Identification of the SS-A/Ro intracellular antigen with autoimmune sera

Evaluation of palatal saliva flow rate and oral manifestations in patients with Sjögren's syndrome

OBJECTIVE

The purpose of this study was to describe the oral properties of Sjögren's syndrome (SS), including the determination of palatal saliva (PS) flow rate.

SUBJECTS AND METHODS

Forty-nine SS patients and 43 healthy controls participated. Subjective symptoms were recorded and clinical assessments of the oral mucosal, dental and periodontal status were made. Unstimulated whole saliva (WS) and PS flow rates, the number of decayed, missing and filled teeth (DMF-T number), the gingival bleeding index (GBI) and the periodontal probing depth (PPD) were determined.

RESULTS

Despite the decrease in the flow rate of WS in SS patients, PS was not different from those of the controls (1.57 +/- 1.02 and 1.35 +/- 2.5 microl cm(-2) min(-1), respectively). GBI (20.0% vs. 10.5%, respectively), DMF-T (27.1 +/- 6.12 vs. 23.0 +/- 6.99, respectively) and PPD (2.28 +/- 1.09 mm vs. 1.82 +/- 0.73 mm, respectively) were higher in SS compared with the controls (P < 0.05). DMF-T and PPD showed a positive correlation with anti-SSA and/or anti-SSB antibody positivity in the serum (P < 0.05).

CONCLUSIONS

Data of the present study suggest that the subjective feeling of xerostomia in SS patients is the result of a decrease in the volume of the whole saliva, and not of the viscous PS. Correlation of DMF-T and PPD with autoantibody positivity reveals that the oral health status of SS patients may be associated with the general autoimmune process.

Evaluation of oral manifestations and masticatory force in patients with polymyositis and dermatomyositis

BACKGROUND

The polymyositis (PM) and dermatomyositis (DM) complex encompasses a heterogeneous group of acquired autoimmune skeletal muscle diseases called idiopathic inflammatory myopathies (IIM). Despite their histological and immunopathological differences, the end result of the affected muscles in all of these entities is the triad of chronic inflammation, fibrosis and the loss of muscle fibres. The aim of this study was to perform a complete analysis of the orofacial abnormalities in 34 patients with PM and DM.

METHODS

Evaluation of subjective oral symptoms, measurement of whole resting saliva flow rate (WS) with the 'spitting method', a visual investigation of the oral soft tissue alterations, light- and electron microscopic analysis of the symptoms of capillary abnormalities or signs of focal infiltration in labial biopsy specimens were carried out. The number of decayed, missing and filled teeth (DMF-T) according to the WHO recommendations (1997), the periodontal probing depth (PPD), the plaque index (PI; Silness-Löe) and the gingival index (GI; Löe-Silness) were determined. For comparison with healthy controls the masticatory force (MF) and the force of the upper extremities' flexors were measured with a specially developed device. The SPSS version 11.0 for Windows software program, two-tailed Student's t-test and Mann-Whitney test were used to statistically analyse all data. Values were considered to be significant if P level was < or = 0.05.

RESULTS

Nine patients complained of subjective xerostomia, 11 showed the signs of salivary hypofunction (WS < or = 0.1 ml/min). The most prominent symptom of the oral mucosa and perioral tissues was the presence of telangiectasia, detected in seven cases. Fibrosis of the minor salivary glands was found in 12 patients, interstitial-perivascular infiltration was detected in eight cases, periductal infiltration in one case. The findings on dental and periodontal conditions indicate, that the patients with IIM diseases had significantly higher DMF-T scores (24.06 +/- 7.04 vs. 19.54 +/- 8.93, respectively; P = 0.002), they had less remaining teeth in average (15 vs. 20; P = 0.002), compared with the control group. Their oral hygiene was significantly worse (PI was 1.46 +/- 0.75 and 0.73 +/- 0.54, P = 0.001). GI was significantly higher in the patients (1.27 +/- 0.60 and 0.66 +/- 0.56, respectively, P = 0.0003), although we could not demonstrate any difference in the severity of the periodontal destruction between patients and controls. Masticatory force was significantly weaker in the first molar region on both sides in the patient group (309 +/- 213 N and 113 +/- 146 N, P = 0.0016 for the right side; 315 +/- 239 N and 123 +/- 76 N, P = 0.009 for the left side), but only the left hands showed to be weaker in the patient group (77 +/- 27 N and 59 +/- 20 N, P = 0.04).

