T and B cell responses to neutrophil cytoplasmic antigens in systemic vasculitis

Identification of proteinase 3 autoreactive CD4+T cells and their T-cell receptor repertoires in antineutrophil cytoplasmic antibody-associated vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is an autoimmune disease involving autoreactivity to proteinase 3 (PR3) as demonstrated by presence of ANCAs. While autoantibodies are screened for diagnosis, autoreactive T cells and their features are less well-studied. Here, we investigated PR3-specific CD4+T cell responses and features of autoreactive T cells in patients with PR3-AAV, using a cohort of 72 patients with either active or inactive disease. Autoreactive PR3-specific CD4+T cells producing interferon γ in response to protein stimulation were found to express the G-protein coupled receptor 56 (GPR56), a cell surface marker that distinguishes T cells with cytotoxic capacity. GPR56+CD4+T cells were significantly more prominent in the blood of patients with inactive as compared to active disease, suggesting that these cells were affected by immunosuppression and/or that they migrated from the circulation to sites of organ involvement. Indeed, GPR56+CD4+T cells were identified in T-cell infiltrates of affected kidneys and an association with immunosuppressive therapy was found. Moreover, distinct TCR gene segment usage and shared (public) T cell clones were found for the PR3-reactive TCRs. Shared T cell clones were found in different patients with AAV carrying the disease-associated HLA-DP allele, demonstrating convergence of the autoreactive T cell repertoire. Thus, we identified a CD4+T cell signature in blood and in affected kidneys that display PR3 autoreactivity and associates with T cell cytotoxicity. Our data provide a basis for novel rationales for both immune monitoring and future therapeutic intervention in PR3-AAV.

IgM ANCA in healthy individuals and in patients with ANCA-associated vasculitis

Low levels of IgM auto-antibodies have been reported in health and disease. IgM anti-neutrophil cytoplasmic antibodies (ANCA) have been reported in patients with ANCA-associated vasculitis (AAV). We sought to investigate if healthy individuals may have IgM ANCA in their sera. The first aim of the study was to determine whether IgM ANCA was present in healthy individuals and in patients with ANCA-associated vasculitis. The second aim was to determine what happens to IgM ANCA levels over time. The third aim was to determine whether bacterial infections affected IgM ANCA levels in non-AAV patients. Sera from healthy individuals and patients with AAV were tested for IgM ANCA by immunofluorescence on fixed neutrophils, immunoprecipitation, Western blot and ELISA. Peripheral blood mononuclear cells were isolated and tested by ELISpot for circulating IgM ANCA B cells. To determine whether infection affected IgM ANCA levels, we studied non-AAV patients with bacterial endocarditis or Staphylococcus aureus bacteraemia and measured IgM ANCA levels over time. IgM ANCA is detectable in both healthy individuals and patients with AAV and the titres decreased with increasing age. Circulating IgM ANCA B cells were identified by ELISpot. In the presence of infection, we could not find a significant change in IgM ANCA levels. We report the presence of low-level specific IgM ANCA in the sera of healthy individuals and in patients with ANCA-associated vasculitis. Bacterial infection did not affect the level of IgM ANCA in this small study.

The immunopathology of ANCA-associated vasculitis

The small-vessel vasculitides are a group of disorders characterised by variable patterns of small blood vessel inflammation producing a markedly heterogeneous clinical phenotype. While any vessel in any organ may be involved, distinct but often overlapping sets of clinical features have allowed the description of three subtypes associated with the presence of circulating anti-neutrophil cytoplasmic antibodies (ANCA), namely granulomatosis with polyangiitis (GPA, formerly known as Wegener’s Granulomatosis), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (eGPA, formerly known as Churg-Strauss syndrome). Together, these conditions are called the ANCA-associated vasculitidies (AAV). Both formal nomenclature and classification criteria for the syndromes have changed repeatedly since their description over 100 years ago and may conceivably do so again following recent reports showing distinct genetic associations of patients with detectable ANCA of distinct specificities. ANCA are not only useful in classifying the syndromes but substantial evidence implicates them in driving disease pathogenesis although the mechanism by which they develop and tolerance is broken remains controversial. Advances in our understanding of the pathogenesis of the syndromes have been accompanied by some progress in treatment, although much remains to be done to improve the chronic morbidity associated with the immunosuppression required for disease control.

