DNA-binding property of Sm nuclear antigen

Antibodies in the sera of patients with systemic lupus erythematosus reacted with a nuclear acidic protein called Sm antigen, and these antibodies were used as reagents to identify Sm antigen in preparative fractionation procedures. DNA affinity chromatography showed that Sm antigen was associated with nuclear protein fractions which had DNA-binding capacity. Evidence was also presented that Sm antigen showed preferential binding for single-strand DNA over double-strand DNA. These studies demonstrate that spontaneously occurring anti-nuclear antibodies in disease states may be used to study the properties of cellular proteins which are present in trace amounts.     

Scl-86, a marker antigen for diffuse scleroderma.

More than 300 sera from patients with a connective tissue disease were analyzed with the immunoblotting technique. The presence of autoantibodies against an 86,000-mol wt marker antigen for diffuse scleroderma (Scl-86) was found in 14 out of 33 patients with scleroderma. The presence of anti-Scl-86 antibodies seemed to correlate with the diagnosis of diffuse scleroderma since they were found in 13 out of 22 diffuse scleroderma patients and in only one out of 11 patients with limited scleroderma. All scleroderma sera (33 patients' sera and 13 reference sera) were also tested for the presence of anti-Scl-70 antibodies. It was found that all anti-Scl-70 positive sera (n = 25) contained anti-Scl-86 antibody as well, suggesting a relationship between these two antigens. However, the Scl-86 antigen was shown to be an extremely insoluble nonchromosomal protein, resistant to boiling in sodium dodecyl sulfate. This contrasts with the Scl-70 antigen, which has been described as a thermolabile, soluble antigen present in the chromatin fraction. Together, our results are consistent with the idea that Scl-70 is a degradation product of Scl-86. The Scl-86 antigen is present in freshly prepared rabbit thymus, spleen, and liver nuclei as well as in nuclei from various cultured cell lines, but is not detectable in extractable nuclear antigen from rabbit thymus. In a limited retrospective study, the anti-Scl-86 antibodies were found in two sera from patients with Raynaud's phenomenon before the development of diffuse scleroderma. Therefore, it is possible that screening of patients' serum for this antibody might predict the development of diffuse scleroderma.     

Elevated Levels of Antibodies to Epstein-Barr Virus Antigens in Sera and Synovial Fluids of Patients with Rheumatoid Arthritis

The frequencies and levels of antibodies to Epstein-Barr virus (EBV)-specific antigens were determined in paired sera and synovial fluids from patients with rheumatoid arthritis (RA) and in sera from patients with other connective tissue diseases; i.e., systemic lupus erythematosus, progressive systemic sclerosis, and osteoarthritis (OA). The specimens were also tested for the presence of antibodies to RA-associated nuclear antigen. Compared to healthy controls, the patients' sera showed increased frequencies of elevated antibody titers (≥320) to Epstein-Barr viral capsid antigen, a correspondingly enhanced (twofold to threefold) geometric mean titer, and an increased frequency of antibodies at elevated titers (≥10), usually to the restricted component and rarely the diffuse component of the early antigen complex. Levels of antibody to the EBV-associated nuclear antigen were within the normal range. Enhancement of antibody titers was more pronounced in seropositive RA patients (i.e., positive for rheumatoid factor) than in those who were not. Enhancement was also found in systemic lupus erythematosus and progressive systemic sclerosis. Antibody to RA-associated nuclear antigen was detected at an increased frequency only in the group of seropositive RA patients (90%), as compared to 8-15% in the other connective tissue diseases and 6-8% in healthy controls. The antibody titers in the synovial fluids equaled or were at most twofold higher or lower than those in the sera. In addition, levels of EBV-specific antibodies were studied serially over a period of 6-10 mo in patients with RA and OA. Parameters of disease activity were determined and compared to antibody levels. EBV-specific antibodies in sera of OA patients remained constant and within normal limits throughout the study. Although EBV-specific antibodies were often elevated in RA patients, they also remained constant, with the exception of three patients, who showed gradual increases in one of the four antibodies, which did not correlate with disease activity.     

Heterogeneity and clinical significance of glomerular-binding antibodies in systemic lupus erythematosus.

