Subclass restriction and polyclonality of the systemic lupus erythematosus marker antibody anti-Sm

Constant isotype pattern of anti-dsDNA antibodies in patients with systemic lupus erythematosus

The isotype profile, particularly emphasizing IgG subclass distribution, of dsDNA antibodies in patients with systemic lupus erythematosus was evaluated using an especially adapted ELISA technique. Anti-dsDNA antibodies were quantified with class-specific antisera and subclass-specific monoclonal antibodies. IgG subclass specificity was proven with 20 myeloma proteins differing in light chains and allotypes. The standardization with myeloma proteins proved to be useful and reliable. Results from more than 100 anti-dsDNA positive sera from SLE patients showed specific antibodies within the three subclasses (IgG1: 52-100%, IgG2: 0-39%, IgG3: 0-48%). IgG4 was not detected in significant amounts. No correlation to the subclass distribution of total IgG was found. Each patients' serum displayed an individual isotype pattern that remained constant in longitudinal studies, independent of anti-dsDNA titre fluctuations. These results suggest a stable population of autoreactive clones in the progress of the disease.

Individual variation in the isotype profile of anti-histone autoantibodies in systemic lupus erythematosus

Using a solid-phase radioimmunoassay we have measured levels of anti-histone autoantibodies of the IgG, IgA and IgM heavy chain classes in 40 patients with systemic lupus erythematosus. Twenty-two patients (55%) had significantly elevated levels of at least one anti-histone isotype. Our results reveal four characteristics of the anti-histone response. (1) There is wide variation between patients in the isotype profile of anti-histone antibodies and these isotype profiles are a consistent individual characteristic. (2) There is no significant correlation between the level of IgG, IgA and IgM anti-histone in individual patients and a marked tendency for a single isotype (either IgG, IgA or IgM) to predominate in any one patient. (3) IgG anti-histone antibodies are predominantly of the IgG1 subclass. (4) Among 12 patients tested, IgG and IgA antibodies showed a preference for histones 1 and 2B whereas IgM antibodies showed no consistent preference for individual histones.

Ig class and IgG subclass responses to Treponema pallidum in patients with syphilis

The Ig class and IgG subclasses of anti-Treponema pallidum antibodies in human serum were quantified using solid-phase enzyme-linked immunosorbent assays. Development of these assays with monoclonal antibodies, each specific for a human immunoglobulin class or IgG subclass, provided quantitative data concerning the major antibody specificities. In patients with primary syphilis, anti-T. pallidum activity was limited almost exclusively to IgG1 and IgM. Coordinate, restricted expression of IgG1 and IgG3 responses in T. pallidum-specific assays was observed with sera from patients with active secondary syphilis. IgG1 and IgG3 accounted for roughly 53 and 43% of the total anti-treponemal IgG antibody activity, respectively. While IgM antibody levels were elevated in the patients with secondary syphilis, IgG2 and IgG4 levels, if present at all, represented less than 10 and 2% of the total IgG activity, respectively. Ig in sera from patients who had been treated adequately for secondary syphilis were restricted almost entirely to IgG3 and IgG1. Considering the low level of IgG3 in serum, disproportionately high percentages of antitreponemal antibodies were found in this subclass during and after treatment for secondary syphilis. The restricted, coexpression of the IgG1 and IgG3 isotypes may reflect the close genetic linkage of the gamma 1 and gamma 3 genes and possibly the impact of immunoregulatory mechanisms in response to the induction and expression of autoantibodies which arise during the course of secondary syphilis.

Expression of an interspecies idiotype in sera of SLE patients and their first-degree relatives

Sera from 29 SLE patients and 81 first-degree healthy family members were tested for quantitative expression of a cross-reactive idiotype present on a murine monoclonal anti-Sm autoantibody (Y2). Forty-one percent of SLE patients and 27% of all relatives showed increased serum levels of the Y2 idiotype compared to 6% in a normal, unrelated control group. In addition, female relatives of SLE patients showed slightly increased levels of anti-Sm antibodies compared to male relatives (15% vs 3%). In one of the 28 families and three unrelated SLE patients studied, there was a significant correlation between the Y2 idiotype expression and expression of another idiotype present on anti-DNA antibodies (1341d). Affinity column absorption studies showed that these two idiotypes were present on different antibody molecules. This study demonstrates: (1) a genetic predisposition for an anti-Sm antibody idiotype expression in humans; and (2) that two different idiotypes may be under parallel or coordinate regulation.