Successful induction of remission with rituximab for relapse of ANCA-associated vasculitis post-kidney transplant: report of two cases

Kidney transplantation should be considered the treatment of choice for patients with end-stage renal disease due to antineutrophil cytoplasmic antibody (ANCA) associated vasculitis (AAV). However, relapses of AAV have been reported to occur in 9-40% of cases following kidney transplantation and may adversely affect allograft outcome. These relapses are usually treated with cyclophosphamide (CYC) and glucocorticoids, but the repeated use of CYC carries a risk of substantial toxicity that may limit or prohibit its use in some patients. B lymphocytes have been implicated in the pathogenesis of AAV, and their depletion has been effective as salvage therapy for refractory disease in the nontransplant setting. We report the successful induction of remission using rituximab in two patients who suffered relapse of AAV post-kidney transplant. Given the substantial morbidity and adverse effects of CYC, rituximab appears to be a suitable alternative agent to treat relapses of AAV posttransplantation.

Is PR3-ANCA formation initiated in Wegener's granulomatosis lesions? Granulomas as potential lymphoid tissue maintaining autoantibody production

In Wegener's granulomatosis (WG), antiproteinase 3 (PR3) autoantibodies (PR3-ANCA) are crucial in the development of generalized vasculitis. Wegener's pathognomonic lesion, a granulomatous inflammation of the upper and lower respiratory tract, contains abundant lymphocytes and macrophages. Lymphocyte clusters in germinal center-like formation within the granulomatous lesion are frequently observed, which suggests antigen-driven B cell maturation. Wegener's autoantigen PR3, the target for autoreactive B and T cells, is expressed in granulomatous lesions. Disease progression in WG is accompanied by a profound generalized alteration of T cell differentiation with an increase of effector memory T cells (CD4(+)CD28(-)). The cytokine profile suggests an aberrant Th1-type response either to an environmental trigger and/or the autoantigen PR3 itself. Staphylococcus aureus, a risk factor for disease exacerbation, is widely present in the upper airways in WG. The Ig gene repertoire from WG lesions indicates a predominance of VH3+ B cells with affinity to PR3 as well as to the S. aureus B cell superantigen SPA. Hence, within the WG lesion, S. aureus might support the maturation of PR3-affinity B cells that enter a germinal center reaction in contact with PR3 and T cells and expand, leading to PR3-ANCA production. Thus, granulomatous lesions could represent a potential lymphoid tissue-maintaining autoantibody production rather than a simple, random leukocyte accumulation in WG.

T cells in crescentic glomerulonephritis

Crescent formation in glomerulonephritis (GN) is a manifestation of severe glomerular injury that usually results in a poor clinical outcome. In humans, crescentic GN is frequently associated with evidence of either systemic or organ-specific autoimmunity. T cells play a major role in initiation of adaptive immune responses that lead to crescentic injury. In experimental models of crescentic GN, Th1 predominant immune responses have been shown to promote crescent formation. Perturbation of regulatory T cell function may contribute to development of autoimmune crescentic GN. The presence of T cells and macrophages in crescentic glomeruli, frequently in the absence of humoral mediators of immunity, suggest a dominant effector role for T cells in crescentic GN. The association of cellular immune mediators with local fibrin deposition implicates cell-mediated "delayed-type hypersensitivity-like" mechanisms in crescent formation. Intrinsic renal cells also contribute to T cell-driven effector mechanisms in crescentic GN, via expression of MHC II and co-stimulatory molecules and by production of chemokines and cytokines that amplify leukocyte recruitment and injury.

