Protective autoantibodies: Role in homeostasis, clinical importance, and therapeutic potential

Toward a new autoantibody diagnostic orthodoxy: understanding the bad, good and indifferent

Rapid advances in diagnostic technologies used to detect autoantibodies have made it difficult for even the most modern laboratory to keep abreast of the changing approaches and platforms, not to mention the clinicians who are hard pressed to keep abreast of evolving diagnostic paradigms attended by these newer techniques. While autoantibody testing is traditionally considered to be primarily serving the realm of diagnostic medicine, there is little doubt that autoantibodies are also being recognized as an approach to providing prognostic and therapeutic information. Accordingly, along with related proteomics, genomics and metabolomics, it is taking on increasing importance in the realm of personalized medicine. In today's world of autoantibody diagnostics, overarching concerns about false-negative and false-positive autoantibodies tests cannot be summarily dismissed by citing pros or cons of any one technology or diagnostic platform, but often point to persisting gaps in our knowledge about, and understanding of, the origin and roles of autoantibodies. Before we can hope to completely understand the enigmas that attend the results of autoantibody diagnostic tests, perhaps it is time to step back and re-examine long-accepted paradigms and beliefs. This review will address some of the issues that impact on autoantibody detection technologies and some of the considerations and issues that will attend a new orthodoxy of autoantibody diagnostics. These issues will be addressed in the context of "bad" (pathogenic), "good" (protective) or "indifferent" (no apparent role in disease) autoantibodies.

Are anti-nucleosome antibodies a better diagnostic marker than anti-dsDNA antibodies for systemic lupus erythematosus? A systematic review and a study of metanalysis

BACKGROUND

Methods to detect anti-nucleosome antibodies (ANuA) have been available for more than 10 years and the test has demonstrated its good sensitivity and high specificity in diagnosing systemic lupus erythematosus (SLE). Despite these data produced through clinical and laboratory research, the test is little used.

OBJECTIVE

To verify the diagnostic performance of methods for measuring ANuA and to compare them with those for anti-dsDNA antibodies.

DATA SOURCES

A systematic review of English and non-English articles using MEDLINE and EMBASE with the search terms "nucleosome", "chromatin", "anti-nucleosome antibodies" and "anti-chromatin antibodies". Additional studies were identified checking reference lists in the selected articles.

STUDY SELECTION

We selected studies reporting on anti-nucleosome tests performed by quantitative immunoassays, on patients with SLE as the index disease (sensitivity) and a control group (specificity). A total of 610 titles were initially identified with the search strategy described. 548 publications were subsequently excluded based on abstract and title. Full-text review was undertaken as the next step on 62 publications providing data on anti-nucleosome testing; 25 articles were then excluded because they did not include either SLE patients or a control group, and 37 articles were selected for the metanalysis. Finally, a sub-metanalysis study was conducted on the 26 articles providing data on both ANuA and anti-dsDNA antibody assays in the same series of patients.

DATA EXTRACTION

Extraction of data from selected articles was performed by two authors independently, using predefined criteria: the number of patients with SLE as the index case, and the number of healthy or diseased controls; specification of the analytical method used to detect anti-nucleosome and anti-dsDNA antibodies; the cut-off used in the study; and the sensitivity and specificity of the assay. Demographic and clinical data on the population investigated (adults or children; lupus patients with or without nephritis; patients with active or inactive disease) were also recorded and analyzed in a separate evaluation.

RESULTS

The systematic review and metanalysis showed that the overall sensitivity of the ANuA assay is 61% (confidence interval-CI, 60-62) and the specificity 94% (CI, 94-95). The overall positive likelihood ratio is 13.81 (CI, 9.05-21.09) and the negative likelihood ratio 0.38 (CI, 0.33-0.44). The odds ratio for having SLE in ANuA-positive patients is 40.7. The comparative analysis on anti-dsDNA antibodies conducted on the 26 studies which provided data for both antibodies showed that ANuA have greater diagnostic sensitivity (59.9% vs 52.4%) and a specificity rating only slightly higher (94.9% vs 94.2%). The probability that a subject with positive ANuA have SLE is 41 times greater than a subject with negative ANuA, while for anti-dsDNA the probability is 28 times greater. These figures are even more impressive in children, in whom ANuA have an odds ratio for the diagnosis of SLE of 146, compared to 51 for anti-dsDNA antibodies. In selected studies, ANuA (p<0.0001) but not anti-dsDNA antibodies (p=0.256) were significantly associated with disease activity measured by the international score systems. However, neither antibody appears to correlate with kidney involvement.

CONCLUSIONS

Data from the metanalysis have shown that ANuA have equal specificity but higher sensitivity and prognostic value than anti-dsDNA antibodies in the diagnosis of SLE. Despite a certain heterogeneity among the various studies, the use of ANuA appears more efficacious than anti-dsDNA.

