Antinuclear antibody-keratinocyte interactions in photosensitive cutaneous lupus erythematosus

Autoimmune diseases are characterized by various circulating autoantibodies, especially antinuclear antibodies (ANA). It has been a long-standing issue as to whether and/or how ANA interact with epidermal cells to produce skin lesions. Of these ANA, the anti-SS-A/Ro antibody is the most closely associated with photosensitivity in patients with systemic lupus erythematosus (SLE) and its subgroups, including subacute cutaneous lupus erythematosus (SCLE) and neonatal lupus erythematosus (NLE). SS-A/Ro antigens are present in the nucleus and cytoplasm, and interestingly, ultraviolet B (UVB) light translocates these antigens to the surface of the cultured keratinocytes. Thus, anti-SS-A/Ro antibodies in the sera can bind to the relevant antigens expressed on the UVB-irradiated keratinocyte surface, and have been speculated to be an important inducer of antibody-dependent keratinocyte damage. This interaction between the anti-SS-A/Ro antibodies and UVB-irradiated keratinocytes may induce the skin lesions through a cytotoxic mechanism. This review will focus on the involvement of antibody-dependent cellular cytotoxicity in the pathogenesis of the skin lesions observed in photosensitive cutaneous lupus erythematosus.     

The Sjogren's syndrome-associated autoantigen Ro52 is an E3 ligase that regulates proliferation and cell death

Patients affected by Sj?gren's syndrome and systemic lupus erythematosus (SLE) carry autoantibodies to an intracellular protein denoted Ro52. Although the serologic presence of Ro52 autoantibodies is used clinically for diagnostic purposes, the function of the protein or why it is targeted as an autoantigen in several rheumatic conditions has not been elucidated. In this study, we show that the expression of Ro52 is significantly increased in PBMC of patients with Sj?gren's syndrome and SLE, and demonstrate that Ro52 is a RING-dependent E3 ligase involved in ubiquitination. Overexpression of Ro52, but not of Ro52 lacking the RING domain, in a mouse B cell line lead to decreased growth in steady state and increased cell death after activation via the CD40 pathway. The role of Ro52 in activation-mediated cell death was further confirmed as a reduction in Ro52 expression restored cell viability. These findings suggest that the increased expression of the Ro52 autoantigen in patients may be directly involved in the reduced cellular proliferation and increased apoptotic cell death observed in Sj?gren's syndrome and SLE, and may thus contribute to the autoantigenic load and induction of autoimmune B and T cell responses observed in rheumatic patients.     

Evidence for multiple shared antigenic determinants within Ro60 and other lupus-related ribonucleoprotein autoantigens in human autoimmune responses

Ab responses directed against several ribonucleoprotein (RNP) Ags are a characteristic feature of systemic lupus erythematosus (SLE). Previous work in our laboratory using mouse model systems had revealed that both epitope spreading and inherent cross-reactivity between ribonucleoproteins contributes to the observed multiple specificities in autoimmune sera. We have now extended these studies to human autoimmune responses. Using purified polyclonal and mAbs derived from SLE patients, cross-reactivity between Ro60 and SmD was demonstrated. The cross-reactive epitope was mapped to nonhomologous regions on Ro60(481-505) and SmD(88-102). Five mAbs specifically recognized apoptotic cells, demonstrated variable levels of cross-reactivity toward other nonhomologous ribonucleoprotein targets and bound multiple, nonoverlapping and nonhomologous epitopes on Ro60. Our study demonstrates that cross-reactivity between frequently targeted autoantigens is an important aspect of human systemic autoimmune responses. The presence of multiple cross-reactive epitopes on Ro60 might be important for the generation of anti-Ro60 Ab in SLE patients and in normal individuals displaying no evidence of clinical disease.     