We used an ELISA employing extracts of human glomerular basement membrane (GBM) to detect, characterize, and evaluate the clinical significance of glomerular-binding IgG in patients with SLE nephritis. Most patients with SLE nephritis exhibited GBM-binding IgG, although many patients with active nonrenal SLE or symptomatic, drug-induced lupus had similar reactivity, albeit at lower levels. IgG binding to GBM in SLE nephritis patients was decreased by DNase pretreatment of GBM, restored after DNase with nuclear antigens (most notably with nucleosomes), inhibited by exogenous nuclear antigens (particularly nucleosomes), but unaffected by exposure of serum to DNase/high ionic strength. The characteristics of IgG binding to GBM largely paralleled the patients' underlying autoimmune response, which was dominated either by antibodies to DNA/nucleosomes or to nucleosomes alone. Binding of lupus sera to nonrenal extracellular matrix (even with nucleosomes) was not equivalent to GBM. Collagenase pretreatment of GBM variably decreased IgG binding, depending on the level and type of binding. SLE nephritis patients with high levels of GBM-binding IgG exhibited more severe disease clinically, but the same renal histopathology, as patients with lower levels. The level of GBM-binding IgG at presentation did not predict the therapeutic response, but decreased in responders to therapy. In sum, glomerular-binding IgG in lupus nephritis binds to epitopes on chromatin, which adheres to GBM in part via collagen. These autoantibodies appear necessary, but not sufficient, for the development of nephritis, and correlate with clinical rather than histopathologic parameters of disease activity.     

Avidity of anti-DNA antibodies in serum and IgG glomerular eluates from patients with systemic lupus erythematosus. Association of high avidity antinative DNA antibody with glomerulonephritis.

Significant differences in both specificity and avidity of anti-DNA antibodies were observed in the sera of groups of patients with active systemic lupus erythematosus glomerulonephritis, active systemic lupus erythematosus without nephritis, and in IgG eluates obtained by DNAase digestion of isolated glomeruli from glomerulonephritic kidneys. With methylated albumin-kieselguhr fractionated 3H-HeLa DNA as a source of native or single-strand DNA antigen in a modified Farr assay, an increased level of antibody to native DNA was associated with active systemic lupus erythematosus, particularly active nephritis. The avidity of antinative DNA estimated from plots of the reciprocals of bound and free antigen according to the Sips distribution formula was significanly lower in active glomerulonephritis sera than in sera from patients with active systemic lupus erythematosus without nephritis. However, antinative DNA of uniformly high avidity was found in the glomerular eluates. Avidity of single-strand DNA antibodies did not differ in the various patient groups. The data stronly supprot a major role for high avidity antinative-DNA in DNA/antiDNA immune complex-induced glomerular injury in systemic lupus erythematosus.     

Antibodies from patients with connective tissue diseases bind specific subsets of cellular RNA-protein particles.

We characterized the RNA-containing antigens precipitated by sera from 260 patients with positive antinuclear antibodies. 49 individuals, most of whom had systemic lupus erythematosus or Sjögren's syndrome, possessed antibodies that precipitated the previously identified RNP, Sm, Ro, and La antigens either singly or in combinations. These antigens, which are located on discrete sets of small nuclear or cytoplasmic RNA-protein particles, exhibited a number of antigenic interrelationships. One patient's serum recognized a new particle containing a small RNA which we have called Th; it also precipitated the Ro complexes. Other patients with systemic lupus erythematosus, hepatitis B virus infection, juvenile rheumatoid arthritis, myositis, and rheumatoid arthritis had antibodies that precipitated specific subsets of ribosomal RNA and transfer RNA. One patient's serum contained a monoclonal immunoglobulin G that precipitated ribosomes. Most of these antibodies identified antigenic determinants constituted at least in part of protein. The specificity of the proteins bound to particular cellular RNA, probably explains the exquisite precision with which antibodies from rheumatic disease patients discriminate among RNA subsets. Such sera should be useful probes for investigating specific roles that different RNA and RNA-protein complexes play in cellular metabolism.     

Ultraviolet light induces binding of antibodies to selected nuclear antigens on cultured human keratinocytes.

