Lupus/Sjögren's autoantibody specificities in sera with paraproteins

Antinuclear antibody and anti-RNA-protein autoantibodies were determined in 143 sera containing paraproteins and 39 control sera. Antinuclear antibodies were commonly present in the paraprotein sera by indirect immunofluorescence. 19 of 143 sera (13%) had elevated anti-Ro/SSA activity in a solid phase Ro/SSA binding assay, and 5 (3.5%) had Ro/SSA precipitating autoantibody. Eighteen sera had La/SSB binding autoantibodies (12%) but only one had an anti-La/SSB precipitin. Anti-nRNP(Sm) was not detected in any of these sera. The solid phase anti-RNA protein assays were repeated using anti-lambda and anti-kappa conjugates. Both lambda and kappa light chain autoantibodies were found in all positive sera consistent with polyclonal anti-Ro/SSA and anti-La/SSB responses. Paraprotein sera containing Ro/SSA precipitins were analyzed by isoelectric focusing followed by exposure to 125I-labeled Ro/SSA and autoradiography. All sera with anti-Ro/SSA binding paraproteins also contained polyclonal anti-Ro/SSA. Our data are consistent with the hypothesis that anti-Ro/SSA paraproteins are common and arise from a previously present polyclonal anti-Ro/SSA response.

The small nuclear ribonucleoprotein SS-B/La binds RNA with a conserved protease-resistant domain of 28 kilodaltons

SS-B/La is a nuclear protein of 48 kilodaltons with two structural domains of Mr 28,000 and Mr 23,000 generated by proteolytic cleavage. UV irradiation was used to cross-link preexisting intracellular La-RNA complexes. Subsequent protease digestion and diagonal gel electrophoresis showed that the RNA-binding site resided in the nonphosphorylated, methionine-rich 28-kilodalton domain.

HLA-DR antigens in systemic lupus erythematosus: association with specificity of autoantibody responses to nuclear antigens

HLA-DR antigens and autoantibodies to the nuclear or cytoplasmic antigens Ro/SSA, La/SSB, Sm, and RNP were determined in North American and Austrian patients with systemic lupus erythematosus (SLE). Analysis of the association of antibodies to these ribonucleic acid (RNA)-protein antigens with HLA-DR antigens showed that HLA-DR3 was related to the presence of anti-Ro/SSA or anti-La/SSB, or both. In contrast, anti-Sm or anti-RNP, or both were associated with HLA-DR4. HLA-DR5 was associated with absence of these autoantibodies. The data extend evidence for the complexity and heterogeneity of SLE. Moreover, they indicate that, in SLE, genes linked to those coding for HLA-DR antigens, are related to the specificity of autoantibody responses rather than to the primary immunological abnormalities of this disorder.

The effect of La(SSB) on PWM-induced immunoglobulin synthesis by anti-La(SSB) positive SLE patients and healthy controls

The effect of affinity purified La(SSB) on immunoglobulin synthesis in vitro by mononuclear cells (MNC) from anti-La(SSB)-positive systemic lupus erythematosus (SLE) patients and healthy controls was studied. La(SSB) was prepared from calf thymus extract and characterized by SDS-polyacrylamide gel electrophoresis and immunoblotting. Silver staining of gels reveals nine major bands at 68 kD, 43-48 kD and 30-33 kD, of which six were recognized on immunoblots by sera from anti-La(SSB) positive SLE patients. Studies in vitro showed that La(SSB) alone did not stimulate total IgG or IgM synthesis in controls or SLE patients. Low concentrations of La(SSB) (optimal dose less than 0.02 ng/ml) suppressed pokeweed mitogen (PWM)-driven IgG synthesis by controls but not by anti-La(SSB) positive SLE patients. IgM responses were unaffected. Anti-La(SSB) and anti-DNA were detected in PWM-stimulated cultures from both study groups. In the presence of La(SSB) IgM anti-La(SSB) synthesis was enhanced in anti-La(SSB)-positive patients in a dose-dependent manner. In contrast, La(SSB) inhibited anti-La(SSB) production by controls (maximal at 2 ng/ml). La(SSB) had no effect on anti-DNA production in either group. Pre-incubation of control or anti-La(SSB)-positive SLE MNC with La(SSB) before addition to autologous PWM-driven cultures did not induce suppressor cells, although pre-incubation with Concanavalin A (ConA) did. Thus we suggest that La(SSB)-induced suppression of IgG synthesis in PWM-driven control cultures may not be due to induction of regulator cells, possibly missing from SLE cultures, but perhaps is a direct effect on B cells.

