Heterogeneity of the Ro/SSA antigen. Different molecular forms in lymphocytes and red blood cells

Autoantibodies against the Immunoglobulin-Binding Region of Ro52 Link its Autoantigenicity with Pathogen Neutralization

Ro52/TRIM21 plays a key role in antibody-dependent pathogen neutralization and is a major autoantigen in systemic lupus erythematosus, Sjögren's syndrome (SS), and other autoimmune diseases. Here we evaluated immunoreactivity against Ro52-related molecules in SS and healthy volunteers. Although most proteins examined were not antigenic, several TRIM paralogs, including TRIM22, and TRIM38, showed sporadic immunoreactivity in SS. In contrast, the murine Ro52 ortholog with limited linear homology demonstrated high levels of autoantibodies implicating the importance of shared conformational epitopes. To further explore the autoantigencity of Ro52, deletion and point mutant analyses were employed revealing previously hidden, robust autoantibodies directed against its C-terminal immunoglobulin-binding domain. Another autoantibody, rheumatoid factor, targeting the Fc region of IgG, strongly overlapped with Ro52 seropositivity (odds ratio 14; P < 0.0001). These convergent mechanistic findings support a model whereby intracellular Ro52-bound antibody-coated pathogen complexes, released or misprocessed from infected cells, drive autoantigenicity against Ro52 and the Fc region of IgG.

Analysis of the downstream mediators of toll-like receptor 3-induced apoptosis in labial salivary glands in patients with Sjögren's syndrome

OBJECTIVES

The aim of this study was to clarify the molecular mechanisms elicited by toll-like receptor (TLR)3 in salivary gland cell death in patients with SS.

METHODS

Expression of TLR3 and its downstream molecules was examined by immunohistochemical analysis, immunofluorescence, Western blot (WB), and antibody dot-blot array in labial salivary glands (LSGs), and cultured primary salivary gland epithelial cells (SGECs) obtained from patients with SS. We also investigated the difference of expression between ducts/alveoli of LSGs and cultured SGECs.

RESULTS

Phosphorylated Fas-associated protein with death domain (p-FADD) or caspase-8 was not found in ducts or alveoli of LSGs from SS patients and controls. Weak expression of receptor-interacting serine/threonine-protein kinase 3 (RIPK3) was found in SS patients, whereas no staining was observed in LSGs of controls. In contrast to LSGs, stimulation of SGECs with polyinosinic:cytidylic acid (poly I:C) significantly induced the expression of RIPK3, p-FADD, and cleaved caspase-8 by immunofluorescence and RIPK3, p-FADD, and cleaved caspase-3 by WB. However, it was counteracted by epidermal growth factor (EGF). Co-localization of anti-apoptotic molecules hemeoxygenase-2, heat shock protein 27, and p-protein kinase B or p-Akt was induced in EGF-stimulated SGECs.

CONCLUSIONS

We observed that poly I:C induced apoptosis of SGECs in vitro compared with a relatively low prevalence of apoptosis found in the ducts and alveoli of LSGs in vivo. Thus, we speculate that other counter-regulatory mechanisms, including those induced by EGF, might exist to protect against TLR3-mediated apoptosis of ductal and acinar epithelial cells in vivo.

Anti-SS-A/Ro antibody determination by indirect immunofluorescence and comparison of different methods of anti-nuclear antibody screening: evaluation of the utility of HEp-2 cells transfected with the 60 kDa SS-A/Ro as a substrate

We evaluated the utility of HEp-2 cells transfected with the 60 kDa SS-A/Ro as a substrate for indirect immunofluorescence (IIF-HEp-2000) to compare several methods for screening Japanese serum samples for anti-SS-A/Ro antibodies. Serum samples from 243 Japanese patients were analyzed by IIF for anti-nuclear antibodies (ANAs), using HEp-2 cells (IIF-HEp-2), and for anti-SS-A/Ro 60 kDa antibodies, using IIF-HEp-2000 and enzyme-linked immunosorbent assay (ELISA). We performed double immunodiffusion and immunoprecipitation experiments, using the products of in vitro transcription and translation, to analyze sera for which there were discrepancies in the results of the IIF-HEp-2000 assay and ELISA. A total of 93 of the 243 serum samples showed findings positive for anti-SS-A/Ro antibodies. Notably, eight of the 93 sera gave positive findings for anti-SS-A/Ro antibodies by IIF-HEp-2000 but ANA-negative by IIF-HEp-2 analysis. Seven sera possessing anti-SS-A/Ro antibodies gave false negative results by IIF-HEp-2000; however, those samples were all ANA positive. ELISA for anti-SS-A/Ro antibodies showed that five and two samples gave false positive and negative results, respectively. Analysis by IIF-HEp-2000 was useful for primary screening of patients for ANAs, especially for anti-SS-A/Ro antibodies; the test could detect anti-SS-A/Ro antibodies not identified on standard substrates in samples obtained from the Japanese population, as reported for the Caucasian population.

SSA/Ro52 autoantigen interacts with Dcp2 to enhance its decapping activity

We identified human decapping enzyme 2 (hDCP2) as a binding protein with Ro52, being colocalized in processing bodies (p-bodies). We also showed that the N-terminus and C-terminus of Ro52 bound to hDCP2. Moreover, Ro52 enhanced decapping activity of hDCP2 in a dose-dependent manner. Our data support the novel notion of the association between Ro52 with hDCP2 protein in cytoplasmic p-bodies, playing a role in mRNA metabolism in response to cellular stimulation.

Sjögren's syndrome in dermatology

Sjogren's Syndrome (SS) is a systemic autoimmune disease characterized by dry eyes (keratoconjunctivis sicca) and dry mouth (xerostomia). To fulfill diagnostic criteria, patients must have objective signs of dryness on examination and laboratory confirmation of an autoimmune process as evidenced by a positive autoantibody to SS-A antigen or a characteristic lip biopsy. SS may exist as a primary condition or in association with other systemic autoimmune disorders (termed secondary SS) such as rheumatoid arthritis, systemic lupus erythematous (SLE), progressive systemic sclerosis (scleroderma), or dermatomyositis. Exclusions to the diagnosis include pre-existing lymphoma, hepatitis C or HIV infection. Pathogenesis involves both genetic (especially HLA-DR) and environmental factors. Both T-cells and B-cells are involved in the generation of cytokines and chemokines within the glands. The epithelial cells of the glands also play a role in pathogenesis. The dermatologic manifestations range from drynessness (sicca) and its complications to vasculitis. There is a significant overlap in the clinical manifestations, as well as treatment, of SS and SLE. However, SS patients require special attention to the complications of ocular dryness (keratocojunctivitis sicca and blepharitis) and oral dryness (rapid tooth loss and oral candidiasis) SS patients have a markedly increased risk of lymphoma and enlarged lymph nodes or persistently enlarged parotid/submandibular glands that require further evaluation.

