The diagnosis value of beta 2-microglobulin and immunoglobulins in primary Sjögren's syndrome

Biomarkers of B cell activation in autoimmune connective tissue diseases: More than markers of disease activity

B cells play a central role in the pathogenesis of many autoimmune diseases, acting as antigen-presenting cells, producing inflammatory cytokines, and acting as a source of autoantibodies after differentiating into plasma cells. In this review, we aim to summarize and synthesize the literature for the utility of biomarkers of B cell activation (plasma immunoglobulins (Ig), free light chains (FLCs), and beta-2 microglobulin (β2M)) in monitoring inflammatory rheumatic connective tissue diseases, such as Sjogren's syndrome (SS), systemic lupus erythematosus (SLE), dermatomyositis (DM), and systemic sclerosis (SSc). Clinically, it is quite difficult to gauge prognosis in these conditions as there, historically, have not been many quantitative markers of disease activity available. From our extensive literature review, Ig, FLC, and β2M may function as invaluable prognostic markers of ongoing disease activity, and potentially as biomarkers for response to therapy or disease relapse. They are inexpensive and unsophisticated tests that are vastly underused in the setting of autoimmune disease. However, clinicians still need to be aware of the potential of false positives in times of infection or plasma cell dyscrasia, as these disease states can artificially increase these biomarkers. Ultimately, the utility of serum Ig, FLCs, and β2M is clearly delineated in SS and SLE, and least investigated in DM, and additional prospective studies utilizing these biomarkers, and specific B cell targeted therapies are still needed.

Beta-2 Microglobulin in Whole Unstimulated Saliva Can Effectively Distinguish Between Sjögren's Syndrome and Non-Autoimmune Sicca Symptoms

Objectives

This study aims to describe salivary beta-2 microglobulin (sB2M) levels in our setting and to assess the performance of sB2M for the diagnosis of Sjögren's syndrome (SS).

Patients and methods

This cross-sectional, comparative study included 192 SS patients (2 males, 190 females; mean age 53.1 years; range 23 to 84 years) and 64 healthy controls (1 male, 63 females; mean age 46.9 years; range 21 to 82 years). Patients were divided into three groups as those with primary SS, secondary SS, and sicca non-Sjögren's syndrome (snSS). sB2M was measured by enzyme-linked immunosorbent assay in whole unstimulated saliva (ng/mL). Differences in sB2M were evaluated using the Kruskal-Wallis test. Receiver operating curves were generated to determine the performance of sB2M for distinguishing between SS and non-autoimmune snSS groups, and between SS group and healthy controls.

Results

The primary SS and secondary SS groups had a significantly higher concentration of sB2M than the other two groups. There was no significant difference in the concentration of sB2M between primary SS and secondary SS groups, and neither between snSS group and healthy controls. The receiver operating curve analysis for distinguishing SS and snSS showed an area under the curve of 0.661 (95% confidence interval 0.590-0.728, p=0.0001) with an optimal cutoff value of 0.582 ng/mL. Sensitivity, specificity, positive predictive value, and negative predictive value were 68.7%, 59.3%, 20.2%, and 92.7%, respectively. The reported prevalence of SS in Mexico was considered when calculating the last two values.

Conclusion

In our setting, sB2M effectively distinguished between SS patients and non-autoimmune sicca symptoms. Including sB2M in our conventional diagnostic arsenal may assist in the evaluation of patients in whom SS is suspected; however, further studies are needed to clarify this hypothesis.

Serum IgG4-negative autoimmune pancreatitis

BACKGROUND

Autoimmune pancreatitis (AIP) is considered to be a pancreatic lesion of IgG4-related systemic disease, but about 20% of AIP patients do not have elevated serum IgG4 levels. This study aimed to clarify the pathophysiology of AIP patients without elevated serum IgG4 levels.

METHODS

Fifty-eight AIP patients were divided into 2 groups: those with elevated serum IgG4 levels (>135 mg/dl; SIgG4-positive AIP) and those without (SIgG4-negative AIP). The 2 groups' clinical, serological, radiological, and histological findings, as well as salivary and lacrimal gland function, were compared.