Systemic lupus erythematosus in the elderly

Late onset systemic lupus erythematosus (SLE) is an important part of the SLE spectrum. In 19 (17%) of 112 patients in this study, the onset of disease was over the age of 60. Onset is often insidious and diagnosis may be delayed (time to diagnosis: 40 months in older patients compared to 18 months in younger patients). Initial presentation may resemble polymyalgia rheumatica but this can indicate an underlying myositis. Age influences disease expression with an increased incidence of lung disease and Sjögrens syndrome. Antibodies to Ro and La are frequently present and may be a helpful laboratory aid to diagnosis. This may also explain the association between late onset SLE and HLA-DR3.

Antibodies to Ro(SSA) and the heterogeneity of systemic lupus erythematosus

The clinical heterogeneity of systemic lupus erythematosus (SLE) is associated with a multiplicity of autoimmune responses to both cellular and soluble antigens. At least part of the clinical heterogeneity is associated with serological heterogeneity and this is particularly striking among patients with SLE who produce anti-Ro(SSA) and anti-La(SSB). Certain subsets within the lupus spectrum are closely associated with the anti-Ro(SSA) response. These include subacute cutaneous lupus erythematosus, the lupus like syndrome associated with homozygous C2 and C4 deficiency, and neonatal lupus erythematosus. Moreover, among the patients with SLE who produce anti-Ro(SSA) are 2 stable groups, on which produces anti-Ro(SSA) alone and one which produces both anti-Ro(SSA) and anti-La(SSB). Clear clinical and serological differences distinguish these groups and it is hypothesized that these differences are due to genetic differences in the HLA-D region. Exact identification of the genes involved and how they control immune responses should lead to a clearer understanding of the clinical phenomena seen in these patients.

The neonatal lupus erythematosus syndrome

Available data support the idea that the neonatal lupus erythematosus syndrome results from an autoantibody produced in the mother and passed across the placenta to the fetus. Despite the evidence for the presence of the Ro(SSA) autoantigen both in the skin and heart and the almost universal presence of the Ro(SSA) autoantibody in mothers of infants with neonatal lupus, there are emerging data to suggest that La(SSB) and, rarely, nRNP antibodies play an important pathologic role in some cases of the neonatal lupus syndrome.

Hazards of lupus pregnancy

Fetal death occurs in about 1/3 of pregnancies in patients with systemic lupus erythematosus (SLE). It is largely predicted by lupus anticoagulant (estimated by activated partial thromboplastin time) and/or antibody to cardiolipin. These antibodies are not synonymous. Neonatal lupus appears in a minority of infants born to women with antibody to the Ro/La antigens. Hypocomplementemia is common in SLE pregnancies, as in pregnancy induced hypertension. Lupus exacerbation is uncommon either during or after pregnancy. Prematurity and fetal death are the greatest hazards.