Incidence and spectrum of neonatal lupus erythematosus: a prospective study of infants born to mothers with anti-Ro autoantibodies

OBJECTIVE

Neonatal lupus erythematosus (NLE) is characterized by complete congenital heart block (CCHB), cutaneous rash, and laboratory abnormalities in infants born to mothers with autoantibodies directed against SSA/Ro, SSB/La, or both. We carried out a prospective study to determine the incidence of individual NLE features.

STUDY DESIGN

The study was performed in two centers: Toronto, Canada, and Milano, Italy. Mothers had been referred for the presence of anti-SSA/Ro autoantibodies, regardless of their diagnosis. All the children were seen at least once within the first 6 months of life for clinical evaluation and laboratory testing. The study group consisted of 128 infants born from 124 pregnancies in 112 women with anti-Ro antibodies with or without anti-La antibodies.

RESULTS

There were two cases of CCHB for an overall percentage of 1.6%. Twenty-one children (16%) developed cutaneous NLE. Laboratory testing showed hematologic abnormalities in 27% of the babies and elevation of liver enzymes in 26%.

CONCLUSIONS

Mothers with autoimmune diseases and anti-Ro antibodies are at risk of delivering a child with NLE but at a low risk of delivering a child with CCHB. Infants born to mothers with anti-Ro or anti-La antibodies should be monitored for other features of NLE in addition to CCHB.

SS-A/Ro52, an autoantigen involved in CD28-mediated IL-2 production

An autoantibody against SS-A/Ro52 (Ro52) is most frequently found in the sera of patients with Sjögren's syndrome, systemic lupus erythematosus, and congenital heart block from anti-Ro52 Ab-positive mother. However, the physiological function of the autoantigen SS-A/Ro52 has not yet been elucidated. In this study, we describe the role of Ro52 protein in T cell activation. Overexpression of SS-A/Ro52 in Jurkat T cell resulted in enhanced IL-2 production following CD28 stimulation. Furthermore, transfection of anti-Ro52-specific small RNA duplexes partially blocked the expression of native and overexpressed Ro52 in Jurkat T cell, resulting in decreased IL-2 production via CD28 pathway in these cells. Finally, intracellular localization of Ro52 dramatically changed following CD28 stimulation. Our data reveal a novel function of Ro52 in CD28-mediated pathway, which eventually contributes to cytokine production and expression of the T cell biological programs.

Specificity of autoantibodies to SS-A/Ro on a transfected and overexpressed human 60 kDa Ro autoantigen substrate

The objective of this study was to analyze apparently discrepant results that arose during the use of an indirect immunofluorescence (IIF) assay using transfected HEp-2 cells to detect anti-SS-A/Ro autoantibodies in human sera. Fourteen sera that had SS-A/Ro antibodies as detected on this commercial substrate, but did not have antibodies to SS-A/Ro as determined by double immunodiffusion (ID) or enzyme-linked immunosorbent assay (ELISA), were studied by immunoprecipitation (IP) of radiolabeled cell extracts and full-length recombinant SS-A/Ro. A multi-antigen strip immunoblotting (IB) assay containing both the 52- and 60-kDa antigens was included in the analysis. We confirmed that 12 of 14 of the sera under study had antibodies to SS-A/Ro protein antigens as determined by at least one other immunoassay. One serum had antibodies to hyRNA but no detectable reactivity with the 52- or 60-kDa antigens. One serum remained negative in all assays for SS-A/Ro autoantibodies.

Comparison of the anti-Ro/SSA autoantibody profile between patients with primary and secondary Sjögren's syndrome

OBJECTIVE

To measure serum levels of anti-Ro52-kD/SSA, anti-Ro60-kD/SSA and anti-La/SSB autoantibodies in patients with primary and secondary Sjögren's syndrome. To examine if there is any connection between the disease and the subtype-spectrum of these antibodies.

METHODS

We measured serum levels of anti-Ro52-kD/SSA, anti-Ro60-kD/SSA and anti-La/SSB autoantibodies by ELISA, in the sera of patients with primary Sjögren's syndrome with or without extraglandular manifestations and with or without anti-La/SSB positivity and of patients with systemic lupus erythematosus/Sjögren's syndrome overlapping disease with or without anti-La/SSB positivity.

RESULTS

Differences of the distribution of the anti-Ro52-kD/SSA and the anti-Ro60-kD/SSA were found between the primary and secondary Sjögren's syndrome patients' groups; when Sjögren's syndrome is accompanied by systemic lupus erythematosus, the occurrence of anti-Ro60-kD/SSA autoantibodies is significantly higher than in primary Sjögren'syndrome.

CONCLUSION

Our results suggest that there is a possible connection between the distribution of the subtypes of the anti-Ro/SSA autoantibodies and the disease type in primary/secondary Sjögren's syndrome.

Interaction cloning and characterization of RoBPI, a novel protein binding to human Ro ribonucleoproteins

Human Ro ribonucleoproteins (RNPs) are autoantigenic particles of unknown function(s) that consist of a 60-kDa protein (Ro60) associated with one hY RNA (hY1-5). Using a modified yeast three-hybrid system, named RNP interaction trap assay (RITA), we cloned a novel Ro RNP-binding protein (RoBPI), based on its property to interact in vivo in yeast with an RNP complex made of recombinant Ro60 (rRo60) protein and hY5 (rhY5) RNA. RoBPI cDNA contains three conserved RNA recognition motifs (RRM) and is present as a family of isoforms differing slightly at their 5' end. The 2.0-kb RoBPI mRNA was detected in all human tissues tested. Highly homologous cDNA sequences were found in banks of expressed sequence tags (ESTs) from mice. Two-hybrid, three-hybrid, and RITA experiments respectively established that 60 kDa RoBPI did not interact in yeast with rRo60 alone, with rhY5 RNA alone, or with bait RNPs consisting of rRo60 and recombinant hY1, hY3, or hY4 RNAs. RoBPI coimmunoprecipitated with Ro RNPs from HeLa cell extracts and partially colocalized with Ro60 in nuclei of cultured cells. Because hY5 RNA and RohY5 RNPs are recent evolutionary additions seen only in primates, but RoBPI seems more conserved, their interaction may represent a gain of function for Ro RNPs. Alternatively, interaction of RohY5 RNPs with RoBPI may have no functional bearing, but may underlie some of the unique biochemical and immunological properties of these RNPs.