Off balance: T-cells in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides

There is substantial evidence that T-cells are off balance in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides. Genetic risk factors may influence shaping of the TCR repertoire and regulatory control of T-cells in predisposed individuals. T-cells are found in inflammatory lesions. Vigorous Th1-type responses are seen in Wegener's granulomatosis and microscopic angiitis, whereas a Th2-type response predominates in Churg-Strauss syndrome. Oligoclonality and shortened telomers indicate antigen-driven clonal expansion and replicative senescence of T-cells in ANCA-associated vasculitides. Potent CD28(-) Th1-type cells displaying an effector-memory/late differentiated, senescent phenotype are expanded in peripheral blood and are found in granulomatous lesions in Wegener's granulomatosis. Differences in proliferative peripheral blood T-cell responses to the autoantigens proteinase 3 (PR3)- and myeloperoxidase (MPO) have not consistently been detected between patients with ANCA-associated vasculitides and healthy controls in vitro. To recognize an autoantigen, break tolerance, and maintain autoimmune disease T- and B-cells require particular triggers and lymphoid structures. There is preliminary evidence of lymphoid-like structures and possible maturation of autoreactive PR3-ANCA-specific B-cells in granulomatous lesions in Wegener's granulomatosis. Alteration of the T-cell response and anomalous autoantigen-presentation in lymphoid-structures could facilitate development of autoimmune disease in ANCA-associated vasculitides.

Production of antineutrophil cytoplasm antibodies derived from circulating B cells in patients with systemic vasculitis

The pathogenesis of systemic vasculitis is complex and is likely to involve many mechanisms. In certain systemic vasculitides, autoimmunity plays an important role with autoantibodies developing towards neutrophils, which are termed antineutrophil cytoplasm antibodies (ANCA). There is a growing body of evidence that T cells may contribute to the pathogenesis of ANCA-associated vasculitides. A system was set up to determine whether B cells require T cell help to produce antibodies in a peripheral blood lymphocyte (PBL) culture system enriched for B cells and dendritic cells (DC). As a control, tetanus toxoid (TT) antibody production was detected from individuals not recently immunized with tetanus vaccine when stimulated with TT antigen. Proteinase 3 (PR3) and myeloperoxidase (MPO) antibodies were produced from B cell and DC enriched cultures prior to the addition of antigen in some ANCA-positive patients with high ANCA titres, but not from patients with low ANCA titres or controls. PBMC from individuals recently immunized with tetanus vaccine were also maximally stimulated in that addition of antibody did not enhance antibody production. We conclude that this system supports a role for T cell help in the production of TT antibodies in individuals not immunized recently with tetanus vaccine. However, in patients with ANCA-associated vasculitis and controls recently immunized with tetanus vaccine, circulating B cells are apparently spontaneously producing autoantibody, possibly reflecting a system already maximally driven in vivo, and therefore masking underlying potential T cell-B cell collaboration. Such B cells may be less responsive to regulatory stimuli in vivo.

In vitro cytokine production and proliferation of T cells from patients with anti-proteinase 3- and antimyeloperoxidase-associated vasculitis, in response to proteinase 3 and myeloperoxidase

OBJECTIVE

To investigate in vitro proliferative responses of CD4+ T cells and generation of specific cytokines induced by stimulation of peripheral blood mononuclear cells (PBMCs) from patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis with the autoantigens proteinase 3 (PR3) and myeloperoxidase (MPO).

METHODS

PBMCs from vasculitis patients with PR3 ANCA or MPO ANCA and from healthy controls were stimulated for 7 days with PR3, MPO, or control stimuli. Proliferation of CD4+ T cells was assessed by flow cytometry, using the proliferation marker Ki-67. Levels of the pro-proliferative cytokines interleukin-2 (IL-2) and IL-6 and of the Th1 and Th2 cytokines interferon-gamma (IFN gamma) and IL-10 in culture supernatants were determined.

RESULTS

PR3 and MPO induced proliferative responses in CD4+ T cells from individual patients with ANCA-associated vasculitides and healthy controls in vitro. Neither PR3 nor MPO elicited significant IL-2 production. Levels of IL-6 were highest after stimulation with PR3 but low after stimulation with MPO, independent of study group. Stimulation with PR3, and to a lesser extent with MPO, induced a Th2 cytokine milieu, characterized by high production of IL-6 and IL-10 and low production of IFN gamma in patients and controls.

CONCLUSION

PR3 and MPO promote proliferation of CD4+ T cells from patients with ANCA-associated vasculitides, but also cross-stimulate T cells from healthy individuals. Strong IL-10 production elicited by PR3 in vitro may act as an inhibitory signal for T cell proliferation and may have an important immunoregulatory function in vivo.

