IgM and IgG subclass distribution of human anti-Ro/SSA 60 kDa autoantibodies

Immunoglobulin G4 in primary Sjögren's syndrome and IgG4-related disease - connections and dissimilarities

Primary Sjögren's syndrome (pSS) is an autoimmune disease, with B cell hyperactivation and autoantibody production as its immunological hallmarks. Although the distinction between immunoglobulin G4-related disease (IgG4-RD) and pSS, based on the presence or absence of certain autoantibodies, seems easy to make, possibility of elevated serum IgG4 concentration and often similar organ involvement may lead to a misdiagnosis. The increased serum concentration of IgG4 in IgG4-RD is not clearly linked to the pathogenesis of IgG-RD and it has been suggested that it may constitute just an epiphenomenon. The aim of this article is to discuss the presence of IgG4 in pSS and IgG4-RD and its potential significance for these two diseases.

The role of B lymphocytes in the progression from autoimmunity to autoimmune disease

Autoimmunity, defined as the presence of autoreactive T and/or B lymphocytes in the periphery, is a frequent and probably even physiological condition. It is mainly caused by the fact that the central tolerance mechanisms, which are responsible for counter-selection of autoreactive lymphocytes, are not perfect and thus a limited number of these autoreactive cells can mature and enter the periphery. Nonetheless, autoreactive cells do not lead automatically to autoimmune disease as evidenced by a multitude of experimental and human data sets. Interestingly, the progression from autoimmunity to autoimmune disease is not only determined by the degree of central tolerance leakage and thus the amount of autoreactive lymphocytes in the periphery, but also by peripheral mechanism of activation and control of the autoreactive cells. In this review, we discuss the contribution of peripheral B lymphocytes in this process, ranging from activation of T cells and epitope spreading to control of the autoimmune process by regulatory mechanisms. We also discuss the parallels with the role of B cells in the induction and control of alloimmunity in the context of organ transplantation, as more precise knowledge of the pathogenic antigens and time of initiation of the immune response in allo- versus auto-immunity allows better dissection of the exact role of B cells. Since peripheral mechanisms may be easier to modulate than central tolerance, a more thorough understanding of the role of peripheral B cells in the progression from autoimmunity to autoimmune disease may open new avenues for treatment and prevention of autoimmune disorders.

Impact of interleukin-21 in the pathogenesis of primary Sjögren's syndrome: increased serum levels of interleukin-21 and its expression in the labial salivary glands

INTRODUCTION

Interleukin (IL)-21 is a cytokine that controls the functional activity of effector T helper cells and the differentiation of Th17 cells, and promotes B-cell differentiation. To test whether IL-21 participates in the pathogenesis of primary Sjögren's syndrome (SS), serum IL-21 level was measured and IL-21 expression in the labial salivary glands (LSG) was examined.

METHODS

Serum IL-21 levels in 40 primary SS, 40 rheumatoid arthritis (RA), and 38 systemic lupus erythematosus (SLE) patients and 20 healthy controls were measured. Serum IL-21 levels of SS patients were assessed for correlations with laboratory data, including anti-nuclear antibody, anti-Ro/La antibodies, globulin, immunoglobulin (Ig) class, and IgG subclass. LSGs from 16 primary SS and 4 controls with sicca symptoms were evaluated for IL-21 and IL-21 receptor (IL-21R) expression by immunohistochemistry. Confocal microscopy was performed to further characterize the IL-21 positive cells.

RESULTS

Primary SS patients had significantly higher serum IL-21 levels than controls, and these increments correlated positively with levels of IgG, IgG1. Serum IgG1 levels correlated with anti-Ro antibody titers. Immunohistochemical analyses showed that lymphocytic foci and the periductal area of the LSGs from SS patients expressed high levels of IL-21 and lower levels of IL-21R, whereas the control LSGs showed minimal expression of both antigens. The more the lymphocyte infiltrated, IL-21 expression in LSGs showed a tendency to increase. Confocal microscopic analyses revealed that IL-21 expressing infiltrating lymphocytes in the LSGs of SS patients also expressed CXCR5.

CONCLUSIONS

Primary SS is associated with high serum IL-21 levels that correlate positively with serum IgG, especially IgG1, levels. The expression of IL-21 is increased as more lymphocytes infiltrated in LSGs. These observations suggest that IL-21 may play an important role in primary SS pathogenesis.

