Histopathological comparison of Sjögren-related features between paired labial and parotid salivary gland biopsies of sicca patients.

OBJECTIVES: To compare focus score (FS) and other histopathological features between paired labial and parotid salivary gland biopsies in a diagnostic cohort of suspected Sjögren's disease (SjD) patients. METHODS: Labial and parotid salivary gland biopsies were simultaneously obtained from patients with sicca complaints, suspected of having SjD. Biopsies were formalin fixed and paraffin embedded. Sections were stained with haematoxylin & eosin (H&E) and for CD3, CD20, CD45, cytokeratin, CD21, Bcl6, activation induced deaminase (AID), and IgA/IgG. FS and other histopathological features characteristic for SjD were analysed. RESULTS: Based on the expert opinion of three experienced rheumatologists, 36 patients were diagnosed as SjD and 63 as non-SjD sicca patients. When taking all patients together, absolute agreement of various histopathological features between labial and parotid biopsies was high and varied between 80% (FS) and 93% ((pre-)lymphoepithelial lesions (LELs)). More labial gland biopsies had a FS ≥ 1 compared with their parotid counterpart. Accordingly, the area of infiltrate was larger in labial gland biopsies. When considering only SjD patients, labial glands contained significantly less B-lymphocytes, GCs/mm2 and less severe LELs compared with parotid glands. CONCLUSION: Labial and parotid glands from SjD patients contain similar histopathological key features, and thus both glands can be used for diagnosis and classification of SjD. However, parotid salivary glands reveal more evident B-lymphocyte related features, while labial glands exhibit more inflammation, which may be partially unrelated to SjD.

Increased Diagnostic Accuracy of the Labial Gland Biopsy in Primary Sjögren Syndrome When Multiple Histopathological Features Are Included.

OBJECTIVE: The aim of this study was to evaluate the diagnostic accuracy of the labial salivary gland biopsy based on multiple histopathological features in patients with suspected primary Sjögren syndrome (pSS). METHODS: Patients from a diagnostic sicca cohort with clinically suspected pSS who underwent a labial gland biopsy were included. Patients were categorized as having pSS or non-Sjögren syndrome sicca (non-SS sicca) based on vignettes scored by an expert panel. Labial gland biopsies were analyzed for the presence of four histopathological features: focus score (FS) ≥1, prelymphoepithelial and lymphoepithelial lesions, immunoglobulin G plasma cell shift, and germinal centers. Sensitivity and specificity of histologic features were calculated, and the optimal cutoff value for the number of histopathological features needed to diagnose pSS was determined with receiver operating curve analysis. RESULTS: A total of 38 patients were categorized as having pSS and 65 as having non-SS sicca. In labial gland biopsies of patients with pSS, the prevalence of FS ≥1 was 82%, followed by 68% for pre-lymphoepithelial and lymphoepithelial lesions, 63% for plasma cell shift, and 24% for germinal centers. Although FS ≥1 showed the highest sensitivity for patients with pSS (82%), specificity was higher for the other three features (98%-100%). The presence of two or more (of four) histopathological features had almost comparable sensitivity to FS alone, but specificity increased with 12% to 100%. For fulfillment of American College of Rheumatology/EULAR criteria, specificity increased from 84% to 95% when an abnormal biopsy was defined by the presence of two or more histopathological features instead of FS ≥1 only. CONCLUSION: The diagnostic accuracy of the labial gland biopsy increases when other histopathological features besides FS are taken into account, by reducing the number of false-positive biopsies.

Low Mutational Burden of Extranodal Marginal Zone Lymphoma of Mucosa-Associated Lymphoid Tissue in Patients with Primary Sjogren's Syndrome.

Patients with primary Sjogren's syndrome (pSS) are at risk of developing extranodal marginal zone lymphoma (ENMZL) of the mucosa-associated lymphoid tissue (MALT) in the parotid glands. Unlike recurrent genomic aberrations observed in MALT lymphoma, which were not associated with pSS (non-pSS), it is unknown which somatic aberrations underlie the development of pSS-associated MALT lymphomas. Whole-exome sequencing was performed on 17 pSS-associated MALT lymphomas. In total, 222 nonsynonymous somatic variants affecting 182 genes were identified across the 17 cases. The median number of variants was seven (range 2-78), including three cases with a relatively high mutational load (≥24/case). Out of 16 recurrently mutated genes, ID3, TBL1XR1, PAX5, IGLL5 and APC are known to be associated with lymphomagenesis. A total of 18 copy number alterations were detected in eight cases. MALT1 translocations were not detected. With respect to outcome, only two cases relapsed outside of the salivary glands. Both had a high mutational load, suggesting a more advanced stage of lymphoma. The low mutational load and lack of a clear lymphoma-related mutation profile suggests that localized pSS-associated MALT lymphomas are genomically more stable than non-pSS MALT lymphomas and most likely depend on a stimulatory micro-environment.