CONCLUSION

In conclusion, the present study showed that, patients with IIM diseases have hyposalivation and mucosal alterations, mainly in the form of telangiectasia. They have increased prevalence of dental caries, which may be secondary to the hyposalivation. The masticatory and the upper extremity flexor forces indicate that the weakness of the masticatory muscles can manifest earlier than that of the arms.

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).

Characterization of eukaryotic protein L7 as a novel autoantigen which frequently elicits an immune response in patients suffering from systemic autoimmune disease

Autoantibodies targeted against cellular proteins and nucleic acids are a common feature of autoimmune diseases. In this study, we show that ribosomal protein L7 is a novel autoantigen in patients suffering from systemic lupus erythematosus (SLE) and other connective tissue diseases. From 24 patients diagnosed as having SLE, 18 produce antibodies which precipitate in vitro translated L7 protein. The anti-L7 titer appears to correlate with the active state of the disease. Anti-L7 autoantibodies were also detected in 7 of 13 patients with mixed connective tissue disease (MCTD), 2 of 7 patients with rheumatoid arthritis (RA), 1 of 4 patients with Sjögren's syndrome (SS) and in 1 patient with progressive systemic sclerosis (PSS). Anti-L7 autoantibodies belong to the IgG-class and detect specifically at least two epitopes on the L7 molecule, as shown by immunoprecipitation and immunoblotting. The epitope(s) of the highly conserved C-terminal region are preferentially recognized. Utilizing rabbit anti-L7 serum, autoimmune sera and affinity-purified anti-L7 autoantibodies in immunoblotting, and rabbit and chicken anti-L7 antibodies in indirect immunofluorescence, we detect L7 protein in the nuclei and in the cytoplasm of various cell-lines. Yet unlike most integral structural components of ribosomes, L7 is absent from nucleoli.

Analysis of the oral manifestations of systemic sclerosis

The oral signs and symptoms in 32 patients with systemic sclerosis were evaluated. Oral mucosal telangiectasia was present in 18 cases (56.3%) and was not restricted to the limited form of systemic sclerosis. The interincisal distance was significantly decreased in the patients with systemic sclerosis compared with the 17 controls (p < 0.001). The distance between the vermillion borders was also significantly decreased when the 14 patients with salivary hypofunction were compared with the 18 cases without decreased salivary secretion (p < 0.05). Twenty-two (69%) of the patients exhibited keratoconjunctivitis sicca, salivary hypofunction, or both. Lip biopsy was performed in 16 cases. Two cases with inflammatory signs characteristic of Sjögren's syndrome were found, and six patients showed the histologic signs of labial gland fibrosis. Five of these cases belonged to the group of limited cutaneous systemic sclerosis that indicates the generalized nature of the fibrotic processes even in systemic sclerosis with less extensive skin involvement. Of the 10 cases investigated by electron microscopy, all but one showed a thickening of the capillary basal lamina, lamellar arrangement within the basement membrane, or capillary endothelial vacuolization. Three of these cases belonged to the patients with disease onset within 2 years, showing that capillary vascular lesion is present in the early cases and that vascular injury affects even those tissues that do not seem to be evidently involved by clinical examination.

Antibody recognition of the recombinant human nuclear antigens RNP 70 kD, SS-A, SS-B, Sm-B, and Sm-D by autoimmune sera

Five human nuclear antigens, RNP 70 kD, SS-A, SS-B, Sm-B and Sm-D, were produced in E. coli using the expression vector pSEM. cDNAs encoding these antigens were ligated to a truncated lacZ' gene of the vector and the beta-galactosidase fusion proteins were efficiently expressed as intracellular inclusion bodies after isopropyl-beta-thiogalactopyranoside induction. The antibody reactivities of these fusion proteins were evaluated by Western blot and by ELISA employing panel sera from patients with autoimmune diseases such as systemic lupus erythematosus, Sjögren's syndrome or mixed connective tissue disease. The three fusion proteins, RNP 70 kD, SS-B, and Sm-B, showed good reactivities in both systems, whereas the other two fusion proteins, SS-A and Sm-D, showed poor and no reactivity in both systems, respectively. It can be concluded that RNP 70 kD, SS-B and Sm-B recombinant antigens are useful reagents for the differential diagnosis of the autoimmune diseases.