Response of Wegener's granulomatosis to anti-CD20 chimeric monoclonal antibody therapy

We report on the successful, compassionate use of the anti-CD20 chimeric monoclonal antibody rituximab in a patient with chronic, relapsing cytoplasmic antineutrophil cytoplasmic antibody (cANCA)-associated Wegener's granulomatosis (WG). The patient initially responded to treatment with glucocorticoids and cyclophosphamide. However, bone marrow toxicity during cyclophosphamide treatment of a relapse precluded its further use. Azathioprine and mycophenolate mofetil treatment had failed to maintain remission of the WG, and methotrexate was contraindicated. Because the patient's 5-year course was characterized by close correlation of cANCA levels with disease activity, selective elimination of cANCA was deemed a treatment option for his latest relapse. He was given 4 infusions of 375 mg/M2 of rituximab and high-dose glucocorticoids. Complete remission was associated with the disappearance of B lymphocytes and cANCA. Glucocorticoid treatment was then discontinued. After 11 months, the cANCA recurred, and rituximab therapy was repeated, without glucocorticoids. At 8 months after the second course of rituximab (18 months after the first course), the patient's WG has remained in complete remission. Elimination of B cells by rituximab therapy may prove to be an effective and safe new treatment modality for ANCA-associated vasculitis and possibly other autoimmune diseases. This modality warrants closer examination in a carefully conducted clinical trial.

In vitro T lymphocyte responses to proteinase 3 (PR3) and linear peptides of PR3 in patients with Wegener's granulomatosis (WG)

T cell-mediated immunity is thought to play an important role in the pathogenesis of WG. In previous studies a minority of WG patients as well as some healthy controls showed in vitro proliferation of their peripheral blood mononuclear cells (PBMC) to PR3, the main autoantigen in WG. The relevant peptides responsible for this in vitro proliferation have not been identified. In order to define immunogenic peptides, PBMC of 13 WG patients in remission and 10 healthy controls were tested for proliferation to linear peptides of PR3 and to whole PR3. Fifty overlapping peptides spanning the whole PR3 sequence were synthesized. Peptides were tested in pools of five peptides and as single peptide. PBMC of two WG patients and one healthy control proliferated to whole PR3 and to peptide pools. In addition, 10 WG patients and eight healthy controls that did not proliferate to whole PR3 did proliferate to pools of PR3 peptides. Although more WG patients tended to react to particular peptide pools, no significant difference was seen between lymphocyte proliferation to PR3 peptides of WG patients and that of healthy controls. The pools of peptides recognized were mainly located at the N- and C-terminus of PR3. No correlation was observed between HLA type and proliferation on particular peptide pools. No proliferation of PBMC was observed to single peptides. In conclusion, T cells of WG patients proliferate in vitro more frequently to PR3 peptides than to the whole PR3 protein. Peptides derived from the signal sequence, the propeptide or peptides located at the C-terminus of PR3 induce highest levels of proliferation. No specific PR3 sequence could be identified that was preferentially recognized by PBMC of WG patients compared with controls.

Irregular cytokine pattern of CD4+ T lymphocytes in response to Staphylococcus aureus in patients with Wegener's granulomatosis

The initial stage of Wegener's Granulomatosis (WG) is often marked by symptoms of infection and it has been postulated that a bacterial infection could be the aetiologic factor of this disease. The objective of our work was to investigate T-cell-mediated immunity in WG by testing proliferative responses on bacterial antigens and particularly Staphylococcus aureus. We investigated the bulk proliferative response of peripheral blood lymphocytes (PBL) from patients with clinically active WG to gram-positive bacteria and purified proteinase 3 (PR-3), the major target antigen of c-ANCA. We generated S. aureus-specific PBL-derived T-cell lines and T-cell clones (TLC). In two WG patients 27 TLC were characterized in terms of reactivity to bacterial antigens/PR-3, phenotype, HLA class II restriction and pattern of cytokine secretion. Compared to coagulase-negative Staphylococci and beta-haemolytic Streptococci A, reactivity to S. aureus was significantly increased in all patients with WG. Using purified PR-3, we found a PBL proliferation in five out of 25 WG patients. The TLC were S. aureus-specific and did not cross-recognize Streptococci or coagulase-negative Staphylococci. The S. aureus-specific TLC were of the alphabeta-TCR+ CD4+ phenotype and HLA-DR-restricted. These TLC predominantly showed a Th2-type of cytokine secretion. Interestingly, seven of the S. aureus-reactive TLC also recognized the PR-3 antigen. From these data we conclude that Staphylococci-specific HLA-DR-restricted CD4+ T cells may play a key role in the initial triggering of immune responses in WG.