Antibodies which bind to different nuclear antigens in tissue sections or in permeabilized cell cultures are useful markers of subsets of connective tissue disease, especially of lupus erythematosus (LE), but whether these antibodies are able to react with these intracellular sequestered antigens in vivo and cause immunologic tissue damage has been a matter of much debate. We report experiments which show that ultraviolet light-irradiated, cultured human keratinocytes bind IgG antibodies from the sera of LE patients with either monospecific anti-SSA/Ro, anti-RNP, or anti-Sm activity, which implies that these antigens have been made accessible on the cell surface by ultraviolet irradiation. Normal human sera or LE patient's sera with anti-double-stranded DNA, anti-single-stranded DNA, or antihistone activity do not bind to the surface of irradiated human keratinocytes. In control experiments, all antisera produced the expected patterns of nuclear and cytoplasmic staining of fixed permeabilized, unirradiated keratinocytes. Careful study of the viability and permeability of irradiated keratinocytes by several techniques showed that this apparent cell membrane expression of extractable nuclear antigens (SSA/Ro, RNP, and Sm) following irradiation was seen on injured keratinocytes whose cell membranes were intact, but not on dead cells. It is particularly significant that all six monospecific anti-SSA/Ro sera bound to irradiated keratinocytes, since this antibody antigen system is highly associated with photosensitive cutaneous LE.     

Autoimmune sera reactive with Sm antigen contain high levels of RNP-like antibodies.

Ribonucleoprotein particles containing Sm antigen were separated from particles containing both Sm and RNP antigens by ion-exchange chromatography to study the recognition of these antigens by autoimmune sera. By using the separated antigens, anti-Sm and/or anti-RNP antibodies were detected in approximately 60% of sera from systemic lupus erythematosus patients by both enzyme-linked immunosorbent assay and immunoprecipitation of radiolabeled antigens followed by analysis on sodium dodecyl sulfate-polyacrylamide gels. These antibodies were detected in 30% of the same sera using the standard passive hemagglutination technique. Competition experiments demonstrated that all of the sera tested that contained anti-Sm antibodies also had anti-RNP-like reactivity. This latter reactivity usually represented 80% or more of the total Sm and RNP binding activity in lupus sera. The binding to RNP-like determinants by several of the sera was uniquely resistant to treatment of the antigen with snake venom exonuclease. These studies indicate that humoral immunity against Sm and RNP antigens in systemic lupus erythematosus is directed primarily against a single type of ribonucleoprotein particle in which the two antigens are physically associated. The specific binding to a single type of ribonucleoprotein particle suggests that this particle may be especially immunogenic and that it might play an important role in induction of the humoral immune response to Sm and RNP.     

Insights into native epitopes of proliferating cell nuclear antigen using recombinant DNA protein products

A cDNA clone encoding full-length human proliferating cell nuclear antigen (PCNA) was used to generate a panel of in vitro translated labeled protein products with COOH-terminal deletions and to construct a set of fusion proteins with COOH- and NH2-terminal deletions. A rabbit antiserum raised against an NH2-terminal peptide, a well-characterized murine monoclonal antibody (mAb), and 14 human lupus sera with autoantibody to PCNA were analyzed for their reactivity with the constructs using both immunoprecipitation and immunoblotting techniques. The rabbit antiserum reacted in immunoprecipitation and immunoblotting with constructs containing the appropriate NH2-terminal sequence and mAb reacted with a sequence from the midregion of PCNA. These experimentally induced antibodies also reacted with 15-mer synthetic peptides in enzyme-linked immunosorbent assay (ELISA). In contrast, none of the lupus sera reacted with synthetic peptides in ELISA. 9 of the 14 lupus sera also failed to react in Western immunoblotting with any recombinant fusion protein, although they all immunoprecipitated in vitro translated full-length protein. Four of the nine had variable patterns of immunoprecipitation with shorter constructs. The remaining five lupus sera were able to immunoprecipitate translation products as well as Western blot recombinant fusion proteins. From analysis of the patterns of reactivity of human lupus sera, it was deduced that the apparent heterogeneity of human autoantibodies to PCNA could be explained by immune response to highly conformational epitopes. These observations demonstrate that there might be special features in "native" epitopes of intranuclear antigens that are recognized by autoantibodies, and that these special features of native epitopes might not be present in prepared antigen used for experimental immunization. These features may be related to protein folding or to association of the antigen with other intranuclear proteins or nucleic acids, as might occur with antigens that are components of subcellular particles.     