The role of the idiotypic network in the induction of experimental systemic lupus erythematosus

Systemic lupus erythematosus (SLE) has been induced in C3H.SW mice by their immunization with a human monoclonal anti-DNA antibody that bears a common idiotype-16/6 Id. Following immunization, high levels of murine anti-16/6 and anti-anti-16/6 antibodies were detected in the sera of the immunized mice. Elevated titers of autoantibodies reacting with ssDNA, dsDNA, poly(I), poly(G), RNP, Ro, and La were also observed. The serological findings were associated with significant proteinuria, leukopenia, and elevated erythrocyte sedimentation rate. Immune complex deposition in the glomerular mesangium and sclerosis of the glomeruli were demonstrated. To study whether or not anti-idiotype antibodies are involved in the induction of the disease, a murine monoclonal antibody against the 16/6 Id was prepared and injected into C3H.SW mice. The anti-16/6 Id antibody induced experimental SLE similarly to the 16/6 Id with an accelerated kidney pathology. A study performed on different mouse strains indicated that the susceptibility to the induction of SLE by the 16/6 Id is strain dependent and directly correlates to their ability to produce anti-16/6 Id specific antibodies.     

Modification of lupus-associated 60-kDa Ro protein with the lipid oxidation product 4-hydroxy-2-nonenal increases antigenicity and facilitates epitope spreading

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with autoantibodies as a near universal feature of the disease. The Ro ribonucleoprotein particle, composed of a 60-kDa protein noncovalently associated with human cytoplasmic RNA, is the target of antibodies in 25-40% of lupus patients. Purified human 60-kDa Ro was found to be oxidatively modified. Earlier investigations from our laboratory revealed increased oxidative damage in SLE patients. Therefore we hypothesized that oxidation by-products, such as 4-hydroxy-2-nonenal (HNE), could lead to neoantigens like HNE-modified 60-kDa Ro, which could in turn initiate autoimmunity or drive epitope spreading. To test this hypothesis we immunized rabbits with either HNE-modified 60-kDa Ro or the unmodified Ro. Intramolecular epitope spreading within the Ro molecule and intermolecular epitope spreading to La, double-stranded DNA, nRNP, and Sm occurred preferentially in HNE-Ro-immunized animals. Nonspecific anti-HNE antibody, generated by immunization with HNE-keyhole limpet hemocyanin conjugate, did not significantly bind to these autoantigens. These data may suggest a hitherto unappreciated mechanism by which oxidative stress facilitates epitope spreading in SLE.     

Autodisplay of 60-kDa Ro/SS-A antigen and development of a surface display enzyme-linked immunosorbent assay for systemic lupus erythematosus patient sera screening

Enzyme-linked immunosorbent assay (ELISA) is a common tool to test human sera on an antibody reaction against a specific antigen. The 60-kDa Ro/SS-A antigen for autoantibodies can be found in sera from systemic lupus erythematosus (SLE) patients. As in the case of 60-kDa Ro/SS-A, antigens used in ELISAs are recombinantly expressed in Escherichia coli and time-consuming purification steps are needed to get the proteins. To avoid these disadvantages, 60-kDa Ro/SS-A was expressed on the surface of E. coli using autodisplay, an efficient surface display system. Cells displaying 60-kDa Ro/SS-A on the surface were applied as an antigen source instead of the purified antigen. In total, 39 patients and 30 control sera were screened on a 60-kDa Ro/SS-A antibody reaction. To eliminate antibodies against native E. coli, human sera were preabsorbed with E. coli cells prior to the assay. The new ELISA protocol (surface display ELISA [SD-ELISA]) using E. coli with autodisplayed 60-kDa Ro/SS-A showed a sensitivity of 86.67% and a specificity of 83.33% by a cutoff value of 0.28. Our results show that autodisplay provides simple, rapid, and cheap access to human antigens for an ELISA to screen human sera against specific antibody reactions.     

