Detection of anti-DNA topoisomerase I antibody by an enzyme-linked immunosorbent assay using overlapping recombinant polypeptides

Anti-topoisomerase, but not anti-centromere B cell responses in systemic sclerosis display active, Ig-secreting cells associated with lung fibrosis

OBJECTIVES

Almost all patients with systemic sclerosis (SSc) harbour autoantibodies. Anti-topoisomerase antibodies (ATA) and anti-centromere antibodies (ACA) are most prevalent and associate with distinct clinical phenotypes. B cell responses underlying these phenotypes are ill-defined. To understand how B cell autoreactivity and disease pathology connect, we determined phenotypic and functional characteristics of autoreactive B cells in ATA-positive and ACA-positive patients.

METHODS

Levels and isotypes of autoantibodies secreted by ex vivo cultured peripheral blood mononuclear cells from patients with ATA-positive (n=22) and ACA-positive (n=20) SSc were determined. Antibody secreting cells (ASCs) were isolated by cell sorting and cultured separately. Correlations were studied between the degree of spontaneous autoantibody production and the presence and degree of interstitial lung disease (ILD).

RESULTS

Circulating B cells secreting either ATA-immunoglobulin G (IgG) or ACA-IgG on stimulation was readily detectable in patients. The ATA response, but not the ACA response, showed additional secretion of autoreactive IgA. ATA-IgG and ATA-IgA were also secreted spontaneously. Additional cell sorting confirmed the presence of ATA-secreting plasmablasts. The degree of spontaneous ATA-secretion was higher in patients with ILD than in those without (p<0.001) and correlated with the degree of pulmonary fibrosis (p<0.001).

CONCLUSION

In contrast to ACA-positive patients, ATA-positive patients show signs of recent activation of the B cell response that hallmarks this disease. The degree of activation correlates with the presence and severity of ILD, the most deleterious disease manifestation. This could explain differential responsiveness to B cell depleting therapy. The abundant and spontaneous secretion of ATA-IgG and ATA-IgA may point toward a continuously activating trigger.

Association of Anti-Topoisomerase I Antibodies of the IgM Isotype With Disease Progression in Anti-Topoisomerase I-Positive Systemic Sclerosis

Objective

Anti–topoisomerase I (anti–topo I) autoantibodies in systemic sclerosis (SSc) are associated with diffuse skin involvement and interstitial lung fibrosis. Thus far, however, the relationship between anti–topo I antibody response and disease course has not yet been fully evaluated. This study was undertaken to gain insight into the association between characteristics of the anti–topo I antibody response and clinical disease course in SSc patients positive for anti–topo I antibodies.

Methods

Levels of anti–topo I IgG, anti–topo I IgM, and anti–topo I IgA were assessed in consecutive serum samples obtained from patients at baseline who were positive for anti–topo I IgG in the Leiden Combined Care In Systemic Sclerosis (CCISS) cohort. One‐year disease progression was defined by a relevant increase in modified Rodnan skin thickness score (MRSS), decline in pulmonary function, development of digital ulcers, renal crisis, and pulmonary hypertension, and/or mortality. Validation was performed in SSc patients who were positive for anti–topo I from the Oslo University Hospital and University Hospital Zurich.

Results

Of the 103 patients with anti–topo I IgG in the CCISS cohort, clinical data were available to assess 1‐year disease progression in 81 patients. Of these 81 patients, 23 (28%) had disease progression. At baseline, patients with disease progression were significantly more often anti–topo I IgM–positive than those who did not experience disease progression (21 [91%] of 23 versus 33 [57%] of 58; P < 0.01). This finding was confirmed in the independent validation samples.

Conclusion

In SSc patients who were anti–topo I IgG–positive, presence of anti–topo I IgM, which might be considered as a surrogate for an ongoing autoreactive B cell immune response, is associated with disease progression.

Heparin-dependent and -independent anti-platelet factor 4 autoantibodies in patients with systemic lupus erythematosus

OBJECTIVE

Antibodies that recognize complexes formed by platelet factor 4 (PF4) and heparin are involved in the pathogenesis of heparin-induced thrombocytopenia (HIT). This study was undertaken to investigate the prevalence and clinical correlations of anti-PF4 autoantibodies in patients with SLE.

METHODS

We studied 118 patients with SLE, 78 with primary immune thrombocytopenia (ITP), 27 with primary APS, 2 with HIT (as positive controls) and 47 healthy controls. Heparin-dependent and -independent anti-PF4 antibodies were measured with an ELISA. Antibody binding was confirmed to be heparin-dependent when inhibited by the presence of a high concentration of heparin. Pathogenic anti-PF4 antibody was assessed by serotonin-release assay.

