Autoantibodies to C-reactive protein is a common finding in SLE,but not in primary Sjögren's syndrome,rheumatoid arthritis or inflammatory bowel disease

The occurrence of antibodies to human C-reactive protein (CRP) was analysed by enzyme-linked immunosorbent assay (ELISA) in 56 patient sera known to contain antibodies to double-stranded DNA (dsDNA) and in 16 sera from patients with primary Sj?gren's syndrome (SS), 15 rheumatoid arthritis, 31 Crohn's disease, and 37 ulcerative colitis. Eighty-seven per cent of the patients with anti-dsDNA antibodies had systemic lupus erythematosus (SLE) and the remaining had autoimmune hepatitis. The cut-off for positive anti-CRP test was set at the 95th percentile of 100 healthy blood donors. Twenty of 56 anti-dsDNA sera (36%) and two of 16 SS sera (13%) had antibodies reactive with human CRP, whereas all other samples were negative. Thirteen of 27 SLE patients (48%) were positive on at least one occasion. The sera containing anti-CRP antibodies only reacted with surface-bound antigen, but not with native CRP in solution. In conclusion, we found that autoantibodies to CRP are common in sera from patients with anti-dsDNA antibodies. It is not likely that this explains the relative failure of CRP response in patients with active SLE. However, it cannot be excluded that anti-CRP autoantibodies have other biological potentials of pathophysiological interest in SLE, for instance by binding to CRP deposited on cell and tissue surfaces.     

Preparative isolation of p67, A, B, B' and D from nRNP/Sm and Sm antigens by reverse-phase chromatography. Use in a polypeptide-specific ELISA for independent quantitation of anti-nRNP and anti-Sm antibodies

The p67 (67 kDa) and A (33 kDa) polypeptides of nRNP/Sm antigen and the B, B' (28 and 29 kda) and D (16 kDa) polypeptides of 'free' Sm antigen were isolated and used in enzyme-linked immunoadsorbent assays (ELISA) for human autoantibodies. ELISA specificity was demonstrated using monoclonal antibodies. The ELISA using HPLC-purified polypeptides was found to be more sensitive than immunoblotting for detecting antibody. 86% of sera with precipitating anti-nRNP antibodies were positive in the ELISA, as were all sera with precipitating anti-Sm antibodies. Patients with rheumatoid arthritis (RA), Sj?grens syndrome (SS) and undifferentiated connective tissue disease (UCTD) had low levels of anti-p67 with a prevalence 11.6% and 18%, respectively, whilst patients with systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD) had high levels and prevalence rates of 55.2% and 80%, respectively. Anti-B or anti-D antibodies were detected at high levels in SLE (prevalence 30%) but were found rarely in UCTD and MCTD (prevalence 7% and 10%) and not at all in RA or SS sera.     

Microhemagglutination test for the detection of nucleoprotein antibody in systemic lupus erythematosus.

A simple and practical microhemagglutination test that detects two antibodies, one showing reactivity to the DNA moiety of soluble nucleoprotein (sNP) and the other to the DNA-histone complex of sNP, is described. The method incorporates human erythrocytes formalinized at 30 C., tanned, and coated with sNP at 37 C. Antibody specificity was determined by inhibition experiments performed on sera with added DNA or sNP antigen. With the indirect LE cell technic, evidence that the anti-sNP antibody detected in this work is related to the serum LE factor commonly associated with the LE cell phenomenon was obtained. The hemagglutination test is helpful in establishing the specific diagnosis of systemic lupus erythematosus (SLE) and may be used to follow the course of the disease and response to therapy in SLE patients, as this is a semiquantitative technic and rise or fall in titer or antibody can be determined.     