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.

Serological cross-reactivity between a human Ro/SS-A autoantigen (calreticulin) and the lambda Ral-1 antigen of Onchocerca volvulus

We have cloned and sequenced a 46-kD Ro/SS-A autoantigen gene that is the human homologue of the calcium-binding protein, calreticulin. The sequence of this 46-kD Ro/SS-A protein (calreticulin) has significant homology to lambda Ral-1, a recombinant cDNA clone corresponding to a major antigen of the nematode, Onchocerca volvulus, the infectious agent of onchocerciasis. We therefore sought to determine whether antibodies produced by onchocerciasis patients might crossreact with the human 46-kD Ro/SS-A autoantigen (calreticulin). 20 of 22 sera from Liberian onchocerciasis patients who had no known evidence of autoimmune disease were found to contain antibodies that reacted with the 46-kD Ro/SS-A (calreticulin) by immunoblot analysis. Characteristic of sera reactive with Ro/SS-A antigens, some onchocerciasis sera also immunoprecipitated the Ro/SS-A-associated hY RNAs. In addition, a monoclonal antibody raised against O. volvulus organisms reacted to purified human WiL-2 cell 46 kD Ro/SS-A antigen (calreticulin) by ELISA. These results strongly suggest that onchocerciasis patients produce antibodies that crossreact with the 46-kD human Ro/SS-A autoantigen (calreticulin) and raise the possibility that infectious organisms such as O. volvulus might play a triggering or exacerbating role in the human Ro/SS-A autoimmune response.

Sera from patients with autoimmune disease recognize conformational determinants on the 60-kd Ro/SS-A protein

Anti-Ro antibodies are found in a large proportion of patients with systemic lupus erythematosus and primary Sjögren's syndrome. These antibodies also characterize neonatal lupus, subacute cutaneous lupus erythematosus, and vasculitis associated with Sjögren's syndrome and rheumatoid arthritis. Anti-Ro-positive sera may contain either or both of 2 sets of antibodies, recognizing either a 60-kd or a 52-kd polypeptide component of the Ro particle. We found in this study that the immune response to the 60-kd Ro antigen is heterogeneous. Some sera specifically recognize the native Ro antigen but fail to bind the corresponding denatured polypeptides. In addition, after immunodepletion using the denatured 60-kd Ro polypeptide, all anti-Ro-positive sera tested still contained high titers of antibodies recognizing conformational determinants on the Ro antigen. The frequent immunodominance of anti-Ro antibodies targeted to conformational determinants suggests that native autoantigens may directly drive the autoimmune response.

The detection of anti-Ro/SS-A and anti-La/SS-B antibodies. A comparison of counterimmunoelectrophoresis with immunoblot, ELISA, and RNA-precipitation assays

The presence in serum of anti-Ro/SS-A and/or anti-La/SS-B autoantibodies is a characteristic of autoimmune diseases such as Sjögren's syndrome and systemic lupus erythematosus. To evaluate different assays currently available for the detection of these antibodies 50 sera were tested using the four different assay methods: counterimmunoelectrophoresis (CIE), RNA precipitation assay, immunoblotting technique and ELISA. The RNA-precipitation assay showed the highest sensitivity and specificity. The CIE for the detection of anti-Ro/SS-A antibodies gave comparable results whereas the Ro/SS-A ELISA and Ro/SS-A or HeLa immunoblot showed lower sensitivities (96% and 80% respectively). Sensitivity was even lower (66%) when only reactivity towards the 60 kDa Ro/SS-A protein was considered. The ELISA for the detection of anti-La/SS-B antibodies showed a sensitivity of 98%, the immunoblotting technique of 86% and the CIE only 67%. The high sensitivity of the La/SS-B ELISA went together with a low specificity of 14%. We conclude from these data that for the detection of anti-Ro/SS-A and anti-La/SS-B antibodies the RNA precipitation assay shows the highest sensitivity and highest specificity. For routine screening purposes the CIE is the most convenient and reliable assay to detect anti-Ro/SS-A antibodies. For the detection of anti-La/SS-B antibodies the immunoblot corresponds most closely to the RNA precipitation assay.