RESULTS

Heparin-dependent anti-PF4 antibodies were detected in 11 SLE (9%) and 2 primary ITP (3%) patients, but at much lower levels than in HIT patients. In serotonin-release assays, only the HIT sera induced platelet activation in vitro. Heparin-independent anti-PF4 antibodies were detected in 17 SLE patients (14%). There was no correlation between the levels of heparin-dependent and -independent anti-PF4 antibodies. Cross-reactivity between these two antibodies was not detectable by ELISA competitive assay. Heparin-dependent anti-PF4 antibodies were associated with thrombocytopenia and IgM aCLs (P = 0.007 for both comparisons), while heparin-independent anti-PF4 antibody levels were correlated with SLE disease activity index (P = 0.0005). None of the SLE patients with anti-PF4 antibodies had previous heparin exposure.

CONCLUSION

PF4 is an autoimmune target in SLE patients. Heparin-dependent and -independent anti-PF4 autoantibodies may be involved in different aspects of pathophysiology of SLE.

IgM, IgG, and IgA anti-DNA topoisomerase I antibodies in systemic sclerosis

BACKGROUND

Anti-DNA topoisomerase I (anti-topo I) antibodies have been broadly studied in systemic sclerosis (SSc). The use of different native and molecularly cloned antigens has shown a predominant IgG response, and a variable frequency of positive IgM and IgA tests. We report herein the serological findings of SSc using a recombinant topo I obtained through a standard bacterial system.

METHODS

Anti-topo I antibodies were studied in 45 SSc patients and 85 healthy controls through ELISA and western blot. Escherichia coli XL1-blue strain and pT7-7 vector were used to amplify a DNA topo I cDNA clone, and to obtain the recombinant polypeptide. The latter was purified by affinity chromatography, and the enzymatic and antigenic properties were evaluated through specific tests. A native antigen was included for comparison.

RESULTS

The SSc group disclosed positive IgM (20%), IgG (86.6%), and IgA (26.6%) anti-topo I tests with the recombinant polypeptide, and a purified calf thymus antigen yielded similar results. IgG autoantibodies were frequently associated with skin involvement, esophageal dysfunction, and restrictive lung disease. The recombinant protein showed a molecular weight of 86.6 kDa, a positive topo I activity using a supercoiled pBR322 DNA relaxation test, and its carboxyl terminus region was recognized by specific antibodies.

CONCLUSION

This report confirms that different immunoglobulin classes with anti-topo I activity may occur in SSc. IgG was the predominant serological feature with both, the recombinant and native antigens. The study also demonstrates the association between high levels of these autoantibodies and some clinical manifestations of SSc.

Autoreactive T-cell responses to myeloperoxidase in patients with antineutrophil cytoplasmic antibody-associated vasculitis and in healthy individuals

The aim of this study was to evaluate the characteristics of autoreactive T cells to myeloperoxidase (MPO) in patients with MPO-antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Peripheral blood T cells from 15 patients with MPO-ANCA-associated vasculitis and 14 healthy individuals were cultured with three recombinant proteins that together comprised the entire MPO sequence (L, all 112 amino acids (AA) of the light chain; HI, AA 1-227 of the heavy chain; HII, AA 212-467 of the heavy chain), and the antigen-specific T-cell proliferative response was measured by 3H-thymidine incorporation. T-cell responses to MPO-L and HI were both detected in four patients and three healthy donors, and responses to MPO-HII were detected in four patients and seven healthy donors. These findings indicate that at least three independent T-cell epitopes exist on the MPO molecule. Interestingly, the patients whose T cells showed these MPO-induced responses were mainly in remission. Peripheral blood T cells reactive with MPO were primarily of the HLA-DR-restricted CD4+ phenotype. In summary, we successfully used recombinant MPO fragments to detect autoreactive CD4+ T cells to multiple MPO epitopes in blood samples from patients with MPO-ANCA-associated vasculitis and healthy individuals.

Autoantibody to CD40 ligand in systemic lupus erythematosus: association with thrombocytopenia but not thromboembolism

OBJECTIVES

To examine the prevalence, clinical associations and pathogenic roles of autoantibodies to CD40 ligand (CD40L) in patients with systemic lupus erythematosus (SLE).

METHODS

Plasma anti-CD40L antibodies from 125 patients with SLE, 24 with primary antiphospholipid syndrome (APS) and 90 with idiopathic thrombocytopenic purpura (ITP) and from 62 healthy individuals were measured with an enzyme-linked immunosorbent assay (ELISA). HeLa cells transfected with human CD40L cDNA (HeLa/CD40L) were used to confirm the presence of anti-CD40L autoantibodies. The effect of anti-CD40L antibodies on the CD40L-CD40 interaction was evaluated by observing CD40L-induced IkappaB activation in CD40-expressing fibroblasts.