The 5S rRNA is associated with Ro60 ribonucleoprotein and is co-precipitated with hYRNAs by anti-Ro antibodies

Ro particles are conserved molecules that contain a YRNA and various Ro proteins, which are recognized by autoimmune sera from patients with lupus erythematosus or Sjögren's syndrome. The Ro60 ribonucleoprotein (RNP) forms complexes with certain 5S rRNAs, in such a manner that Ro60 could participate in the control of 5S rRNA production. The present studies were carried out to explore the interaction of Ro components, and to address the question whether Ro60 RNP binds simultaneously 5S rRNA and hYRNA. Anti-Ro60 antibodies were used to immunoprecipitate the RNA. Immunoprecipitates were reverse transcribed with specific oligonucleotides and the resulting cDNAs from 5S and hY4 were amplified by PCR. We found that 5S rRNA is complexed with hY4 and hY5 RNAs by means of the Ro60 RNP. Moreover, by in situ hybridization assays we were able to demonstrate that these molecules have a similar nuclear distribution. According to these results, it seems reasonable to assume that the Ro60 protein could be involved in ribosome assembly.

Analysis of B-cell epitopes of the Ro/SS-A autoantigen

Autoantibodies to the Ro and La ribonucleoprotein antigens are found in several rheumatoid diseases. The important epitopes have been studied using synthetic peptides and recombinant antigens to understand how they arise and their implication in disease. Here, we analyse the results of epitope mapping studies of Ro60 and Ro52 autoantigens and focus on the major findings to date.

Ro/SS-A and La/SS-B antibody level variation in patients with Sjögren's syndrome and systemic lupus erythematosus

To examine both possible correlations between anti-Ro/SS-A and anti-La/SS-B levels and their correlation with clinical disease activity in patients with Sjögren's syndrome (SS) or systemic lupus erythematosus (SLE), an ELISA was developed using purified recombinant Ro 60 kDa, Ro 52 kDa and La antigens. The ELISA was used for testing sequential serum samples from 16 patients with either SS or SLE. The patients were followed for periods between 15 and 128 months, and 3-15 serum samples per patient were analysed and compared with clinically apparent disease activity at the time of sampling in 14 patients. A temporal correlation of antibody levels to Ro and La antigens was found, and antibodies to different epitopes of the Ro 60 kDa protein showed parallel variation in seven of eight patients tested. Co-variation of autoantibody levels and disease activity was found in 11 of 14 patients. In seven of these 11 patients the anti-Ro and anti-La levels were stable and changes in disease activity were minimal during the observation period. In the other four of these 11, changes in disease activity were noted, with an associated change in autoantibody levels. The results suggest that the serological response to Ro and La antigens, as well as to different epitopes of the Ro 60 kDa protein, is antigen driven and regulated by common mechanisms, and indicate a correlation of Ro and La antibodies with pathogenic events.

Systemic lupus erythematosus: clinical expression and anti-Ro/SS--a response in patients with and without lesions of subacute cutaneous lupus erythematosus

Patients with subacute cutaneous lupus erythematosus (SCLE) have recurrent annular and/or psoriasiphorm skin lesions, with or without systemic disease.

OBJECTIVE

To analyse the clinical expression and the Ro/SS-A response associated with SCLE in patients with systemic lupus erythematosus (SLE).

METHODS

128 consecutive patients with SLE were studied. Anti-Ro/SS-A antibodies were detected by ELISA, (anti-60 kD Ro/SSA antibodies), immunoblotting (anti-60 kD and anti-52 kD Ro/SS-A antibodies) and counterimmunoelectrophoresis (CIE).

RESULTS

Seventeen patients (13.2%) showed SCLE lesions. Photosensitivity was more frequent in patients with SCLE (82%) than in patients without these cutaneous lesions (45%) (OR: 5.6). Arthritis (OR: 6.3), Raynaud's phenomenon (OR: 4.9), pleuritis (OR: 7.6), central nervous system disorder (OR: 6.4), renal disease (OR: 6.3), anemia (OR: 7.9), hypocomplementemia (OR: 6.1) and anti-dsDNA antibodies (OR: 12.7) were significantly more frequent in patients without SCLE. Anti-Ro/SS-A antibodies were detected in 15 (88.2%) patients with SCLE and 62 (55.8%) patients without SCLE by ELISA, in 10 (58.8%) and 34 (30.6%) patients by immunoblotting, and in 13 (76.4%) and 34 (30.6%) by CIE, respectively. Anti-60 kD-Ro/SS-A and anti-La antibodies, but not anti-52 kD-Ro/SS-A, were significantly more frequent in patients with SCLE than in patients without SCLE.

CONCLUSIONS

The presence of SCLE lesions in patients with SLE is associated with a more favourable prognosis. The major anti-Ro/SS-A response is directed against the native 60 kD Ro/SS-A protein.

A subpopulation of WIL-2 cell calreticulin molecules is associated with RO/SS-A ribonucleoprotein particles

A subpopulation of human calreticulin (CR) molecules that is reactive with human Ro/SS-A autoimmune sera was identified in a nucleic acid- enriched Wil-2 cell fraction derived by anion exchange column chromatography. Further resolution of this fraction by gel filtration size separation demonstrated that the appearance of CR (true mol. weight 46 kD) coincided with the emergence of Ro/SS-A ribonucleoprotein (mol. weight > 250 kD) antigenic activity and increasing 260 nm ultraviolet absorbance. This high nucleic acid fraction could be further partitioned into four small RNA-containing Ro/SS-A antigenic subfractions by a second passage over the anion exchange column. CR was enriched in one subfraction and present in the other three subfractions as well. No CR was found in the RNA-free fraction of the repartition eluate. These results represent the first direct demonstration that CR, a high-affinity calcium binding protein, exists in a form that is directly associated with all four varieties of native, human Ro/SS-A ribonucleoprotein particles (hY1-5).

17-beta-estradiol increases expression of 52-kDa and 60-kDa SS-A/Ro autoantigens in human keratinocytes and breast cancer cell line MCF-7

SS-A/Ro autoantibodies are detected in high frequency in patients with subacute cutaneous lupus, neonatal lupus, systemic lupus erythematosus, and Sjögren syndrome. It has been reported that estrogen was capable of inducing cell surface expression of SS-A/Ro antigens in human keratinocytes, although the molecular forms of the antigen or antigens were not defined. In this study, we analyzed the effects of estrogen on cultured cells by reverse transcriptase polymerase chain reaction and Western blot analysis with respect to both 52-kDa and 60-kDa SS-A/Ro autoantigens. At concentrations of 10(-8) to 10(-7) M, 17-beta-estradiol induced up to a 5-fold increase of both 52-kDa and 60-kDa SS-A/Ro mRNA in human keratinocytes compared with untreated cells. Hormonal depletion of the human breast cancer cell line MCF-7 showed decreased levels of SS-A/Ro mRNA and protein, and the addition of estradiol led to an increase in SS-A/Ro expression. The estrogenic effect might be mediated through estrogen receptor and the putative estrogen response element at the 5' region of both SS-A/Ro genes. If the production of autoantibodies is governed at least in part by an antigen-driven process, as has been proposed, our results linking the expression of both forms of SS-A/Ro proteins to estrogenic stimulation may help to explain the high frequency of anti-SS-A/Ro autoantibodies observed in diseases affecting predominantly females.