A human Ro/SS-A autoantigen is the homologue of calreticulin and is highly homologous with onchocercal RAL-1 antigen and an aplysia "memory molecule"

The Ro/SS-A (Ro) autoantigens consist of at least four immunologically distinct proteins which are recognized by autoantibodies typically found in sera from patients with primary Sjogren's syndrome and in subsets of patients with lupus erythematosus. We recently isolated a 1.9-kb human cDNA clone which encodes one of these Ro autoantigens. Synthetic oligonucleotides corresponding to the human Ro sequence were used to amplify the homologous gene from a murine B cell cDNA library using the polymerase chain reaction. The mouse cDNA-encoded amino acid sequence was found to be 94% homologous to the human Ro sequence and is 100% homologous to murine calreticulin, a high affinity calcium-binding protein which resides in the endoplasmic and sarcoplasmic reticulum. The amino acid sequence of rabbit calreticulin is 92% homologous to both murine calreticulin and human Ro. Onchocerca volvulus and Drosophila melanogaster also have molecules that are highly homologous to human Ro. In addition, human Ro has a molecular mass, isoelectric point, and significant amino acid sequence similar to the Aplysia californica snail neuronal protein 407. These homologies suggest that this Ro protein has a very basic cellular function(s) which may in part involve calcium binding.

Molecular cloning, expression, and chromosome 19 localization of a human Ro/SS-A autoantigen

Ro/SS-A antibodies are found in a number of human autoimmune disorders including Sjogren's syndrome and several systemic lupus erythematosus-related disorders. These heterogeneous autoantibodies are known to recognize several distinct cellular antigens. With synthetic oligonucleotides corresponding to amino acid sequence information we have isolated a full-length cDNA clone which encodes a human Ro ribonucleoprotein autoantigen. The 1,890-base pair clone contains an open reading frame that encodes a 417-amino acid, 48-kD polypeptide that migrates aberrantly at 60 kD by SDS-PAGE. Rabbit antibodies raised against this protein's recently described amino-terminal epitope react with a previously identified 52-kD human Ro protein and immunoprecipitate the human cytoplasmic RNAs. Ultraviolet light cross-linking studies suggest that this Ro protein binds each of the four major human cytoplasmic RNAs. The deduced amino acid sequence is 63% homologous to an Onchocerca volvulus antigen. Southern filter hybridization analysis indicates that this gene is not highly polymorphic and exists as a single copy in the human genome. Chromosomal localization studies place this gene on the short arm of chromosome 19 near the gene encoding the low density lipoprotein receptor.

Comparison of IgG subclass autoantibodies in patients with systemic lupus erythematosus and subacute cutaneous lupus erythematosus

Circulating antinuclear antibodies and in vivo bound immunoglobulins at the dermal-epidermal junction are frequently seen in patients with lupus erythematosus. The present study was designed to examine the distribution of the IgG subclasses of in vivo skin bound IgG and circulating antinuclear antibodies (ANA) in patients with systemic lupus erythematosus (SLE) or subacute cutaneous lupus erythematosus (SCLE). Immunofluorescence studies on skin biopsies showed IgG1 to be the predominant IgG subclass in SCLE patients, present in 20 of 21 (95%) of the specimens. IgG2 was present in 4 patients (19%), IgG3 in 1 (5%), and IgG4 in 7 (33%). The frequencies of IgG2, IgG3, and IgG4 skin staining were significantly higher in the seven SLE patients who were studied: IgG1 in 7/7 (100%), IgG2 in 7/7 (100%) and IgG4 in 6/7 (86%). Immunoblot analysis for the IgG subclasses was performed on serum of 29 patients with SCLE who had antibodies to SSA/Ro antigen. Twenty-seven (93%) of these patients were positive for IgG1 anti-SSA/Ro antibody, while the frequencies for IgG2, IgG3, and IgG4 anti-SSA/Ro were very low. These studies indicate that there is a difference in the IgG subclass antibody response in patients with SLE and SCLE. The presence of more than one subclass antibody may be indicative of systemic disease.