RESULTS

Anti-CD40L autoantibody was detected in seven (6%) SLE, three (13%) primary APS and 11 (12%) ITP patients, but in no healthy controls. Antibody binding in an ELISA was competitively inhibited by membrane components of HeLa/CD40L. Anti-CD40L antibody-positive IgG specifically bound the surface of living HeLa/CD40L, as shown by flow cytometry. The frequency of thrombocytopenia was significantly higher in SLE patients with the anti-CD40L antibody than in those without (100 vs 14%; P<0.00001), whereas there was no association between the anti-CD40L antibody and thrombosis. Binding of the anti-CD40L antibodies in patients' plasma to CD40L was competitively inhibited by a series of mouse anti-CD40L monoclonal antibodies. Anti-CD40L antibody-positive IgG failed to inhibit CD40L-induced IkappaB activation.

CONCLUSIONS

Anti-CD40L autoantibody is associated with thrombocytopenia but not thromboembolism. Our findings are potentially useful in understanding the complex roles of CD40L in the pathophysiology of thrombosis and haemostasis as well as the thromboembolic complications that occur during treatment with anti-CD40L humanized antibody.

Enzyme-linked immunosorbent assay for detection of anti-RNA polymerase III antibody: analytical accuracy and clinical associations in systemic sclerosis

OBJECTIVE

We have recently developed an enzyme-linked immunosorbent assay (ELISA) for detection of anti-RNA polymerase III (anti-RNAP III) antibody, using a recombinant fragment containing the immunodominant epitope as the antigen source. This study was conducted to assess the analytical accuracy and clinical associations of the anti-RNAP III ELISA in patients with systemic sclerosis (SSc).

METHODS

To evaluate analytical sensitivity and specificity of the ELISA, both immunoprecipitation tests and ELISA were used to detect anti-RNAP III antibody in 534 SSc sera from patients at 3 medical centers. Sera from 522 SSc patients and 516 controls, including patients with other connective tissue diseases and blood bank donors, were also evaluated to assess the clinical sensitivity and specificity of the ELISA. Clinical findings in anti-RNAP III antibody-positive SSc patients were compared between patient groups stratified according to anti-RNAP III antibody levels determined by the ELISA.

RESULTS

In SSc patients, our ELISA showed analytical sensitivity of 91% and analytical specificity of 99% compared with the immunoprecipitation assay (a gold standard for detection of anti-RNAP III antibody). The additional analysis using a large series of SSc and control sera showed that clinical sensitivity and specificity of the ELISA with respect to the diagnosis of SSc were 17% and 98%, respectively. A high level of anti-RNAP III antibody was associated with diffuse cutaneous SSc, higher maximum total skin score, and increased frequency of tendon friction rubs.

CONCLUSION

The anti-RNAP III ELISA is analytically accurate and clinically specific. With this assay, testing for anti-RNAP III antibody can be made routinely available.

Molecular Recognition Patterns of Serum Anti-DNA Topoisomerase I Antibody in Systemic Sclerosis

Autoreactive anti-DNA topoisomerase I (anti-Topo I) Abs are commonly detected in sera of systemic sclerosis (SSc) patients. Our studies have established a positive correlation between the levels of serum anti-Topo I Abs and both disease severity and activity of SSc. The molecular targets of anti-Topo I Ab on Topo I domains remain to be further defined. In this report, we studied the molecular recognition pattern of serum anti-Topo I Ab in 52 SSc patients. The highest reactivity of serum anti-Topo I Abs was against the core subdomains I and II (aa 207-441) and, to a lesser extent, against the core subdomain III (aa 433-636) of Topo I. The linker domain (aa 636-712) and the C-terminal domain (aa 713-765) had much less reactivity than the core domain (aa 207-636). Strikingly, very little reactivity was directed against the N-terminal domain (aa 1-213) by serum anti-Topo I Ab. This molecular recognition pattern was consistent among all SSc serum samples studied. Results from patients with serial serum samples indicated that this pattern remained unchanged over time. Interestingly, some naive B cells from healthy controls, upon transformation by EBV, produced IgM Abs against Topo I. These Abs had low affinity for Topo I and reacted equally to all domains of Topo I. The molecular recognition pattern of serum anti-Topo I Ab in SSc suggests the presence of a unique antigenic stimulation in vivo in this disease.