Heterogeneity in the expression of Ro and La antigens in human skin

OBJECTIVE

To determine whether there are variations in the expression of Ro and La antigens in human skin.

METHODS

Levels of expression of Ro and/or La antigens in 26 specimens of normal human skin (11 sun-exposed, 15 sun-protected) were measured by indirect immunofluorescence with monospecific antisera.

RESULTS

Levels of expression of both antigens varied by more than 2,000-fold in the skin of different individuals. There usually was a correlation between the levels of expression of Ro and La antigens in the same skin specimen. There was no correlation found between the levels of Ro or La antigen expression and sun exposure, nor was there a correlation found between levels of antigen expression and location of the skin on the body.

CONCLUSION

There is a marked heterogeneity in the expression of both Ro and La antigens in the skin of different individuals. The present study findings suggest that the levels of expression of these antigens may play a role in the propensity of some individuals to develop anti-Ro or anti-La antibodies and/or skin lesions associated with the presence of these antibodies.

Characterization of murine monoclonal antibodies against 60-kD Ro/SS-A and La/SS-B autoantigens

Small cytoplasmic ribonucleoproteins (scRNPs) are important autoantigens in patients with systemic lupus erythematosus and Sjögren's syndrome. MoAbs against these proteins were made by immunization of BALB/c mice with purified human recombinant 60-kD Ro/SS-A or 50-kD La/SS-B proteins. Five stable hybridoma cell lines were obtained, of which four secreted anti-Ro/SS-A antibodies (clones 1D8, 1D11, 2G10 and 6G8) and one produced anti-La/SS-B antibodies (clone 7F6). The MoAbs were further characterized using four different immunoassays: immunofluorescence, immunoblotting, RNA precipitation combined with Northern blotting, and recombinant protein precipitation. All four MoAbs against Ro/SS-A recognized the native protein and one of them (2G10) recognized also intact scRNP particles. Interestingly, hY3-RNA was reproducibly not efficiently precipitated by MoAb 2G10. Epitope mapping using deletion mutants of the 60-kD Ro/SS-A antigen showed that MoAb 1D8 recognized the C-terminal part of this protein, while 1D11 and 2G10 recognized distinct epitopes in the region between the RNP motif and the putative zinc finger domain. The epitopes recognized by these MoAbs are highly conserved among species, and the epitope recognized by MoAb 2G10 may be identical to an autoepitope recognized by sera of patients. This is the first report describing the isolation and characterization of MoAbs of the IgG class against the 60-kD Ro/SS-A and La/SS-B autoantigens obtained by immunization with purified human recombinant proteins. These MoAbs can be of great use in studying the cellular processes in which scRNPs are involved, and may help to determine why these scRNPs become autoantigenic in autoimmune diseases.

Purification of antigenically intact Ro ribonucleoproteins; biochemical and immunological evidence that the 52-kD protein is not a Ro protein

Anti-Ro sera immunoprecipitate Ro ribonucleoproteins (RNPs) from human cell extracts. Ro RNPs are biochemically heterogeneous particles whose functions are unknown and whose exact composition remains controversial. In addition to 60-kD Ro and to La proteins, a 52-kD polypeptide (p52) has been proposed to be a stable component of the Ro RNPs. To confirm the immunological studies supporting this hypothesis, we have biochemically purified Ro RNPs from HeLa cells using non-denaturing conditions. Ro RNPs segregated into three distinct populations, one of which only contained hY5 RNA (RohY5 RNPs). No p52 co-purified with Ro RNPs. Despite the absence of p52, purified Ro RNPs had biochemical and immunological properties identical to those of unfractionated Ro RNPs. Many anti-Ro sera only recognize p52 in immunoblots, and are said to be monospecific anti-p52. Preincubation with purified RohY5 RNPs (free of p52) of all human anti-Ro (including so-called monospecific anti-p52) sera abolished their capacity to immunoprecipitate Ro RNPs from unfractionated HeLa cell extracts. Conversely, preincubation of anti-Ro sera with purified p52 protein specifically inhibited recognition of p52 in immunoblots, but did not interfere with immunoprecipitation of Ro RNPs. Our data demonstrate that anti-p52 antibodies do not target intact Ro RNPs, nor do they target the native 60-kD Ro protein. Contrary to previous reports, p52 protein is not a stable component of antigenically intact Ro RNPs.

Pristane induces high titers of anti-Su and anti-nRNP/Sm autoantibodies in BALB/c mice. Quantitation by antigen capture ELISAs based on monospecific human autoimmune sera

Autoantibodies to Su and anti-nRNP/Sm are common in human and murine systemic lupus erythematosus (SLE), and are also produced by BALB/c mice with SLE-like autoimmunity induced by pristane. Antigen capture ELISAs employing monospecific human autoimmune IgG were developed to quantitate the production of anti-Su and anti-nRNP/Sm autoantibodies in 77 sera from BALB/c mice with pristane-induced autoimmunity. The sensitivity and specificity of the anti-Su antigen capture ELISA were 100% compared with immunoprecipitation of 35S-labeled cellular proteins. All 16 immunoprecipitation positive sera were positive in the anti-nRNP/Sm antigen capture ELISA (100% sensitivity), whereas 55/61 immunoprecipitation negative sera were negative by ELISA (90% specificity). The 6/61 immunoprecipitation negative sera that were ELISA positive were probably true positives because subsequent sera obtained from the same mice were positive by both techniques. Thus, the antigen capture ELISA may be somewhat more sensitive than immunoprecipitation. The titers of anti-Su and anti-nRNP/Sm positive antibodies in the sera were as high as 1:25,000-1:250,000 by ELISA, suggesting that autoantibodies may be produced in pristane-primed BALB/c mice at levels comparable to those seen in spontaneous autoimmune disease. We conclude that antigen capture ELISAs based on human autoimmune sera were highly sensitive and specific for detecting murine anti-Su and anti-nRNP/Sm antibodies. This technique will be useful for quantitating antibodies in murine autoimmune disease models, since antigen capture ELISA avoids the use of denatured or recombinant antigens, permitting antibodies recognizing tertiary and quaternary structures to be detected.

