What you should know about PR3-ANCA. Structural aspects of antibodies to proteinase 3 (PR3)

Reactive antigenic epitopes on presumed autoantigens of biologic interest have been examined by many researchers. The central third complementarity-determining region (CDR3) residues of a human monoclonal anti-proteinase 3 (PR3) antibody contained many negatively charged aspartic acid residues, perhaps contributing to its reactivity with positively charged PR3 regions. Examination of four other human monoclonal anti-PR3 antibodies shows a number of negatively charged residues within their CDR3 regions. Mapping of segments of linear PR3-epitopes reacting with anti-neutrophil cytoplasmic antibodies (ANCA) demonstrated a preliminary estimate of structures contributing to antigenic determinants. T-cell epitopes on PR3 are reported in studies of chronic myeloid leukemia. These T-cell epitopes appear to be human leukocyte antigen (HLA) A2.1 restricted.

Characterization of monoclonal antibodies to proteinase 3 (PR3) as candidate tools for epitope mapping of human anti-PR3 autoantibodies

Anti-neutrophil cytoplasmic antibodies directed against PR3 (PR3-ANCA) in patients with Wegener's granulomatosis are supposedly involved in the pathophysiology of this disease as different functional characteristics of the autoantibodies correlate with disease activity. However, little is known about the epitopes of PR3 that are recognized by PR3-ANCA and how epitope specificity may relate to functional characteristics of PR3-ANCA. As candidate tools for epitope mapping we studied 13 anti-PR3 MoAbs, including nine widely used and four newly raised MoAbs, for their mutual binding characteristics to PR3 using biosensor technology. Antigen specificity was confirmed by indirect immunofluorescence, immunoblotting, FACS analysis and antigen-specific ELISA. Competition between anti-PR3 MoAbs in binding to PR3 was investigated in a capture system set up in a BIAcore. In this system grouping of 12 of the 13 anti-PR3 MoAbs based on their mutual recognition patterns was achieved. Four MoAbs, from different research groups, namely 12.8, PR3G-2, 6A6 and Hz1F12, recognized comparable epitopes (group 1). Group 2 MoAbs including PR3G-4 and PR3G-6 bound to overlapping regions on PR3. The MoAbs PR3G-3, 4A5 and WGM2 recognized similar epitopes as they inhibited binding of each other (group 3). The fourth group of related MoAbs consisted of MC-PR3-2, 4A3 and WGM3. Because of its binding characteristics MoAb WGM1 could not be grouped. These results demonstrate that eight well-established anti-PR3 MoAbs produced by different research groups and four newly produced anti-PR3 MoAbs recognize four separate epitope areas on PR3, including one area detected with newly raised MoAbs only.

C3 and C4 allotypes in anti-neutrophil cytoplasmic autoantibody (ANCA)-positive vasculitis

In ANCA-associated small vessel vasculitis few genetic factors have proven to be of importance for disease susceptibility, an exception being deficiency of alpha1-anti-trypsin, the main inhibitor of proteinase 3 (PR3). Alerted by our finding that myeloperoxidase has affinity for C3, and the finding of an increased frequency of the C3F allele in systemic vasculitis in a British cohort, we examined polymorphism of C3 and C4 in patients with ANCA+ small vessel vasculitis. After identification of all patients at our department with a positive ANCA test during the period 1991-95 and a diagnosis of small vessel vasculitis, blood samples were collected after informed consent. The 67 included patients were grouped according to ANCA serology and disease phenotype using the Chapel Hill nomenclature. The gene frequency of C3F was found to be increased (0. 32) compared with controls (0.20; P < 0.05) in the PR3-ANCA+ subgroup. The frequency of C4A3 was increased in the group as a whole, but no increase of C4 null alleles was seen. The findings imply a role for the complement system in the pathogenesis of ANCA-associated small vessel vasculitis.