A novel protein highly expressed in testis is overexpressed in systemic sclerosis fibroblasts and targeted by autoantibodies

Nearly all autoantibody specificities in sera from patients with systemic sclerosis (SSc) target proteins distributed ubiquitously, and Abs against proteins whose expression is restricted to the affected sites have not been identified. In this study we describe SSc-specific autoantibody to a novel testicular Ag, termed protein highly expressed in testis (PHET), which is ectopically overexpressed in SSc dermal fibroblasts. A partial cDNA encoding PHET was isolated by immunoscreening of a HepG2 cDNA library with an SSc serum. PHET appeared to be a member of the UniGene cluster Hs.129872, but had a unique exon composition and a characteristic mRNA expression profile restricted to the testis. Serum Abs to a recombinant PHET fragment were detected in nine (8.4%) of 107 SSc patients, but in none of 50 systemic lupus erythematosus patients or 77 healthy controls. In SSc patients, the presence of anti-PHET Abs was associated with diffuse cutaneous SSc and lung involvement (p = 0.02 and 0.01, respectively). PCR-based quantitative analysis of PHET mRNA expression in cultured dermal fibroblasts showed increased expression of PHET mRNA in SSc fibroblasts compared with control fibroblasts. PHET-reactive Abs purified from SSc sera stained the cytoplasm of SSc dermal fibroblasts, and the staining intensity tended to be more prominent on SSc compared with control fibroblasts. These findings suggest that the autoantibody response to PHET can be induced by ectopic overexpression of PHET in dermal fibroblasts in SSc patients.

Correlation of serum anti-DNA topoisomerase I antibody levels with disease severity and activity in systemic sclerosis

OBJECTIVE

To investigate correlations between serum levels of topoisomerase I-specific antibody (anti-topo I) and clinical features of systemic sclerosis (SSc), including disease severity (the total skin score [TSS]) and disease activity.

METHODS

Using highly sensitive enzyme-linked immunosorbent assays, we measured the levels of anti-topo I antibody, including total IgG, individual IgG subclasses, and IgA, and analyzed their correlations with the TSS in 59 patients with SSc, all of whom had diffuse cutaneous involvement. Serial serum samples were obtained from 11 of these patients.

RESULTS

The titers of anti-topo I antibody, including IgG and IgA, were positively correlated with the TSS, a measure of SSc disease severity. In 8 of the 11 patients from whom serial serum samples were obtained, changes in the levels of both IgG and IgA, when detectable, paralleled changes in the TSS. In 3 patients, an increasing anti-topo I IgG level preceded an increase in the TSS. The level of each IgG subclass also correlated with and tended to parallel the TSS. The patients with very active disease had higher mean IgG (P < 0.001) and IgA (P < 0.05) titers than did those with inactive disease.

CONCLUSION

Serum levels of anti-topo I antibody correlate positively with disease severity and disease activity in SSc.

Autoreactive T cells to the P3A+ isoform of AChR alpha subunit in myasthenia gravis

In vitro T cell proliferative response to an alternative splicing variant of acetylcholine receptor alpha subunit (AChR alpha) with the P3A exon-encoded region was examined in peripheral blood samples from 28 myasthenia gravis (MG) patients and 14 healthy donors using recombinant fragments and synthetic peptides. T cells responsive to the P3A region-specific sequences were detected in five MG patients, all of whom were late-onset disease with thymoma, but in none of healthy donors. These autoreactive T cells may be involved in the pathogenic process in a subset of MG patients.

Identification of an immunodominant epitope on RNA polymerase III recognized by systemic sclerosis sera: application to enzyme-linked immunosorbent assay

OBJECTIVE

To characterize an immunodominant epitope on RNA polymerase III (RNAP III) recognized by systemic sclerosis (SSc) sera and to develop an enzyme-linked immunosorbent assay (ELISA) for the detection of serum anti-RNAP I/III antibodies.

METHODS

RNAP III-specific subunits RPC62 and RPC155 were generated in a bacterial expression system as a series of recombinant fragments. Reactivities to these recombinant fragments were examined by immunoblots and/or ELISA in 16 SSc sera containing anti-RNAP I/III antibodies, 89 SSc sera lacking anti-RNAP I/III antibodies, 61 systemic lupus erythematosus (SLE) sera, and 61 healthy control sera.

RESULTS

Anti-RNAP I/III-positive SSc sera recognized several distinct epitopes on RPC62 and RPC155 in various combinations, but the fragment encoding amino acids at positions 732-1166 of RPC155 was recognized by all 11 anti-RNAP I/III-positive SSc sera tested. Carboxyl- and amino-terminal deletion studies showed that at least 130 amino acids at positions 891-1020 of RPC155 were necessary for the antibody binding, but strong reactivity required an additional amino-terminal extension. When a purified recombinant fragment containing the immunodominant epitope was used as the antigen source in an ELISA, elevated antibody reactivity was detected in all 16 anti-RNAP I/III-positive SSc sera, but in no anti-RNAP I/III-negative SSc, SLE, or healthy control sera, representing a sensitivity of 100% and a specificity of 100%.