Lupus autoantibodies target ribosomal P proteins

All nine SLE (systemic lupus erythematosus) sera with antiribosomal antibody activity targeted the same three ribosomal protein antigens, of molecular masses 38 and 17/19 kD when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting. One serum reacted with an additional protein of approximately kD. Ribosomal subunit fractionation by composite gel electrophoresis and sucrose density ultracentrifugation showed that these proteins were part of the large subunit. Isoelectric focusing in agarose, and two-dimensional polyacrylamide gel electrophoresis revealed that the antigens had pI between 4.5 and 6.5, but that the 17/19 kD antigens were more acidic than the 38 kD antigen. Similarities in the molecular masses, charges, as well as the presence of highly conserved crossreactive epitopes, failure to bind to carboxymethylcellulose at pH 4.2, and extractability of the 17/19 kD proteins by 400 mM NH4Cl-ethanol at 0 degrees C indicated that these antigens were analogous to the proteins P0 (38 kD) and P1/P2 (17/19 kD) described previously (25, 36). Co-identity was confirmed using reference antibodies and antigen. Although antibodies to these proteins were only found in 5-10% of more than 50 sera screened by radioimmunoassay or Western blotting, the selective production of antibodies to epitopes on three (out of a total of more than 80) ribosomal proteins may provide further clues to autoantibody induction of SLE.     

Antibodies to Histones in Drug-Induced and Idiopathic Lupus Erythematosus

When tissue sections are extracted with 0.1 N HCl, cellular nuclear proteins, including histones, are removed but nuclear DNA is retained. Histones can be reconstituted back to nuclear DNA in acid-extracted tissue sections so that the resulting nuclear substrate is composed only of DNA and histones and does not contain acidic nuclear protein antigens. The resulting DNA-histone tissue substrate can be used in the immunofluorescent method for specific detention of antibodies to histones. Sera from 23 patients with drug-induced lupus erythematosus (procainamide 19, isoniazid 2, nitrofurantoin 2) and 20 patients with idiopathic (not drug-induced) systemic lupus erythematosus (SLE) were studied. All 23 patients with drug-induced lupus erythematosus (LE) lost nuclear staining on acid-extracted sections. In contrast, only 12 of 20 with idiopathic SLE lost nuclear staining on acid-extracted tissues, and in the remaining 8, there was no significant fall in titer. In the drug-induced LE group, loss of nuclear staining was due to the absence of histones on the substrate because with histone-reconstituted sections, 22 of 23 again became positive for nuclear staining at titers equal to or at one doubling dilution below titers on unextracted tissues. In contrast, of the 12 idiopathic SLE sera which lost nuclear staining, only 5 regained nuclear staining on histone-reconstituted tissue sections. In idiopathic SLE, antinuclear antibodies are heterogeneous in specificities and may consist of antibodies to native DNA, histones, or nonhistone proteins. In contrast, antinuclear antibodies in drug-induced LE are less heterogeneous and mainly consist of antibodies to histones.     

Relationship between snRNA species contained in nuclear antigens recognized by autoantibodies and the clinical profile in systemic rheumatic diseases

Antibodies to extractable nuclear antigens (ENA) are generally used in the diagnosis of connective tissue diseases. Using a rapid, very sensitive method we have shown that extractable nuclear antigens, which are now well-characterized at the molecular level, differ by their RNA content. The method was applied to the sera of 17 patients suffering from different connective tissue diseases. The results show that mixed connective tissue disease (MCTD) and other mild connective tissue diseases are characterized by the presence in the antigen of U1 small nuclear RNA (U1 snRNA) only. On the other hand, antibodies from 6 out of 8 patients tested with Systemic Lupus Erythematosus (SLE) recognize antigens exhibiting a more complex RNA pattern. Three of them precipitated all five snRNAs U2, U1, U4, U5, U6 whereas some snRNAs were lacking or quantitatively less important in precipitates obtained with the three others.     

A soluble acidic protein of the cell nucleus which reacts with serum from patients with systemic lupus erythermatosus and Sjögren''s syndrome.

A soluble nuclear antigen that reacts with sera obtained from patients with systemic lupus erythematosus and Sj?gren's syndrome has been described. The antigen, tentatively named the Ha antigen after the prototype serum, was shown to react with specific antibodies by precipitin, complement fixation, and immunofluorescence techniques. The Ha antigen prepared from isolated nuclei of calf thymus glands, calf liver, and rat liver showed identical immunological reactivities; a wide distribution among different species and tissues is presumed. The Ha antigen was destroyed by trypsin and relatively mild heat or pH variation from neutrality, but was resistant to DNase or RNase. Many of these characteristics are similar to those of the "B" antigen to which antibodies have recently been described in Sj?gren's syndrome. The nuclear origin of the Ha antigen was confirmed by the speckled nuclear immunofluorescence staining pattern given by purified antibody to Ha obtained from a specific immune precipitate. Preliminary results showed approximately 13% of patients with systemic lupus erythematosus and 30% of patients with Sj?gren's syndrome had precipitating antibodies to the Ha antigen.     

