IL-35-producing B cells are critical regulators of immunity during autoimmune and infectious diseases.

B lymphocytes have critical roles as positive and negative regulators of immunity. Their inhibitory function has been associated primarily with interleukin 10 (IL-10) because B-cell-derived IL-10 can protect against autoimmune disease and increase susceptibility to pathogens. Here we identify IL-35-producing B cells as key players in the negative regulation of immunity. Mice in which only B cells did not express IL-35 lost their ability to recover from the T-cell-mediated demyelinating autoimmune disease experimental autoimmune encephalomyelitis (EAE). In contrast, these mice displayed a markedly improved resistance to infection with the intracellular bacterial pathogen Salmonella enterica serovar Typhimurium as shown by their superior containment of the bacterial growth and their prolonged survival after primary infection, and upon secondary challenge, compared to control mice. The increased immunity found in mice lacking IL-35 production by B cells was associated with a higher activation of macrophages and inflammatory T cells, as well as an increased function of B cells as antigen-presenting cells (APCs). During Salmonella infection, IL-35- and IL-10-producing B cells corresponded to two largely distinct sets of surface-IgM(+)CD138(hi)TACI(+)CXCR4(+)CD1d(int)Tim1(int) plasma cells expressing the transcription factor Blimp1 (also known as Prdm1). During EAE, CD138(+) plasma cells were also the main source of B-cell-derived IL-35 and IL-10. Collectively, our data show the importance of IL-35-producing B cells in regulation of immunity and highlight IL-35 production by B cells as a potential therapeutic target for autoimmune and infectious diseases. This study reveals the central role of activated B cells, particularly plasma cells, and their production of cytokines in the regulation of immune responses in health and disease.

Splenic proliferative lymphoid nodules distinct from germinal centers are sites of autoantigen stimulation in immune thrombocytopenia.

To understand more specific abnormalities of humoral autoimmunity, we studied 31 spleens from immune thrombocytopenia (ITP) patients and 36 control spleens. Detailed analysis identified at least 2 different splenic structures accommodating proliferating B cells, classic germinal centers (GCs), and proliferative lymphoid nodules (PLNs). PLNs were characterized by proliferating Ki67(+) B cells close to follicular dendritic cells (FDCs) and lacked polarization into dark and light zones. As opposed to cells in GCs, proliferating B cells in PLN lacked expression of Bcl6. In both PLNs and GCs of ITP spleens, the density of T cells was significantly reduced. Both T follicular helper cells (T(FH)) and regulatory T cells were reduced within PLNs of ITP spleens suggesting a defect of tolerance related to a loss of T-cell control. Within PLNs of ITP, but not controls, abundant platelet glycoprotein (GP) IIb/IIIa autoantigens was found in IgM containing immune complexes tightly bound to FDCs and closely approximated to proliferating B cells. GPIV was found less often, but not in the same PLNs as GPIIb/IIIa. Autoantigens were not found in the GCs of ITP or controls indicating that PLNs are the sites of autoantigen stimulation in ITP potentially related to a lack of control by T cells and/or the present autoantigen.

Steady-state generation of mucosal IgA+ plasmablasts is not abrogated by B-cell depletion therapy with rituximab.

The anti-CD20 antibody rituximab depletes human B cells from peripheral blood, but it remains controversial to what extent tissue-resident B cells are affected. In representative patients with rheumatoid arthritis, we here demonstrate that recently activated presumably short-lived plasmablasts expressing HLA-DR(high) and Ki-67 continuously circulate in peripheral blood after B-cell depletion by rituximab at 26%-119% of their initial numbers. They circulate independent of splenectomy, express immunoglobulin A (IgA), ß7 integrin, and C-C motif receptor 10 (CCR10) and migrate along CCL28 gradients in vitro, suggesting their mucosal origin. These plasmablasts express somatically hypermutated V(H) gene rearrangements and spontaneously secrete IgA, exhibiting binding to microbial antigens. Notably, IgA(+) plasmablasts and plasma cells were identified in the lamina propria of patients treated with rituximab during peripheral B-cell depletion. Although a relation of these "steady state"-like plasmablasts with rheumatoid arthritis activity could not be found, their persistence during B-cell depletion indicates that their precursors, that is, B cells resident in the mucosa are not deleted by this treatment. These data suggest that a population of mucosal B cells is self-sufficient in adult humans and not replenished by CD20(+) B cells immigrating from blood, lymphoid tissue, or bone marrow, that is, B cells depleted by rituximab.