CONCLUSION

A major epitope commonly recognized by SSc sera containing anti-RNAP I/III antibodies was identified on RPC155. The ELISA using a recombinant fragment expressing the immunodominant epitope should be a valuable tool for routine screening for anti-RNAP I/III antibodies in clinical diagnostic laboratories.

Autoantibody to c-Mpl (thrombopoietin receptor) in systemic lupus erythematosus: relationship to thrombocytopenia with megakaryocytic hypoplasia

OBJECTIVE

To examine the prevalence, clinical associations, and pathogenic role of autoantibodies to c-Mpl, the thrombopoietin (TPO) receptor, in patients with systemic lupus erythematosus (SLE).

METHODS

Sera from 69 SLE patients, 84 patients with idiopathic thrombocytopenic purpura (ITP), and 60 healthy individuals were screened for anti-c-Mpl antibodies by enzyme-linked immunosorbent assay using recombinant c-Mpl as an antigen. Clinical findings, autoantibody profiles, and serum TPO levels were compared between SLE patients with and without anti-c-Mpl antibodies. A pathogenic role for the anti-c-Mpl antibody was evaluated by examining its inhibitory effect on TPO-dependent cell proliferation and megakaryocyte colony formation.

RESULTS

Serum anti-c-Mpl antibody was detected in 8 SLE patients (11.6%) and 7 ITP patients (8.3%), but in none of the healthy controls. Anti-c-Mpl antibody was associated with thrombocytopenia (P = 0.0002) and a decrease in bone marrow megakaryocytes (P = 0.02) in SLE patients. Serum TPO levels in thrombocytopenic SLE patients with anti-c-Mpl antibodies were significantly elevated compared with levels in those without the antibodies (P = 0.007). IgG fractions purified from anti-c-Mpl antibody-positive sera bound to c-Mpl expressed on the cell surface and inhibited TPO-dependent cell proliferation and megakaryocyte colony formation.

CONCLUSION

Autoantibody to c-Mpl is present in a subset of SLE patients with thrombocytopenia and megakaryocytic hypoplasia. It is likely that the impaired thrombopoiesis in these patients is mediated by the anti-c-Mpl antibody, which functionally blocks an interaction between TPO and c-Mpl.

[Immunological diagnosis of scleroderma]

Systemic sclerosis is characterized by a fibrosis and a microvascular injury. These vascular lesions can affect internal organs causing severe visceral damages. The pathogenesis of this disease is complex but some immunological disorders with a production of antinuclear auto-antibodies can be useful to the clinicians, especially for an early diagnosis and to distinguish the scleroderma/myositis overlap syndromes. This review presents the target antigens and the methods of detection of the different antinuclear auto-antibodies. Sensitivity, specificity and clinical association between the antinuclear auto-antibodies and the different subclasses of scleroderma are also presented in detail.

Autoantibodies to the amino-terminal fragment of beta-fodrin expressed in glandular epithelial cells in patients with Sjögren's syndrome

Sjögrens's syndrome (SS) is an autoimmune disease characterized by destruction of lacrimal and salivary glands, but the mechanisms underlying the disease process are unclear. By immunoscreening a HepG2 cDNA library with serum from an SS patient we isolated a cDNA encoding amino-terminal 616 aa of beta-fodrin, a membrane skeleton protein associated with ion channels and pumps. Serum Ab to the amino-terminal fragment of beta-fodrin was frequently detected in SS patients compared with rheumatic disease patients without SS or healthy controls (70 vs 12 or 4%; p < 0.00001). All the anti-beta-fodrin-positive sera recognized the amino-terminal fragment with no homology to alpha-fodrin. Anti-beta-fodrin Abs in patients' sera as well as mouse polyclonal sera raised against the amino-terminal beta-fodrin fragment did not react with intact beta-fodrin, but recognized the 65-kDa amino-terminal fragment generated through cleavage by caspase-3 or granzyme B. When expression of intact and fragmented beta-fodrin in lacrimal glands was assessed by immunohistochemistry, the antigenic amino-terminal fragment was distributed diffusely in acinar epithelial cell cytoplasm, whereas the carboxyl-terminal fragment and/or intact beta-fodrin were localized in peripheral cytoplasm, especially at the basal membrane, in SS patients. In contrast, intact beta-fodrin was detected primarily at the apical membrane of epithelia, and the amino-terminal fragment was scarcely detected in control patients with chronic graft-vs-host disease. These findings suggest that cleavage and altered distribution of beta-fodrin in glandular epithelial cells may induce impaired secretory function and perpetuate an autoimmune response to beta-fodrin, leading to autoantibody production and glandular destruction in SS.