Anti-class a scavenger receptor autoantibodies from systemic lupus erythematosus patients impair phagocytic clearance of apoptotic cells by macrophages <Emphasis Type="Italic">in vitro</Emphasis>

Introduction  

Inadequate clearance of apoptotic cells by macrophages is one of the reasons for the breakdown of self-tolerance. Class A scavenger receptors, macrophage receptor with collagenous structure (MARCO) and scavenger receptor A (SR-A), which are expressed on macrophages, play important roles in the uptake of apoptotic cells. A previous study reported the presence of the anti-MARCO antibody in lupus-prone mice and systemic lupus erythematosus (SLE) patients. The purpose of this study was to investigate the prevalence of anti-class A scavenger receptor antibodies in patients with various autoimmune diseases, in particular SLE, and the functional implication of those autoantibodies in the phagocytic clearance of apoptotic cells by macrophages.     

Is disturbed clearance of apoptotic keratinocytes responsible for UVB-induced inflammatory skin lesions in systemic lupus erythematosus?

Apoptotic cells are thought to play an essential role in the pathogenesis of systemic lupus erythematosus (SLE). We hypothesise that delayed or altered clearance of apoptotic cells after UV irradiation will lead to inflammation in the skin of SLE patients. Fifteen SLE patients and 13 controls were irradiated with two minimal erythemal doses (MEDs) of ultraviolet B light (UVB). Subsequently, skin biopsies were analysed (immuno)histologically, over 10 days, for numbers of apoptotic cells, T cells, macrophages, and deposition of immunoglobulin and complement. Additionally, to compare results with cutaneous lesions of SLE patients, 20 biopsies of lupus erythematosus (LE) skin lesions were analysed morphologically for apoptotic cells and infiltrate. Clearance rate of apoptotic cells after irradiation did not differ between patients and controls. Influx of macrophages in dermal and epidermal layers was significantly increased in patients compared with controls. Five out of 15 patients developed a dermal infiltrate that was associated with increased epidermal influx of T cells and macrophages but not with numbers of apoptotic cells or epidermal deposition of immunoglobulins. Macrophages were ingesting multiple apoptotic bodies. Inflammatory lesions in these patients were localised near accumulations of apoptotic keratinocytes similar as was seen in the majority of LE skin lesions. In vivo clearance rate of apoptotic cells is comparable between SLE patients and controls. However, the presence of inflammatory lesions in the vicinity of apoptotic cells, as observed both in UVB-induced and in LE skin lesions in SLE patients, suggests that these lesions result from an inflammatory clearance of apoptotic cells.     

Is disturbed clearance of apoptotic keratinocytes responsible for UVB-induced inflammatory skin lesions in systemic lupus erythematosus?

Apoptotic cells are thought to play an essential role in the pathogenesis of systemic lupus erythematosus (SLE). We hypothesise that delayed or altered clearance of apoptotic cells after UV irradiation will lead to inflammation in the skin of SLE patients. Fifteen SLE patients and 13 controls were irradiated with two minimal erythemal doses (MEDs) of ultraviolet B light (UVB). Subsequently, skin biopsies were analysed (immuno)histologically, over 10 days, for numbers of apoptotic cells, T cells, macrophages, and deposition of immunoglobulin and complement. Additionally, to compare results with cutaneous lesions of SLE patients, 20 biopsies of lupus erythematosus (LE) skin lesions were analysed morphologically for apoptotic cells and infiltrate. Clearance rate of apoptotic cells after irradiation did not differ between patients and controls. Influx of macrophages in dermal and epidermal layers was significantly increased in patients compared with controls. Five out of 15 patients developed a dermal infiltrate that was associated with increased epidermal influx of T cells and macrophages but not with numbers of apoptotic cells or epidermal deposition of immunoglobulins. Macrophages were ingesting multiple apoptotic bodies. Inflammatory lesions in these patients were localised near accumulations of apoptotic keratinocytes similar as was seen in the majority of LE skin lesions. In vivo clearance rate of apoptotic cells is comparable between SLE patients and controls. However, the presence of inflammatory lesions in the vicinity of apoptotic cells, as observed both in UVB-induced and in LE skin lesions in SLE patients, suggests that these lesions result from an inflammatory clearance of apoptotic cells.     