Secondary immunization generates clonally related antigen-specific plasma cells and memory B cells.

Rechallenge with T cell-dependent Ags induces memory B cells to re-enter germinal centers (GCs) and undergo further expansion and differentiation into plasma cells (PCs) and secondary memory B cells. It is currently not known whether the expanded population of memory B cells and PCs generated in secondary GCs are clonally related, nor has the extent of proliferation and somatic hypermutation of their precursors been delineated. In this study, after secondary tetanus toxoid (TT) immunization, TT-specific PCs increased 17- to 80-fold on days 6-7, whereas TT-specific memory B cells peaked (delayed) on day 14 with a 2- to 22-fold increase. Molecular analyses of V(H)DJ(H) rearrangements of individual cells revealed no major differences of gene usage and CDR3 length between TT-specific PCs and memory B cells, and both contained extensive evidence of somatic hypermutation with a pattern consistent with GC reactions. This analysis identified clonally related TT-specific memory B cells and PCs. Within clusters of clonally related cells, sequences shared a number of mutations but also could contain additional base pair changes. The data indicate that although following secondary immunization PCs can derive from memory B cells without further somatic hypermutation, in some circumstances, likely within GC reactions, asymmetric mutation can occur. These results suggest that after the fate decision to differentiate into secondary memory B cells or PCs, some committed precursors continue to proliferate and mutate their V(H) genes.

TLR2 is one of the endothelial receptors for beta 2-glycoprotein I.

During the antiphospholipid syndrome, beta2-gpI interacts with phospholipids on endothelial cell (EC) surface to allow the binding of autoantibodies. However, induced-pathogenic intracellular signals suggest that beta2-gpI associates also with a receptor that is still not clearly identified. TLR2 and TLR4 have long been suspected, yet interactions between TLRs and beta2-gpI have never been unequivocally proven. The aim of the study was to identify the TLR directly involved in the binding of beta2-gpI on EC surface. beta2-gpI was not synthesized and secreted by ECs in vitro, but rather taken up from FCS. This uptake occurred through association with TLR2 and TLR4 which partitioned together in the lipid rafts of ECs. After coimmunoprecipitation, mass-spectrometry identification of peptides demonstrated that TLR2, but not TLR4, was implicated in the beta2-gpI retention. These results were further confirmed by plasmon resonance-based studies. Finally, siRNA were used to obtain TLR2-deficient ECs that lost their ability to bind biotinylated beta2-gpI and to trigger downstream phosphorylation of kinases and activation of NFkappaB. TLR4 may upregulate TLR2 expression, thereby contributing to beta2-gpI uptake. However, our data demonstrate that direct binding of beta2-gpI on EC surface occurs through direct interaction with TLR2. Furthermore, signaling for anti-beta2-gpI may be envisioned as a multiprotein complex concentrated in lipid rafts on the EC membrane.

Ectopic germinal centers are rare in Sjogren's syndrome salivary glands and do not exclude autoreactive B cells.