Induction of antigen-specific human CD4(+) T cell anergy by peripheral blood DC2 precursors

Dendritic cells (DC) are antigen (Ag)-presenting cells that are essential for initiation of T cell-dependent immunity, and distinct DC subsets are known to direct different classes of immune responses. DC2 precursors (pDC2) or plasmacytoid DC were recently identified as a Th2-skewing and IFN-alpha-producing human DC subset. Here, we demonstrate that pDC2 enriched from human peripheral blood have a capacity to induce an anergic state in human Ag-specific CD4(+) T cell lines. Tetanus toxoid-specific T cell lines incubated with tetanus toxoid-pulsed autologous pDC2 failed to proliferate in secondary cultures with optimal Ag stimulation. T cell anergy induction required TCR engagement with Ag/MHC complex presented on pDC2. T cells rendered anergic lost IL-2 production but produced IFN-gamma and IL-10 upon stimulation. The pDC2-induced unresponsiveness was completely or partially reversible when a high concentration of exogenous IL-2 was added in the secondary cultures. Autoreactive CD4(+) T cell clones specific for topoisomerase I derived from a patient with scleroderma were also rendered anergic after co-culture with topoisomerase I-pulsed autologous pDC2,resulting in failure to proliferate or provide help to B cells. These results suggest that pDC2 are involved in maintenance of peripheral T cell tolerance and have potential for use in the suppression of pathogenic T cell responses in autoimmune diseases and organ transplantation.

Autoreactive T cells to topoisomerase I in monozygotic twins discordant for systemic sclerosis

OBJECTIVE

To examine T and B cell responses to topoisomerase I (topo I) in a monozygotic twin pair discordant for systemic sclerosis (SSc).

METHODS

The peripheral blood T cell proliferative responses induced by topo I and in vitro anti-topo I antibody production in cultures of T and B cells were examined in an SSc patient with serum anti-topo I antibody and in her healthy monozygotic twin. Topo I-reactive T cell lines were generated from the twin pair and analyzed for antigenic specificity, major histocompatibility complex class II restriction, and T cell receptor (TCR) gene usage.

RESULTS

T cell proliferative responses to topo I were detected in both the SSc patient and her healthy twin, although the kinetics of the T cell response were accelerated in the patient compared with the healthy twin. The estimated frequency of circulating topo I-reactive T cells was 1/6,700 in the SSc patient and 1/39,000 in the healthy twin. Anti-topo I antibody production was observed in cultures of T and B cells from the SSc patient, but not in those from the healthy twin. When the cells from the twins were mixed in different combinations, T cells from the healthy twin did stimulate the SSc patient's B cells to produce anti-topo I antibody through a CD40-dependent mechanism. Topo I-reactive T cell lines generated from the twins had similar characteristics, including a CD4+ phenotype, restriction by HLA-DR, recognition of epitopes within amino acid residues 209-386 of topo I, and dominant usage of the TCR Vbeta20 gene segment.

CONCLUSION

These results indicate that topo I-reactive T cells were activated and clonally expanded in the SSc patient. However, there were no substantial differences in either phenotypic or functional properties of topo I-reactive T cells obtained from the SSc patient and those obtained from her healthy identical twin. It is likely, therefore, that the anti-topo I antibody response in the SSc patient is induced by in vivo activation of topo I-reactive T cells derived from the normal T cell repertoire.

Distinct autoreactive T cell responses to native and fragmented DNA topoisomerase I: influence of APC type and IL-2

Systemic sclerosis (SSc) is an autoimmune connective tissue disease of unknown etiology in which T cell responses to various autoantigens, including DNA topoisomerase I (Topo I), have been implicated. We investigated whether dendritic cells, generally considered to be the most potent APCs for the initiation of immune responses, would present either of two forms of Topo I to T cells more efficiently than PBMC APCS: Using cells from healthy controls and SSc patients, several important observations were made. First, neither APC type was able to initiate T cell proliferative responses to full-length native Topo I unless exogenous IL-2 was added. This is in contrast to vigorous T cell proliferation in response to Topo I polypeptide fragments presented by either APC type. Second, T cell responses to the full-length form of Topo I presented by dendritic cells were considerably lower than responses to Ag presented by PBMC APCS: Finally, no secondary T cell responses were observed unless the same Ag/APC combination as that used in the primary stimulation was maintained. These data indicate that different peptides are generated based upon the form of the Topo I and the APC that processes it. Taken together, these results suggest that a very specific combination of antigenic form and APC may be involved in breaking tolerance to Topo I in the early stages of development of SSC:

Diversity and plasticity of the anti-DNA topoisomerase I autoantibody response in scleroderma

OBJECTIVE

To examine domain recognition by anti-DNA topoisomerase I (anti-DNA topo I, or anti-topo I) antibodies over time in scleroderma patients.