Serologic follow-up of children born to mothers with Ro/SSA autoantibodies

Neonatal lupus erythematosus (NLE) develops in foetuses of mothers with Ro/SSA and La/SSB antibodies and may include foetal atrioventricular block and dermatologic manifestations. In this study, we investigated postnatal Ro and La IgG, IgA and IgM antibody levels up to 1 year of age in 32 children born to Ro/SSA positive mothers. Antibody levels were correlated with NLE manifestations, and the role of breast feeding in transfer of autoantibodies from mother to child was evaluated. Ro52, Ro60 and La IgG antibodies all transferred from the mothers to their foetus in utero and were present in the infant at birth as detected by enzyme-linked immunosorbent assay using recombinant antigens and a synthetic peptide. A significant decrease in Ro52, Ro60 and La IgG autoantibody levels of the infants was observed from birth to 4-5 weeks of age (P < 0.05, P < 0.05 and P < 0.01). Ro- and La-specific IgA and IgM antibodies were detected in the serum from a subset of mothers. However, Ro- and La-specific IgA and IgM antibody levels were low or non-detectable in children raised both with and without breastfeeding. Furthermore, NLE skin lesions developed independently of breastfeeding. Our findings support a role for placental materno-foetal transfer of IgG autoantibodies in the pathogenesis of NLE and indicate that refraining from breastfeeding does not protect from NLE skin involvement.

The minor salivary gland proteome in Sjögren's syndrome

OBJECTIVE

To identify the global protein expression (the proteome) in the minor salivary glands from primary Sjögren's syndrome (pSS) patients and non-SS controls.

MATERIALS AND METHODS

Minor labial salivary glands were obtained from six pSS patients and from six age-matched non-SS controls, lysed in SDS buffer and pooled into two groups, respectively. The lysates were analysed by liquid chromatography electrospray ionization combined with tandem mass spectrometry. Also, the proteins were separated by two-dimensional polyacrylamide gel electrophoresis and protein spots were subjected to mass spectrometry.

RESULTS

Heat shock proteins, mucins, carbonic anhydrases, enolase, vimentin and cyclophilin B were among the proteins identified. The differences in the proteomes of minor salivary glands from pSS patients and non-SS controls were mainly related to ribosomal proteins, immunity and stress. Alpha-defensin-1 and calmodulin were among six proteins exclusively identified in pSS patients.

CONCLUSION

We have identified several minor salivary gland proteins that may have implications for clarifying the SS pathophysiology. This experiment adds to the knowledge of proteins produced in salivary glands in health and disease, and may form the basis of further studies on biomarkers of prognostic and diagnostic value.

Autoantibody Determination in the Diagnosis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease that usually develops in young women aged 18-50 years and is characterized by the presence of autoantibodies. Diagnosis is difficult as SLE is a great imitator of other diseases. When SLE is suspected clinically in a patient (involvement of two or more organ systems), an initial laboratory evaluation would be antinuclear antibody (ANA) testing. If ANA is negative, SLE is unlikely and results positive at less than 1:40 strongly argue against SLE. Other explanations for organ system involvement should be pursued. Results positive at greater than 1:40 may merit further evaluation for SLE and at times referral to a rheumatologist for a full SLE evaluation. While the American College of Rheumatology classification criteria for SLE are primarily a tool for research, they may be useful clinically, in that those patients fulfilling four or more criteria are highly likely to have SLE.

Ro52, Ro60 and La IgG autoantibody levels and Ro52 IgG subclass profiles longitudinally throughout pregnancy in congenital heart block risk pregnancies