This study reports on the characterization of B cells of germinal center (GC)-like structures infiltrating the salivary glands (SGs) of patients with Sjögren's syndrome. Eight two-color combinations were devised to characterize the phenotype of these B cells in 11 SG specimens selected from biopsies obtained from 40 Sjögren's syndrome patients and three normal tonsils. The 9G4 mAb, which recognizes V4.34-encoded autoAbs, enabled us to identify autoreactive B cells. Quantitative RT-PCR was used to determine the level of mRNAs for activation-induced cytidine deaminase (AICDA), repressors and transcription factors. CD20(+)IgD(-)CD38(+)CD21(+)CD24(-) B cells, similar to those identified in tonsil GCs, were seen in the SGs of four patients and, and since they expressed AICDA, they were termed "real GCs". CD20(+)IgD(+)CD38(-)CD21(+)CD24(+) B cells, seen in aggregates from the remaining seven samples, were characteristically type 2 transitional B cells and marginal zone-type B cells. They lacked AICDA mRNAs and were termed "aggregates". Real GCs from SGs contained mRNAs for Pax-5 and Bcl-6, like tonsil GC cells, whereas aggregates contained mRNAs for Notch-2, Blimp-1, IRF-4, and BR3, similar to marginal zone B cells. Further experimental data in support of this dichotomy included the restriction of CXCR5 expression to real GC cells, while sphingosine 1-phosphate receptor 1 was expressed only in aggregates. In contrast, both types of B cell clusters expressed the idiotype recognized by the 9G4 mAb. Our data indicate that, in SGs, a minority of B cell clusters represent genuine GC cells, while the majority manifest features of being type 2 transitional B cells and marginal zone cells. Interestingly, both types of B cell aggregates include autoreactive B cells.

Anticytokine therapy impacting on B cells in autoimmune diseases.

PURPOSE OF REVIEW: To evaluate the impact of particular anticytokine therapies able to indirectly target B cells with emphasis on the tumor necrosis factor (TNF) family members, B cell activating factor/B lymphocyte stimulator (BAFF/BLyS) and a proliferation-inducing ligand (APRIL). RECENT FINDINGS: Although blockade of TNF/lymphotoxin by etanercept has been shown to have an impact on memory B cells, recent studies of inhibiting the TNF family members BAFF/BlyS or simultaneously blocking BAFF/BlyS and APRIL in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) clearly demonstrated biologic activity, including reductions of immunoglobulin levels. However, clear evidence of clinical activity by any of the compounds interfering with BAFF/BLys or APRIL has not yet been shown. SUMMARY: Although anticytokine therapies mainly blocking signaling pathways of innate immunity, that is TNF-alpha, have shown efficacy in the treatment of arthritides and have partial effects on memory B cells, current studies evaluate effects on adaptive immunity by blocking BAFF/BlyS and/or APRIL which indirectly act on B and plasma cells.

New ELISA for B cell-activating factor.

BACKGROUND: The B cell-activating factor of the TNF family (BAFF) is upregulated in autoimmune diseases, but a number of conflicting results have cast doubts on the reliability of the ELISA protocols currently used for its quantification. This situation led us to develop a new ELISA for the measurement of BAFF. METHODS: BAFF was purified for use alongside nonglycosylated recombinant BAFF. Two monoclonal antibodies (mAbs) and two polyclonal antibodies (pAbs) to BAFF were used. RESULTS: The optimization process showed that the pAb format was preferable to the mAb format as capture antibody, because the pAbs recognized the glycosylated as well as the nonglycosylated forms of BAFF. The most efficient pair of Abs involved using the unconjugated form of a goat pAb to capture BAFF and the same biotinylated goat pAb to detect bound BAFF. This ELISA was not influenced by the presence of rheumatoid factor. CONCLUSIONS: This new ELISA helped provide insights into why serum concentrations of BAFF vary between studies for a given population of patients. It is a reliable tool for the management of the diseases in which BAFF is an indication of response to therapy.

BAFF, APRIL, TWE-PRIL: who's who?

BAFF and APRIL are two members of the TNF superfamily that have co-stimulatory activity on B cells and contribute to autoimmunity. While BAFF is processed at the cell surface, APRIL is processed inside the cell by a furin-convertase and is able to perform its function only as a soluble factor. However, APRIL can be expressed as a cell surface fusion protein with TWEAK called TWE-PRIL. BAFF can also exist as a soluble molecule and can be detected in human serum. Whether the biological functions controlled by membrane-bound BAFF differ from those triggered by soluble BAFF is unclear. In addition to this complexity, DeltaBAFF, an alternative splice isoform of BAFF shows different properties. BAFF can also, in autoimmune disease form heterotrimers with APRIL but the control and function of these heterotrimers remain unclear. In order to understand the function of these molecules we need to elucidate the complexity of the various forms of these members of the TNF family.