Primary biliary cirrhosis and the nuclear pore complex

Experimental models of autoimmune diseases have led to the conclusion that an immune response to nuclear antigens is a sentinel marker for loss of tolerance and potential tissue damage. Various proteins are targets of antinuclear antibodies in a variety of autoimmune diseases, ranging from systemic rheumatologic disorders to diseases affecting specific organs such as the liver. Autoantibodies against specific nuclear constituents have also been used as probes to understand the structure and the function of the targeted components and their relevance to disease pathogenesis. Approximately a quarter of patients with primary biliary cirrhosis (PBC) have antibodies targeting proteins of the nuclear pore complex (NPC), a multi-protein structure that mediates molecular transport across the nuclear envelope. Autoantibodies against the integral membrane glycoprotein gp210 and nucleoporin p62 appear to be highly specific for PBC, an autoimmune disease characterized by progressive destruction of intrahepatic biliary epithelial cells. This review discusses the diagnostic and clinical relevance of anti-NPC antibodies in PBC and the possibility that this autoimmune response may arise as a result of molecular mimicry.

B Cell in Autoimmune Diseases

The role of B cells in autoimmune diseases involves different cellular functions, including the well-established secretion of autoantibodies, autoantigen presentation and ensuing reciprocal interactions with T cells, secretion of inflammatory cytokines, and the generation of ectopic germinal centers. Through these mechanisms B cells are involved both in autoimmune diseases that are traditionally viewed as antibody mediated and also in autoimmune diseases that are commonly classified as T cell mediated. This new understanding of the role of B cells opened up novel therapeutic options for the treatment of autoimmune diseases. This paper includes an overview of the different functions of B cells in autoimmunity; the involvement of B cells in systemic lupus erythematosus, rheumatoid arthritis, and type 1 diabetes; and current B-cell-based therapeutic treatments. We conclude with a discussion of novel therapies aimed at the selective targeting of pathogenic B cells.

New insights into autoantibody profiles from immune privileged sites in the eye: a glaucoma study

Glaucoma is a chronic neurodegenerative disease and one of the leading causes of blindness. Autoantibody based immune processes are assumed to be involved in its pathogenesis. However, it is still unclear to what extent autoantibody patterns found in the eye (aqueous humor) are congruent to systemic autoantibodies (blood). Consistency would underline the specificity of known serum antibody markers for glaucoma. In this study we used antigen microarrays to analyze autoantibody reactivities in sera and corresponding aqueous humor samples of primary open-angle glaucoma patients (N=37) and non-glaucomatous controls (N=31). Compared to control subjects several divergent immunoreactivities were identified for the glaucoma group in both body fluids. Interestingly, 20% of the tested antigens revealed increased immunoreactivities (e.g., against HSP27, MBP, and α-1-antitrypsin) and 7.5% decreased immunoreactivities (e.g., against GFAP and β-L-crystallin), thus demonstrating a significant alteration of the autoantibody profiles in glaucoma patients. Using an artificial neural network in combination with a unique serum autoantibody pattern on prospective sera we were able to detect glaucoma with a specificity and sensitivity of approximately 93%. The intraindividual comparison revealed a strong correlation of detected immunoreactivities in sera and comparative aqueous humor samples in both study groups. These results emphasize the specificity of immunoreactions found in blood samples of glaucoma patients. Furthermore they indicate the necessity of analyzing not only up-regulated but also down-regulated antibody reactivities, which might be likewise relevant for the understanding of other diseases.

B cells lacking the tumor suppressor TNFAIP3/A20 display impaired differentiation and hyperactivation and cause inflammation and autoimmunity in aged mice

The ubiquitin-editing enzyme A20/TNFAIP3 is essential for controlling signals inducing the activation of nuclear factor-κB transcription factors. Polymorphisms and mutations in the TNFAIP3 gene are linked to various human autoimmune conditions, and inactivation of A20 is a frequent event in human B-cell lymphomas characterized by constitutive nuclear factor-κB activity. Through B cell-specific ablation in the mouse, we show here that A20 is required for the normal differentiation of the marginal zone B and B1 cell subsets. However, loss of A20 in B cells lowers their activation threshold and enhances proliferation and survival in a gene-dose-dependent fashion. Through the expression of proinflammatory cytokines, most notably interleukin-6, A20-deficient B cells trigger a progressive inflammatory reaction in naive mice characterized by the expansion of myeloid cells, effector-type T cells, and regulatory T cells. This culminates in old mice in an autoimmune syndrome characterized by splenomegaly, plasma cell hyperplasia, and the presence of class-switched, tissue-specific autoantibodies.