Histopathology, salivary flow and ultrasonography of the parotid gland: three complementary measurements in primary Sjögren's syndrome.

OBJECTIVE: The involvement of salivary glands in primary SS (pSS) can be assessed in different ways: histopathology, salivary flow and ultrasonography. To understand the relative value of these different approaches, it is crucial to understand the relationship between them. As we routinely perform these three modalities in the parotid gland for disease evaluation, our aim was to investigate the construct validity between these modalities in one and the same gland. METHODS: Consecutive sicca patients underwent a multidisciplinary diagnostic workup including parotid gland biopsy, collection of parotid gland-specific saliva and parotid gland ultrasonography. Patients who were classified as pSS according to the ACR-EULAR criteria were included. Construct validity was assessed using Spearman's correlation coefficients. RESULTS: The 41 included pSS patients completed a full workup within a mean time interval of 2.6 months. Correlations between histopathological features and stimulated parotid salivary flow were fair (ρ = -0.123 for focus score and ρ = -0.259 for percentage of CD45+ infiltrate). Likewise, poor correlations were observed between stimulated parotid salivary flow and parotid ultrasonography (ρ = -0.196). Moderate to good associations were found between the histopathological items focus score and the percentage of CD45+ infiltrate, with parotid US scores (total US score: ρ = 0.510 and ρ = 0.560; highest for homogeneity: ρ = 0.574 and ρ = 0.633). CONCLUSION: Although pSS-associated ultrasonographic findings did correlate with histopathological features, the three modalities that evaluate salivary gland involvement assess different (or at best partly related) constructs. Therefore histopathology, salivary flow and ultrasonography are complementary measurements and cannot directly replace each other in the workup of pSS.

The Transcriptome of Paired Major and Minor Salivary Gland Tissue in Patients With Primary Sjögren's Syndrome.

Background: While all salivary glands (SGs) can be involved in primary Sjögren's syndrome (pSS), their respective role in pathogenesis remains unclear. Our objective was to assess immunopathway activation in paired parotid and labial gland tissue from biopsy-positive and biopsy-negative pSS and non-SS sicca patients. Methods: Paraffin-embedded, paired parotid and labial salivary gland tissue and peripheral blood mononuclear cells were obtained from 39 pSS and 20 non-SS sicca patients. RNA was extracted, complementary DNA libraries were prepared and sequenced. For analysis of differentially expressed genes (DEGs), patients were subdivided based on fulfillment of ACR-EULAR criteria and histopathology. Results: With principal component analysis, only biopsy-positive pSS could be separated from non-SS sicca patients based on SG gene expression. When comparing the transcriptome of biopsy-positive pSS and biopsy-negative non-SS sicca patients, 1235 and 624 DEGs (FDR<0.05, log2FC<-1 or >1) were identified for parotid and labial glands, respectively. The number of DEGs between biopsy-negative pSS and non-SS sicca patients was scarce. Overall, transcript expression levels correlated strongly between parotid and labial glands (R2 = 0.86, p-value<0.0001). Gene signatures present in both glands of biopsy-positive pSS patients included IFN-α signaling, IL-12/IL-18 signaling, CD3/CD28 T-cell activation, CD40 signaling in B-cells, DN2 B-cells, and FcRL4+ B-cells. Signature scores varied considerably amongst pSS patients. Conclusion: Transcriptomes of paired major and minor SGs in pSS were overall comparable, although significant inter-individual heterogeneity in immunopathway activation existed. The SG transcriptome of biopsy-negative pSS was indistinguishable from non-SS sicca patients. Different patterns of SG immunopathway activation in pSS argue for personalized treatment approaches.

Salivary Gland Mucosa-Associated Lymphoid Tissue-Type Lymphoma From Sjögren's Syndrome Patients in the Majority Express Rheumatoid Factors Affinity-Selected for IgG.