Role of apoptosis in autoimmunity

Apoptosis is a physiological form of cell death required to ensure that the rate of cell division is balanced by the rate of cell death in multicellular organisms. Dysregulation of apoptosis is associated with the pathogenesis of a wide array of diseases: cancer, neurodegeneration, autoimmunity, heart disease and others. In this review we collect arguments supporting a hypothesis of a dysregulated apoptosis leading to development of autoimmunity like systemic lupus erythematosus (SLE). This notion is supported by occurence of known autoantigens in apoptotic blebs, in vitro findings of an increased rate of apoptotic lymphoblasts despite optimal cytokine stimulation combined with a defective in vitro clearance of apoptotic bodies by SLE phagocytes. Moreover, we and others could generate histone-specific lymphocytic cell lines from cells after activation with autologous apoptotic material. These lymphocytes could stimulate autologous B-lymphocytes to produce of anti-dsDNA antibodies, a diagnostic hallmark for SLE. Finally, antibodies against phospholipids like phosphatidylserine are often associated with systemic autoimmunopathies like SLE and others. Phosphatidylserine is exposed on apoptotic cells as early sign of programmed cell death and serves as phagocyte recognition molecule for apoptotic cells. Formation of immune complexes and deposition in tissues might lead to organ damage and disease. This scenario will be discussed in this review in detail.     

Serum antibodies to human fetal antigens in patients with systemic lupus erythematosus (SLE)

Serum antibodies to human fetal antigens were measured by a radiolabeled anti-immunoglobulin binding assay by using human fetal fibroblasts (Flow cell line No. 1000) as target cells. High titers of IgG antibody to the fetal cells were found in sera of patients with systemic lupus erythematosus (SLE). The antibody reacted with surface membrane antigens shared by various fetal tissues of human and murine origin but not by adult tissues. The reaction of the SLE antibody to the fetal cells was inhibited by heterologous antiserum to the Flow 1000 cells and antiserum to murine embryonic fibroblasts, but not by antiserum to human alpha-fetoprotein or human fibronectin. Absorption of SLE serum with isolated nuclei did not abolish the reaction indicating that these were not anti-nuclear antibodies. The antibody activity was found to reside in the F(ab')2 fragment. The serum titer of the anti-fetal antibody was higher in SLE patients with active disease than those in clinical remission.     

High Affinity Antibodies against Influenza Characterize the Plasmablast Response in SLE Patients After Vaccination

Breakdown of B cell tolerance is a cardinal feature of systemic lupus erythematosus (SLE). Increased numbers of autoreactive mature naïve B cells have been described in SLE patients and autoantibodies have been shown to arise from autoreactive and non-autoreactive precursors. How these defects, in the regulation of B cell tolerance and selection, influence germinal center (GC) reactions that are directed towards foreign antigens has yet to be investigated. Here, we examined the characteristics of post-GC foreign antigen-specific B cells from SLE patients and healthy controls by analyzing monoclonal antibodies generated from plasmablasts induced specifically by influenza vaccination. We report that many of the SLE patients had anti-influenza antibodies with higher binding affinity and neutralization capacity than those from controls. Although overall frequencies of autoreactivity in the influenza-specific plasmablasts were similar for SLE patients and controls, the variable gene repertoire of influenza-specific plasmablasts from SLE patients was altered, with increased usage of JH6 and long heavy chain CDR3 segments. We found that high affinity anti-influenza antibodies generally characterize the plasmablast responses of SLE patients with low levels of autoreactivity; however, certain exceptions were noted. The high-avidity antibody responses in SLE patients may also be correlated with cytokines that are abnormally expressed in lupus. These findings provide insights into the effects of dysregulated immunity on the quality of antibody responses following influenza vaccination and further our understanding of the underlying abnormalities of lupus.     