METHODS

Serial serum samples from scleroderma patients with known reactivity to Scl-70, a 70-kd topo I breakdown product, were tested by immunoblot for IgM, IgG, IgA, kappa, and lambda reactivity to Scl-70 and 8 overlapping recombinant peptide fragments (F1-F8) that span the human topo I molecule.

RESULTS

IgM, IgG, kappa, and lambda anti-topo I antibodies in both early-disease and late-disease serum samples preferentially recognized the Scl-70 molecule rather than the F1-F8 peptides, suggesting preferential recognition of conformational determinants on Scl-70 throughout the disease course. Amounts of both primary and secondary anti-topo I antibodies to Scl-70 varied over time, including increases in primary antibody responses late in the disease course. Striking variability in recognition of the F1-F8 peptides by IgM, IgG, IgA, kappa, and lambda anti-topo I antibodies was seen in serial samples. Most often, the change in FI-F8 recognition from one sample to the next was unpredictable, although occasionally patterns of antibody recognition were reciprocal in serial samples. Of note, in several patients, what could have been interpreted as domain spreading among F1-F8 in 2 successive samples was just a part of changing antibody reactivity to these peptides that again became more restricted in a third sample.

CONCLUSION

Titers and immunodominant domains recognized by both primary and secondary anti-topo I antibodies are highly variable over time. This suggests continual antigen presentation and regulation of the anti-topo I antibody response in scleroderma, even late in the disease course.

Analysis of soluble and cell surface factors regulating anti-DNA topoisomerase I autoantibody production demonstrates synergy between Th1 and Th2 autoreactive T cells

The cellular and subcellular events governing Ab production with specificity for self Ags are poorly understood. In this study we examined the role of cellular interactions and cytokines in regulating the production of anti-DNA topoisomerase I (topo I) Ab, a major autoantibody in patients with systemic sclerosis (SSc). Topo I-specific T cell clones derived from SSc subjects and healthy donors were cultured with autologous peripheral blood B cells. Anti-topo I Ab production was induced by five of seven topo I-specific T cell clones derived from SSc subjects, but by none of eight T cell clones generated from healthy controls. However, two of the T cell clones from healthy controls provided help to HLA-DR-matched SSc B cells to produce anti-topo I Ab. The analysis of cytokine mRNA expression revealed that the ability to promote anti-topo I autoantibody production was strictly correlated with IL-2 and IL-6 expression by the T cell clones. Kinetic studies showed that IL-2 was required throughout the culture period for maximal autoantibody production and that both MHC-TCR and CD40-CD40L interactions were essential during the early phase of the culture. IL-6 was important in the late phase. Th1 clones (producing IL-2, but no IL-6) and Th2 clones (producing IL-6, but no IL-2) synergically activated autologous B cells to produce anti-topo I Ab. These results indicate that T cell-dependent B cell activation resulting in anti-topo I autoantibody production requires a series of temporally defined cell contact and soluble stimuli.

T cells that are autoreactive to beta2-glycoprotein I in patients with antiphospholipid syndrome and healthy individuals

OBJECTIVE

To identify the T cells responsive to beta2-glycoprotein I (beta2GPI) that mediate antiphospholipid antibody production in patients with antiphospholipid syndrome (APS).

METHODS

In vitro proliferative responses and anti-beta2GPI antibody production induced by beta2GPI were examined in peripheral blood mononuclear cell (PBMC) cultures from 12 APS patients, 13 systemic lupus erythematosus patients without APS, and 12 healthy donors.

RESULTS

Peripheral blood T cells from all subjects failed to respond to beta2GPI in its native form. In contrast, reduced beta2GPI was able to stimulate T cells not only from all 12 patients with anti-beta2GPI antibodies, but also from 10 of 25 individuals without anti-beta2GPI antibodies. The specificity of the responses to beta2GPI was confirmed by activation of the reduced beta2GPI-primed T cells by recombinant beta2GPI in secondary cultures. Characterization of the T cell response induced by beta2GPI revealed that the response was associated with the presence of the DR53-associated alleles, the responding T cells were CD4+ and restricted by HLA class II, and antigenic peptides were located in domains IV and/or V. Anti-beta2GPI antibody production was induced specifically in anti-beta2GPI antibody-positive patients, in PBMC cultures with reduced beta2GPI. Anti-beta2GPI antibodies produced in vitro recognized beta2GPI immobilized with cardiolipin or beta2GPI coated on "high-binding" polystyrene plates.

CONCLUSION

These results strongly suggest that CD4+ and HLA class II-restricted T cells responsive to beta2GPI are involved in the production of antiphospholipid antibodies in APS patients.