Immunological studies of post-streptococcal sequelae. Evidence for presence of streptococcal antigens in circulating immune complexes.

Since elevated levels of circulating complexes have been noted to occur in the sera of patients with post-streptococcal sequelae, the possibility that these complexes contained streptococcal antigens within the complex was investigated. Sera from these patients were precipitated with polyethylene glycol to extract a fraction rich in these complexes, which was then injected into rabbits. The rabbit sera were then reacted with both cellular and extracellular fractions obtained from streptococcal strains associated with either acute post-streptococcal nephritis (APSGN) or acute rheumatic fever (ARF) by using immunoelectrophoresis and ELISA techniques. The data demonstrate that both ARF and APSGN complexes contain streptococcal antigens. However, APSGN complexes react uniquely to certain extracellular antigens present in those strains associated with nephritis, while ARF complexes react specifically to certain streptococcal extracellular antigens excreted by strains associated with rheumatic fever. Neither of the two groups of complexes appear to contain streptococcal antigens related to any cellular antigens derived from the group A streptococcus. Additionally, a rabbit serum immunized with streptococcal extracellular products reacted directly with complexes isolated from nephritis patients. Removal of the gamma globulin by absorption with an anti-human Fc serum resulted in the concomitant loss of reactivity with the anti-streptococcal serum, strongly suggesting an intimate association of the streptococcal antigen with these complexes. The presence of streptococcal antigens within the circulating immune complex of patients with APSGN coupled with their specific presence in those strains associated with post-streptococcal glomerulonephritis argues strongly for a causal role of these antigens in the disease process.     

Anti‐C1q antibodies: association with nephritis and disease activity in systemic lupus erythematosus

Background: Anti‐C1q antibodies have been described in systemic lupus erythematosus (SLE) as well as in other connective tissue diseases. They have been considered as a marker for disease activity and presence of nephritis. Objective: The aim of this study was to determine the prevalence of anti‐C1q antibodies in Brazilian lupus patients as well as analyze their association with different clinical and serologic parameters. Methods: Sera from 81 SLE patients, based on the American College of Rheumatology (ACR) criteria, were collected from a lupus referral outpatient clinic in Salvador, Brazil. Antibodies to C1q were detected by an enzyme‐linked immunoassay (ELISA) kit and antibodies to other cellular antigens identified by indirect immunofluorescence on HEp‐2 cell substrate (ANA), or Crithidia luciliae (dsDNA), and to nucleosome by ELISA. A cutoff of 20 U wasestablished for anti‐C1q and antinucleosome assays. Results: Anti‐C1q antibodies were detected in 39.5% (32/81) of SLE sera. The presence of anti‐C1q antibodies was associated with proteinuria (P=0.028) but not with other laboratory or clinical features, such as antinucleosome or anti‐dsDNA antibodies, hematuria, urinary casts or renal failure, leukopenia, pericarditis, pleuritis, malar rash, seizures, and psychosis. There was a positive correlation between the titers of anti‐C1q antibodies and the systemic lupuis erythematosus disease activity index (SLEDAI) score (r=0.370; P=0.001). Conclusion: This study in Brazilian SLE patients confirms previous findings of the association of anti‐C1q antibodies with nephritis and disease activity. J. Clin. Lab. Anal. 23:19–23, 2009. © 2009 Wiley‐Liss, Inc.     

Natural antibodies in sera of patients with systemic lupus erythematosus

Sera obtained from fifty-five patients with active systemic lupus erythematosus (SLE) and from four patients with mixed connective tissue disease (MCTD) previously shown by immunofluorescence and by double immunodiffusion to possess antinuclear antibodies, were tested for the presence of natural antibodies of IgG, IgA, and IgM isotypes. Antibody activity to actin, myosin, DNA, TNP, albumin, and tubulin was examined, using an enzyme-linked immunosorbent assay (ELISA). It was found that, in comparison with the antibody titers in normal sera, most of the SLE and MCTD sera possessed statistically greater amounts of IgG, IgA, and IgM antibodies directed against all the antigens tested. Furthermore, the IgG, IgA, and IgM antibody activity to DNA and TNP, compared to that found with all the other antigens, was significantly higher. Antibodies reacting with a saline extract of calf thymus (ECT) were studied by ELISA and by immunodiffusion. No correlation was observed between the natural antibody titers and the serum antibody levels to ECT detected either by ELISA or by immunodiffusion.     