Differential B- and T-cell activation in Wegener's granulomatosis

BACKGROUND

Autoimmune mechanisms are postulated to play a role in the development and progression of Wegener's granulomatosis (WG), a form of systemic, idiopathic necrotizing vasculitis.

OBJECTIVE

We investigated the relation between lymphocyte activation and disease activity in patients with WG.

METHODS

B- and T-lymphocyte activation was studied by cytometric assessment of the expression of the activation markers CD38 on B cells and CD25 and HLA-DR on CD4(+) and CD8(+) T-cell subsets, respectively. Activation at the cellular level was related to serum levels of antineutrophil cytoplasmic antibodies and soluble IL-2 receptor, which can be regarded as soluble activation markers of B and T cells.

RESULTS

Percentages of CD38(bright) activated B cells were higher in patients with active WG than in patients experiencing disease remission (P <.05) or in healthy control subjects (P <.05). Percentages of activated CD4(+) and CD8(+) T cells were higher in patients with active WG (CD4 subset, P <.0001; CD8 subset, P <.005) than in healthy individuals. An increased percentage of activated T cells of both subsets was also seen in patients whose condition was in remission, as compared with healthy control subjects (CD4 subset, P <.0005; CD8 subset, P <. 001). Lymphocyte activation at the cellular level did not correlate with plasma levels of antineutrophil cytoplasmic antibodies or soluble IL-2 receptor.

CONCLUSION

In WG, B-cell activation is related to active disease, whereas T-cell activation persists during remission of the disease, which points to an intrinsic disordered immune system in this disease.

Expression of major histocompatibility class II antigens on polymorphonuclear neutrophils in patients with Wegener's granulomatosis

BACKGROUND

Wegener's granulomatosis is a systemic inflammatory disease of unknown etiology. Many studies suggest that autoimmune reactions are involved, and there is good evidence for the participation of immunocompetent cells. In that context, we examined the activation of polymorphonuclear neutrophils (PMNs) of patients with Wegener's granulomatosis.

METHODS

In a prospective study, the expression on the surface of PMNs of CD64 and of the major histocompatibility class II (MHC II) antigen was measured by cytofluorometry in whole blood. The expression of those antigens was correlated to disease activity.

RESULTS

Up to 15% of the peripheral PMNs of patients with active disease expressed MHC II. Follow-up studies showed that expression correlated closely with disease activity and that it decreased rapidly under immunosuppressive therapy. Expression of CD64 was seen in approximately 50% of the patients, regardless of disease activity.

CONCLUSION

MHC II expression on PMNs might serve as a novel diagnostic marker for active disease and appears to be suitable for monitoring immunotherapy. Moreover, our data provide evidence that PMNs, which are normally MHC II negative, acquire MHC II antigens in the course of disease and may be an unrecognized function within the afferent limb of the immune response.

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.

Central nervous system vasculitis

Vasculitis is inflammation of blood vessel walls, which produces dysfunction in both the peripheral and central nervous system (CNS). Cerebral ischemia is the major cause for neurological manifestations of CNS vasculitis. Unfortunately, a universally accepted classification of vasculitis has not emerged. Vasculitis affecting the CNS alone is referred to as primary angiitis of the CNS; secondary vasculitis occurs in association with a variety of conditions, including infections, drug abuse, lymphoproliferative disease and connective tissue diseases. The pathogenesis of vasculitis includes different immunological mechanisms. Recently, anti-neutrophil cytoplasmatic antibody (ANCA) has been demonstrated to play an active role in the immunopathogenesis of the vasculitis. Diagnosis of vasculitis depends on a combination of clinical, radiographic and pathologic features. A wide spectrum of clinical features may occur. The most typical clinical picture of CNS vasculitis is troke, encephalopathy or seizures. Assays for ANCA, serum cytokines, antibodies to endothelial cell antigens have been reported to be useful in diagnosing or monitoring the disease activity. The gold standard in diagnosis is confirmation of vasculitis in a biopsy specimen. Angiography may suggest the diagnosis but no abnormalities are pathognomonic. Ideally, the therapy of each vasculitis would focus on the specific immunologic mechanism causing the disease. Such specific interventions are not yet available. In general the most important approaches induce global immunosuppression. The goal of therapy, however, is to prevent recurrence of disease.