An immunodominant epitope on DNA topoisomerase I is conformational in nature: heterogeneity in its recognition by systemic sclerosis sera

OBJECTIVE

To characterize an immunodominant epitope recognized by anti-DNA topoisomerase I (topo I) antibody, a major autoantibody in sera of patients with systemic sclerosis (SSc).

METHODS

Topo I fragments were generated as fusion proteins using a bacterial expression system as well as polypeptides translated in vitro using a eukaryotic expression system. Reactivities to the 2 preparations of recombinant topo I polypeptides in anti-topo I-positive sera from SSc patients of varied ethnic backgrounds were examined by immunoblotting, immunoprecipitation, and/or enzyme-linked immunosorbent assay.

RESULTS

The fragment encoding amino acids 489-573 of topo I was recognized by 98 of 100 anti-topo I-positive SSc sera. Both carboxyl- and amino-terminal deletion studies as well as competitive inhibition assays using topo I synthetic peptides showed that a region of > or =52 amino acids (512-563) was necessary for recognition by anti-topo I antibodies. The minimum epitope region and conformation required for this reactivity were variable among sera from Caucasian, African American, Japanese, and Choctaw SSc patients.

CONCLUSION

An immunodominant epitope recognized by anti-topo I autoantibody is located in the region of amino acids 489-573 of the topo I protein and is largely conformational in nature. The recognition pattern of this region by anti-topo I-positive sera is heterogeneous and is influenced by ethnic background.

Influence of ethnic background on clinical and serologic features in patients with systemic sclerosis and anti-DNA topoisomerase I antibody

OBJECTIVE

To investigate the effect of ethnicity on clinical and serologic expression in patients with systemic sclerosis (SSc) and anti-DNA topoisomerase I (anti-topo I) antibody.

METHODS

Clinical and serologic features, as well as HLA class II allele frequencies, were compared among 47 North American white, 15 North American black, 43 Japanese, and 12 Choctaw Native American SSc patients with anti-topo I antibody.

RESULTS

The frequency of progressive pulmonary interstitial fibrosis was lower, and cumulative survival rates were better in white compared with black and Japanese patients. Sera of white and black patients frequently recognized the portion adjacent to the carboxyl terminus of topo I, sera of Japanese patients preferentially recognized the portion adjacent to the amino terminus of topo I, and sera of Choctaw patients recognized both portions of topo I. Anti-RNA polymerase II and anti-SSA/Ro antibodies were present together with anti-topo I antibody more frequently in sera of Japanese patients than in sera of white patients. The HLA-DRB1 alleles associated with anti-topo I antibody differed; i.e., DRB1*1101-*1104 in whites and blacks, DRB1*1502 in Japanese, and DRB1*1602 in Choctaws. Multivariate analysis showed that ethnic background was an independent determinant affecting development of severe lung disease as well as survival.

CONCLUSION

Clinical and serologic features in SSc patients were strongly influenced by ethnic background. The variability of disease expression in the 4 ethnic groups suggests that multiple factors linked to ethnicity, including genetic and environmental factors, modulate clinical manifestations, disease course, and autoantibody status in SSc.

Antinuclear antibody in systemic sclerosis (scleroderma)

The presence of autoantibodies to intracellular molecules is the hallmark immunologic finding of SSc. Recent sophisticated methods have contributed to characterization of unidentified antigens of ANA in sera from patients with SSc. Antibodies to RNA polymerases are the third major SSc-specific ANA, in addition to anti-topo I and anticentromere antibodies, and it is now possible to identify over 85% of SSc patients. These antibodies have proved helpful in diagnosis of this disease. An immunogenetic predisposition to synthesis of the ANAs has been unveiled. Both antigen-driven and molecular mimicry hypotheses have been proposed for ANA production in SSc. Although the role of ANAs in the pathogenesis of SSc is not yet known, it is logical to assume that the origin of ANAs is linked to the causes of this disease because each antibody is associated with its own unique constellation of clinical features.

Enhancement of anti-DNA topoisomerase I autoantibody response after lung cancer in patients with systemic sclerosis. A report of two cases

Anti-DNA topoisomerase I (anti-topo I) antibody profiles were compared before and after lung cancer in 2 patients with systemic sclerosis (SSc). Both patients developed adenocarcinoma of the lung late in the course of SSc and died of the cancer. Anti-topo I antibody levels, determined by double immunodiffusion and enzyme-linked immunosorbent assay, increased markedly at the time of diagnosis of lung cancer. Furthermore, patients' sera obtained after lung cancer reacted with multiple epitopes on the entire topo I molecule, some of which had not previously been recognized. These results further support the concept that anti-topo I antibody production in SSc patients is due to an antigen-driven process.