Detection of an antigen (AN6520), possibly related to non-A, non-B hepatitis, by monoclonal antibodies. I

The antibody to AN6520 antigen, which was isolated from the liver of a patient with non-A, non-B hepatitis (NANBH), has been detected frequently in convalescent sera from patients with NANBH by the passive hemagglutination (PHA) test. In a further study, we established hybridoma cells secreting antibodies against AN6520 antigen and obtained ascitic fluids with PHA titers ranging from 1:10(5) to 1:10(7). In immunodiffusion with AN6520 antigen, all monoclonal antibodies were found to form an identical precipitin line. These lines were also identical to those formed by rabbit antiserum against AN6520 antigen and by convalescent sera from patients with NANBH. With one of the monoclonal antibodies, 1-F12, solid-phase radioimmunoassay (SP-RIA) for detecting AN6520 antigen was developed as well as blocking RIA for anti-AN6520 antibody detection. The antigen assay was 50 times more sensitive than the reverse passive hemagglutination (R-PHA) test, with a sensitivity threshold of the 1 ng/ml of antigen solution; the antibody assay was 10 times more sensitive than PHA. The results with this blocking RIA were mostly in agreement with the data obtained by PHA. Furthermore, the antigen in human sera, which had never been detected by R-PHA test, could be detected by SP-RIA.     

The incidence of antibodies to a soluble nuclear antigen in the sera of patients with systematic lupus erythematosus and rheumatoid arthritis estimated with the mixed haemadsorption technique

The incidence of antibodies to a `soluble' nuclear antigen in sera from cases of connective tissue disease was studied with the mixed haemadsorption technique, which was more sensitive than the indirect immunofluorescent test and more accurate for quantitative determinations. The results with unabsorbed sera were not affected by the coexistence of antibodies to nucleoprotein and desoxyribonucleic acid (DNA). Antibodies to soluble nuclear antigen were four times more common in sera from cases of systemic lupus erythematosus (SLE) than in sera from cases of rheumatoid arthritis, where they were about as frequent as in sera from healthy male blood donors. However, their incidence in SLE was 50% and thus not high enough to make them useful as an independent diagnostic criterion.

The antigenicity of the soluble nuclear material was preserved after treatment with acetone but not with ethanol.

     

The fine specificity of IgG antiguanosine antibodies in systemic lupus erythematosus

The antigen specificity, isotype, and subclass of antinuclear antibodies may be related to their pathogenicity in systemic lupus erythematosus (SLE). Our laboratory found that IgG antibodies that bound the nucleoside, guanosine, occurred frequently in SLE patients. In contrast, sera from healthy subjects contained IgM but not IgG antiguanosine antibodies. The present studies were designed to characterized the fine specificity of IgG antiguanosine antibodies in SLE and compare them with IgM antiguanosine antibodies in normal sera. Serum antinuclear antibodies from six healthy subjects and six SLE patients were isolated by affinity binding to guanosine and measured by an enzyme-linked immunosorbent assay (ELISA). IgM in normal sera, and both IgM and IgG in SLE sera bound guanosine. IgM antiguanosine antibodies in normal sera were polyspecific and bound other nucleosides and 1-methylguanosine but not denatured DNA (ssDNA). In contrast, IgG antiguanosine antibodies from the SLE patients bound guanosine and ssDNA but not other nucleosides or 1-methylguanosine. SLE IgM antiguanosine antibodies had the same fine specificity and bound guanosine and ssDNA but not any of the other nucleosides. These results suggest that SLE IgG and IgM antiguanosine antibodies have fine specificity in contrast to the polyspecific IgM antibodies in normal sera. In addition, subclass analysis indicated that all SLE patients had either IgG1 or IgG3 subclass of antiguanosine antibodies that bind complement. Characterizing the isotype, subclass, and fine antigen specificity of antiguanosine antibodies should assist in evaluating their potential pathogenicity in SLE.     