T lymphocyte responses to anti-neutrophil cytoplasmic autoantibody (ANCA) antigens are present in patients with ANCA-associated systemic vasculitis and persist during disease remission

ANCA with specificity for myeloperoxidase (MPO) and proteinase 3 (PR3) are present in patients with systemic vasculitis. The aim of this work was to determine whether such patients have T cell responses to these antigens and whether these responses are related to disease activity. Peripheral blood lymphocytes from 45 patients and 19 controls were cultured with ANCA antigens and proliferation measured. The antigens used were heat-inactivated (HI) MPO, HI PR3, native (non-HI) PR3, HI whole alpha-granules, and 25 overlapping peptides covering the entire PR3 sequence. Significant responses to both whole PR3 preparations were seen from patient and control groups, and to the alpha-granules from the patient group. Patients responded at all stages of disease: active, remitting, treated or untreated. Only two patients responded significantly to MPO. Responses were significantly higher with the patient group than the control group to all four whole ANCA antigens. Responses to those PR3 peptides containing epitopes known to be recognized by ANCA were detected from one patient. Thus, these studies demonstrate that T cells from vasculitis patients can proliferate to PR3 and occasionally to associated ANCA antigens. Further, responses may persist even after disease remission has been achieved.

Human mast cells expressing recombinant proteinase 3 (PR3) as substrate for clinical testing for anti-neutrophil cytoplasmic antibodies (ANCA)

We have expressed conformationally intact, enzymatically active recombinant PR3 in HMC-1 cells (HMC-1/PR3 cells) that is recognized by C-ANCA. Here we directly compared the clinical utility of C-ANCA testing by indirect immunofluorescence (IIF) using HMC-1/PR3 cell cytospin versus polymorphonuclear neutrophil (PMN) cytospin preparations and commercially available anti-PR3 ELISA kits. Two hundred sera were tested independently by three investigators: 101 previously determined to be C-ANCA-positive by routine clinical laboratory testing using standard IIF on PMN cytospins, and 99 control samples chosen primarily because they contained antibodies against other cytoplasmic target antigens. Discrepant test results between the two cellular substrates were found in seven samples: 2/7 were PMN-positive and HMC-1/PR3 cell-negative (one Sjogren's syndrome, one hand injury); 5/7 were PMN-negative and HMC-1/PR3-positive (all Wegener's granulomatosis (WG)). All C-ANCA-positive WG patients were also positive on HMC-1/PR3 cells. IIF using HMC-1/PR3 cells was as sensitive as the most sensitive anti-PR3 ELISA (79.8% versus 80.7%, P = 0.739), and more sensitive than standard IIF C-ANCA testing using PMN cytospins (79.8% versus 75.2%, P = 0.025) or the anti-PR3 ELISA with the least false-positive test results (79.8% versus 63%, P < 0.01). These findings indicate that HMC-1/PR3 cells are a very sensitive antigen-specific substrate for clinical anti-PR3 ANCA testing which appears superior to standard C-ANCA testing using PMN cytospin substrates and anti-PR3 ELISA. Our results also suggest that in WG the C-ANCA fluorescence pattern is not caused by antibodies against target antigens other than PR3.

Transforming growth factor-beta (TGF-beta) expression and interaction with proteinase 3 (PR3) in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis

TGF-beta is a multifunctional cytokine modulating the onset and course of autoimmune diseases as shown in experimental models. The aim of this study was to investigate TGF-beta expression in ANCA-associated vasculitis (AAV), and the possible interactions of this cytokine with lysosomal enzymes identified as ANCA autoantigens (e.g. PR3). This included TGF-beta effects on the translocation of the lysosomal enzymes to the cell surface of polymorphonuclear neutrophils (PMN), and the presumed activation of non-bioactive, latent TGF-beta by these enzymes. Patients with various types of systemic vasculitis (SV) were studied, including three different types of AAV (Wegener's granulomatosis (WG), Churg-Strauss syndrome (CSS) and microscopic polyangiitis (MPA)). Regardless of the type of assay applied, the TGF-beta 1 isoform was found to be over-expressed in SV, including AAV, and to correlate with disease activity as shown for WG. Mean TGF-beta 1 plasma levels in AAV patients ranged from 8.9 ng/ml (WG) to 13.3 ng/ml (CSS) (control 4.2 ng/ml; P < 0.01), while TGF-beta 2 levels were not elevated. Flow cytometry analysis showed TGF-beta 1 to be a potent translocation factor for PR3 comparable to other neutrophil-activating factors such as IL-8. PR3 membrane expression on primed PMN increased by up to 51% after incubation with TGF-beta 1. PR3 itself was revealed as a potent activator of latent TGF-beta, thus mediating bioeffects of this cytokine. These findings, together with other features of TGF-beta such as induction of angiogenesis and its strong chemotactic capacity, indicate that TGF-beta might serve as a proinflammatory factor in SV, especially in AAV.