RESULTS

Serum IgG4 levels were elevated in 45 AIP patients and normal in 13 patients. In SIgG4-negative AIP patients, the female ratio tended to be high; obstructive jaundice was less likely; abdominal pain and acute pancreatitis were more likely; segmental swelling of the pancreatic body and/or tail was more common; sclerosing extrapancreatic lesions, salivary and lacrimal gland dysfunction, and abundant infiltration of IgG4-positive plasma cells in the gastric mucosa were less likely; and conservative follow-up was sometimes implemented. Histological examination of the pancreas of SIgG4-negative AIP showed lymphoplasmacytic sclerosing pancreatitis (LPSP) rather confined to the pancreas (n = 4), inadequate material (n = 2), and pancreatic fibrosis showing infiltration of lymphocytes without infiltration of IgG4-positive cells or neutrophils (n = 2).

CONCLUSIONS

Clinicopathological features of SIgG4-negative AIP differed from those of SIgG4-positive AIP. Some SIgG4-negative AIP cases are LPSP rather confined to the pancreas. SIgG4-negative AIP may include idiopathic duct-centric pancreatitis (IDCP) or sclerosing pancreatitis other than LPSP or IDCP, but further studies are needed to clarify this issue.

Activation of the interferon pathway in peripheral blood of patients with Sjogren's syndrome

OBJECTIVE

DNA microarray analysis and quantitative real-time polymerase chain reaction (PCR) were performed to identify key target genes in peripheral blood from patients with Sjögren's syndrome (SS).

METHODS

DNA microarray analysis was performed in 19 patients with SS (all women) and 10 healthy controls (5 men and 5 women) using a low-density DNA microarray system with 778 genes. For confirmation, the expression of upregulated genes was analyzed by quantitative real-time PCR in another 37 SS patients (35 women and 2 men) and 9 healthy controls (8 women and 1 man). Relationships between gene signatures and various clinical measures, such as disease duration, symptoms and signs, complications, immunological findings, and salivary and lacrimal functions, were analyzed.

RESULTS

Interferon-α (IFN-α)-inducible protein 27 (IFI27) showed the most significant difference between SS patients and controls in the microarray screening. We performed quantitative RT-PCR for IFI27. IFI27 gene expression level was increased in patients with SS compared with controls (p < 0.01) by real-time PCR, supporting our observations from the microarray data. The level of IFI27 was significantly correlated with serum IgG levels (r = 0.462, p < 0.01) and ß(2)-microglobulin (r = 0.385, p < 0.05), soluble interleukin 2 receptor (r = 0.473, p < 0.01), erythrocyte sedimentation rate (r = 0.333, p < 0.05), and antinuclear antibody titer (speckled pattern; r = 0.445, p < 0.01).

CONCLUSION

Our results suggest that upregulation of IFN-inducible genes in SS patients is a systemic phenomenon, and IFN may play an important role in the pathogenesis of SS. The expression level of IFI27 could be an effective and specific biomarker associated with SS.

Preclinical validation of salivary biomarkers for primary Sjögren's syndrome

OBJECTIVE

Sjögren’s syndrome (SS) is a systemic autoimmune disease with a variety of presenting symptoms that may delay its diagnosis. We previously discovered a number of candidate salivary biomarkers for primary SS using both mass spectrometry and expression microarray analysis. In the current study, we aimed to verify these candidate biomarkers in independent patient populations and to evaluate their predictive values for primary SS detection.

METHODS

In total, 34 patients with primary SS, 34 patients with systemic lupus erythematosus (SLE), and 34 healthy individuals were enrolled for the validation studies. Salivary protein biomarkers were measured using either Western blotting or enzyme-linked immunosorbent assay, and the messenger RNA (mRNA) biomarkers were measured using quantitative polymerase chain reaction. Statistical analysis was performed using R software, version 2.9.