OBJECTIVE: Patients with SjÓ§gren's syndrome (SS) have an increased risk of developing malignant B cell lymphomas, particularly mucosa-associated lymphoid tissue (MALT)-type lymphomas. We have previously shown that a predominant proportion of patients with SS-associated salivary gland MALT lymphoma express somatically hypermutated IgM with strong amino acid sequence homology with stereotypic rheumatoid factors (RFs). The present study was undertaken in a larger cohort of patients with SS-associated MALT lymphoma to more firmly assess the frequency of RF reactivity and the significance of somatic IGV-region mutations for RF reactivity. METHODS: B cell antigen receptors (BCRs) of 16 patients with SS-associated salivary gland MALT lymphoma were analyzed. Soluble recombinant IgM was produced of 12 MALT lymphoma samples, including 1 MALT lymphoma sample that expressed an IgM antibody fitting in a novel IGHV3-30-encoded stereotypic IGHV subset. For 4 of the 12 IgM antibodies from MALT lymphoma samples, the somatically mutated IGHV and IGKV gene sequences were reverted to germline configurations. Their RF activity and binding affinity were determined by enzyme-linked immunosorbent assay and surface plasmon resonance, respectively. RESULTS: Nine (75%) of the 12 IgM antibodies identified in patients with SS-associated salivary gland MALT lymphoma displayed strong monoreactive RF activity. Reversion of the IGHV and IGKV mutations to germline configuration resulted in RF affinities for IgG that were significantly lower for 3 of the 4 somatically mutated IgM antibodies. In stereotypic IGHV3-7/IGKV3-15-encoded RFs, a recurrent replacement mutation in the IGKV3-15-third complementarity-determining region was found to play a pivotal role in the affinity for IgG-Fc. CONCLUSION: A majority of patients with SS-associated salivary gland MALT lymphoma express somatically mutated BCRs that are selected for monoreactive, high-affinity binding of IgG-Fc. These data underscore the notion that soluble IgG, most likely in immune complexes in inflamed tissues, is the principal autoantigen in the pathogenesis of a variety of B cell lymphomas, particularly SS-associated MALT lymphomas.

Gene expression profiling of epithelium-associated FcRL4+ B cells in primary Sjögren's syndrome reveals a pathogenic signature.

In primary Sjögren's syndrome (pSS), FcRL4+ B cells are present in inflamed salivary gland tissue, within or in close proximity to ductal epithelium. FcRL4 is also expressed by nearly all pSS-related mucosa-associated lymphoid tissue (MALT) B cell lymphomas, linking FcRL4 expression to lymphomagenesis. Whether glandular FcRL4+ B cells are pathogenic, how these cells originate, and how they functionally differ from FcRL4- B cells in pSS is unclear. This study aimed to investigate the phenotype and function of FcRL4+ B cells in the periphery and parotid gland tissue of patients with pSS. First, circulating FcRL4+ B cells from 44 pSS and 54 non-SS-sicca patients were analyzed by flow cytometry. Additionally, RNA sequencing of FcRL4+ B cells sorted from parotid gland cell suspensions of 6 pSS patients was performed. B cells were sorted from cell suspensions as mini bulk (5 cells/well) based on the following definitions: CD19+CD27-FcRL4- ('naive'), CD19+CD27+FcRL4- ('memory'), and CD19+FcRL4+ B cells. We found that, although FcRL4+ B cells were not enriched in blood in pSS compared with non-SS sicca patients, these cells generally exhibited a pro-inflammatory phenotype. Genes coding for CD11c (ITGAX), T-bet (TBX21), TACI (TNFRSF13B), Src tyrosine kinases and NF-κB pathway-related genes were, among others, significantly upregulated in glandular FcRL4+ B cells versus FcRL4- B cells. Pathway analysis showed upregulation of B cell activation, cell cycle and metabolic pathways. Thus, FcRL4+ B cells in pSS exhibit many characteristics of chronically activated, pro-inflammatory B cells and their gene expression profile suggests increased risk of lymphomagenesis. We postulate that these cells contribute significantly to the epithelial damage seen in the glandular tissue and that FcRL4+ B cells are an important treatment target in pSS.

Massive B-Cell Infiltration and Organization Into Artery Tertiary Lymphoid Organs in the Aorta of Large Vessel Giant Cell Arteritis.