Isotypic restriction of the antibody response to human immunodeficiency virus

HIV-infected individuals progress toward AIDS despite the early elicitation of a specific immune response. Analysis of the isotypic distribution of HIV-specific antibodies appears of special interest for two reasons: first, isotypic diversity is partly under the control of antigen-specific T-helper cells, the very cells infected by HIV; second, isotype determines antibody functions, effector (neutralization, antibody-dependent complement, or cell-mediated cytotoxicity) as well as blocking functions. We have investigated by Western blot analysis the isotypic profile of the antibody response to HIV structural proteins (env, gag, pol) and to the nonstructural protein F (3' orf), which is absent from the virion and might primarily target infected cells. In 115 asymptomatic individuals, infected by sexual contact (homosexual men) or intravenously (hemophiliacs), the response to gag-products was polyisotypic, including IgM, IgG1, IgG3 and IgA; the response to F was more restricted (IgM, IgG1, IgA) and the response to env strikingly restricted to the IgG1 isotype, suggesting different regulatory mechanisms in the B-cell response to these proteins. The isotypic distribution was also influenced by the route of infection, IgG4 and IgE (gag-specific) being exclusively elicited in the hemophiliac group. Finally, observations of potential diagnostic interest were made in a limited number of at-risk individuals; these included the presence of gag- and pol-specific IgM or IgA in the absence of any HIV-specific IgG isotypes; and the presence of gag- and F-specific antibodies in the absence of env-specific antibodies, suggesting the early occurrence of both isotypic and antigenic selection mechanisms during the course of HIV infection.

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.

Lupus anti-ribosomal P peptide antibodies show limited heterogeneity and are predominantly of the IgG1 and IgG2 subclasses

A 22-amino acid synthetic peptide (P peptide) containing the conserved, shared autoantigenic determinants of the ribosomal P proteins was conjugated to rabbit serum albumin and used to analyze anti-P heterogeneity in 17 lupus sera. Anti-P peptide antibodies demonstrated moderate restriction in isotype (IgM and IgG, but not IgA), subclass (predominantly IgG1 and IgG2), light chain type (predominantly kappa) and spectrotype. In one serum, almost exclusive use of IgG2 and the kappa light chain was observed. These findings indicate that there is a nonrandom selection of heavy and light chain constant region genes as well as limited variable region diversity in the anti-P peptide response.

Stochastic control of anti-Sm autoantibodies in MRL/Mp-lpr/lpr mice

MRL/Mp-lpr/lpr autoimmune mice consistently show an approximately 25% incidence of the systemic lupus erythematosus marker autoantibody anti-Sm. In the present report, we show that the failure to find anti-Sm antibodies in three-quarters of 5-mo-old MRL/lpr mice was not an artifact of an insensitive assay, but rather that the mice fell into two populations as regards their anti-Sm positivity. Based on an extensive analysis of the incidence of anti-Sm positivity in 5-mo-old mice according to their cage of residence, we found no evidence for genetic, environmental, or parental influences on the propensity of an individual animal to become anti-Sm positive. Also, the gender of the mouse, its Sm antigen level, or its length of survival were not related to anti-Sm antibody, nor was the anti-Sm antibody status of either parent. Some animals became anti-Sm positive after 5 mo of age, but this was less likely than becoming positive before 5 mo of age. Finally, a survey of 205 autoimmune C57BL/6-lpr/lpr mice confirmed the uniqueness of the MRL background for this autoantibody response. These results together indicate that the possibility of making anti-Sm antibodies is under genetic control, but that the expression of this capability in an individual animal is governed by stochastic events. We hypothesize further that such random processes may involve the expression of particular immunoglobulin variable-region genes combined with mechanisms of extensive somatic mutation or positive feedback amplification, which would transmute an initial monoclonal response into an eventual polyclonal one.