Human Ro ribonucleoprotein particles: characterization of native structure and stable association with the La polypeptide

Anti-Ro autoantibodies, found in sera of patients with systemic lupus erythematosus, Sjogren's syndrome, and related diseases, target the Ro ribonucleoprotein particles (RNPs). Although the polypeptide and RNA components of the Ro RNPs have been characterized, much less is known about the native structure of these particles. We have now characterized by biochemical techniques intact Ro ribonucleoprotein particles from cultured HeLa cells. These particles segregated in three discrete subpopulations with characteristic physicochemical properties: one containing hY5 RNA (RohY5 particles), one containing only hY4 RNA (RohY4 particles) and one with hY1, hY3, and hY4 RNAs (RohY1-hY4 particles). The RohY5 particles were purified free of contaminating ribonucleoproteins; both the La and the 60-kD Ro polypeptides were stable components of this portion of the Ro RNPs. The La RNPs co-purified with the RohY4 particles and contaminated the RohY1-hY4 RNPs. The stable association between the La and the 60-kD Ro polypeptides provides a potential macromolecular target for the linked set of anti-Ro and anti-La antibodies, and suggests a possible functional association of these polypeptides.

A simple method for the biochemical purification of Ro/SS-A antigen

In the present study, Ro/SS-A antigen has been isolated from human spleen by a two-step procedure. In the first step most of the non-antigenic material was removed by means of ammonium sulphate precipitation and ion exchange chromatography. The final purification was obtained by passing the Ro/SS-A-containing fractions twice through a Mono Q ion exchange fast protein liquid chromatography (FPLC) column. The purified antigen showed identical immunoreactivity with crude material on CIE and was composed of two polypeptides with a molecular weight of approximately 60,000 and 55,000 respectively on SDS-PAGE, both reacting on Western blotting with a panel of anti-Ro/SS-A antisera. This system permits milligrams of highly purified antigen to be obtained from grams of human spleen.

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

Ro(SSA) is an intracellular ribonucleoprotein against which autoantibodies are found in a portion of patients with Sjögren's syndrome and systemic lupus erythematosus. A form of Ro(SSA) is described in red blood cells that shares a line of identity with purified Ro(SSA) from bovine spleen and human lymphocytes in counterimmunoelectrophoresis, but has different molecular properties. Ro(SSA) from red blood cells exists in association with only two small RNAs as opposed to four in other cell types, as determined by RNA extraction of protein A-assisted immunoprecipitates. In addition to the common 60-kD Ro(SSA) protein, Western blot analysis revealed an additional 52-kD protein in lymphocytes and a 54-kD protein in red blood cells. The 60-kD form of Ro(SSA) in red cells was found to be antigenically distinct from that in the lymphocyte, because sera were identified that bound each exclusively. Finally, a rabbit antibovine Ro(SSA) serum distinguished red cell from lymphocyte Ro(SSA). These results suggest two distinctive populations of Ro(SSA) proteins and distributions of Ro(SSA) RNAs in the lymphocyte and red blood cell.

Molecular characterization of human Ro/SS-A antigen. Amino terminal sequence of the protein moiety of human Ro/SS-A antigen and immunological activity of a corresponding synthetic peptide

The Ro/SS-A antigen was purified from an Epstein-Barr virus-transformed human B lymphoblastoid cell line. The amino terminal amino acid sequence of the 60-kD polypeptide bearing this antigenic epitope was determined to be: (formula; see text) A peptide composed of residue 6-19 was synthesized by the solid-phase method. Immunodiffusion-defined monospecific autoimmune sera to Ro/SS-A reacted with this synthetic peptide in ELISA, whereas autoantibodies with other specificities such as anti-La/SS-B and anti-Sm, as well as normal human sera, were not reactive. In addition, rabbit anti-peptide 6-19 antisera reacted specifically with native human Ro/SS-A antigen in ELISA. Furthermore, this synthetic peptide inhibited the binding of rabbit anti-peptide antiserum to native human Ro/SS-A. An additional synthetic peptide corresponding to residues 7-24 partially inhibited the binding of a patient anti-Ro/SS-A serum to native Ro/SS-A. These results suggest that the amino terminal portion of the molecule represents a major epitope of Ro/SS-A. The determination of the amino acid sequence of Ro/SS-A and the availability of synthetic peptide(s) bearing this antigen should provide additional approaches to further characterize the autoimmune response to this antigen.