Giant cell arteritis (GCA) can be classified into Cranial(C)-GCA and Large Vessel(LV)-GCA. Based on analysis of temporal arteries, GCA is postulated to be T-cell-mediated. Recently, a disturbed B-cell homeostasis was documented in newly diagnosed GCA patients. In the current study, we assessed the presence of B-cells and their level of ectopic organization in the aorta of LV-GCA patients. Aorta tissue samples of 9 histologically-proven LV-GCA patients and 22 age- and sex-matched atherosclerosis patients who underwent aortic aneurysm surgery were studied by immunohistochemistry. Sections were stained for B-cells, T-cells, follicular dendritic cells, high endothelial venules, germinal center B-cells, proliferating B-cells, macrophages, and plasma cells. Aortas of LV-GCA patients showed massive infiltration of B-cells, which clearly outnumbered T-cells, as opposed to C-GCA patients where, as previously reported, T-cells outnumber B-cells. B-cells were mainly found in the adventitia of the vessel wall and were organized into artery tertiary lymphoid organs. These tertiary lymphoid organs had germinal centers, proliferating B-cells and plasma cell niches. In conclusion, we found massive and organized B-cell infiltrates in the aorta of LV-GCA patients, which is in line with the previously documented decrease of circulating B-cells in active GCA. Our data indicate a role for B-cells in the pathogenesis of GCA and thus evoke further investigation into the factors determining the tissue tropism and organization of B-cells in GCA.

The role of salivary gland histopathology in primary Sjögren's syndrome: promises and pitfalls.

The formation of lymphomononuclear cell infiltrates organising as periductal infiltrates in the salivary glands of patients with primary Sjögren's syndrome (pSS) is one of the hallmarks of the disease. Historically, the clinical role of salivary gland histopathology, most commonly performed on labial salivary gland biopsies, has been confined to the clinical classification and diagnosis of pSS whereby according to the ACR-EULAR a positive histopathology finding is a requirement for the diagnosis of pSS in the absence of anti-Ro/SSA antibodies. In recent years, further understanding of the heterogeneity of the immune cell infiltration and organisation within the salivary glands of pSS patients and its correlation with clinical manifestations of the disease has led to propose salivary gland histopathology as a novel tool able to identify patients at higher risk of developing more severe extraglandular manifestations and lymphoma. Furthermore, recent clinical developments in ongoing randomised clinical trials with novel biologics in pSS have focused on salivary glands histopathology to inform on patients stratification based on target validation, proof of drug efficacy and mechanisms of response/resistance to therapy. However, lack of standardisation of methodology and analysis has hindered the reproducibility of data from different groups and no definitive evidence in support of the use of salivary glands histopathology to inform clinical management of patients with pSS has been provided. In this review, we summarise recent evidence highlighting the promises and pitfalls of salivary glands histopathology in pSS emphasising the need for an international consensus on standardisation of methodology with validation in large prospective multicentre initiatives.

Validation of the ACR-EULAR criteria for primary Sjögren's syndrome in a Dutch prospective diagnostic cohort.

Objectives: To validate the ACR-EULAR classification criteria for primary SS (pSS), and compare them to the American-European Consensus Group (AECG) and ACR criteria in a Dutch prospective diagnostic cohort. Methods: Consecutive patients (n = 129) referred for suspicion of pSS underwent a multidisciplinary evaluation, including a labial and/or parotid gland biopsy. Patients with an incomplete work-up (n = 8) or associated systemic auto-immune disease (n = 7) were excluded. The ACR-EULAR classification was compared with expert classification, AECG and ACR classification. Additionally, the accuracy of individual ACR-EULAR items in discriminating pSS from non-pSS was evaluated. The validity of criteria sets was described separately using parotid or labial gland biopsy results for classification. Results: Of the 114 evaluated patients, the expert panel classified 34 (30%) as pSS and 80 (70%) as non-pSS. Using labial gland biopsy results, ACR-EULAR classification showed 87% absolute agreement (κ = 0.73) with expert classification, with a sensitivity of 97% and specificity of 83%. Using the parotid gland biopsy results, the ACR-EULAR criteria performed excellently as well. Focus score, anti-SSA titre and ocular staining score showed good to excellent accuracy, whereas unstimulated whole saliva and Schirmer's test had poor accuracy. The ACR-EULAR and AECG criteria had equal validity. Compared with ACR classification, ACR-EULAR classification showed higher sensitivity but lower specificity. Conclusion: The ACR-EULAR criteria showed good agreement with expert classification, but some patients may be misclassified as pSS. Unstimulated whole saliva and Schirmer's test showed poor discriminative value. The ACR-EULAR criteria performed equally to the AECG criteria, and had higher sensitivity but lower specificity than the ACR criteria.

Germinal centres in diagnostic labial gland biopsies of patients with primary Sjögren's syndrome are not predictive for parotid MALT lymphoma development.

