytes in the lower respiratory tract in Wegener's granulomatosis

Levels of cell products released by neutrophils, eosinophils and lymphocytes were measured in the bronchoalveolar lavage fluid (BALF) of 19 patients with pulmonary active Wegener's granulomatosis (WG) to assess in vivo the magnitude of cellular activation at sites of active disease. Measurements included the BAL cell profile and BALF levels of myeloperoxidase (MPO), free proteinase 3 (fPR3), complexes of PR3 and alpha1-antitrypsin (PR3/alpha1-AT), eosinophil cationic protein (ECP), peroxidase activity (PEROX), and soluble interleukin-2 receptor (sIL-2R). Six patients also underwent a repeat examination after immunosuppressive treatment. Pulmonary active WG was found to be associated with elevated MPO, PEROX, ECP, and sIL-2R levels in BALF. Only trace amounts of fPR3 were detected, the bulk of PR3 being found in PR3/alpha1-AT complexes. Clinically effective treatment depressed BAL neutrophil counts and reversed elevated levels of MPO and PEROX but had an inconsistent effect on the BAL lymphocyte count and the sIL-2R level. In conclusion, the elevated levels of extracellular MPO and PEROX at a site of active disease and the correlation between these and clinical disease activity support the view that neutrophils are indeed an important effector cell population in WG lung disease. The present data also suggest that oxidative injury is an important aspect of neutrophil-mediated lung injury, whereas it remains unresolved whether the low levels of fPR3 in the BALF adequately reflect the situation at inflammatory tissue sites.

Inflammatory cells and cellular activation in the lower respiratory tract in Churg-Strauss syndrome

BACKGROUND

To obtain insight into the mechanisms of tissue injury in lung disease due to Churg-Strauss syndrome (CSS), the bronchoalveolar lavage (BAL) cell profile and the levels in the BAL fluid of cell products released by activated eosinophils and neutrophils were assessed.

METHODS

Thirteen patients with active progressive CSS (n = 7) or CSS in partial remission (n = 6) underwent clinical staging and bronchoalveolar lavage. The levels of eosinophil cationic protein (ECP), myeloperoxidase (MPO), and peroxidase activity in the BAL fluid were determined and the results were compared with those of 19 patients with pulmonary active Wegener's granulomatosis (WG) and nine control subjects.

RESULTS

In patients with progressive CSS the BAL cell profile was dominated by eosinophils, neutrophil elevation being the exception. The eosinophilia was associated with high ECP levels (4.39 ng/ml and 0. 40 ng/ml in the two CSS groups compared with unmeasurable values in the controls). Individual patients with highly active CSS also had raised MPO levels, comparable to the levels in the most active WG patients. Peroxidase activity in the BAL fluid was 1.26 U/ml and 0. 10 U/ml in the two groups of patients with CSS and 0.20 U/ml in the controls. Pulmonary disease in patients with WG was characterised by an extensive increase in MPO (0.30 ng/ml versus 0.13 ng/ml in the controls) together with high peroxidase activity in the BAL fluid (4. 37 U/ml), but only a small increase in ECP levels was seen. No correlation was found between the ECP and MPO levels in patients with CSS which suggests that eosinophil and neutrophil activation vary independently of each other.

CONCLUSIONS

These findings suggest that, in addition to eosinophil activation, neutrophil activation is an important feature in some patients with highly active CSS. The balance of neutrophil and eosinophil involvement appears to be variable and this may be one explanation for the individually variable treatment requirements of patients with CSS.

Identification of proteinase 3 as the major caseinolytic activity in acute human wound fluid

Wound fluid contains several proteinases that are important in the repair process. In this study, we analyzed caseinolytic activity in wound fluid obtained from acute (burn) wounds. Caseinolytic activity in wound fluid increased markedly 2 d after injury and appeared on casein zymographs as a series of bands or a smear ranging from 30 to 100 kDa. Most of the enzyme activity was inhibited by the synthetic human neutrophil elastase inhibitor MDL 27,367 but not by the naturally occurring inhibitor of elastase, human secretory leukoproteinase inhibitor. Fractionation of wound fluid indicated that a single enzyme accounted for approximately 80% of the caseinolytic activity. This enzyme degraded the elastase substrate methoxysuccinyl-ala-ala-pro-val-p-nitroanilide at a slow rate. The above findings suggested that the enzyme responsible for caseinolytic activity might be proteinase 3, an elastase-related enzyme whose physiologic functions are poorly understood. Consistent with the above possibility, we found that monoclonal antibodies against proteinase 3 removed caseinolytic activity from wound fluid, and that purified proteinase 3 had a similar caseinolytic profile and inhibitor sensitivity to burn fluid.