RESULTS

Three protein biomarkers (cathepsin D [CPD], α-enolase, and ß₂-microglobulin [ß₂m]) and 3 mRNA biomarkers (myeloid cell nuclear differentiation antigen [MNDA], guanylate binding protein 2 [GBP-2], and low-affinity IIIb receptor for the Fc fragment of IgG) were significantly elevated in patients with primary SS compared with both SLE patients and healthy controls. The combination of 3 protein biomarkers, CPD, α-enolase, and ß₂m, yielded a receiver operating characteristic (ROC) value of 0.99 in distinguishing primary SS from healthy controls. The combination of protein biomarkers ß₂m and 2 mRNA biomarkers, MNDA and GBP-2, reached an ROC of 0.95 in discriminating primary SS from SLE.

CONCLUSION

We have successfully verified a panel of protein and mRNA biomarkers that can discriminate primary SS from both SLE and healthy controls. If further validated in patients with primary SS and those with sicca symptoms but no autoimmune disease, these biomarkers may lead to a simple yet highly discriminatory clinical tool for diagnosis of primary SS.

Proteomic diagnosis of Sjögren's syndrome

In the last few years, a growing interest has arisen in the application of proteomic analysis to rheumatic disease. Sjögren's syndrome is a systemic disease that affects exocrine glands directly, and is therefore expected to influence the composition of the whole human saliva and lachrymal fluid. Therefore, a rising number of studies have been performed in an attempt to characterize the salivary and lachrymal protein profiles of patients with Sjögren's syndrome by using a proteomic approach. This review summarizes the state of the art and the potential application of proteomics in the systematic search for diagnostic biomarkers in Sjögren's syndrome.

Salivary proteomic and genomic biomarkers for primary Sjögren's syndrome

OBJECTIVE

To identify a panel of protein and messenger RNA (mRNA) biomarkers in human whole saliva (WS) that may be used in the detection of primary Sjögren's syndrome (SS).

METHODS

Mass spectrometry and expression microarray profiling were used to identify candidate protein and mRNA biomarkers of primary SS in WS samples. Validation of the discovered mRNA and protein biomarkers was also demonstrated using real-time quantitative polymerase chain reaction and immunoblotting techniques.

RESULTS

Sixteen WS proteins were found to be down-regulated and 25 WS proteins were found to be up-regulated in primary SS patients compared with matched healthy control subjects. These proteins reflected the damage of glandular cells and inflammation of the oral cavity system in patients with primary SS. In addition, 16 WS peptides (10 up-regulated and 6 down-regulated in primary SS) were found at significantly different levels (P < 0.05) in primary SS patients and controls. Using stringent criteria (3-fold change; P < 0.0005), 27 mRNA in saliva samples were found to be significantly up-regulated in the primary SS patients. Strikingly, 19 of 27 genes that were found to be overexpressed were interferon-inducible or were related to lymphocyte filtration and antigen presentation known to be involved in the pathogenesis of primary SS.

CONCLUSION

Our preliminary study has indicated that WS from patients with primary SS contains molecular signatures that reflect damaged glandular cells and an activated immune response in this autoimmune disease. These candidate proteomic and genomic biomarkers may improve the clinical detection of primary SS once they have been further validated. We also found that WS contains more informative proteins, peptides, and mRNA, as compared with gland-specific saliva, that can be used in generating candidate biomarkers for the detection of primary SS.

Human saliva proteome and transcriptome

This paper tests the hypothesis that salivary proteins and their counterpart mRNAs co-exist in human whole saliva. Global profiling of human saliva proteomes and transcriptomes by mass spectrometry (MS) and expression microarray technologies, respectively, revealed many similarities between saliva proteins and mRNAs. Of the function-known proteins identified in saliva, from 61 to 70% were also found present as mRNA transcripts. For genes not detected at both protein and mRNA levels, we made further efforts to determine if the counterpart is present. Of 19 selected genes detected only at the protein level, the mRNAs of 13 (68%) genes were found in saliva by RT-PCR. In contrast, of many mRNAs detected only by microarrays, their protein products were found in saliva, as reported previously by other investigators. The saliva transcriptome may provide preliminary insights into the boundary of the saliva proteome.