Classification, pathogenesis, and treatment of systemic vasculitis

Patients with systemic vasculitis (SV), especially Wegener's granulomatosis and microscopic polyangiitis, regularly present with renal involvement. Although considered a rare disease, either the incidence of SV is increasing or it is being increasingly recognized. Accurate classification systems are required to allow comparison of data from different groups investigating and treating these patients. Systemic vasculitis is known to be an autoimmune disease, but the mechanisms of pathogenesis have not been established, despite many studies on this topic in recent years. Most of this work has been done in vitro, although development of animal models is underway. Patient and renal survival have improved with aggressive immunosuppressive treatment, but morbidity is high and controversies remain in establishing the most effective regimens with minimum adverse effects. In this review we discuss the classification of SV, review the current knowledge of pathogenic mechanisms, and consider the relative merits of different treatment protocols.

Detection of anti-myeloperoxidase antibodies in the serum of patients with type 1 diabetes mellitus

Anti-myeloperoxidase (anti-MPO) antibodies were detected in 34 of 88 (38%) patients with type 1 diabetes mellitus but in only 3 of 55 (5.7%) healthy subjects and in 4 of 20 patients with autoimmune disease. Specificity of anti-MPO antibodies was assessed by MPO inhibition studies. No relationship was found between the occurrence of anti-MPO and anti-thyroperoxidase antibodies. Levels of soluble intercellular adhesion molecule 1 (ICAM-1) were found to be higher in anti-MPO antibody-positive (n = 28, 508 +/- 126 ng/ml) than in anti-MPO antibody-negative (n = 58, 438 +/- 140 ng/ml: P < 0.05) patients. A state of chronic neutrophil activation has been described in diabetes mellitus. As anti-MPO antibodies can stimulate neutrophils to damage endothelial cells in systemic vasculitis, this suggests that a similar mechanism may be operative in the development of diabetic angiopathy.

Decreased frequency of HLA-DR13DR6 in Wegener's granulomatosis

The pathogenesis of Wegener's granulomatosis, microscopic polyangiitis and idiopathic rapidly progressive glomerulonephritis (RPGN) is still unclear; in vitro data support both humoral and cellular autoimmune mechanisms. An association of Wegener's granulomatosis with HLA antigens has been described, with conflicting results concerning the antigens involved. We have performed serological HLA typing of patients at two different laboratories within the Netherlands (N = 118 and N = 106,N respectively). A significant decrease in the frequency of HLA-DR13DR6 was present in both patient groups in comparison to controls (chi 2 = 21.9; corrected P value < 0.004 for both groups together). There were no differences in the distribution of HLA-antigens between patients with Wegener's granulomatosis and microscopic polyangiitis, between cANCA (cytoplasmic anti-neutrophil cytoplasmic antibodies) and pANCA (perinuclear ANCA, anti-MPO) positive patients, and between patients with and without relapsing disease.

Cell-mediated autoimmunity in patients with Wegener's granulomatosis (WG)

Despite the well described infiltration of cells of the cellular immune system in vasculitic lesions and the granuloma formation in patients with WG, the role of T cell-mediated autoimmunity in WG is not clear. Reports of T cell proliferation in response to neutrophil azurophilic granule proteins are contradictory. In this study we have assessed the proliferation of T cells of WG patients to purified proteinase 3 (PR3) and to total azurophilic granule proteins in two different assays. In addition to the classical proliferation assay with isolated peripheral blood mononuclear cells, we have used a whole blood proliferation assay. In both assays we found proliferative responses to PR3 in patients with WG. The number of patients reacting to the azurophilic granule extract was higher than the patients reacting to the purified PR3, suggesting that other autoantigens may also be involved. We have identified epitopes of PR3 that may be potential targets of class I-restricted T cell responses in the context of HLA-A*0201, the most common MHC class I molecule. These epitopes were determined by the binding of synthetic PR3 peptides to HLA-A*0201 on the antigen-processing defective cell line, T2. In addition, T cell lines were established from tissue biopsies, obtained from WG patients, and assessed for cytolytic reactivity against T2 cells, preloaded with synthetic PR3 peptides. We conclude that T lymphocytes of WG patients have increased proliferative responses to purified PR3 and to a larger extent to non-fractionated proteins of azurophilic granules of polymorphonuclear neutrophilic leucocytes (PMN).