Multiple phosphorylation of human SS-B/LA autoantigen and its effect on poly(U) and autoantibody binding

The metabolic turnover rates and the effect of in vitro phosphorylation on poly(U) and autoantibody binding of human SS-B/La ribonucleoprotein, an autoantigen expressed in various autoimmune disorders, were studied. The determination of the metabolic turnover rates of SS-B/La protein, SS-B/La protein phosphorylation and RNA binding yielded values of 12.1 h, 3.6 h and 3.7 h, respectively, indicating a possible functional correlation of RNA-binding and phosphorylation. This assumption was confirmed by studies of in vitro phosphorylation using purified SS-B/La protein and purified casein kinase type II as a model system. A high degree of phosphorylation of the SS-B/La protein (molecular mass 49 kDa) substantially diminished its binding capacity for poly[3H]U. However, binding of human autoantibodies against SS-B/La antigen increases 2-fold with increased SS-B/La phosphorylation. Complete phosphorylation in vitro led to partial molecular transformation, yielding an antigenically cross-reacting component with an apparent molecular mass of 51 kDa which could not be detected during in vivo phosphorylation.

Familial systemic lupus erythematosus: evidence for separate loci controlling C4 deficiency and formation of antibodies to DNA, nRNP, Ro and La

A family has been identified in the Canadian province of Prince Edward Island in which 2 sisters have systemic lupus erythematosus in a sibship of 14. Studies are reported on 11 of the siblings and 16 other family members. The affected siblings, and 4 other members of their sibship, are halfnull homozygotes for the C4A component of complement. We studied the distribution in family members of antibodies to ss and dsDNA, and to Ro(SSA), La(SSB), Sm and nRNP. Eight of 11 members of the affected sibship are antibody producers, compared to only 3 of 13 members of the parental generation. Our study provides further evidence for an association between null genes for C4A and familial lupus, and suggests, in an unusually large kindred, that several other genetic factors are involved in the production of antinuclear antibodies.

Identification of the Ro and La antigens in the endoribonuclease VII--ribonucleoprotein complex

45 S RNP (ribonucleoprotein) particles from calf thymus or L5178y mouse lymphoma cells contain the poly(A)-modulated and oligo(U)-binding endoribonuclease VII [Bachmann, Zahn & Müller (1983) J. Biol. Chem. 258, 7033-7040]. From these particles a 4.5 S RNA was isolated that possesses an oligo(U) sequence. By using monospecific and non-cross-reacting antibodies directed against the La or Ro antigen, both proteins were identified in the endoribonuclease VII-RNP complex after phosphorylation in vitro. In a second approach, endoribonuclease VII activity was identified in immunoaffinity-purified Ro RNPs after preparative isoelectric focusing. Therefore we conclude that the 4.5 S RNA belongs to the Ro RNAs. The results indicate a possible function of endoribonuclease VII in activating stored mRNAs.

Implications of anti-Ro/Sjögren's syndrome A antigen autoantibody in normal sera for autoimmunity

We have applied a sensitive assay to analyze lupus and Sjögren's syndrome autoantibodies in 40 normal sera. Seven of these bound Ro/Sjögren's syndrome A antigen (SSA). Although this binding was 1,000-fold lower than the highest anti-Ro/SSA level measured from patients, it was inhibited by human Ro/SSA. Positive normal serum-bound Ro/SSA in Western immunoblots and binding activity was demonstrated in the F(ab')2 fragment of IgG. Affinity purification of normal anti-Ro/SSA IgG increased the specific anti-Ro/SSA binding by greater than 17-fold. This purified antibody formed a Ro/SSA precipitin and had a relative affinity for Ro/SSA identical to that of Ro/SSA precipitin-positive patients. These data demonstrate that the anti-Ro/SSA present in healthy normal donors is true autoantibody. Anti-La/Sjögren's syndrome B antigen (SSB) autoantibodies were found in 3 of the 40 normal sera, while none bound nuclear ribonucleoprotein (Sm). Finding low levels of anti-Ro/SSA and anti-La/SSB among normals may indicate that anti-Ro/SSA and anti-La/SSB occur in disease by enhancement of a preexisting immune response.