9G4 autoreactivity is increased in HIV-infected patients and correlates with HIV broadly neutralizing serum activity

The induction of a broadly neutralizing antibody (BNAb) response against HIV-1 would be a desirable feature of a protective vaccine. Vaccine strategies thus far have failed to elicit broadly neutralizing antibody responses; however a minority of HIV-infected patients do develop circulating BNAbs, from which several potent broadly neutralizing monoclonal antibodies (mAbs) have been isolated. The findings that several BNmAbs exhibit autoreactivity and that autoreactive serum antibodies are observed in some HIV patients have advanced the possibility that enforcement of self-tolerance may contribute to the rarity of BNAbs. To examine the possible breakdown of tolerance in HIV patients, we utilized the 9G4 anti-idiotype antibody system, enabling resolution of both autoreactive VH4-34 gene-expressing B cells and serum antibodies. Compared with healthy controls, HIV patients had significantly elevated 9G4+ serum IgG antibody concentrations and frequencies of 9G4+ B cells, a finding characteristic of systemic lupus erythematosus (SLE) patients, both of which positively correlated with HIV viral load. Compared to the global 9G4-IgD--memory B cell population, the 9G4+IgD--memory fraction in HIV patients was dominated by isotype switched IgG+ B cells, but had a more prominent bias toward "IgM only" memory. HIV envelope reactivity was observed both in the 9G4+ serum antibody and 9G4+ B cell population. 9G4+ IgG serum antibody levels positively correlated (r = 0.403, p = 0.0019) with the serum HIV BNAbs. Interestingly, other serum autoantibodies commonly found in SLE (anti-dsDNA, ANA, anti-CL) did not correlate with serum HIV BNAbs. 9G4-associated autoreactivity is preferentially expanded in chronic HIV infection as compared to other SLE autoreactivities. Therefore, the 9G4 system provides an effective tool to examine autoreactivity in HIV patients. Our results suggest that the development of HIV BNAbs is not merely a consequence of a general breakdown in tolerance, but rather a more intricate expansion of selective autoreactive B cells and antibodies.     

High mobility group box 1 (HMGB1) and anti-HMGB1 antibodies and their relation to disease characteristics in systemic lupus erythematosus

Introduction  

High Mobility Group Box 1 (HMGB1) is a nuclear non-histone protein. HMGB1, which is secreted by inflammatory cells and passively released from apoptotic and necrotic cells, may act as a pro-inflammatory mediator. As apoptotic cells accumulate in systemic lupus erythematosus (SLE), HMGB1 levels might be increased in SLE. HMGB1 may also serve as an autoantigen, leading to the production of anti-HMGB1 antibodies. In this study we determined levels of HMGB1 and anti-HMGB1 in SLE patients in comparison to healthy controls (HC) and analysed their relation with disease activity.     

Differentiation of RNP- and SM-antibody subsets in SLE and MCTD patients by a new ELISA using recombinant antigens.

Connective tissue diseases often have overlapping clinical features and laboratory abnormalities. The distinctiveness of mixed connective tissue disease (MCTD) as an entity is of scientific interest and practical importance. In order to discriminate between MCTD and SLE patients we used a newly developed, commercially not available ELISA with recombinant antigen expressed in Baculovirus infected cells. This ELISA detects antibodies against RNP and Sm in complex as well as the subsets U1-snRNP 68 kDa, RNP-A, RNP-C (RNP), Sm-BB' and SS-D. We analyzed 66 RNP-positive consecutive patients prediagnosed as SLE or MCTD/overlap-syndrome. 45/66 patients were found to be U1-snRNP-68 kDa positive (27 SLE, 18 MCTD), 51/66 RNP-A [36,15] and 44/66 RNP-C [31,13]. 35/66 had antibodies against Sm-BB' (30 SLE, 5 MCTD), 10/66 against Sm-D (all SLE). 28/66 were found to be U1-snRNP-68 kDa and Sm-BB' positive (23 SLE, 5 MCTD), while 8/66 where U1-snRNP-68 kDa and Sm-D positive (all SLE). The combination of antibodies against 68 kDa, Aand C was exclusively observed in 6 MCTD patients, while the combination against 68 kDa, A, C, Sm-BB' and Sm-D was restricted to 8 patients with SLE. The antibody combination to 68 kDa, A, C and Sm-BB' was also found in 11/20 SLE patients with major organ involvement. In SLE and MCTD, determination of subsets of antibodies against Ul-snRNP-68 kDa and Sm-complex allows a differentiation of patient subgroups with more definite diagnoses and potential prognostic impact.     