Immunoglobulin G class and subclass antibodies to pneumococcal capsular polysaccharides

Enzyme immunoassays were developed to measure immunoglobulin G (IgG) and IgG1-4 subclass antibodies to pneumococcal capsular polysaccharides (PCP) types 4 and 7F. In healthy subjects, anti-PCP antibodies were predominately of the IgG1 and IgG2 subclasses. There was a significant increase in IgG, IgG1, and IgG2 anti-PCP antibody concentrations following immunization with pneumococcal vaccine. IgG and IgG2, but not IgG1, anti-PCP antibody concentrations correlated with total anti-PCP antibody concentrations measured by the standard radioimmunoassay and with serum opsonic activity for serotype 7F Streptococcus pneumoniae. Such IgG and IgG subclass antigen-specific antibody assays may be useful to investigate the immune response to pneumococcal polysaccharides.

Analysis of anticentromere autoantibodies using cloned autoantigen CENP-B

A cDNA clone encoding CENP-B, the 80-kDa human centromere autoantigen, was used to construct a panel of hybrid proteins containing four different regions of CENP-B. These have allowed us to identify three independent epitopes on CENP-B that are targets of autoantibodies. Two of these are recognized concurrently in greater than or equal to 90% of patient sera containing anticentromere autoantibodies (ACA), conclusively demonstrating that this autoimmune response is polyclonal. When present and previous data are combined, ACA are shown to recognize at least five independent epitopes on CENP-B. A radioimmunoassay based on cloned CENP-B has demonstrated that sera from greater than or equal to 96% of patients with ACA recognize the cloned antigen, thus defining a region of the protein that is recognized by virtually all patients with ACA. These findings have significant implications for models that seek to explain the origin of ACA and for the future detection of this group of autoantibodies in the clinical setting.

Impaired anti-pneumococcal antibody response in patients with AIDS-related persistent generalized lymphadenopathy

Pre- and post-immunization serum antibodies to pneumococcal polysaccharides (PPS) and tetanus toxoid (TT) were measured in 25 patients with persistent generalized lymphadenopathy and serum antibodies to the human immunodeficiency virus (HIV). The increase in post-immunization anti-PPS antibodies was lower than 40% in 16/25 patients. Isotype analysis indicated that the IgM, IgA, IgG2, but not the IgG1 antibody responses were lower in patients that in healthy controls, whereas pre-immunization values were similar. For TT, no difference was found between the patients and the healthy group in total and IgG1 antibody response whereas IgG4 response was lower in patients. No significant association was found between the defect in anti-PPS antibody response and associated thrush or constitutional symptoms or other immunological parameters. These findings suggest that defective response to a thymo-independent polysaccharide antigen is a distinctive consequence of HIV infection.

Immunoglobulin G subclass distribution of autoantibodies in systemic sclerosis, primary biliary cirrhosis, and overlap syndromes

The IgG subclass reactivities of six anticellular antibodies were measured by indirect immunofluorescence on HEp2 cells using murine monoclonal antibodies to the four human IgG subclasses. Patients with scleroderma, primary biliary cirrhosis (PBC), systemic lupus erythematosus, and mixed connective tissue disease were studied. Anticentromere antibody (ACA) was virtually all IgG1 and 3; antibody to multiple nuclear dots (NSpI) was IgG1, 2, and 3; antimitochondrial antibody was mainly IgG2 and 3; nucleolar staining was varied in subclass reactivity but most often IgG4; the diffusely grainy staining associated with Scl-70 antibody was chiefly IgG1; and the speckled pattern associated with anti-RNP antibody was always IgG1 and 4, with IgG2 and 3 in some cases. These data fail to support the hypothesis that the various patterns of autoimmune disease reflect differences in the biological properties of the associated antibodies. The prominence of IgG2 in antibodies associated with PBC suggests the possibility of an immune response independent of T cells in that condition. Differential subclass staining showed an unexpectedly high frequency of antibody to multiple nuclear dots in ACA positive sera, and such patients (all with CREST syndrome) could be at increased risk of developing PBC later.

IgG-subclass expression of anti-DNA and anti-ribonucleoprotein autoantibodies in human malaria

To understand further the autoimmune phenomena associated with human malaria, we examined the IgG-subclass expression of antibodies to DNA and to ribonucleoproteins (RNP) in the serum of 99 patients with acute malaria. Of the sera, 22% were positive for single-stranded DNA (ssDNA), 18% for double stranded DNA (dsDNA) and 32% for RNP. Using a set of human IgG-subclass-specific murine monoclonal antibodies, we found that autoantibodies to dsDNA were predominantly expressed in the IgG1 subclass. In contrast, anti-ssDNA antibodies were more evenly distributed among the three other isotypes. Antibodies to RNP were essentially of the IgG1 and IgG2 isotypes. However, there was no correlation between these restricted IgG-subclass in the sera. These results are discussed in the context of previous findings of isotype expression of these autoantibodies in patients with the autoimmune disease systemic lupus erythematosus.