Identification of parotid salivary biomarkers in Sjögren's syndrome by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry and two-dimensional difference gel electrophoresis

OBJECTIVES

To identify the most significant salivary biomarkers in Sjögren's syndrome (SS) using proteomic methods.

METHODS

Parotid saliva from 20 non-SS subjects and 41 primary SS patients was analysed. Protein expression profiles for each sample were generated by surface-enhanced laser desorption/ionization time-of-flight-mass spectrometry (SELDI-TOF-MS). Mean peak intensities of SS patients and non-SS subjects were compared by univariate analyses. Samples pooled by diagnosis (SS and non-SS) and labelled with different Cy dyes were compared by two-dimensional difference gel electrophoresis (2D-DIGE). Two protein levels that were most significantly different by SELDI-TOF-MS and 2D-DIGE were validated by enzyme-linked immunosorbent assay in individual samples.

RESULTS

SELDI-TOF-MS of 10-200 kDa peaks revealed eight peaks with >2-fold changes in the SS group that differed from non-SS at P < 0.005. Peaks of 11.8, 12.0, 14.3, 80.6 and 83.7 kDa were increased, while 17.3, 25.4, and 35.4 kDa peaks were decreased in SS samples. 2D-DIGE identified significant increases of beta-2-microglobulin, lactoferrin, immunoglobulin (Ig) kappa light chain, polymeric Ig receptor, lysozyme C and cystatin C in all stages of SS. Two presumed proline-rich proteins, amylase and carbonic anhydrase VI, were reduced in the patient group. Three of these ten biomarkers have not been associated previously with SS.

CONCLUSIONS

The salivary proteomic profile of SS is a mixture of increased inflammatory proteins and decreased acinar proteins when compared with non-SS. Future studies will test the ability of these biomarker levels, alone and in combination, to diagnose the salivary component of SS.

Correlation of serum B lymphocyte stimulator and beta2 microglobulin with autoantibody secretion and systemic involvement in primary Sjogren's syndrome

BACKGROUND

In primary Sjögren's syndrome (pSS), extraglandular involvement might result from more intense stimulation of autoreactive B cells. Thus markers of B cell activation could be useful in the clinical assessment of this disease.

OBJECTIVE

To investigate the association of serum B lymphocyte stimulator (BLyS) and beta2 microglobulin with autoantibody production and extraglandular involvement in pSS.

METHODS

Serum concentrations of BLyS and beta2 microglobulin were analysed in 177 patients with pSS according to the American-European consensus group criteria. Serum beta2 microglobulin was determined serially in 25 patients.

RESULTS

Autoantibody secretion (presence of anti-SSA antibody alone or of both anti-SSA and anti-SSB) was associated with increased serum BLyS and beta2 microglobulin. No correlation was found between BLyS and beta2 microglobulin levels (p = 0.36). Serum concentrations of beta2 microglobulin and C reactive protein and positive anti-SSB antibody results were associated with extraglandular involvement on univariate analysis (p<10(-4), p = 0.003, and p = 0.004, respectively). Serum beta2 microglobulin was also significantly increased in patients with extraglandular involvement without autoantibodies (mean (SD): 1.75 (0.7) v 1.39 (0.5) mg/l, p = 0.039). Multivariate analysis showed that extraglandular involvement was associated only with increased serum beta2 microglobulin (p = 0.035, odds ratio = 2.78 (95% confidence interval, 1.07 to 7.22)). Among the 25 patients who had serial determinations of serum beta2 microglobulin, the concentrations were increased in all those with disease flare and decreased in three following treatment. Serum BLyS, gamma globulin, IgG, and rheumatoid factor levels were not associated with features of systemic involvement.

CONCLUSIONS

Serum beta2 microglobulin and BLyS reflect B cell activation in different ways in pSS. Serum beta2 microglobulin assessment could be helpful as an activity marker in pSS.