Congenital heart block occurs in fetuses of Ro/SSA and La/SSB positive women. To investigate the stability of maternal autoantibody levels during pregnancy, we followed Ro52, Ro60 and La autoantibody IgG level variation and Ro52 subclass profiles longitudinally in selected congenital heart block risk pregnancies. Serum samples were obtained from 12 Ro/La positive women diagnosed with a systemic rheumatic disease and followed on average 60 months (range two to 84) which included 13 pregnancies. Seven children were affected by neonatal lupus, whereof four developed complete congenital heart block. Serum was also collected from the babies at birth. Ro52, Ro60 and La IgG as well as subclass antibodies were analysed by ELISA using recombinant antigens. Six Ro/La negative rheumatic patients were included as controls for antibody levels during pregnancy. Ro52, Ro60 and La IgG levels decreased progressively from early to late pregnancy, significantly for Ro52 and Ro60 (P < 0.01). No peaks or persistent elevation of antibody levels were noted in any of the CHB risk pregnancies. Ro52 IgG1 antibody levels were significantly higher than IgG2 (P < 0.01), IgG3 (P < 0.01) and IgG4 (P < 0.05) levels in the mothers during pregnancy. Ro52 IgG1 and IgG4 levels decreased significantly from early to late pregnancy (P = 0.02), while levels of IgG2 and IgG3 were low and the decrease was not significant. All IgG subclasses were transferred to the children. We conclude that maternal levels of Ro52, Ro60 and La autoantibodies tended rather to decrease than to increase during pregnancy.

Gene expression profiling of minor salivary glands clearly distinguishes primary Sjögren's syndrome patients from healthy control subjects

OBJECTIVE

To identify gene expression signatures in minor salivary glands (MSGs) from patients with primary Sjogren's syndrome (SS).

METHODS

A 16K complementary DNA microarray was used to generate gene expression profiles in MSGs obtained from 10 patients with primary SS and 10 control subjects. The data were analyzed by 2 different strategies, one strict primary analysis and one subanalysis that allowed for inclusion of genes with no signal in more than 3 samples from each group. The results were validated by quantitative reverse transcriptase-polymerase chain reaction techniques.

RESULTS

We found a distinct difference in gene expression levels in MSGs, enabling a simple class prediction method to correctly classify 19 of the 20 samples as either patient or control, based on the top 5 differentially expressed genes. The 50 most differentially expressed genes in the primary SS group compared with the control group were all up-regulated, and a clear pattern of genes involved in chronic inflammation was found. CXCL13 and CD3D were expressed in >/=90% of primary SS patients and in </=10% of the controls. Lymphotoxin beta, as well as a number of major histocompatibility complex genes, cytokines, and lymphocyte activation factors, manifested its role in the pathogenesis of SS. Numerous type I interferon genes related to virus infection were found among the top 200 genes, with increased expression in primary SS. Interestingly, the expression of carbonic anhydrase II, which is essential in saliva production and secretion, and the apoptosis regulator Bcl-2-like 2 were down-regulated in primary SS patients.

CONCLUSION

We have identified distinct gene expression profiles in MSGs from patients with primary SS that provide new knowledge about groups of genes that are up-regulated or down-regulated during disease, constituting an excellent platform for forthcoming functional studies.

Anti-Ro/SSA and anti-La/SSB autoantibodies in the tear fluid of patients with Sjögren's syndrome

PURPOSE

To investigate the presence of anti-Ro/SSA and anti-La/SSB antibodies in the tear fluid and serum of patients with Sjögren's syndrome and to evaluate the association of these autoantibodies with the severity of keratoconjunctivitis sicca.

METHODS

Tear fluid and serum were obtained from 28 patients with Sjögren's syndrome and 17 age matched normal control subjects. Evaluation of tear fluid and sera anti-Ro/SSA and anti-La/SSB levels was done by using a quantitative enzyme linked immunosorbent assay kit designed for the quantitative measurement of IgG class autoantibodies directed against highly purified SSA and SSB antigens. Tear function and ocular surface were evaluated by Schirmer I test, tear break up time, and rose bengal staining. Dry eye symptom scores were recorded.

RESULTS

Increased levels of anti-Ro/SSA and anti-La/SSB antibodies were detected in sera of 57.1% and 50% of SS patients, respectively. Six patients had increased levels of anti-Ro/SSA in the tear fluid, in one case anti-Ro/SSA being detected in tear fluid when it was negative in serum. Ten patients had positive anti-La/SSB titres in tear fluid and in four of these patients, anti-La/SSB titres were not elevated in serum. A positive correlation was observed between serum and tear fluid titres of anti-Ro/SSA (r = 0.43, p = 0.02), but not of anti-La/SSB. Serum anti-Ro/SSA and anti-La/SSB concentrations correlated positively with dry eye symptom scores (r = 0.42, p = 0.02 and r = 0.48, p = 0.01, respectively) and negatively correlated with Schirmer I test scores (r = -0.39, p = 0.04 and r = -0.40, p = 0.03, respectively). Significant correlations were found between tear anti-La/SSB concentrations and dry eye symptom score (r = 0.56, p = 0.02) and also rose bengal staining scores of the ocular surface (r = 0.44, p = 0.02).