Antibodies against Ku protein in sera from patients with autoimmune diseases

Immunoaffinity-purified Ku protein was used to screen sera from patients with systemic lupus erythematosus (SLE), scleroderma, myositis and Sjögren''s syndrome for anti-Ku antibodies in a quantitative immunoblot assay. Sixteen percent of the 159 studied sera were reactive with the Ku protein; significantly increased frequencies of anti-Ku antibodies were found in SLE (19%) and scleroderma (14%) sera. Patients with myositis and Sjögren''s syndrome showed similar frequencies. All positive sera had antibodies to the 86 kD subunit of Ku protein; only one serum did not react with 70 kD subunit. Frequencies of other autoantibodies were compared in anti-Ku positive and negative patients. Only anti-Sm antibodies, especially in the absence of anti-nRNP, appear to be associated with the presence of anti-Ku antibodies. A strong correlation between anti-Ku antibodies and the class II HLA antigen DQw1 (89% of the positive sera) was observed, suggesting participation of MHC genes in the mounting of the anti-Ku immune response.     

Micro-hemagglutination tests for detection of native and single-strand DNA antibodies and circulating DNA antigen

A practical micro-titration hemagglutination test which can be helpful in the detection of either anti-DNA antibodies or circulating free DNA is described. The procedure utilizes formalinized human erythrocytes coated with sonically disrupted DNA which are capable of reacting with antibodies to both native and single-strand DNA and show minimal non-specific agglutination. By an inhibition assay, the test could be adapted to detect circulating DNA antigen. Eleven of 51 SLE sera revealed anti-DNA antibody titer of 1 : 4 - 1 : 512 and 9 of the 40 sera showing no anti-DNA antibody had circulating DNA levels ranging from 0.8–25 μg/ml. The test provides a reliable method to determine circulating DNA antibody or antigen and may be used to follow the course of the disease and response to therapy in patients with systemic lupus erythematosus.     

Complement activation by antibodies to DNA in systemic lupus erythematosus measured by enzyme immunoassay

An enzyme immunoassay to detect complement-fixing antibodies to DNA (CF-antiDNA) was developed. Of SLE sera, 64% had these antibodies as did 6% of 50 rheumatoid arthritis and 3.2% of 93 normal human sera. The mean CF-antiDNA level was higher in the sera of SLE patients with renal disease than those SLE patients who had no renal disease (P less than 0.0001), and higher in those SLE patients with active rather than inactive renal disease (P = 0.006). CF-antiDNA was more closely associated with renal activity than total IgG-antiDNA or CH50. These observations suggest that both the quality and quantity of anti-DNA antibodies play a role in the pathogenesis of renal disease, and that modern enzyme immunoassays help distinguish the relative importance of complement-fixing antibodies to anti-DNA from that of total anti-DNA.     

Glyceraldehyde 3-phosphate dehydrogenase is a novel autoantigen leading autoimmune responses to proliferating cell nuclear antigen multiprotein complexes in lupus patients

Using 2-dimensional electrophoresis and ion-pair chromatography, we have identified elements of proliferating cell nuclear antigen (PCNA) multiprotein complexes that are reactive to antibodies in sera from patients with systemic lupus erythematosus. Among the various elements of the complexes, a 37 kDa protein (PI 8.5) that specifically reacted with SLE sera, but not with sera from patients with other connective tissue diseases, was identified as glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Immunoblot analysis showed that SLE sera reactive with the 37 kDa protein specifically reacted with GAPDH, as did anti-GAPDH mAbs. The purified autoantibodies to GAPDH from lupus serum showed both nuclear speckled and cytoplasmic staining patterns in immunofluorescence on Hep-2 cells. In addition, enzyme-linked immunosorbent assay (ELISA) revealed the presence of anti-GAPDH autoantibodies in 47% of lupus patients. Longitudinal analysis of the reactivity of lupus sera to PCNA complexes showed the autoimmune response to spread from GAPDH to other elements of PCNA complexes, and the presence of anti-GAPDH antibodies was significantly correlated with increased levels of serum PCNA. Taken together, these findings suggest that GAPDH interacting with PCNA in association with its cellular function is a novel autoantigen recognized by lupus sera, and that GAPDH thus plays an important role in the induction of autoimmune responses against the PCNA complex.     

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting as a serological tool in the diagnosis of syphilitic infections.