Antibodies to proteinase 3 mediate expression of vascular cell adhesion molecule-1 (VCAM-1)

VCAM-1 was first identified as an adhesion molecule induced on human endothelial cells (HEC) by inflammatory cytokines such as IL-1, tumour necrosis factor (TNF), and lipopolysaccharide (LPS). The molecule binds to a variety of leucocytes, including B cells, T cells, basophils, eosinophils and monocytes. Vascular expression of VCAM-1 has been associated with a number of disease states, including rheumatoid arthritis and vasculitis. The detection of anti-neutrophil cytoplasmic antibodies (ANCA), especially to proteinase 3 (PR3), has become important in the diagnosis of Wegener's granulomatosis (WG) and related vasculitides. Recently we were able to demonstrate a direct effect of anti-PR3 antibodies on neutrophil-endothelial interactions (Blood 1993; 82:1221). Binding of anti-PR3 antibodies to their antigen translocated into the membrane of HEC leads to an enhanced adhesion of neutrophils via induction of E-selectin (Clin Exp Immunol 1993; 94:440). The aim of this study was to investigate the effect of anti-PR3 antibodies on the expression of VCAM-1. HEC were isolated from umbilical vein and cultured on microtitre plates. After preincubation with purified anti-PR3 antibody, purified control antibodies (SS-A, SS-B, RNP) (IgG and F(ab')2 fragments) or different cytokines (controls), VCAM-1 was detected on the surface of unfixed HEC by cyto-ELISA and polymerase chain reaction analysis. Incubation of HEC with anti-PR3 antibodies led to a marked increase of endothelial VCAM-1 expression with a peak after 8 h. Incubation with TNF-alpha also led to maximal VCAM-1 expression after 4-6 h (control). Increased adhesion of T lymphocytes to HEC after binding of anti-PR3 antibodies to their antigen could be confirmed by performing adherence assays. This effect could be inhibited by antibodies to VLA-4. In conclusion, we have been able to show that cytokine-like effects of anti-PR3 antibodies on HEC are not limited to induction of neutrophil adhesion. Anti-PR3 antibodies may thus contribute to the regulation of T lymphocyte migration from the blood by HEC in ANCA-related vasculitides.

T cell responses to myeloperoxidase (MPO) and proteinase 3 (PR3) in patients with systemic vasculitis

T cell-mediated immune responses are likely to be important in the pathogenesis of systemic vasculitis. However, identifying the T cells involved has proved difficult, and there are conflicting reports regarding T cell proliferation in response to different autoantigens. Perinuclear (P) and cytoplasmic (C) anti-neutrophil cytoplasmic antibodies (ANCA) are closely associated with systemic vasculitis, and are generally specific for MPO or PR3, respectively. We studied the proliferative responses to MPO and PR3 of peripheral blood mononuclear cells from patients with P-ANCA or C-ANCA specific for these antigens by ELISA. These responses were compared with those of normal controls, and of disease controls with P- or C-ANCA not specific for MPO or PR3. The patient group as a whole showed significant T cell proliferation in response to the autoantigens compared with controls (P = 0.005). Cells from nine of 13 P-ANCA-positive, anti-MPO-positive patients proliferated in response to MPO, compared with five of 16 controls (P = 0.04). Cells from five of eight C-ANCA-positive, anti-PR3-positive patients proliferated in response to PR3, compared with two of 11 controls (P = 0.05). These experiments demonstrate that patients with P-ANCA or C-ANCA possess T cells which respond to MPO or PR3, respectively. As in other autoimmune diseases, responses to both antigens were also seen in a proportion of healthy controls. Further analysis of these responses will be important in understanding the pathogenesis of systemic vasculitis and in designing specific immunotherapy.