The capped U6 small nuclear RNA is transcribed by RNA polymerase III

U6 RNA is an abundant, capped, small nuclear RNA (snRNA) species associated with heterogeneous nuclear ribonucleoproteins in eukaryotic cells. U4 RNA and U6 RNA are hydrogen bonded in a 1:1 ratio in discrete small nuclear ribonucleoprotein particles that are required in pre-mRNA processing. Previous reports have established that the mRNAs and U1 to U5 U-snRNAs are synthesized by RNA polymerase II. Evidence is presented here for synthesis of U6 RNA by RNA polymerase III. The synthesis of U6 RNA in vitro, using Novikoff hepatoma or HeLa whole cell extracts, was not inhibited at low (1 microgram/ml) concentrations of alpha-amanitin, and only 35% inhibition occurred at 10 micrograms/ml concentration. The in vitro synthesized U6 RNA, like other RNA polymerase III transcripts, was associated with La antigen. The U6 RNA synthesized in vitro by the whole cell extracts was capped, but no other internal post-transcriptional modifications were found. Uridylic acid residues were also added post-transcriptionally to the 3'-end of U6 RNA in vitro. U6 RNA, though capped on its 5'-end, is transcribed by RNA polymerase III; this is the first report of a capped RNA molecule synthesized by RNA polymerase III.

[Detection and differentiation of autoantibodies to extractable nuclear antigens with immunoenzyme tests]

Nuclear antigens were extracted from calf thymus with phosphate-buffered saline The 60-80% ammonium sulfate fraction (ASF) of thymus extract contained SS-B-, the 30-60% ASF Sm- and U1-RNP-, and the chromatographically purified 30-60% ASF only Sm antigen. With these fractions enzyme immunoassays were developed for quantitative determination of Sm-, U1-RNP-, and SS-B autoantibodies. Out of 144 sera with antinuclear antibodies 85% were positive in the enzyme immunoassays, 41% in immunofluorescence tests on liver sections (12% speckled, 29% homogeneous immunofluorescence pattern), and 10% in Ouchterlony tests. 26% of the sera were positive in enzyme immunoassays and immunofluorescence tests. All antibody specificities detected by immunodiffusion could be confirmed by enzyme immunoassay. The enzyme immunoassay is far more sensitive then immunodiffusion and in contrast to immunofluorescence allows antibody specificities to be determined. Enzyme immunoassays are recommended for the diagnosis of rheumatic diseases.

[Quantification of SS-B autoantibodies in patient sera using highly purified human SS-B antigens and their clinical interpretation]

For the identification of SS-B autoantibodies in the sera of patients with rheumatic diseases (n = 319) a sensitive and specific enzyme-linked immunosorbent assay was developed using highly purified human SS-B antigen as a reference antigen. In 30/319 patients' sera SS-B autoantibodies were detected. In this group, the ratio female : male patients was outstandingly high (29:1), the serum of the single male patient exhibiting the lowest titer of SS-B autoantibodies. The highest portion of anti-SS-B positive sera was observed in the group of patients with systemic Lupus erythematosus (48%) followed by the groups with undifferentiated connective tissue disease (17%), Sjögren-syndrome (13%) and rheumatoid arthritis (6%). The protein components reacting with human SS-B autoantibodies were characterized in permanent cell lines of various species. In each of 9 human cell lines only one component with a molecular weight of 49 kD reacted; in cell lines of other species analogously, only one component reacted, showing slightly different molecular weights depending on the species. The SS-B antigen isolated from human cells contained at least 7 isoelectric variants, all reacting with human SS-B autoantibodies.

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.

Association of La and Ro antigens with intracellular structures in HEp-2 carcinoma cells

Monoclonal antibodies were raised against homogeneous Ro and La antigens, two proteins associated with Ro and La ribonucleoproteins (RNPs). The specificity of the monoclonal antibodies was proven by immunoblot analysis and by immunoprecipitation. The anti-Ro antibody reacted with a Mr 95,000 protein in a mouse lymphoma cell extract and with a Mr 60,000 polypeptide in extracts from human spleen. The anti-La antibody recognized a Mr 50,000 polypeptide in the mouse L5178y cell extract. The two monoclonal antibodies precipitated RNPs that contained the typical RNA species of Ro or La RNPs. The localization of Ro and La antigen was performed by direct immunofluorescence microscopy. It was found that the anti-Ro antibody reacted with a fibrous network that behaves like cytokeratin, one of the intermediate filament systems. The anti-La antibody reacted with nuclear structures that gave a speckled-type pattern.