A 52-kD protein is a novel component of the SS-A/Ro antigenic particle

Anti-SS-A/Ro autoantibodies are found in the sera of patients with Sjogren's syndrome (SS) and SLE. In the course of analyzing 61 SS patients for their autoantibody profiles, we found that 42 were positive for anti-SS-A by double diffusion in agarose and demonstrated precipitin lines identical to that produced by a prototype anti-SS-A serum. Further analysis of these SS-A antibody-positive sera by Western blotting of cell extracts revealed that 21 sera reacted with two proteins of 60 and 52 kD, 13 sera reacted with 52-kD protein, two detected only 60 kD, while six were nonreactive. Affinity-purified anti-60-kD and anti-52-kD antibodies reacted exclusively with their corresponding antigens. Partial proteolysis of these proteins did not reveal common degradation fragments. Thus the 52- and 60-kD proteins were found to be antigenically and apparently structurally distinct from each other. They were also distinct from 48-kD SS-B/La protein. In immunoprecipitation using labeled cell extracts, affinity-purified anti-52-kD antibodies brought down the 52-kD protein as well as the 60-kD band. In [32P]orthophosphate-labeled HeLa cell extract both antibodies precipitated the same spectrum of small RNAs (hYl-5). In indirect immunofluorescence, anti-52-kD and anti-60-kD antibodies immunolocalized in similar subcellular structures and showed similar punctate nuclear staining patterns. Western blot analysis revealed that both proteins were present in lymphocytic as well as epithelial human cell lines tested. The data above define a new antigen of 52 kD which is another component of the SS-A particle and is associated in complex formation with the previously reported 60-kD protein.

Antinuclear antibodies (ANAs): diagnostically specific immune markers and clues toward the understanding of systemic autoimmunity

The convergence of studies in the clinical and basic sciences has resulted in the definitive identification of many intracellular antigens which are the targets of autoantibodies in patients with systemic lupus erythematosus, scleroderma, dermatomyositis/polymyositis, Sjogren's syndrome, mixed connective tissue disease, and drug-induced autoimmunity. Some of this new knowledge includes the identification of the Sm and RNP antigens as ribonucleoprotein particles involved in splicing of precursor messenger RNA, Scl-70 as DNA topoisomerase I, proliferating cell nuclear antigen as auxiliary protein of DNA polymerase delta, and certain antigens in myositis as aminoacyl transfer RNA synthetases. This information confirms, at a molecular level, the presence of specific profiles of autoimmune responses so that autoantibodies can be used in clinical medicine as diagnostically useful immune markers. In addition the data give compelling reasons to consider that certain autoimmune diseases are antigen-driven. Many auto-antibodies have the interesting feature of recognizing epitopes on the antigens which are active or functional sites of the molecule. It is suggested that the data provide clues to the nature of the intracellular particle initiating the immune response and may help to elucidate some of the early mechanisms of the autoimmune process.