Pancreatic endocrine and exocrine function and salivary gland function in autoimmune pancreatitis before and after steroid therapy

INTRODUCTION

Autoimmune pancreatitis (AIP) is a distinct clinical entity in which an autoimmune mechanism may be involved in pathogenesis.

AIM

To investigate salivary gland function in addition to pancreatic endocrine and exocrine function in patients with AIP, and to determine changes occurring after steroid therapy.

METHODOLOGY

Fasting serum glucose levels, oral glucose tolerance tests or glycosylated hemoglobin values were examined in 19 patients with AIP. N-benzoyl-L-tyrosyl-p-aminobenzoic acid excretion test, sialochemistry and parotid gland scintigraphy were performed in 8 patients.

RESULTS

Eight patients had evidence of DM. Steroid therapy subsequently improved insulin secretion and glycemic control in 3 of 5 patients treated. Pancreatic exocrine function was reduced in 88% of patients. Impaired pancreatic exocrine function improved after steroid therapy in 3 of 6 patients treated. The 3 patients also showed treatment-related improvement in endocrine function. Concentration of beta2-microglobulin in saliva was significantly raised in patients with AIP compared with controls (P < 0.05). Ratio of cumulative peak count to injected radionuclide and washout ratio in parotid scintigraphy in patients with AIP was significantly lower than those of controls (P < 0.01). Salivary gland dysfunction improved after steroid therapy in all 5 patients treated.

CONCLUSIONS

Pancreatic endocrine and exocrine and salivary gland function were frequently impaired in patients with AIP, and steroid therapy was occasionally effective for these dysfunctions.

Salivary and serum beta2-microglobulin and gamma-glutamyl-transferase in patients with primary Sjögren syndrome and Sjögren syndrome secondary to systemic lupus erythematosus

BACKGROUND

Sialochemistry has been proposed as a simple and useful tool for the diagnosis of Sjögren syndrome (SS). Although many changes have been detected in several constituents of saliva from patients with SS, none are individually sensitive or specific enough for diagnosing SS. The aim of this study was to assess the value of the combined determination of beta2-microglobulin (beta2m) and gamma-glutamyl-transferase (GGT) activity in serum and saliva as a diagnostic instrument for differentiating primary and secondary [to systemic lupus erythematosus (SLE)] SS patients from normal subjects.

METHODS

Nineteen primary SS (pSS) patients, 15 patients with SS secondary to SLE, and 25 SLE patients without SS were studied. Thirty healthy subjects were included in the study as control group.

RESULTS

By means of a mathematical model, (a) 84.1%, (b) 85.7%, and (c) 87.0% of patients were correctly classified as SS or normal when (a) salivary beta2m and GGT values, (b) serum beta2m and salivary GGT values, and (c) salivary beta2m and GGT along with serum beta2m values, respectively, were considered. To differentiate between pSS and sSS by means of the mathematical model, the combination of serum beta2m and salivary GGT values achieved that 81.8% of the patients were correctly classified.

CONCLUSION

Since sialochemistry is an easy, safe and reliable test, the combined determination of beta2m and GGT in saliva and serum was useful for differentiating SS patients from normal subjects, but not excessively good for differentiating pSS from sSS patients.

Salivary proteins in rheumatoid arthritis and Sjögren's syndrome: one-dimensional and two-dimensional electrophoretic studies

Parotid saliva from patients with rheumatoid arthritis and Sjögren's syndrome contains elevated levels of multiple anionic proteins of pI approximately 3.75-4.75 and Mr approximately 32,000. Further studies on these components involving narrow range pH 3.5-5.0 immobilized pH gradients (IPGs) and two-dimensional (2D) electrophoresis with narrow- or broad-range IPGs in the first dimension have confirmed their association with these disorders. Immunoblotting showed that these proteins include multiple forms of tissue kallikrein. Treatment with neuraminidase results in removal of these anionic substances from the pH 3.75-4.75 region of gels, thereby indicating that heterogeneity arises from differences in sialation of the carbohydrate residues. The results of treatment with endo-beta-N-acetylglucosaminidase (Endo F) or peptide N-glycosidase (PNGase F) and comparison of the results with studies on human urinary kallikrein suggest that proteins other than kallikrein may also comigrate in the anionic region of gels and that deglycosylation of kallikrien is incomplete in the experimental conditions used, probably because of inadequate denaturation. The paper also reviews the limitations of current criteria used in the investigation of salivary gland function associated with connective tissue disorders and the diagnosis of these. It assesses the potential of electrophoresis in forming the basis of new diagnostic techniques and furthering the understanding of the nature of these diseases. The findings presented in this paper could make a key contribution to this.