A human auto-immune antibody specifically recognizing initiator methionine tRNA from yeast and higher eucaryotes

Analysis of sera from 168 patients with autoimmune disorders revealed that one patient with Sjôgren's syndrome produced antibodies against deproteinized initiator methionine tRNA in addition to those against La protein. This anti-tRNAimet recognizes also tRNAimet from yeast but not from Phaseolus vulgaris chloroplasts (bean) or E. coli. It appears therefore that the epitope could be located in the TF loop in which an A residue in position 60 and the AUCG sequence are the only common features in yeast and human tRNAimet.

Purification and characterization of the Ro and La antigens. Modulation of their binding affinities to poly(U) by phosphorylation and the presence of ATP

Both the La and the Ro antigen (the latter for the first time) were purified to apparent homogeneity. Ro was found to be a 94 (90)-kDa and La a 50-kDa polypeptide. Both antigens bind to RNA with a high preference for poly(U). The binding hierarchy is U much greater than G greater than A greater than C for La and U much greater than C greater than G greater than A for Ro. Only 15% of the total amount of La or 21% of that of Ro, present in the L5178y cell extract, is able to bind to poly(U), indicating the existence of RNA binding and nonbinding subclasses of La and Ro. The purified antigens were used for the isolation of monospecific antibodies. These antibodies were specific for their respective antigen and did not cross-react. Both the Ro and the La antigen are phosphorylated in vitro by the cytoplasmic protein kinase CII, whereas the nuclear protein kinases NI and NII are unable to phosphorylate the antigens. After phosphorylation or in the presence of ATP the binding affinity of both antigens to poly(U) strongly decreases. The phosphorylation reaction together with the immunoprecipitation by the monospecific antibodies represents a highly sensitive and specific assay which was used during purification and characterization of the Ro and La antigen.

Antibodies to La, Jo-1, nRNP and Sm detected by multi-track immunoblotting using a novel filter holder: a comparative study with counterimmunoelectrophoresis and immunodiffusion using sera from patients with systemic lupus erythematosus and Sjögren's syndrome

The use of Western blotting or immunoblotting to detect autoantibodies in the serum of patients with autoimmune connective tissue diseases was investigated. An apparatus suitable for simultaneously screening 16 sera on immunoblots was used to show that a complex pattern of antibody binding polypeptides was present in whole HeLa cells. A simpler and readily interpreted pattern of binding was achieved using affinity-purified rabbit thymus antigens. Seventy-seven patients with systemic lupus erythematosus, 44 with primary Sjögren's syndrome and 50 normals were screened for anti-Sm, anti-La, anti-nRNP and anti-Jo-1 by immunoblotting and the results compared with those obtained by counterimmunoelectrophoresis and immunodiffusion. It was shown that both IgG and IgM antibodies must be analysed on immunoblots to detect the maximum number of positive sera, and that the immunoblot detects many anti-La sera which do not form precipitins.

A multiple sample immunoblotting system (MSIS) for the intrinsic detection of antinuclear autoantibodies

A multiple sample immunoblotting system (MSIS) is described. The MSIS permits the detection and classification of antinuclear antibodies (ANA) according to the pattern of antigenic polypeptides recognized in four different extracts: calf thymus whole tissue, nuclear extract, and two ammonium sulphate fractions of the nuclear extract. The procedure permits the classification of anti-RNP, anti-SS/B and anti-Sm, and the detection of new ANAs in sera from SLE patients. The reaction patterns presented are specific and unambiguous, and make the use of validated control sera unnecessary.