CONCLUSION

This study shows that autoantibodies against Ro/SSA and La/SSB antigens are present in the tear fluid of some patients with SS and their presence in serum or tear fluid is associated with the severity of keratoconjunctivitis sicca. Additional measurement of tear fluid levels of anti-Ro/SSA and anti-La/SSB may serve as a valuable diagnostic indicator of SS.

Cellular basis of ectopic germinal center formation and autoantibody production in the target organ of patients with Sjögren's syndrome

OBJECTIVE

To investigate functional properties of the germinal center (GC)-like structures observed in salivary glands of patients with Sjögren's syndrome (SS) and to determine the frequency with which such structures develop.

METHODS

Hematoxylin and eosin-stained sections from 165 minor salivary gland biopsy samples were screened for GC-like structures. Expression of markers for GCs (CD3, CD20, Ki-67, CD35, CD31), adhesion molecules (intercellular adhesion molecule 1, lymphocyte function-associated antigen 1, vascular cell adhesion molecule 1, very late activation antigen 4), chemokines (CXCL13, CCL21, CXCL12), and production of autoantibodies (anti-Ro/SSA and anti-La/SSB) was investigated by immunohistochemistry. Apoptosis was investigated by TUNEL staining.

RESULTS

GC-like structures were observed in 28 of 165 patients (17%). When GCs were defined as T and B cell aggregates with proliferating cells with a network of follicular dendritic cells and activated endothelial cells, such microenvironments were found in all patients in whom structures with GC-like morphology were observed. The defined microenvironments were not found in patients without apparent GC-like structures. The GCs formed within the target tissue showed functional features with production of autoantibodies (anti-Ro/SSA and anti-La/SSB) and apoptotic events (by TUNEL staining), and the local production of anti-Ro/SSA and anti-La/SSB autoantibodies was significantly increased (P = 0.04) in patients with GC development.

CONCLUSION

Lymphoid neogenesis and functional ectopic GC formation take place in salivary glands of a subset of patients with SS. Our data suggest that the ectopic secondary lymphoid follicles contain all elements needed for driving the autoimmune response. Our findings underscore a key role for the target organ in recruitment of inflammatory cells and propagation of the disease process.

The use of laboratory tests in the diagnosis of SLE

ANA IIF is an effective screening assay in patients with clinical features of SLE and will detect most anti-ssDNA, anti-dsDNA, ENAs, and other autoantibodies. False positives are common. The clinical importance cannot be extrapolated from the ANA titre or pattern, although higher titres (> 1/160) are more likely to be important. HEp-2 cells are the most sensitive substrate for ANA detection, but this must be balanced against an increased incidence of insignificant positivity. ANA positive samples should be subjected to more specific assays for the diagnosis of SLE. A combination of ENA (Ro/La/Sm/RNP) and dsDNA assays will detect most patients with SLE as long as the characteristics of the assays used are well understood. ESR and CRP measurements provide useful additional information. Sjogren's syndrome and MCTD will produce overlapping serology with SLE, and anti-dsDNA titres are sometimes seen in autoimmune hepatitis and rheumatoid arthritis. All results should be reported in the light of the clinical details, by an experienced immunologist. A suggested diagnostic protocol is outlined in fig 1. The type of assay used crucially influences the predictive value of the tests. ELISA technology dominates routine laboratory practice, but tends to produce more false positive and true weak positive results, which may reduce the PPV of the test. This can be minimised by using IgG specific conjugates and careful assay validation. The NPV for SLE [figure: see text] is high for most assays but the PPV varies. Where necessary, laboratories should use crithidia or Farr dsDNA assays to confirm dubious ELISA dsDNA results, and ID/IB to confirm dubious ENA results. For monitoring, a precise, quantitative assay is required. It is unclear whether the detection of IgM or low affinity antibodies has a role here. A combination of anti-dsDNA, C3, C4, CRP, and ESR assays provides the most useful clinical information. Anti-ssDNA assays are likely to be useful, and are potentially more robust than anti-dsDNA assays, but require more validation. Local validation of individual assays and EQA participation is essential. Not all assays that apparently measure the same antibody specificities have equal clinical relevance, even within a single technology. Insufficient international or national reference preparations are currently available for many antibody specificities to enable effective standardisation. Quality assurance schemes reveal large differences in units reported by different assays for some analytes, even when calibrated against an IRP or equivalent reference preparation. Serial results can therefore only be compared from the same laboratory at present. Most autoantibodies increase during active disease, but few prospective data are currently available to justify treatment on the basis of rising titres. Further randomised prospective studies are required to examine the importance of antibody isotype and affinity in the monitoring of SLE by individual assay methods. The most important aspect of the appropriate use of laboratory assays is to become familiar with the limitations of the technology currently in use in your local laboratory, and to consult with your clinical immunologist in cases of doubt, preferably before commencing serological screening.