The utility of sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting as a serological tool in the diagnosis of human syphilitic infections was examined. In model experiments, rabbits were immunized with Treponema pallidum or T phagedenis, and the antisera were tested for cross-reactivities with both sets of antigens. A major T. pallidum antigen with a molecular weight of ca. 17,000 appeared to be the most reliable specific antigenic marker as assessed by the immunoblotting technique with peroxidase-labeled second antibodies. Antibodies to this antigen were never detected in hyperimmune rabbit anti-T. phagedenis sera or in the sera of nonsyphilitic humans. In contrast, reactive antibodies were found in all syphilitic human sera and also in liquor samples that were positive in the passive hemagglutination test. Differentiation between immunoglobulin M and immunoglobulin G antibodies was directly possible by applying the respective specific second antibodies. Immunoblotting tests were performed with sera exhibiting low passive hemagglutination test titers and equivocal fluorescent treponemal antibody and rapid plasma reagin card reactions. In more than 60% of these cases, immunoblot positivity with respect to the 17,000-molecular-weight antigen was found. The same results were obtained with partially purified 17,000-molecular-weight antigen. The immunoblot technique should be useful as an additional diagnostic tool for differentiating between true and false-positive serological reactions.     

Systemic lupus erythematosus sera inhibit antigen presentation by macrophages to T cells

Several reports have demonstrated that systemic lupus erythematosus (SLE) patients have a decreased response to exogenous antigens both in vivo and in vitro. We examined the effects of SLE sera on macrophage (M phi) antigen-presenting functions. M phi from normal donors were pulsed with tetanus toxoid antigen in the presence of SLE or normal human serum (NHS), fixed in paraformaldehyde, and incubated with autologous T cells. Of 16 SLE sera tested, 11 inhibited the T-cell proliferative response (measured by [3H]thymidine uptake) compared to control NHS; mean percentage inhibition was 53 +/- 23%. This inhibition did not result from interference with antigen uptake by M phi and was found in both IgM and IgG fractions of the sera. There was a positive correlation between the amount of inhibition and the cytotoxic reactivity of the SLE sera against M phi as measured by Terasaki assay (r = 0.659, P less than 0.01). However, the presence and the amount of the inhibition did not correlate with serum immune complexes by Clq ELISA, serum anti-DR antibodies, or clinical disease activity of the SLE patients. We conclude that some SLE sera possess IgM and IgG antibodies reactive with M phi which affect M phi antigen-presenting functions, and might relate to decreased antigenic response in SLE patients.     

Frequency of MIC antibody in rejected renal transplant patients without HLA antibody

Antibodies to MICA and MICB antigens were sought in the sera of 139 kidney transplant recipients. MICA*001, *002, *007, *008, and MICB*002 antigens were produced in Escherichia coli and then tested using enzyme-linked immunosorbent assay plates. Among 35 normal sera, 6% had MIC antibodies, and among 14 sera from pregnant women, 21% had MIC antibodies. Among 34 patients with functioning transplants with human leukocyte antigen (HLA) antibodies, 24% had MIC antibodies, and 19% of 32 patients without HLA antibodies had MIC antibodies. Among 46 patients who lost grafts with HLA antibodies, 26% had MIC antibodies, and among 27 failed patients without HLA antibodies, 37% had MIC antibodies. We conclude that antibodies to MIC are produced in the course of immunization by pregnancies and kidney transplants. They also occurred more frequently in rejected patients (30%) than in those with functioning grafts (21%).     

A common idiotype expressed on a murine anti-Sm monoclonal antibody and antibodies in SLE sera.

A rabbit anti-idiotypic antiserum made against a murine monoclonal anti-Sm autoantibody (Y2) was used in a solid-phase radioimmunoassay to investigate idiotypic cross-reactivity among anti-Sm antibodies present in sera from patients with systemic lupus erythematosus. Sera from 25 of 51 SLE patients (49%) containing anti-Sm antibodies were positive for this Y2 idiotype compared to only one of 22 normal human sera. Nine of 28 SLE patients (32%) whose sera were anti-Sm negative were also positive for the Y2 idiotype in low titre. Binding was not due to rheumatoid factor-like activity but was specific for the Y2 determinant and could be eliminated by absorption with Y2 monoclonal antibodies. The anti-idiotypic antibody blocked the ability of 12 of 25 anti-Sm positive lupus sera to bind Sm. Conversely, Sm antigen inhibited the binding of anti-idiotypic antibody in nine of 12 lupus sera.     