Phosphorylation profiles of 60 kD Ro antigen in synchronized HEp-2 cells

The purpose of this study was to determine whether phosphorylation has an effect on the characteristics of the 60 kD Ro antigen throughout the cell cycle. Cell extracts of synchronized HEp-2 cells were phosphorylated in vitro with exogenous ATP, examined by SDS-PAGE and Western blot, and probed with specific anti-Ro sera. In addition, cellular ATP pools were radiolabelled in vivo with 32P. The presence of the Ro protein was detected with a molecular weight of 60 kD during all phases of the cell cycle, except at the M phase, where it was increased to 65 kD. Phosphorylation of the in vitro and in vivo cell extracts increased the molecular mass to 65 kD. Moreover immunoprecipitation assays demonstrated that Ro is hyperphosphorylated in the M phase. Phosphorylation did not change the recognition pattern of the anti-Ro sera.

Detection of autoantibodies to SS-A/Ro by indirect immunofluorescence using a transfected and overexpressed human 60 kD Ro autoantigen in HEp-2 cells

The objective of the study was to determine the sensitivity and specificity of an indirect immunofluorescence (IIF) assay using transfected HEp-2 cells to detect anti-SS-A/Ro autoantibodies in human sera. Seventy-three sera having SS-A/Ro autoantibodies as determined by double immunodiffusion (ID) and immunoblotting (IB) were tested by IIF on a HEp-2 cell substrate that had been transfected with a full-length cDNA encoding a human 60 kD SS-A/Ro autoantigen. Controls included 30 normal human sera and 50 sera with a variety of other antinuclear antibodies. Prototype human and rabbit sera directed against the 60 kD SS-A/Ro antigen produced intense speckled nuclear and nucleolar staining of transfected cells. Sixty-nine of 73 (95%) SS-A/Ro positive sera also produced this characteristic staining pattern. The endpoint autoantibody titers on transfected cells was fivefold greater than on untransfected cells. The 30 normal human sera and the 50 sera with other antinuclear antibodies did not produce this characteristic staining. Six of 32 (19%) unselected sera that were sent for autoantibody testing had reactivity with transfectants by IIF. Four of the six sera were confirmed to have anti-SS-A/Ro antibodies by ID and 5/6 by IB. By contrast, only three of these sera were scored as having a staining pattern compatible with SS-A/Ro antibodies by IIF on standard HEp-2 substrates. We conclude that SS-A/Ro autoantibodies can be detected by an IIF assay using a HEp-2 cell substrate transfected with a SS-A/Ro cDNA. This new substrate detects SS-A/Ro antibodies that were not identified on standard HEp-2 substrates and by other immunoassays.

Stress-induced cell surface expression and antigenic alteration of the Ro/SSA autoantigen

Recent studies have shown that Ro/SSA autoantigen is heterogeneous. There are two isoform families; the 60 kD forms (Ro60) and the 52 kD forms (Ro52). Recently we have found that autoantibodies to the Ro/SSA proteins are conformation dependent. Anti-Ro60 antibodies are mainly directed to the native protein and conversely anti-Ro52 antibodies are directed only to the denatured protein. It has been known that UV irradiation to cultured keratinocytes induces cell surface expression of Ro/SSA and this phenomenon has been thought to be related with photosensitivity in patients with anti-Ro/SSA antibodies. We studied the quantitative and qualitative changes of the Ro/SSA protein induced by stress, such as with heat shock and UV irradiation, and found that only Ro52 could be expressed on the cell surface of human peripheral lymphocytes by either heat shock or UV irradiation. Moreover, flow cytometric analysis revealed that HS-treated and UV-treated lymphocytes could be stained with patient sera, and by using a technique which combined immunoprecipitation and Western immunoblotting, it has been confirmed that Ro52 expressed on the cell surface can be recognized by anti-Ro/SSA antibodies in native form while cytoplasmic Ro52 cannot be recognized. These data suggest that Ro52 can be antigenic in vivo when expressed on the cell surface and may explain the mechanism of direct tissue damage by anti-Ro/SSA antibodies.

Analysis of the intracellular localization and assembly of Ro ribonucleoprotein particles by microinjection into Xenopus laevis oocytes

Xenopus laevis oocytes have been used to determine the intracellular localization of components of Ro ribonucleoprotein particles (Ro RNPs) and to study the assembly of these RNA-protein complexes. Microinjection of the protein components of human Ro RNPs, i.e., La, Ro60, and Ro52, in X. laevis oocytes showed that all three proteins are able to enter the nucleus, albeit with different efficiencies. In contrast, the RNA components of human Ro RNPs (the Y RNAs) accumulate in the X. laevis cytoplasm upon injection. Localization studies performed at low temperatures indicated that both nuclear import of Ro RNP proteins and nuclear export of Y RNAs are mediated by active transport mechanisms. Immunoprecipitation experiments using monospecific anti-La and anti-Ro60 antibodies showed that the X. laevis La and Ro60 homologues were cross-reactive with the respective antibodies and that both X. laevis proteins were able to interact with human Y1 RNA. Further analyses indicated that: (a) association of X. laevis La and Ro60 with Y RNAs most likely takes place in the nucleus; (b) once formed, Ro RNPs are rapidly exported out of the nucleus; and (c) the association with La is lost during or shortly after nuclear export.

Lymphocyte and neuronal antigens in neuropsychiatric lupus: presence of an elutable, immunoprecipitable lymphocyte/neuronal 52 kd reactivity

OBJECTIVE

To examine specific lymphocyte or neuronal antigens immuno-precipitated by systemic lupus erythematosus (SLE) sera.

METHOD

SLE sera were screened for the presence of antibodies binding to surface antigens of CD4(+) HUT-78 or SK-N-SH and IMR-6 neuroblastoma cells using Western blotting or radioimmunoprecipitation.

RESULTS

IgG eluates from both lymphocytes and neuroblastoma cells recognised a 52 kd band in HUT 78 cell lysates. Eight sera studied further using radioimmunoprecipitation also demonstrated binding to a 52 kd antigen (4/8 on HUT-78, 8/8 on SK-N-SH cells), partially depleted by absorption with viable HUT-78.

CONCLUSION

A 52 kd antigen recognised by SLE sera on lymphocytes and neuronal cells may play a role in the pathogenesis of neuropsychiatric-SLE.