Lysis of prostate carcinoma cells by trifunctional bispecific antibodies (alpha EpCAM x alpha CD3).

Bispecific monoclonal antibodies (bsAbs) are a promising immunotherapeutic option for treatment of cancer, especially in situations of minimal residual disease. The combination of an anti-CD3 and anti-tumor-associated antigen antibody redirects cytotoxic T-lymphocytes towards malignant cells. Using a trifunctional bispecific antibody against EpCAM x CD3, that additionally activates Fc gamma R(+) accessory cells via its Fc region, we investigated the interaction between three EpCAM(+) prostate carcinoma cell lines and peripheral blood mononuclear cells (PBMCs) of healthy donors and patients with prostate carcinoma (PC). Visualization was performed by double immunocytochemical methods and computerized sequential video microscopy. Tumor cells and PBMCs supplemented with alpha EpCAM x alpha CD3 in 16-well chamber slides resulted in lysis of tumor cells within 1--3 days without any differences between patient and healthy donor PBMCs. The characteristic necrotic way of tumor cell killing (rounding, swelling, disrupting) could be observed in computerized sequences of video frames. Simultaneously, we could not reveal any form of apoptotic signal using three different apoptotic markers (TUNEL, M30 cyto death, anti-active caspase 3). Within the first 48 hr we observed typical PBMC cluster formation with increasing cell proliferation. PBMCs surrounding the tumor cells were not dominated by CD4(+), CD8(+), or CD14(+) cells. Lymphocytes with pore-forming perforin proteins concentrated towards the tumor target cells. Our combination of double immunocytochemical and computerized video microscopic techniques may serve as an important improvement of validity of cell-cell interaction experiments using in vitro models. (J Histochem Cytochem 49:911-917, 2001)     

Anti-Ro autoantibody with cross-reactive binding to the heavy chain of immunoglobulin G.

Autoantibodies directed at the intracellular Ro ribonucleoprotein complex are found in the serum of patients with systemic lupus erythematosus (SLE) and related autoimmune diseases. The antigenic stimulus for the induction of these autoantibodies is unknown, although we have previously demonstrated that the Ro protein and immunoglobulin G (IgG) share immunologic determinants bound by anti-Ro antibodies. The present study further defines the fine specificity of this cross-reactive binding. Using both patient autoanti-Ro antibodies and antigen-induced rabbit anti-Ro serum, the binding specificity for IgG was located to the heavy chains of IgG outside the Fc domain. F(ab')2 fragments of IgG were observed to inhibit specific Ro binding by either human or antigen-induced rabbit sera, while Fc fragments of IgG failed to inhibit Ro binding. Anti-Ro sera were found to bind the heavy chains of IgG in immunoblots, and the antibodies eluted from these heavy chains were capable of immunoprecipitating the Ro particle from human cell extracts. Not all patient sera with anti-Ro antibodies possessed IgG binding antibodies. Studies of cyanogen bromide digestion fragments of IgG implicate the hinge region of IgG as the region cross-reactive with the Ro protein. The nature of this cross-reactivity may be important in understanding the induction and/or perpetuation of the anti-Ro response in patients with autoimmune disease.     

