Relationship of precipitating antibodies to soluble cellular antigens and histologically defined renal lesions in systemic lupus erythematosus

New insights into the role of antinuclear antibodies in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by antinuclear antibodies (ANAs) that form immune complexes that mediate pathogenesis by tissue deposition or cytokine induction. Some ANAs bind DNA or associated nucleosome proteins, whereas other ANAs bind protein components of complexes of RNA and RNA-binding proteins (RBPs). Levels of anti-DNA antibodies can fluctuate widely, unlike those of anti-RBP antibodies, which tend to be stable. Because anti-DNA antibody levels can reflect disease activity, repeat testing is common; by contrast, a single anti-RBP antibody determination is thought to suffice for clinical purposes. Experience from clinical trials of novel therapies has provided a new perspective on ANA expression during disease, as many patients with SLE are ANA negative at screening despite previously testing positive. Because trial results suggest that patients who are ANA negative might not respond to certain agents, screening strategies now involve ANA and anti-DNA antibody testing to identify patients with so-called 'active, autoantibody-positive SLE'. Evidence suggests that ANA responses can decrease over time because of the natural history of disease or the effects of therapy. Together, these findings suggest that, during established disease, more regular serological testing could illuminate changes relevant to pathogenesis and disease status.

Fine binding characteristics of human autoantibodies—partial molecular characterization

The fine binding characteristics of three well-characterized human autoantibodies B3, RH14 (anti-DNA) and UK4 (anti-cardiolipin) in their IgG and cloned Fab formats, were investigated. Although in severe combined immunodeficiency (SCID) mice B3 and RH14 both induce proteinuria, only RH14 induces early features of lupus nephritis, whereas UK4 exhibits lupus anticoagulant activity. RH14 exhibited up to 10 fold higher binding to DNA compared to that shown by B3 or UK4 and involved significant electrostatic and phosphate group interactions. Only RH14 exhibited strong anti-Sm cross-reactivity residing on the C-terminus of the antigen as determined by the use of 76 overlapping 15mer peptides. Chain shuffling experiments indicate that anti-Sm/RNP and anti-Jo-1 activities of B3 and UK4 co-exist on one of the two chains (light, B3; heavy, UK4). The present study provides evidence that a human anti-DNA antibody can also be an anti-ENA antibody. Furthermore, the anti-DNA antibodies also exhibited cross-reactivity against glutathione-S-transferase and DNA polymerase PolIV of bacterial origin. This is the first demonstration of the presence of such cross-reactivities on lupus anti-DNA antibodies. We now demonstrate that subsets of sera from the patients with lupus, recognise these antigens. This observation may in some cases provide a mechanism for the common expression of a variety of autoantibodies observed in systemic lupus erythematosus (SLE).

Association between polymorphisms at the human IL-10 locus and systemic lupus erythematosus

Recent studies have shown elevated IL-10 levels in several rheumatic autoimmune diseases, and particularly in systemic lupus erythematosus (SLE). Such changes may have a genetic basis. We studied two novel polymorphic dinucleotide repeats in the IL-10 promoter region (IL10.G and IL10.R) in order to investigate their possible significance in association with this condition in a group of 56 Caucasian SLE patients compared with 102 ethnically matched controls. The results show that there is an allelic imbalance between SLE patients and controls at the IL10.G microsatellite; this observation is supported by a significant difference in genotype distribution. The nature of autoantibody production and the presence or absence of renal involvement also appeared to be associated with certain IL10.G microsatellite alleles, although the small size of individual clinical sub-groupings may have influenced this result. No association with the IL10.R microsatellite was observed. Overall, the differences observed at the IL10.G microsatellite between SLE patients and controls suggest that the IL-10 locus contributes to the genetic background important for the development of this disease. Although the moderate sample size described in this study requires that the results be interpreted carefully, they provide an interesting and useful framework for future study.