Molecular composition of Ro small ribonucleoprotein complexes in human cells. Intracellular localization of the 60- and 52-kD proteins

Ro small ribonucleoprotein complexes (RoRNPs) are thought to comprise several proteins, including the 60-kD Ro and the 52-kD Ro proteins, and several small RNAs, designated Y RNAs. Although RoRNPs are fairly ubiquitous in nature, their precise composition remains unknown, their function has been elusive, and their intracellular localization has been controversial. We have analyzed HeLa cell extracts by glycerol density gradient fractionation in order to determine the distribution of the individual protein and RNA components of RoRNPs. We found that 52-kD Ro was not detectable in an RNP complex with the 60-kD protein under a variety of conditions. Pretreatment of cell extracts with ribonuclease affected gradient migration of the 60-kD but not the 52-kD protein, suggesting that the latter is not complexed with RNA. The migration of the hY RNAs in these gradients closely followed that of 60-kD and not 52-kD Ro. Immunofluorescence analysis of two different cell lines with monospecific antibodies against 52- and 60-kD proteins strongly suggests that these two proteins are not present on overlapping sets of structures in vivo. We conclude that the 52-kD Ro protein is not a detectable component of the RoRNP complex under these conditions despite its reactivity with Ro autoimmune antisera.

Lymphocyte antigens in neuropsychiatric systemic lupus erythematosus. Relationship of lymphocyte antibody specificities to clinical disease

OBJECTIVE

To examine the relationships among specific lymphocyte antigenic reactivities of lupus sera and central nervous system complications of systemic lupus erythematosus (SLE), lymphocytotoxic antibody (LCA) positivity, and specific cognitive impairment.

METHODS

Sera from 115 patients with SLE were examined for the presence of IgM- and IgG-class autoantibodies binding to surface target antigens on lymphocytes, by immunoblotting and microdroplet lymphocytotoxicity studies. Seventy-three of these patients also underwent detailed neuropsychological testing within the same time period.

RESULTS

Significant associations were found between reactivities to several lymphocyte antigenic moieties and neuropsychiatric SLE (NPSLE) or cognitive impairment. Specifically, immunoblot reactivities to 31-32-kd, 50-52-kd, 54-56-kd, and 97-98-kd targets were associated with clinical NPSLE; there was a significant association between reactivity to the 50-52-kd moiety in particular and cognitive impairment. There were also associations between LCA and immunoblot reactivity. Furthermore, the previously reported association between LCA positivity and specific visuospatial cognitive impairment was confirmed with data obtained from 2 different batteries of neuropsychological tests.

CONCLUSION

In some cases, specific antigenic targets of LCA-containing sera may be implicated in the pathogenesis of NPSLE:

Epitope mapping of the 52-kD Ro/SSA autoantigen

Autoantibodies to Ro/SSA are commonly found in sera of patients with systemic lupus erythematosus (SLE) and primary Sjögren's syndrome. The presence of these antibodies is related to lymphopenia, photosensitive dermatitis, and pulmonary and renal disease, suggesting that they have an immunopathologic role [1-6]. We previously isolated a cDNA clone which encodes the 52-kD human Ro/SSA protein. In this study we have determined the number and location of epitopes recognized by SLE sera using recombinant proteins encoded by the full-length or overlapping subclones of this cDNA. An immunodominant epitope was detected using Western blots and ELISA on the NH2-terminal side of this protein's putative leucine zipper. The data suggest that 11 amino acids are critical for the recognition of this molecule by these autoantibodies. Although the titres of anti-52-kD Ro/SSA antibodies vary between different patient sera, no heterogeneity in the location of antigenic epitopes to which their autoantibodies bound was detected. This homogeneous pattern of reactivity to a single rather than multiple regions of this protein is unusual for lupus autoantigens which have been identified, and suggests that these antibodies may have arisen as by a cross-reaction to an epitope on another molecule.

IgM and IgG subclass distribution of human anti-Ro/SSA 60 kDa autoantibodies

The Ro/SSA and La/SSB antigens are common targets for autoantibodies found in the sera of patients with Sjögren's syndrome and SLE. The anti-Ro/SSA and anti-La/SSB antibodies often appear together but are not cross-reactive. This paper describes the humoral autoimmune response to the Ro/SSA 60 kDa protein moiety with respect to the presence of IgM and IgG1-4 antibodies. IgM antibodies to the Ro 60 kDa protein coexisted with IgG anti-Ro 60 kDa antibodies in nearly half of the sera. A similar fraction also contained IgM anti-La/SSB antibodies. The frequency of sera with IgM antibodies of both specificities was that expected from random overlap. A predominating IgG1 anti-Ro 60 kDa response was found in all patients, but anti-Ro 60 kDa antibodies of the other IgG subclasses were present also in a high number of sera. This is in contrast to the reported IgG subclass distribution of anti-La/SSB antibodies. Mapping of IgM and IgG1-4 antibody recognition of different parts of the Ro 60 kDa protein was also performed. IgM and IgG1-4 antibodies of all sera reacted with the central part of the Ro 60 kDa protein, encompassing amino acid residues 181-320.

Ro RNP associated Y RNAs are highly conserved among mammals

Y RNAs are small cytoplasmic RNAs which are components of the Ro ribonucleoprotein complexes in higher eukaryotes. These complexes are frequently recognized by antibodies present in autoimmune sera. In this study we analysed the occurrence of Y RNAs in various mammalian and human cell lines and erythrocytes by means of hybridization with human Y RNA probes. Y RNAs homologous to their human counterparts, both in length and in sequence, were detected in all mammalian cells analysed. While hY1 and hY3 analogues were found in all cells, Y4 and Y5 RNA could not be detected in rodent cells. In addition, Y5 RNA was absent from bovine cells. Attempts to determine the sequence of rat Y RNAs by genomic cloning resulted in the isolation of a presumptive Y1 RNA pseudogene. Analysis of the hY RNA content of various human cell lines showed that all four human Y RNAs were present in all cell lines examined. However, the relative levels to which these RNAs were expressed showed marked differences.