T cell reactivity to proteinase 3 and myeloperoxidase in patients with Wegener's granulomatosis (WG)

T cell-mediated immunity is hypothesized to play an important role in the pathogenesis of granulomatous inflammation and vasculitis as found in patients with WG. The antigenic specificities of those T cells remain, however, unknown. Anti-neutrophil cytoplasmic antibodies (ANCA) present in patients with WG are directed to proteinase 3 (PR3) and myeloperoxidase (MPO). In the present study we investigated the proliferative capacity of peripheral blood mononuclear cells (PBMC) from patients with WG and age- and sex-matched controls in response to the WG autoantigens PR3 and MPO. Possible mitogenic effects of active PR3 and toxic effects of active MPO were excluded by using heat-inactivated PR3 and MPO. Antigen-specific stimulation induced by these autoantigens was studied by using processed PR3 and MPO in the lymphocyte stimulation test (LST). Proliferation induced by processed antigen correlated with that by heat-inactivated free antigen. The general capacity to proliferate in response to mitogens and recall antigens did not differ between patients and controls. However, patients with WG who were or had been positive for PR3-ANCA (n = 17) responded more strongly to PR3 than to MPO and showed higher responses to PR3 compared with controls (n = 13). Within the PR3-ANCA group T cell proliferation did not correlate with ANCA titre. In a small group of patients with MPO-ANCA (n = 5) no differences were observed compared with controls for MPO-specific proliferation. The data presented demonstrate that autoreactive PR3-specific T cells are present in patients with WG. Their fine specificity and possible role in the pathogenesis of WG have to be defined in further studies.

Serum soluble interleukin 2 receptor levels in anti-neutrophil cytoplasmic autoantibodies--positive systemic vasculitis

Systemic vasculitis is characterized by the presence of autoantibodies to neutrophil cytoplasmic antigens (ANCA). The role of T-lymphocytes in systemic vasculitis remains uncertain. In the present study, we attempted to explore the role of T-lymphocytes in systemic vasculitis by measuring the serum soluble interleukin 2 receptor (sIL2R) levels in seven vasculitic patients and comparing the sequential measurements with the titres of ANCA which satisfactorily reflect the disease activity. The serum levels of both ANCA and sIL2R were elevated at clinical presentation. Contrary to ANCA, the serum sIL2R remained elevated in most patients despite clinical remission following immunosuppressive therapy. These findings suggest that T-lymphocytes may be activated in the acute phase of the disease. The finding of elevated serum sIL2R levels in most patients during clinical remission indicates that it is not a good measure of the disease activity and tends to argue against the role of T-lymphocytes as a major effector mediating inflammatory injuries in systemic vasculitis.

ANCA and associated diseases: immunodiagnostic and pathogenetic aspects

The past decade has seen an explosion of data on the new group of autoantibodies known collectively as ANCA (anti-neutrophil cytoplasmic antibodies). ANCA are specific for granule proteins of granulocytes and monocytes and induce distinct fluorescence patterns, e.g. the cytoplasmic (classic) cANCA and the perinuclear pANCA. cANCA is induced by antibodies directed against Proteinase 3 (PR3; PR3-ANCA) in about 90% of all ANCA-positive sera, and pANCA is induced by antibodies against myeloperoxidase (MPO; MPO-ANCA) in about 40%. A further staining pattern, which does not have a clear cut association with a distinct granule protein, is sometimes seen in chronic inflammatory bowel diseases. PR3-ANCA are serological markers for Wegener's granulomatosis (WG) and MPO-ANCA are associated with certain subtypes of primary vasculitides. Evidence exists that both the autoantigen and ANCA participate in the pathogenesis of at least the group of 'ANCA-associated vasculitides'.