Autoantibodies to the delta-opioid receptor function as opioid agonists and display immunomodulatory activity

In this report, we show that affinity purified human anti-delta opioid receptor (DOR) autoantibodies from IVIG are specific to DOR and possess agonistic properties displayed by their ability to dramatically decrease forskolin stimulated cAMP accumulation. Anti-DOR autoantibody also caused phosphorylation of the opioid receptor. Anti-DOR autoantibody treatment showed a significant reduction in CXCR4 gene expression as well as surface protein expression. In contrast, anti-DOR autoantibody treatment significantly upregulated CCR5 gene and protein expression. The presence of anti-DOR autoantibodies in IVIG and their potent immunomodulatory activity is further evidence to support the cross-talk between the neuroendocrine and immune systems.

Decreased levels of autoantibody against histone deacetylase 3 in patients with systemic sclerosis

Systemic sclerosis (SSc) is characterized by immunological abnormalities, especially the production of autoantibodies against various cellular components. Treatment with histone deacetylase (HDAC) inhibitors prevents collagen accumulation in a mouse SSc model. Additionally, autoantibody against HDAC-3 is produced in colon cancer patients, while HDAC-1 and HDAC-2 do not elicit autoantibody response. To determine the presence and levels of antibodies (Abs) against HDAC-3 in SSc. Anti-HDAC-3 Ab was examined by enzyme-linked immunosorbent assay (ELISA) and immunoblotting using human recombinant HDAC-3. The HDAC-3 activity was evaluated by ELISA using the fluorimetric HDAC lysyl substrate that comprises an acetylated lysine side chain. Contrary to our hypothesis that autoimmune background in SSc induced the production of autoantibody against HDACs, IgG and IgM anti-HDAC-3 Ab levels in SSc patients were significantly lower than in normal controls (p < 0.0005 and 0.001, respectively). Furthermore, decreased levels of IgG anti-HDAC-3 Ab were specific to SSc, since IgG anti-HDAC-3 Ab levels in patients with dermatomyositis (DM) and those with systemic lupus erythematosus (SLE) were similar and slightly increased relative to normal controls, respectively. Immunoblotting analysis showed that anti-HDAC-3 Ab was detected in normal controls and patients with DM or SLE, while it was absent in SSc patients. The HDAC-3 activity was significantly inhibited by IgG isolated from sera of normal controls, whereas such inhibitory effect was not observed by IgG isolated from sera of SSc patients. These results indicate the lack of anti-HDAC-3 autoantibody in SSc patients, which is produced in healthy individuals as well as DM and SLE patients, suggesting that this autoantibody might function as protective Ab.

IgM antibodies against dsDNA in SLE

IgG antibodies against dsDNA are involved in the pathogenesis of systemic lupus erythematosus (SLE) glomerulonephritis. In contrast, glomerulonephritis is rare in SLE patients with IgM antibodies against dsDNA. Therefore, a possible protective effect of IgM antibodies has been studied in more detail. In murine models of SLE, the lack of secreted IgM was associated with more severe glomerulonephritis. In more recent studies, the treatment of lupus-prone mice with a murine IgM monoclonal antibody against dsDNA prevented renal damage. Furthermore, the clearance of pathogenic immune complexes may be improved by IgM. Therefore, IgM antibodies against dsDNA are indeed protective and may be a new treatment modality of lupus nephritis in humans.

Predictive, protective, orphan autoantibodies: the example of anti-phospholipid antibodies

Anti-phospholipid antibodies (aPL) are one of the most recent examples of autoantibodies that can appear even long time before any clinical manifestation can be associated with them. There is a general agreement that they may represent a strong risk factor for recurrent thrombosis and/or fetal losses. Anti-phospholipid antibodies represent a necessary but not sufficient factor (first hit) for thrombosis, and require additional triggering factors (second hit) to disclose the thrombogenic activity. Several factors may affect the predictive value of aPL, including titre, immunoglobulin isotype, fine antigenic specificity and affinity binding activity. Their careful evaluation is suggested in order to characterize the true predictive value of aPL.

Antibody clustering helps refine lupus prognosis

OBJECTIVE

Our aim was to investigate a possible association between patterns of anti-dsDNA antibody isotypes (IgG, IgM, and IgA), rheumatoid factor (RF) isotypes (IgG, IgM, IgA), and IgG anti-C reactive protein (CRP) and systemic lupus erythematosus (SLE) disease activity (SLEDAI).

METHODS

Our study group included 98 patients, 86 women and 12 men, with a mean SLEDAI score of 7.9 +/- 4.1. We divided the patients into 4 groups by the serum anti-dsDNA antibody isotype intensity level.