Family distribution of anti-F(ab'')2 antibodies in relatives of patients with systemic lupus erythematosus.

Recently we reported an inverse relationship between the levels of anti-F(ab')2 antibodies and disease activity in systemic lupus erythematosus (SLE). The present study focused on anti-F(ab')2 antibodies in unaffected relatives of SLE patients. Sixty sera from first degree family members from 11 SLE families and 49 sera from 8 control families were studied. Percentage of SLE family members with anti-DNA antibodies (15%) was higher than than control family sera (8%, P less than 0.05). Anti-F(ab')2 antibodies were measured using ELISA assays. The SLE family sera had higher amounts of anti-F(ab')2 antibodies than the normal control family group (P = 0.0051). In an effort to determine if anti-F(ab')2 antibodies found in high titres in the sera of some SLE family members had specificity for the F(ab')2 fragment of anti-DNA antibodies of the SLE relative patients, DNA-anti-DNA inhibition experiments were performed using anti-F(ab')2 prepared from the relative in parallel with anti-F(ab')2 prepared from normal controls with equivalent high titres of serum anti-F(ab')2. Inhibition exhibited by anti-F(ab')2 of first degree relatives was higher than that obtained from control normal donors (P less than 0.02). Such differences in inhibition were not recorded using a control tetanus toxoid-anti-tetanus toxoid assay. In direct binding ELISA experiments, peroxidase-conjugated anti-F(ab')2 antibodies from the same first degree relative showed high relative specificity against purified anti-DNA antibodies of his SLE proband when compared to those obtained against different anti-DNA antibodies isolated from unrelated SLE patients (P less than 0.001). Such a substantial difference was not observed in parallel experiments using peroxidase conjugated anti-F(ab')2 antibodies from normal controls unrelated to SLE subjects.     

Measurement of anti-DNA antibodies by ELISA: a comparative study with Crithidia and a Farr assay

One hundred and twenty six sera from 116 patients with systemic lupus erythematosus (SLE) and from 51 control patients were assayed for the presence of anti-DNA antibodies, using a commercial enzyme linked immunosorbent assay (ELISA). Fifty three sera (42%) from SLE patients were positive and a further 13 sera (10%) fell in the 'equivocal' positive range. Three control sera were positive. In a standard 14C DNA Farr assay, 67 sera (53%) from SLE patients were positive. One control serum was weakly positive. There was a good linear correlation between absorption in the ELISA and the 14C DNA binding result (r = 0.73). Results in the ELISA and Farr assays were concordant in 96 of the 126 SLE sera, and 47 of 51 control sera. Sequential sera from a further 6 patients with fluctuating clinical activity of SLE showed similar patterns of change of anti-DNA antibodies in both assays. The ELISA was more sensitive than the Crithidia luciliae immunofluorescence assay which detected 44 positive sera (35%) in the SLE group. These results suggest that this ELISA assay may be a useful alternative to the Crithidia assay or an effective screen prior to testing in the more technically difficult and time consuming Farr assay for the measurement of anti-DNA antibodies.     

Reactivity of autoantibodies in systemic lupus erythematosus with synthetic core histone peptides

The specificity of autoantibodies present in the serum of 151 patients with systemic lupus erythematosus (SLE) was investigated by ELISA using as antigen individual histones as well as 17 different core histone synthetic peptides. Many of the sera reacted with four terminal peptides (residues 1-21 and 130-135 of H3, 1-29 of H4 and 1-25 of H2B) while fewer reacted with internal peptides (residues 65-85 of H2A and 40-55 of H3). Of the 151 SLE sera, 88% reacted with one or more of the six core histone peptides whereas only 57% reacted with one or more of the complete core histone molecules. Antibodies to mononucleosomes from chicken erythrocytes were also prepared in rabbits. The rabbit antisera were tested by ELISA using as antigen chromatin subunits, native and denatured DNA, individual histones and 23 natural and synthetic peptides of histones. The antinucleosome antibodies were found to recognize the same peptide fragments as those recognized by the SLE sera.     