The Relation of Immunoglobulin Class, Pattern of Antinuclear Antibody, and Complement-Fixing Antibodies to DNA in Sera from Patients with Systemic Lupus Erythematosus

Sera from 55 patients with systemic lupus erythematosus were studied to clarify the significance of the patterns of nuclear fluorescence observed. The sera in which the IgG fraction produced a peripheral pattern of nuclear fluorescence were found to contain complement-fixing antibodies to native DNA and to DNA-histone complexes. This correlation did not exist when complement-fixing activity was compared to the IgM nuclear patterns. Sera which contained only complement-fixing antibodies to denatured DNA and which did not react with native DNA or nucleoprotein did not produce the peripheral pattern of nuclear fluorescence. The data suggest that single strands of DNA were not the reactive groups in the nucleus responsible for the peripheral pattern. The results support the conclusion that DNA within a DNA-protein complex may be the nuclear antigen responsible for the peripheral pattern of nuclear fluorescence.Analysis of the clinical data revealed that a close correlation existed between the presence of IgG peripheral pattern, complement-fixing antibodies to DNA and histone-DNA complexes, and clinical manifestation of active disease.     

Immunoassay with fluorescein-labelled antigens--device of a method and its clinical application.

A simple, sensitive, highly reproducible method for assay of antibodies using fluorescein-labelled antigens according to the method by Farr is described. We measured titers of anti-BSA antibodies and antigen binding capacity of sera in BSA immunized rabbits by fluorometric assay with fluorescein isothiocyanate (FITC) labelled BSA, and obtained highly reproducible and quantitative results. The resultd times more sensitive than the results from single radial immunodiffusion. FITC-labelled double or single stranded calf thymus DNA was incubated with sera of patients with systemic lupus erythematosus and New Zealand Black mice. Both anti-double and single stranded DNA antibodies were detected in sera of systemic lupus erythematosus, but only anti-single stranded DNA antibodies in sera of New Zealand Black mice.     

Demonstration of circulating autoantibodies against the plasma membrane of isolated thyroid cells in Graves' disease

Antibodies against the plasma membrane of isolated human and porcine thyroid cells were demonstrable by a linear fluorescence pattern in sera from 29 out of 37 patients with Graves' disease. In 3 cases the antibodies reacted only with human thyroid cells. In a group of patients with Hashimoto's thyroiditis, 6 of 8 sera reacted with human thyroid cells in a granular fluorescence pattern. With one exception, sera from patients with non-toxic goiter showed no binding of IgG to thyroid cells. Sera from healthy controls were negative in this test system. There was no correlation between the presence of antibodies against thyroid cells and antibodies against thyroglobulin. Antibodies against thyroid microsomal antigens were found in 80% of patients with circulating thyroid cell membrane antibodies; 5 sera with membrane antibodies were negative for microsomal antibodies. Twenty sera of patients with Graves' disease were tested by passive haemagglutination test against peak I and peak II of the human thyroid fractionation with Sephadex G100. Antibodies against peak I were found in 14 sera and against peak II in all 20 sera. The data indicate that the antibodies in sera from patients with Graves' disease are directed mainly against a species-unspecific antigen of the plasma membrane from thyroid cells with a probable molecular weight between 4-7 S and are unrelated to thyroglobulin.     

Particle agglutination assay for sm antibodies using purified sm antigen

Sm antibodies are specific serum markers for the diagnosis of systemic lupus erythematosus (SLE) and are identified by immunodiffusion (ID), counterimmunoelectrophoresis (CIE), and passive hemagglutination (PHA) in the clinical laboratories. These current methods have certain disadvantages of sensitivity, specificity, and complexity. In this report, Sm antigen free from other nuclear antigens was purified. Synthetic particles were coated with Sm antigen and used to test for Sm antibodies in patient's sera. The particle agglutination test was specific for only Sm antibodies among different antinuclear antisera from patients with systemic rheumatic diseases. The particle agglutination test had the same sensitivity and specificity as the enzyme-linked immunoassay (ELISA) test for Sm and RNP antibodies. The correlation coefficient between the ELISA quantitation and the titers obtained by particle agglutination was 0.82. The particle agglutination test can be used for rapid screening and titer determination of anti-Sm antibodies.