RESULTS

We found that patients in group 1 (IgG > IgM, 42 patients) had a statistically significantly higher SLEDAI score than group 2 (IgG < IgM, 13 patients) (10.57 +/- 4.62 versus 5.6 +/- 4, P = 0.0012), group 3 (IgG = IgM, 8 patients) (10.57 +/- 4.62 versus 6.2 +/- 1.98, P = 0.04), and group 4 (none, 35 patients) (10.57 +/- 4.62 versus 6 +/- 1.5, P = 0.0001). SLE patients with IgG RF or IgM RF isotype present had a significantly higher SLEDAI score compared with those without IgG RF or IgM RF (10.57 +/- 4.8 versus 7.6 +/- 4.1, P = 0.03, 10.6 +/- 5 versus 7.6 +/- 3.9, P = 0.046). The presence of IgA RF isotype was not associated with a higher SLEDAI score. IgG anti-CRP did not correlate differentially with SLEDAI scores.

CONCLUSIONS

A combination of high-titer IgG anti-dsDNA with a positive RF of IgM isotype may serve as a marker for more active SLE.

Gluten-free vegan diet induces decreased LDL and oxidized LDL levels and raised atheroprotective natural antibodies against phosphorylcholine in patients with rheumatoid arthritis: a randomized study

Introduction

The purpose of this study was to investigate the effects of vegan diet in patients with rheumatoid arthritis (RA) on blood lipids oxidized low-density lipoprotein (oxLDL) and natural atheroprotective antibodies against phosphorylcholine (anti-PCs).

Methods

Sixty-six patients with active RA were randomly assigned to either a vegan diet free of gluten (38 patients) or a well-balanced non-vegan diet (28 patients) for 1 year. Thirty patients in the vegan group completed more than 3 months on the diet regimen. Blood lipids were analyzed by routine methods, and oxLDL and anti-PCs were analyzed by enzyme-linked immunosorbent assay. Data and serum samples were obtained at baseline and after 3 and 12 months.

Results

Mean ages were 50.0 years for the vegan group and 50.8 years for controls. Gluten-free vegan diet induced lower body mass index (BMI) and low-density lipoprotein (LDL) and higher anti-PC IgM than control diet (p < 0.005). In the vegan group, BMI, LDL, and cholesterol decreased after both 3 and 12 months (p < 0.01) and oxLDL after 3 months (p = 0.021) and trendwise after 12 months (p = 0.090). Triglycerides and high-density lipoprotein did not change. IgA anti-PC levels increased after 3 months (p = 0.027) and IgM anti-PC levels increased trendwise after 12 months (p = 0.057). There was no difference in IgG anti-PC levels. In the control diet group, IgM anti-PC levels decreased both after 3 and 12 months (p < 0.01). When separating vegan patients into clinical responders and non-responders at 12 months, the effects on oxLDL and anti-PC IgA were seen only in responders (p < 0.05).

Conclusion

A gluten-free vegan diet in RA induces changes that are potentially atheroprotective and anti-inflammatory, including decreased LDL and oxLDL levels and raised anti-PC IgM and IgA levels.

Characterization of discriminant human brain antigenic targets in neuropsychiatric systemic lupus erythematosus using an immunoproteomic approach

OBJECTIVE

To characterize discriminant human brain antigenic targets in patients with neuropsychiatric systemic lupus erythematosus (NPSLE), using a standardized immunoproteomic approach.

METHODS

Self-IgG reactivity against normal and injured human brain tissues was studied by Western blotting of sera from 169 subjects, 16 patients with NPSLE, 12 patients with SLE without neuropsychiatric manifestations (non-NPSLE), 32 patients with Sjögren's syndrome with or without central nervous involvement, 82 patients with multiple sclerosis, and 27 healthy subjects. A proteomic approach was then applied to characterize discriminant antigens identified after comparisons of all patterns.

RESULTS

The serum self-IgG reactivity patterns against human brain tissue differed significantly between patients with NPSLE and the control groups. Four normal brain antigenic bands were specifically or preferentially recognized by sera from NPSLE patients (p240, p90, p77, and p24). Protein band p240 was characterized as microtubule-associated protein 2B (MAP-2B), p77 as Hsp70-71, and p24 as triosephosphate isomerase. Protein band p90 was not characterized. In contrast, 1 other protein band (p56, characterized as septin 7) was never recognized by sera from NPSLE patients but was recognized by a majority of sera from non-NPSLE patients.

CONCLUSION

Our findings show that the immunoproteomic approach is a reliable method for assessing serum self-IgG reactivities against human brain tissue in NPSLE. Our characterization of some of the identified discriminant antigens, such as MAP-2B, triosephosphate isomerase, and septin 7, suggests that the stability of neuronal microtubules might be involved in the pathophysiology of NPSLE.