Immunization of mice with purified U1 small nuclear ribonucleoprotein (RNP) induces a pattern of antibody specificities characteristic of the anti-Sm and anti-RNP autoimmune response of patients with lupus erythematosus, as measured by monoclonal antibodies

Sera of patients with systemic lupus erythematosus and related autoimmune diseases often possess anti-Sm and anti-ribonucleoprotein (RNP) autoantibodies that recognize antigenic sites on small nuclear (sn) RNPs containing the snRNAs U1, U2, U4, U5, and U6. Although the major immunoreactive Sm polypeptides B', B, and D are present in snRNPs U1-U6, the RNP-antigenic proteins termed 70 kDa, A, and C are found only in U1 snRNP particles. We have immunized genetically nonautoimmune C57BL/6 mice with isolated human U1 snRNP particles and found that the major RNP and Sm antigenic polypeptides are also primarily immunogenic in the experimental immune response. Monoclonal antibodies (mAbs) derived from the mice thus immunized reacted specifically with polypeptides 70 kDa or A or recognized the Sm polypeptides B', B, and D simultaneously. One mAb reacted with an epitope shared by the U1 RNP polypeptide A and the U2 RNP polypeptide B". Competitive binding studies with the mAbs and anti-RNP/Sm patient sera indicated that the mAbs recognize the same regions on the antigenic snRNP polypeptides as the autoantibodies. This shows that B cells capable of producing autoantibodies against snRNPs are in principle present in the normal immune system. The striking similarity that we observed between the antibody pattern produced by the mice against exogenous U1 snRNP particles and that of systemic lupus erythematosus patients suggests the possibility that the anti-Sm and anti-RNP autoimmune response may be triggered by the endogenous U snRNPs rather than by a crossreacting viral or bacterial neoantigen. The possibility of eliciting anti-RNP and -Sm-type autoantibodies against exogenous snRNPs in normal mice should also allow potential pathogenic effects of such circulating antibodies to be investigated.

Antibody class differences are detected in anti-nRNP and anti-Sm antibodies directed against distinct antigen subunits

Antibodies to nRNP, Sm and La were detected and characterised by immunoblot analysis. A comparison was made between IgG and IgM autoantibodies in 77 patients with systemic lupus erythematosus (SLE) and 50 normal subjects. No antibodies were detected in the normal subjects. In all 3 antigen specificity groups, a heterogeneity of antibody class was observed between patients. Antibodies to the 2 nRNP-specific polypeptides (33 and 67 kD) were approximately equally frequent. Although IgG antibodies to the 67 kD polypeptide were detected in 88% of patients with antibodies to this polypeptide, IgG antibodies to the 33 kD polypeptide were only detected in 43% of patients with antibodies to this polypeptide. This suggested either that anti-33 kD antibody is produced by a B cell which cannot mature to an IgG-secretor, or that anti-33 kD antibody production succeeds an initial immune response producing anti-67 kD. Reactivity with the 29 kD, Sm-specific polypeptide appeared to be the most frequent in anti-Sm sera compared with the 16 kD polypeptide suggesting that this polypeptide may be the primary immunogenic component of Sm.

Subclass restriction of anti-SS-B (La) autoantibodies

Antibodies to the SS-B (La) nuclear ribonucleoprotein particle are relatively specific for the diagnoses of Sjögren's syndrome or systemic lupus erythematosus. The formation of such autoantibodies is likely, then, to reflect the basic immunopathogenesis of these disorders. We have studied the isotype distribution of anti-SS-B antibodies as a clue to their immunoregulation. Using specific ELISA assays, we found that nearly all anti-SS-B antibodies in 39 patients were IgG, and, of these, only the IgG1 and, to a much lesser extent, IgG3 subclasses were represented. Both kappa and lambda light chain antibodies were found in most sera, and the overall kappa/lambda ratio approximated that of normal serum immunoglobulin. These results suggest that the formation of anti-SS-B antibodies is T-cell dependent and that the response is polyclonal in most patients.