Immunoglobulin class and subclass profile of the Ro/SS-A autoantibody response

We have developed an enzyme-linked immunosorbent assay (ELISA) for autoantibody to Ro/SS-A antigen (anti-Ro/SS-A) in order to more fully characterize the autoimmune response that occurs to this antigen in patients with subacute cutaneous lupus erythematosus (SCLE). The microtiter plate-immobilized, biochemically purified Ro/SS-A antigen reacted with anti-Ro/SS-A antibody, but not with other closely related specificities (anti-La/SS-B, anti-SM, anti-U1-RNP) or normal sera. The optimal pH of antigen-antibody reaction in this ELISA was 7.2. The binding of sera containing anti-Ro/SS-A was inhibited 80% by preincubation with the same amount of Ro/SS-A antigen used for coating the plate. Although 11 of the 14 (79%) SCLE sera studied had precipitating anti-Ro/SS-A antibody by immunodiffusion, 13 (93%) sera had abnormally elevated IgG, IgA, or IgM ELISA binding levels. A good correlation between IgG anti-Ro/SS-A ELISA binding levels and immunodiffusion titers was observed (r - 0.8588, p less than or equal to 0.001) suggesting that IgG is the major anti-Ro/SS-A antibody class detected by double immunodiffusion, Sera with a combination of high rheumatoid factor levels (latex 3+ or higher) and high anti-Ro/SS-A titers (1:8 or higher in immunodiffusion) tended to give an abnormally high IgM anti-Ro/SS-A ELISA binding levels. After rheumatoid factor activity was removed by absorption with heat-aggregated human IgG, a 50% decrease in IgM anti-Ro/SS-A ELISA binding was noted. On the other hand, absorption of rheumatoid factor-negative sera that contained high IgM anti-Ro/SS-A binding activity did not significantly decrease ELISA binding levels. Prednisone and 6-azathioprine reduced the level of IgG anti-Ro/SS-A autoantibody in sera of treated SCLE patients by 50%. The IgG subclass profile of anti-Ro/SS-A autoantibody was analyzed by using mouse monoclonal antibodies specific for the 4 human IgG subclasses. Of anti-Ro/SS-A positive SCLE sera, 91% had predominantly IgG1 subclass autoantibody. The coexistence of IgM and IgG anti-Ro/SS-A autoantibody and the predominance of the IgG1 subclass is compatible with the possibility that this autoantibody response is under T-cell control. The predominance of IgG1 in the autoimmune response to Ro/SS-A antigen in SCLE patients is consistent with the hypothesis that antibody dependent cell mediated cytotoxicity could be an important immunologic effector mechanism in this disorder.

Relationship between circulating anti-Ro/SS-A antibody levels and skin disease activity in subacute cutaneous lupus erythematosus

Anti-Ro/SS-A antibody levels in 80 serum specimens from 12 patients with subacute cutaneous lupus erythematosus (SCLE) were determined by immunodiffusion and enzyme-linked immunosorbent assay in order to examine the changes in this autoantibody response with time and to study the relationship between levels of this antibody and SCLE skin disease activity. Anti-Ro/SS-A antibody levels were found to vary considerably over time in a given patient when measured by both assays. Several patients who did not have detectable levels of this antibody at the time of their initial examination were found to be antibody positive at follow-up examinations. However, no significant relationship was found between antibody levels in either assay and SCLE skin disease activity. While not ruling out a pathogenetic role for this antibody in the elicitation of SCLE skin lesions, these results would suggest that other factors are likely to be involved.

Discordance of SSA/Ro and SSB/La cellular antigens in synchronized cells

SSA/Ro and SSB/La are soluble cellular proteins to which antibodies are frequently produced in patients with Sjögren's syndrome and systemic lupus erythematosus. In this investigation, we examined anti-SSA/Ro and anti-SSB/La staining patterns on synchronized WiL2 cells and mixed lymphocyte culture cells using monospecific antisera. In addition to its presence in the nucleoplasm, the SSB/La antigen was highly concentrated in the nucleolus of cells during the late G1 and early S phase and is thus cell cycle-related. In contrast, the SSA/Ro antigen was found to be independent of cell cycle, showing a nuclear speckled pattern in all phases. Blocking experiments indicated that free SSB/La is responsible for the nucleolar staining, whereas the combination of both SSA/Ro and SSB/La determines the nucleoplasmic speckled staining pattern.