Relationship between antibodies to dsDNA and to soluble cellular antigens and histologically defined glomerulonephritis in patients with SLE

To better define the relationships between circulating autoantibodies and renal involvement in systemic lupus erythematosus (SLE), antibodies to both dsDNA and soluble cellular antigens were detected in sera from a large series of SLE patients. Significantly higher dsDNA binding activities and lower complement levels at onset were found in patients with renal disease; however, this was uniquely due to subjects with diffuse or focal proliferative glomerulonephritis. Patients with membranous nephropathy (MGN) showed very low dsDNA binding activities (6/9 of them being negative for dsDNA antibodies) and normal mean C3 and C4 levels. A comparison between patients with proliferative nephritis and patients without renal involvement with high dsDNA binding activities revealed significantly lower complement levels in the former group. No significant difference was observed in the prevalence of antibodies to soluble cellular antigens between patients with or without renal disease; however, nRNP antibody was two-fold more frequent in patients with MGN than in all other subgroups. This study highlights the close relationship between concurrently high anti-dsDNA and low complement levels and proliferative glomerulonephritis in SLE, and suggests that subjects with MGN may represent a subgroup of SLE patients showing peculiar serological features. Different mechanisms possibly involved in the pathogenesis of MGN in SLE are discussed.

Specificity of anti-Sm antibodies by ELISA for systemic lupus erythematosus: increased sensitivity of detection using purified peptide antigens

Sm antigen was purified by immunoaffinity chromatography using a murine monoclonal anti-Sm antibody and was confirmed to be free from contaminating polypeptides. This was then used to detect anti-Sm antibodies in patients' sera by enzyme linked immunosorbent assay (ELISA). Antibodies against Sm were detected in only 9/52 (17%) patients with systemic lupus erythematosus (SLE) by immunodiffusion, but 15/52 (29%) were positive for IgG anti-Sm antibodies by ELISA. The presence of anti-Sm antibodies remained disease specific despite the increase in sensitivity of this assay and validates its potential use for clinical application. There was no correlation between the presence of anti-Sm antibodies and any clinical features of SLE. In 23 renal biopsies a membranous component to the glomerulonephritis correlated with anti-Sm antibodies (p less than 0.05). Patients from West Africa, the Carribean Islands, and Asia had a higher prevalence of anti-Sm antibodies than the local Caucasian population.

Systemic lupus erythematosus in North Indian Asians. A prospective analysis of clinical and immunological features

One hundred and one patients with systemic lupus erythematosus (SLE) from North Indian stock are presented. The clinical manifestations, laboratory parameters, causes of death, and survival are compared and contrasted with the other major reported series. SLE of North Indian Asians has several features comparable to those reported from the West, but other features are more similar to the SLE seen in Mongoloid races.

Serum immune complexes in systemic sclerosis: relationship with precipitating nuclear antibodies

In a comparative study of antinuclear antibodies (ANA) and immune complexes in the serum of 43 patients with systemic sclerosis (SS) ANA were detected by indirect immunofluorescence on Hep 2 cells and/or double immunodiffusion in 90% of patients, while immune complex assays were positive in 32% of patients. The immune complex assays were positive only in sera containing antibodies to Scl 70, n-RNP, Ro, and La. The presence of immune complexes in SS sera is therefore related to ANA specificity. This might explain the variable findings of several previous studies of immune complexes in SS.

Tissue uptake and catabolic studies of 125I SS-B (La) injected into mice

The radiolabeled soluble cellular antigen 125I SS-B (La) has a plasma half-life of 3 min following iv injection into BALB/C mice. Uptake by Kupffer cells (KC) and proximal renal tubular (PRT) cells was demonstrated by autoradiography (ARG). That trichloracetic acid (TCA)-soluble products of 125I SS-B appeared in plasma within 1 min of iv injection suggests rapid in vivo breakdown. Activated peritoneal macrophages (APM) degraded 125I SS-B in a time- and cell-dose-dependent fashion. These findings suggest that the plasma clearance and catabolism of 125I SS-B may be dependent on its interaction with phagocytic cells. This rapid antigen elimination may protect against harmful autoantibody responses.