Crossreactivity of Human Anti-dsDNA Antibodies to Phosphorylcholine: Clues to Their Origin

The presence of anti-double stranded DNA (dsDNA) antibodies is a serological diagnostic feature of systemic lupus erythematosus (SLE), an autoimmune rheumatic disorder. Studies by several investigators have suggested that a response to a microbial antigen can lead to the induction of SLE-like autoimmunity, in both humans and mice, since anti-dsDNA antibodies have been shown to crossreact with foreign antigens. In particular, anti-DNA antibodies have been shown to crossreact with phosphorylcholine (PC), a dominant epitope on pneumococcal cell wall polysaccharide. We have investigated the binding characteristics of human polyclonal anti-DNA antibodies from the sera of SLE patients. In this study we show that the DNA binding of polyclonal serum derived antibodies can be partially inhibited by phosphorylcholine (PC). The binding of affinity-purified anti-DNA antibodies from the sera of patients with SLE was also found to be inhibited by PC. We further demonstrated that the serum IgG1 (T dependent) anti-DNA response was more likely to crossreact with PC than the IgG2 (T independent) response to DNA. The studies suggest there may be a T dependent and T independent response to DNA with the T dependent response displaying more crossreactivity with microbial antigen.     

Enzyme-linked immunosorbent assay for titration of Haemophilus influenzae capsular and O antigen antibodies.

The enzyme-linked immunosorbent assay (ELISA) was elaborated for the detection of immunoglobulin M (IgM) and IgG antibodies against capsular and O antigens of Haemophilus influenzae. Purified capsular polysaccharide and lipopolysaccharide were used as antigens, with optimal coating concentrations being about 50 and 100 micrograms/ml, respectively. The antibody content was expressed as the highest serum dilution (-log10) showing an absorbance of 0.2 above the background level. The titers of hyperimmune sera (reference sera) ranged between 5 and 7 -log10. The sensitivity of the method was about 80 ng/ml with regard to anticapsular antibodies and 3 to 5 ng/ml with regard to anti-lipopolysaccharide antibodies. For detection of antibodies against capsular polysaccharide in sera obtained after primary immunization, ELISA was about 100-fold more sensitive than the indirect hemagglutination assay, whereas in hyperimmune sera, ELISA was about 10-fold more sensitive than the indirect hemagglutination assay. The sensitivity of ELISA for detecting anticapsular antibodies after primary and booster immunizations was 50-fold higher than that of the bactericidal assay using capsulated bacteria, whereas the sensitivity of the two methods was the same when hyperimmune sera were tested. ELISA performed with lipopolysaccharide as the antigen was about 50- and 150-fold more sensitive than the complement fixation and bactericidal assays tested with noncapsulated variants after primary injection and hyperimmunization, respectively.     

Persistence of antibody to hepatitis B surface antigen.

Sera from military personnel found to have antibodies to hepatitis B surface antigen (anti-HBS) in an epidemiological study of a hepatitis B outbreak were tested for persistence of that antibody 1 year later. Initially, 64% of the anti-HBS-positive sera reacted in passive hemagglutination tests with erythrocytes coated with hepatitis B surface antigen of both ayw and adw subtypes; the remaining sera reacted only with adw-coated erythrocytes (19%) or ayw-coated erythrocytes (17%). After 1 year, anti-HBS was detectable by passive hemagglutination tests in 87% of individuals with initial antibody to both subtypes but in only 41% and 16% (P less than 0.001) of those initially reacting only to adw- or ayw-coated erythrocytes, respectively. Seropositivity for anti-HBS correlated best with history of contact with jaundiced people (20.3%) and duty in Asia.