OBJECTIVE: Patients with primary Sjögren's syndrome (pSS) have an increased risk of developing non-Hodgkin's lymphoma (NHL), particularly parotid gland mucosa-associated lymphoid tissue (MALT) lymphomas. Presence of germinal centres (GCs) in labial gland biopsies has been suggested as predictive factor for NHL. We assessed whether presence of GCs is increased in labial gland biopsies from patients with pSS who developed parotid MALT lymphoma, the dominant NHL-subtype in pSS, compared with patients with pSS who did not develop lymphoma. METHODS: Eleven labial gland biopsies from patients with pSS that were taken prior to parotid MALT lymphoma development were compared with biopsies of 22 matched pSS controls (1:2) who did not develop lymphoma. Biopsies were evaluated for GCs (H&E and Bcl6). RESULTS: Labial gland biopsies of pSS MALT lymphoma patients, revealed GCs in 2/11 (18%) H&E sections and 3/11 (27%) Bcl6 stained sections. In controls, GCs were present in 4/22 (18%) of H&E sections and 5/22 (23%) of Bcl6 stained sections. CONCLUSION: Presence of GCs in labial gland biopsies does not differ between patients with pSS that develop parotid MALT lymphoma and patients with pSS who do not develop lymphoma. The presence of GCs in labial gland biopsies is therefore not a predictive factor for pSS-associated parotid MALT lymphomas.

FcRL4+ B-cells in salivary glands of primary Sjögren's syndrome patients.

Fc receptor-like protein 4 (FcRL4) is normally expressed on a small subset of mucosa-associated B-cells, as well as on mucosa-associated lymphoid tissue (MALT) lymphoma B-cells. Primary Sjögren's syndrome (pSS) patients have an increased risk of developing MALT lymphomas, preferentially in the parotid glands. For this reason we studied here by immunohistochemistry and mRNA analysis whether FcRL4 expressing B-cells are present in salivary gland tissue (labial and parotid) of pSS patients (n = 54) and non-pSS sicca patients (n = 16) and whether parotid gland MALT lymphomas in pSS patients (n = 49) also express this receptor. We also studied the effect of treatment (rituximab and abatacept) on the presence of FcRL4+ B-cells, and whether numbers in labial gland biopsies at time of diagnosis of pSS can predict whether patients are at risk for MALT lymphoma development. We demonstrate that FcRL4+ cells are present in salivary gland tissue of pSS patients where they are closely associated with ductal epithelial cells forming lymphoepithelial lesions. The glandular FcRL4+ cells are highly proliferative, genuine PAX5+ B-cells. These FcRL4+ B-cells are far more frequent in parotid gland than in labial gland tissue (p = 0.003). We further show that expression of FcRL4 is present in pSS-related parotid MALT lymphomas. The FcRL4 mRNA expression level in parotid MALT lymphoma is increased compared to parotid gland tissue of pSS patients without lymphoma (p = 0.017). However, numbers of FcRL4+ B-cells in labial gland biopsies taken at the time of pSS diagnosis, are not predictive for later development of MALT lymphoma. Reduction of parotid gland FcRL4+ B-cells by rituximab, but not abatacept is accompanied by restoration of the glandular epithelium, illustrating the crosstalk between these B-cells with the ductal cells. In conclusion, intraepithelial FcRL4+ B-cells are present in the salivary glands of pSS patients. These cells are likely involved in the epithelial changes seen in pSS. Their enrichment in parotid glands may explain why MALT lymphomas in pSS patients preferentially develop at this specific location.

Abatacept treatment of patients with primary Sjögren's syndrome results in a decrease of germinal centres in salivary gland tissue.

OBJECTIVES: The aim of this study was to assess the histopathological changes in parotid gland tissue of primary Sjögren's syndrome (pSS) patients treated with abatacept. METHODS: In all 15 pSS patients included in the open-label Active Sjögren Abatacept Pilot (ASAP, 8 abatacept infusions) study parotid gland biopsies were taken before treatment and at 24 weeks of follow up. Biopsies were analysed for pSS-related histopathological features and placed in context of clini- cal responsiveness as assessed with EULAR Sjögren's syndrome disease activity index (ESSDAI). RESULTS: Abatacept treatment resulted in a decrease of germinal centres (GCs)/ mm2 (p=0.173). Number of GCs/mm2 at baseline was associated with response in the glandular domain of ESSDAI (Spearman ρ=0.644, p=0.009). Abatacept treatment did not reduce focus score, lymphoepithelial lesions, area of lymphocytic infiltrate, amount of CD21+ networks of follicular dendritic cells, and numbers of CD3+ T-cells or CD20+ B- cells. Number of IgM plasma cells/mm2 increased (p=0.041), while numbers of IgA and IgG plasma cells/mm2 were unaffected during abatacept treatment. CONCLUSIONS: Abatacept affects formation of GCs of pSS patients in parotid glands, which is dependent on co-stimulation of activated follicular-helper-T-cells. Herewith, local formation of (autoreactive) memory B-cells is inhibited. Presence of GCs at baseline predicts responsiveness to abatacept in the ESSDAI glandular domain.