Further characterization and subcellular localization of Sm and U1 ribonucleoprotein antigens

Sera from patients with systemic autoimmune diseases often contain antibodies against small nuclear ribonucleoprotein (snRNP) particles. Anti-Sm antibodies react with the entire set of U1, U2, U4, U5 and U6 (U1-U6) RNP particles whereas anti-(U1)RNP sera specifically recognize particles containing U1 RNA. Here we performed semi-quantitative immunoblotting using 16 human anti-Sm, 15 human anti-(U1)RNP sera and two mouse monoclonal antibodies to establish which snRNA-associated proteins carry antigenic determinants. Almost every (15/16) human anti-Sm sera recognized epitopes present on a 28-kDa (B/B') protein doublet and on a 16-kDa (D) polypeptide. Nine anti-(U1)RNP sera also recognized the B/B' doublet, but in all cases a much stronger reaction was observed with one or more of the specifically U1 RNA-associated 70 kDa, A or C antigens. With affinity-purified antibody fractions eluted from individual antigen bands on nitrocellulose blots it is shown that the anti-Sm-reactive polypeptides B/B' and D contain common epitopes. We also report the finding of one human anti-Sm serum with exclusive specificity for the B/B' doublet and a mouse monoclonal anti-Sm antibody recognizing only the D protein, indicating that these antigens also carry unique epitopes. In immunoprecipitation assays, purified anti-B/B' and -D antibodies react with (U1-U6) RNP while purified anti-70 kDa, anti-A and anti-C antibodies precipitate exclusively U1 RNP particles. Finally, we established the subcellular localization of Sm and U1 RNP antigens using a biochemical cell fractionation procedure. Part of the 70 kDa and B/B' antigens were found in a nuclease and high salt-resistant nuclear substructure, usually referred to as nuclear matrix, while the A and D antigens could be extracted completely from HeLa nuclei by ribonuclease treatment and subsequent high salt extraction.

The demonstration of SS-A/Ro antigen in human fetal tissues and in neonatal and adult skin

Anti-SS-A/Ro antibodies have been statistically associated with congenital heart block and cutaneous lupus in the neonatal lupus syndrome, and with photosensitive cutaneous lupus in subacute cutaneous lupus erythematosus, but it had not been demonstrated that SS-A/Ro antigen is present in fetal tissues or at any age in human skin. We examined normal fetal tissues, normal neonatal and adult skin, and keratinocytes from purified serum-free cultures by immunofluorescence (IF) and by immunodiffusion or counterimmunoelectrophoresis (CIE) to determine the presence of SS-A/Ro antigen. We found SS-A/Ro antigen to be present in fetal hearts and in other internal organs. SS-A/Ro antigen could be demonstrated in biopsies of neonatal and adult skin by IF and was confirmed to be in keratinocytes by CIE. SS-A/Ro antigen may be found on the surface of keratinocytes in culture and therefore may be present at a relevant site for antibody binding. We have shown that SS-A/Ro antigen is a normal component of tissues that may be affected in neonatal lupus (fetal myocardium, neonatal epidermis) and in subacute cutaneous lupus erythematosus (adult epidermis).

Molecular characteristics of SS-B/La and SS-A/Ro cellular antigens

Anti-SS-B/La and anti-SS-A/Ro antibodies coexist in certain patients with connective tissue diseases such as systemic lupus erythematosus or Sjögren's syndrome. The respective antigenic structures with which these autoantibodies bind have not been fully characterized. The present study was conducted to better define these two different cellular antigens. WiL2 cell extracts were used to obtain partially purified SS-B/La and SS-A/Ro antigens. Both were found to be present in most fractions obtained after sequential purification with ammonium sulfate salt precipitation, G-200 gel filtration, DE-52 ion exchange chromatography, and preparative slab gel electrophoresis. However, SS-B/La antigenic activity was also found to be present in some fractions that did not contain detectable SS-A/Ro activity. These findings suggested the existence of two different forms of SS-B/La antigen: one containing the SS-B/La antigen only and the other containing both the SS-B/La and SS-A/Ro antigens. The RNA and protein components of these two ribonuclear protein particles were further defined by immunoprecipitation experiments using 32P-labeled WiL2 cell extract. The SS-B/La antigen was found to be associated with several RNAs while the SS-A/Ro antigen was associated with several other distinct RNAs. Both antibodies precipitated a common 43K molecular weight phosphoprotein. The antigenic peptides of these 2 antibodies were analyzed using an immunoblot system. The SS-B/La antigen was present on a 43K peptide which was unstable and could be degraded to several peptides of lower molecular weight (40K, 38K, 30K), while the SS-A/Ro antigen occurred on a peptide having a molecular weight of about 60K.