Oral fluids as an alternative to serum for measurement of markers of immune activation

Oral fluids are convenient alternatives to blood sampling for evaluating significant metabolic components. Two forms of oral fluids, oral mucosal transudates (OMT) and saliva, were collected and compared for content of soluble products of immune activation. The data confirm that OMT and saliva represent distinct body fluids. The concentrations, outputs, and analyte/protein ratios of beta-2-microglobulin (beta2M), soluble tumor necrosis factor alpha receptor II (sTNFalphaRII), and neopterin were measured. Both the OMT and the saliva of most of the individuals in the control healthy populations had measurable levels of all three activation markers. When the immune system is activated, as in human immunodeficiency virus (HIV) infection, the levels of beta2M and sTNFalphaRII are increased in both OMT and saliva compared to those in a healthy control population. OMT levels correlated better with levels in serum than did saliva and appear to reflect systemic immune activation in HIV infection. Because acquisition of oral fluids is noninvasive and easily repeatable, measurement of beta2M and/or sTNFalphaRII content in OMT could be useful in the assessment of disease activity in patients with HIV infection or chronic inflammatory diseases.

A possible role for saliva as a diagnostic fluid in patients with chronic pain

OBJECTIVES

The focus of this review was on proteins and peptides found in saliva. Of greatest interest were those neuropeptides relevant to nociception and to the pathogenesis of chronic pain syndromes. An additional goal was to develop a standardized protocol to collect saliva for laboratory assessment.

METHODS

Data were obtained through discussion with experts at the medical schools in San Antonio and Heidelberg and a Medline literature search involving all relevant studies from 1966 to 1997. The literature search was based on the following key terms: saliva, serotonin, neuropeptide, substance P (SP), calcitonin gene-related peptide (CGRP), and nerve growth factor (NGF).

RESULTS

The mean concentration of SP in the saliva of healthy normal controls ranged from 9.6 to 220 pg/mL. Generally, the concentration of SP was approximately three times higher in saliva than in plasma. In a number of painful conditions, particularly tension headache, substantial elevations of salivary SP were found. Mean values for salivary CGRP in healthy controls were approximately 22 pmol/L and were significantly elevated in patients with migraine attacks or cluster headache. There were no data to indicate prior quantitative determination of NGF in human saliva.

CONCLUSIONS

After sampling and processing techniques have been standardized, measurement of neuropeptides in human saliva could provide a valuable tool for study of patients with chronic painful disorders such as rheumatoid arthritis, osteoarthritis, and even fibromyalgia syndrome.

Saliva: an additional diagnostic tool in Sjögren's syndrome

OBJECTIVE

To assess the available data and the place of salivary analysis in the diagnosis of Sjögren's syndrome (SS).

METHODS

A Medline search of English language articles published between 1985 and 1996 and a manual search of the reference lists of relevant articles formed the data sources. These were combined with our clinical and experimental experience in this field. Each method of salivary analysis was assessed according to study design, type of saliva used for the study, sensitivity/ specificity for the diagnosis of SS, and correlation to the histopathological findings.

RESULTS

Increased levels of salivary Na+, immunoglobulins (particularly IgA), anti-Ro and La antibodies, lactoferrin, lysozyme, beta 2 microglobulin, prostaglandin E2, thromboxane B2, interleukin-6, and hyaluronic acid have been detected in various studies. Results varied according to the different methods used for saliva collection.

CONCLUSION

Although many changes have been detected in various constituents of saliva in SS patients, no test has proved sensitive or specific enough for diagnosing SS.