5' sequences of rubella virus RNA stimulate translation of chimeric RNAs and specifically interact with two host-encoded proteins

Sequences at the 5' and 3' ends of the rubella virus (RV) genomic RNA can potentially form stable stem-loop (SL) structures that are postulated to be involved in virus replication. We have analyzed the function of these putative SL structures in RNA translation by constructing chimeric chloramphenicol acetyltransferase (CAT) RNAs, flanked either by both 5'- and 3'-terminal sequence domains from the RV genome or several deletion derivatives of the same sequences. After in vitro transcription of chimeric RNAs, the translational efficiencies of these RNAs were compared by the rabbit reticulocyte lysate translation system. For in vivo translation studies, the level of CAT activity was measured for chimeric RV/CAT RNAs expressed in transfected cells by the adenovirus major late promoter. Both in vivo and in vitro translation activities of the chimeric RNAs revealed that the presence of 5' and 3' SL sequences of RV RNA, in correct (+) orientation and context [5'(+)SL and 3'(+)SL, respectively] was necessary for efficient translation of chimeric RV/CAT RNAs. The presence of the RV 5'(+)SL sequence had the primary enhancing effect on translation. To identify host proteins which interact with the 5'(+)SL which may be involved in RV RNA translation, RNA gel-shift and UV cross-linking assays were employed. Two host proteins 59 and 52 kDa in size, present in cytosolic extracts from both uninfected and RV-infected cells, specifically interacted with the RV 5'(+)SL RNA. Direct binding comparisons between wild-type and mutant 5'(+)SL RNAs demonstrated that sequences in and around the bulge region of the terminal stem domain of this structure constituted a protein binding determinant. Human serum, qualified for anti-Ro/SS-A antigen specificity, immunoprecipitated 59- and 52-kDa protein-RNA complexes containing the RV 5'(+)SL RNA. However, poly- and monoclonal antisera raised against the recombinant 60- and 52-kDa Ro proteins failed to precipitate complexes containing the 5'(+)SL RNA. The identity of the proteins binding this RV cis-acting element remains to be determined; however, their role in RV translation is discussed.

A distinctive autoantibody profile in black female patients with lupus nephritis

OBJECTIVE

Lupus nephritis has often been associated with anti-DNA, but, based on the findings in eluate studies, it appears that other antigen-antibody reactions, such as those involving anti-Ro/SS-A, anti-nuclear RNP (anti-nRNP), and/or anti-Sm, may also contribute to the pathogenesis of nephritis. In the present investigation, we identified and further studied a distinctive precipitin profile present in black women with nephritis.

METHODS

Longitudinal clinical and serologic studies of a cohort of university-based systemic lupus erythematosus (SLE) patients (n = 120) were carried out over an 8-year period.

RESULTS

A subset of 20 black female patients was identified, of whom 8 had lupus nephritis (group I) and 12 did not (group II). Group I was characterized by a distinct precipitin profile consisting of anti-Ro/SS-A, anti-SM, and anti-nRNP, but no anti-La/SS-B. SLE disease duration at presentation was significantly shorter in group I than in group II (mean 1.94 years versus 5.21 years; P = 0.02). The distinctive precipitin profile of anti-Ro/SS-A, anti-Sm, and anti-nRNP occurred exclusively in group I patients (6 of 8, versus 0 of 12 in group II; P < 0.001). In white lupus nephritis patients, this precipitin profile was not seen.

CONCLUSION

While the mechanism responsible for the relationship of this distinctive serologic profile to the development of nephritis in black female lupus patients remains to be determined, its presence may be used as a marker for severe and progressive renal disease.

Subcellular distribution of Ro ribonucleoprotein complexes and their constituents

Ro ribonucleoprotein particles (Ro RNPs) are complexes of several proteins with a small RNA polymerase III-transcribed Ro RNA. Despite their relative abundance and evolutionary conservation no function has as yet been ascribed to these complexes. Also their subcellular distribution is still largely unknown as immunofluorescence studies concerning their localization have produced conflicting data. We have used cell enucleation to fractionate cells into cytoplasmic and nuclear fractions. Analysis of these fractions revealed an exclusively cytoplasmic localization for the Ro RNPs. The majority of the Ro RNAs are shown to be stably associated with all three known Ro RNP proteins. Although no Ro RNAs could be detected in the nuclear fraction, the Ro RNP-specific proteins were abundantly present. These nuclear non-Ro RNA-associated proteins are shown to be capable of binding Ro RNAs.

Neonatal lupus liver disease

Neonatal lupus erythematosus (NLE) is an autoimmune disease characterized by complete congenital heart block and/or transient skin lesions of subacute cutaneous lupus erythematosus. We report that in approximately 10% of cases of NLE with heart block or skin disease, liver disease also occurs (4 of 35 cases in our series). Cholestasis was the major feature in our cases. Although the cholestasis may be severe, the disease process appears to be transient and surviving babies have been healthy on follow-up. In one liver examined for antibody deposition, IgG antibody deposits, presumably of maternal origin, were present. Three maternal sera were examined for autoantibodies, including liver-specific autoantibodies. No liver-specific autoantibodies were found. Rather, the maternal autoantibodies too were the ubiquitous Ro/SSA-associated autoantigens. The autoantibodies bound the 60 kDa SSA/Ro ribonuclear protein (three of three sera), the 52 kDa SSA/Ro protein (two of three sera) and the SSB/La ribonuclear protein (two of three sera).

Clinical relevance of antibodies to Ro/SS-A and La/SS-B in subacute cutaneous lupus erythematosus and related conditions

Ro/SS-A autoantibodies are frequently associated with subacute cutaneous lupus erythematosus, neonatal lupus erythematosus and Sjögren's syndrome. The Ro/SS-A autoantigen is a ribonucleoprotein complex consisting of at least four protein components and four small cytoplasmic RNA components designated hY RNA 1, 3, 4 and 5. Three of the Ro/SS-A peptides have been isolated and cloned. The function of this ribonucleoprotein complex is as yet unknown.

Autoantibodies to the Ro/SSA antigen are conformation dependent. I: Anti-60 kD antibodies are mainly directed to the native protein; anti-52 kD antibodies are mainly directed to the denatured protein

Recent studies have shown that Ro/SSA autoantigen is heterogeneous and the autoanti-Ro/SSA response is correspondingly heterogeneous. There are two isoform families; the 60 kD forms and the 52 kD forms. We studied the antigenic difference between the native and denatured Ro/SSA isoforms and found that the autoanti-Ro/SSA response to the native 60 kD antigen is quite homogeneous. All anti-Ro/SSA sera recognize the native kD antigen regardless of the reactivities to the 60 kD band on the Western blot. Surprisingly, no anti-Ro/SSA sera without anti-La/SSB reacts with the native 52 kD Ro/SSA, although sera with both precipitating anti-Ro/SSA and anti-La/SSB can immunoprecipitate the native 52 kD antigen. Anti-Ro/SSA sera exist which react exclusively with the native 60 kD Ro/SSA protein (10/43, 23%) while no anti-Ro/SSA sera have been found which react exclusively with the denatured 52 kD Ro/SSA antigen. In sera with anti-Ro/SSA precipitins alone, only antibody to the denatured 52 kD Ro/SSA molecule is found! In sera with anti-Ro/SSA and anti-U1 RNP precipitins, no antibody to either native or denatured 52 kD Ro/SSA is found, while in sera with both anti-Ro/SSA and anti-La/SSB precipitins, antibodies to both the native and denatured forms of 52 kD Ro/SSA are present. These data suggest that the anti-Ro/SSA response to the 60 kD molecule is driven by the native 60 kD Ro/SSA molecule while the molecular identification of the antigen drive in the anti-52 kD Ro/SSA response is unknown.