Ro/SSA and La/SSB specific IgA autoantibodies in serum of patients with Sjögren's syndrome and systemic lupus erythematosus

OBJECTIVE

To investigate the occurrence of IgA autoantibodies to Ro 52 kDa, Ro 60 kDa and La antigen in serum of patients with primary Sjögren's syndrome (pSS) and systemic lupus erythematosus (SLE).

METHODS

Recombinant Ro 52 kDa, Ro 60 kDa and La antigens were used to analyse autoantibodies in serum from 25 patients with pSS, 30 patients with SLE and 20 controls using a semiquantitative immunoblotting approach.

RESULTS

Among the patients with pSS, 21 (84%) had detectable IgA autoantibodies to Ro 52 kDa, 13 (52%) to Ro 60 kDa and 20 (80%) to La antigen. The corresponding results for the patients with SLE were 22 (73%), 14 (47%) and 20 (67%), respectively. No IgA autoantibodies against the three antigens were detected in 20 normal controls. A comparison of several clinical features with the titres of IgA antibodies to Ro 52 kDa, Ro 60 kDa and La, revealed a significant relation between IgA anti-Ro 52 and IgA anti-La to sicca (p< 0.05). Semiquantitative data suggest that IgG is the dominating antibody to the three antigens followed by IgM > IgA in both SLE and pSS patients. Specificity studies of IgA autoantibodies with different subfragments of Ro 52 kDa and Ro 60 kDa antigens showed that IgA antibodies did not differ from IgG and IgM in their recognition pattern.

CONCLUSION

These results suggest that besides IgM and IgG, IgA autoantibodies are also detected at high frequency in patients with pSS and SLE. Further studies are necessary to evaluate the contribution of these IgA autoantibodies to inflammation as well as their diagnostic value.

Analysis of B-cell epitopes of the Ro/SS-A autoantigen

Autoantibodies to the Ro and La ribonucleoprotein antigens are found in several rheumatoid diseases. The important epitopes have been studied using synthetic peptides and recombinant antigens to understand how they arise and their implication in disease. Here, we analyse the results of epitope mapping studies of Ro60 and Ro52 autoantigens and focus on the major findings to date.

Development of the anti-Ro autoantibody response in a patient with systemic lupus erythematosus

OBJECTIVE

To characterize the initial events in anti-Ro production by a patient with systemic lupus erythematosus, in whom this autoantibody is developing.

METHODS

The immune response to the Ro ribonucleoprotein and other autoantigens were studied by enzyme-linked immunosorbent assay for IgG and IgM, by isoelectric focusing, and by inhibition studies to determine apparent avidity.

RESULTS

The patient's sera showed an oligoclonal response to Ro that increased in complexity and affinity with time. IgM anti-Ro appeared shortly before IgG anti-Ro, and disappeared as IgG anti-Ro increased in titer and affinity. IgG antiribosomal P autoantibodies also appeared during the patient's course, but in contrast to anti-Ro, were not preceded by IgM antiribosomal P.

CONCLUSION

These data are consistent with the Ro autoantigen being presented and processed in a manner similar to heterologous antigen, and with differences in the mechanisms that lead to the production of IgG anti-Ro autoantibodies as opposed to antiribosomal P autoantibodies.