52-kDa Ro/SSA epitopes preferentially recognized by antibodies from mothers of children with neonatal lupus and congenital heart block

Neonatal lupus erythematosus is a rare disorder caused by the transplacental passage of maternal autoantibodies. The 52-kDa Ro/SSA antigen (Ro52) ribonucleoprotein represents an antigenic target strongly associated with the autoimmune response in mothers whose children have neonatal lupus and cardiac conduction disturbances, mainly congenital heart block. The objective of this study was to identify putative Ro52/60-kDa Ro/SSA antigen (Ro60) epitopes associated with neonatal lupus and congenital heart block. The reactivity of IgG antibodies present in the sera from mothers with systemic lupus erythematosus and Sj?gren's syndrome and in the sera from asymptomatic mothers (a longitudinal study of 192 samples from 66 subjects) was investigated by ELISA using Ro52, Ro60 and 48-kDa La/SSB antigen proteins, as well as 45 synthetic peptides, 13-24 residues long, of Ro52/Ro60 proteins. One to 19 samples collected before, during and after pregnancy were available for each mother. Forty-three disease controls selected randomly and normal sera were tested in parallel. Although no differences were found between Sj?gren's syndrome and asymptomatic mothers of group I, who had at least one infant with neonatal lupus, and of group II, who had healthy babies only, significant differences were observed between lupus mothers from both groups. In the former group of lupus mothers, a significantly higher frequency of antibodies to Ro52 peptides 107-122 and 277-292 was observed. Between 18 and 30 weeks of gestation, the period of risk, there was clearly an elevated level of antibodies reacting with Ro52 peptides 1-13, 277-292 and 365-382. Antibodies to Ro52 peptide 365-382 have been shown previously to cross-react with residues 165-185 of the heart 5-HT4 serotoninergic receptor, and might be pathologically important. The level of these Ro52 antibody subsets decreased at the end of pregnancy and after delivery. IgG antibodies to Ro52 peptides 1-13, 107-122, 277-292 and 365-382 may therefore represent important biomarkers to predict a complication in pregnant lupus women with Ro52 antibodies.     

Association between anti-nucleophosmin and anti-cardiolipin antibodies in (NZW x BXSB)F1 mice and human systemic lupus erythematosus

We showed previously that nucleophosmin (NPM), a nucleolar phosphoprotein, is recognized by sera from (NZW x BXSB)F1 (WB) mice, a model of systemic lupus erythematosus (SLE) and anti-phospholipid syndrome. In the present study we analysed the prevalence and kinetics of anti-NPM autoantibodies in WB mice by a solid-phase ELISA with recombinant human (rh) NPM as the antigen and showed that most male WB mouse sera had anti-NPM antibodies that were responsible for their indirect immunofluorescence staining pattern on Hep-2 cells. Anti-NPM antibodies were significantly associated with anti-cardiolipin (aCL) antibodies. This antibody profile mirrored that observed in certain human SLE sera because anti-NPM antibodies were detected in 28% of the sera from patients with SLE and were similarly associated with aCL antibodies. The demonstration that rhNPM bound to cardiolipin (CL) in vitro and increased the CL-binding activity of a WB-derived aCL monoclonal antibody indicates that NPM can interact with CL to form SLE-related immunogenic particles that might be responsible for the concomitant production of anti-NPM and aCL antibodies.     

Association between anti-nucleophosmin and anti-cardiolipin antibodies in (NZW × BXSB)F1 mice and human systemic lupus erythematosus

We showed previously that nucleophosmin (NPM), a nucleolar phosphoprotein, is recognized by sera from (NZW × BXSB)F₁ (WB) mice, a model of systemic lupus erythematosus (SLE) and anti-phospholipid syndrome. In the present study we analysed the prevalence and kinetics of anti-NPM autoantibodies in WB mice by a solid-phase ELISA with recombinant human (rh) NPM as the antigen and showed that most male WB mouse sera had anti-NPM antibodies that were responsible for their indirect immunofluorescence staining pattern on Hep-2 cells. Anti-NPM antibodies were significantly associated with anti-cardiolipin (aCL) antibodies. This antibody profile mirrored that observed in certain human SLE sera because anti-NPM antibodies were detected in 28% of the sera from patients with SLE and were similarly associated with aCL antibodies. The demonstration that rhNPM bound to cardiolipin (CL) in vitro and increased the CL-binding activity of a WB-derived aCL monoclonal antibody indicates that NPM can interact with CL to form SLE-related immunogenic particles that might be responsible for the concomitant production of anti-NPM and aCL antibodies.