Towards personalised treatment in primary Sjögren's syndrome: baseline parotid histopathology predicts responsiveness to rituximab treatment.

OBJECTIVES: The aims of this study were (1) to assess the effect of rituximab (RTX; anti-CD20) treatment in patients with primary Sjögren's syndrome (pSS) based on sequential parotid biopsies obtained in a placebo-controlled, randomised clinical trial, and (2) to assess the prognostic value of the histological characteristics of parotid gland tissue with regard to responsiveness to RTX treatment. METHODS: In a double-blinded, placebo-controlled trial, sequential parotid gland biopsies were taken from 20 RTX-treated and 10 placebo-treated patients with pSS, at baseline and 12 weeks after treatment. The relative amount of lymphocytic infiltrate (stained for CD45), absolute number of T cells and B cells per mm2 parenchyma (stained for CD3 and CD20, respectively), focus score, number of germinal centres and of lymphoepithelial lesions per mm2 in parotid gland parenchyma were assessed. Histopathological data were compared between clinical responders (decrease in European League Against Rheumatism Sjögren's Syndrome Disease Activity Index (ESSDAI) score of ≥3 at 12 weeks compared with baseline) and non-responders (change in ESSDAI<3) to RTX treatment. RESULTS: In RTX-treated patients, a significant reduction in the number of CD20+ B cells/mm2 parenchyma was observed, while no such reduction was observed in placebo-treated patients. The number of CD3+ T cells/mm2 in parenchyma did not change in either group. Furthermore, the number and the severity of lymphoepithelial lesions/mm2 and number of germinal centres/mm2 was significantly reduced in RTX-treated patients, but did not change in placebo-treated patients. When comparing the pretreatment characteristics of clinical responders with non-responders, the median number of CD20+ B cells/mm2 parenchyma at baseline was significantly higher in responders (1871 vs 353 cells/mm2, p<0.05). Other histopathological baseline characteristics were not predictive for response to RTX treatment. CONCLUSIONS: RTX treatment in pSS leads to a major reduction of lymphocytic infiltration and to fewer B cells, germinal centres and lymphoepithelial lesions in parotid gland parenchyma. A high pretreatment number of CD20+ B cells/mm2 parotid gland parenchyma predicts better responsiveness of patients with pSS to RTX treatment. Pretreatment parotid gland histopathological characteristics could therefore contribute to a more personalised treatment approach to pSS.

Persistence of immunoglobulin-producing cells in parotid salivary glands of patients with primary Sjögren's syndrome after B cell depletion therapy.

OBJECTIVES: To assess the persistence of immunoglobulin-producing cell populations in the parotid salivary glands of patients with primary Sjögren's syndrome (pSS) after B cell depletion therapy with rituximab. METHODS: Thirteen patients with pSS and four control patients were included in this study. Patients with pSS were treated with rituximab or placebo. Sequence analysis was carried out on IgA- and IgG-encoding transcripts extracted from parotid salivary gland biopsy specimens taken before treatment and at 12-16 and 36-52 weeks after treatment. RESULTS: At baseline, many clonally related sequences were seen in patients with pSS. The number of clonal expansions was significantly higher in patients with pSS than in control patients. Clonal expansions were composed of IgA- and/or IgG-expressing cells. Rituximab did not significantly alter the degree of clonal expansions. Groups of clonally related cells had members which were shared between biopsy specimens taken before and after treatment. Mutation frequencies of immunoglobulin sequences from clonally related cells in patients with pSS were higher after treatment. CONCLUSIONS: Rituximab treatment does not alter the characteristic features of increased clonal expansions seen in the parotid salivary glands of patients with pSS. The presence of clonally related immunoglobulin-producing cells before and after rituximab treatment strongly suggests that immunoglobulin-producing cells persist in salivary glands of patients with pSS despite B cell depletion. The presence of mixed isotype expression within groups of clonally related cells indicates local class switching in salivary glands of patients with pSS. Persistent immunoglobulin-producing cells may underlie disease relapse after treatment.