Ro/SSA inhibits the autologous mixed lymphocyte reaction

To test the hypothesis that the Ro/SSA autoantigen can be recognized as antigenic by the human immune system, lymphocytes obtained from normal volunteers were used in in vitro assays evaluating the ability of Ro/SSA (mol. wt 60 kD) to induce B and/or T cell responses. Bovine Ro/SSA strongly inhibited the autologous mixed lymphocyte reaction in a dose-dependent manner without similar effects on concurrently performed allogeneic mixed lymphocyte reactions or T cell proliferation induced by phytohaemagglutinin. Using three colour FACS analysis, Ro/SSA was found to decrease the percentage of CD4+CD45+RA+ T cells in the proliferative, S+(G2+M), phase of the cell cycle. Associated with the decrease in the percentage of suppressor-inducer cells, was the finding that Ro/SSA was able to augment RF production in pokeweed mitogen stimulated cultures of peripheral blood lymphocytes.

Molecular characterization of the Ro/SS-A autoantigens

Molecular techniques have recently revealed that there are several immunologically distinct Ro/SS-A antigens. Three genes encoding putative Ro/SS-A protein antigens with calculated masses of 46, 52, and 60 kD have been isolated. The encoded amino acid sequence of each is quite dissimilar. The 46-kD antigen is calreticulin (CR), a highly conserved calcium-binding protein that resides predominately in the endoplasmic reticulum where it may be involved in protein assembly. Although CR has recently been confirmed to be a new human rheumatic disease-associated autoantigen, its relationship to the other components of the Ro/SS-A ribonucleoprotein has become somewhat controversial owing predominately to the fact that recombinant forms of calreticulin have not displayed the same pattern of autoantibody reactivity possessed by the native form of this protein. The 52-kD antigen most likely resides in the nucleus and may be involved in the regulation of gene expression. The cellular location and function of the 60-kD antigen is uncertain but studies indicate that it is a RNA-binding protein. The 46- and 60-kD antigens share homology with foreign polypeptides, suggesting that an immune response initially directed against a foreign protein may give rise to the autoimmune response directed at cross-reacting self proteins.

Characterization of human-human hybridoma monoclonal anti-Ro(SS-A) autoantibodies derived from normal tonsil lymphoid cells

Human-human hybridomas obtained from the separate fusion of tonsillar lymphoid cells from three different normal individuals to the lymphoblastoid cell line GM 4672 were screened by ELISA for the presence of autoantibody to Ro(SS-A). Those anti-Ro(SS-A) reactive hybridomas were then cloned by limiting dilution. Nineteen monoclonal IgM anti-Ro(SS-A) antibodies were obtained, which showed specificity to Ro(SS-A) by ELISA and Western blotting (60 kDa). Some of these monoclonal anti-Ro(SS-A) antibodies showed reactivity to DNA (2/19), cardiolipin (9/19), Sm/RNP (15/19) by ELISA, and to IgG (12/19) and La(SS-B) (19/19) by ELISA and Western blotting. None showed reactivity to the unrelated proteins casein and BSA, nor to RNA. Inhibition studies revealed that the binding to Ro(SS-A) of both IgM hybridoma monoclonal and SLE serum polyclonal IgM anti-Ro(SS-A) antibodies was inhibited with Ro(SS-A), La(SS-B) and Sm/RNP but not with IgG, DNA, RNA and BSA. These data indicate that (1) normal humans have the genetic potential to express antibodies to Ro(SS-A) and (2) the normally derived monoclonal and SLE serum IgM anti-Ro(SS-A) antibodies share similar antigen binding properties and therefore may possibly originate from a common pool of precursor B cells.

Target antigens of the SSA/Ro and SSB/La system

The SSA/Ro and SSB/La antigens are polypeptides which serve as autoantigens in systemic lupus erythematosus and Sjogren's syndrome. The SSA/Ro contains two major isoforms of 60 kD and 52 kD. The former is the main native antigen while the latter is a major autoantigen in its denatured form. The SSB/La is a single phosphorylated protein of 48 kD. Recently a new protein of 46 kD, termed calregulin, was suggested as an additional component of the SSA/Ro antigens. However, extensive investigations failed to confirm its relation to the SSA/Ro system. Based on molecular techniques and cDNA cloning of these antigens, it was demonstrated that the 60 kD protein is capable of binding RNA and DNA molecules, suggesting a regulatory role in transcription for this antigen. The 52 kD polypeptide contains multiple zinc finger motifs and its sequence is homologous to the mouse rptl protein, which is a T-cell regulating peptide. The SSB/La is associated with precursors of 5S RNA and tRNA, implying that it has a role in the synthesis and maturation of RNA polymerase III transcripts. The 60 kD and 52 kD SSA/Ro components may be associated within the cell. The SSA/Ro and SSB/La may also be in complex in some points of the cell cycle.

Clinical, histologic, and immunofluorescent distinctions between subacute cutaneous lupus erythematosus and discoid lupus erythematosus

Subacute cutaneous lupus erythematosus (SCLE) was originally described and distinguished from discoid lupus erythematosus (DLE) on the basis of clinical examination of the skin, but subsequent reports have questioned the concept of SCLE as a marker of a unique subset of LE patients. We classified 27 lupus patients, on the basis of cutaneous exam, as having discoid lupus skin lesions, subacute cutaneous skin lesions, or systemic lupus erythematosus (SLE) without DLE or SCLE lesions. Clinical features most characteristic of SCLE rather than DLE were superficial, non-indurated, non-scarring lesions, and photosensitivity, with lack of induration being the single most helpful finding. Histologic examination of lesional skin showed a relatively sparse, superficial infiltrate in SCLE and a denser, deeper infiltrate in DLE. A distinctive pattern of staining with direct immunofluorescence, particulate epidermal IgG deposition, was found in seven of seven SCLE patients (all anti-Ro/SSA positive) and none of the other patients. This distinctive pattern can be reproduced experimentally when anti-Ro/SSA autoantibodies are infused into human skin-grafted mice. Particulate dermal-epidermal junctional staining was the pattern seen in the patients who did not have SCLE. Clinically defining SCLE as a superficial inflammatory form of cutaneous lupus (i.e., considering lesions to be DLE if they are indurated) results in a meaningful segregation of SCLE and DLE patient groups. The epidermal IgG deposits unique to SCLE provide independent evidence that the clinical findings that were used to identify the patient groups actually identify distinctive cutaneous lupus subsets. The observation that antibodies are present in a different location in the skin in SCLE than in DLE indicates that SCLE and DLE are likely to have different pathomechanisms.