Polarization of B effector cells in Sjögren's syndrome.

Analysis of salivary glands of patients with primary Sjögren's syndrome has yielded conflicting results with respect to T helper (Th)1/Th2 polarization. This balance might parallel the progress of the local lesions. B-cells are now taking center stage in this disease. They can also be primed to differentiate into two cytokine-production pathways, dubbed B effector (Be) 1 and Be2 cells. This is discussed in the light of our recent finding that Be1 accompany Th1, while Be2 accompany in the tissue lesions.

Enhanced Tyrosine Phosphatase Activity Underlies Dysregulated B Cell Receptor Signaling and Promotes Survival of Human Lupus B Cells.

OBJECTIVE: Systemic lupus erythematosus (SLE) is associated with hyperactivity of B cells and abnormalities of B cell receptor (BCR) signaling. To address the linkage between dysregulated BCR signaling and increased B cell function, we assessed immediate phosphorylation events in lupus B cells. METHODS: B cells from SLE patients and healthy donors were analyzed by flow cytometry to assess phosphorylated CD22, Syk, and Akt as well as the basal expression of the BCR coreceptors CD22 and CD19. Confocal microscopy studies determined the recruitment of CD22 and the tyrosine phosphatase SH2 domain-containing phosphatase 1 to the activated BCR complex. Additionally, phosphatase activity in SLE versus healthy donor B cells was measured. RESULTS: B cells from SLE patients showed diminished Syk phosphorylation and reduced intracellular calcium release after BCR activation as compared to B cells from healthy donors. This was related to an enhanced activity of tyrosine, but not serine/threonine, phosphatases and was corrected by inhibition of tyrosine phosphatase activity. In contrast to reduced Syk phosphorylation after BCR activation, phosphorylation of Akt was significantly increased in SLE B cells. The disturbed balance between Syk and Akt phosphorylation was significantly correlated with B cell survival following BCR engagement. Furthermore, CD27-, but not CD27+, B cells from SLE patients displayed increased expression and phosphorylation of the inhibitory BCR coreceptor CD22. CONCLUSION: These results indicate that an imbalance between serine and tyrosine phosphatases in SLE contributes to an intrinsically disturbed balance of BCR-initiated signaling pathways, resulting in enhanced survival of lupus B cells and differentiation into plasma cells.

Engagement of CD22 on B cells with the monoclonal antibody epratuzumab stimulates the phosphorylation of upstream inhibitory signals of the B cell receptor.

The binding of antigen to the B cell receptor (BCR) results in a cascade of signalling events that ultimately drive B cell activation. Uncontrolled B cell activation is regulated by negative feedback loops that involve inhibitory co-receptors such as CD22 and CD32B that exert their functions following phosphorylation of immunoreceptor tyrosine-based inhibition motifs (ITIMs). The CD22-targeted antibody epratuzumab has previously been shown to inhibit BCR-driven signalling events, but its effects on ITIM phosphorylation of CD22 and CD32B have not been properly evaluated. The present study therefore employed both immunoprecipitation and flow cytometry approaches to elucidate the effects of epratuzumab on direct phosphorylation of key tyrosine (Tyr) residues on both these proteins, using both transformed B cell lines and primary human B cells. Epratuzumab induced the phosphorylation of Tyr(822) on CD22 and enhanced its co-localisation with SHP-1. Additionally, in spite of high basal phosphorylation of other key ITIMs on CD22, in primary human B cells epratuzumab also enhanced phosphorylation of Tyr(807), a residue involved in the recruitment of Grb2. Such initiation events could explain the effects of epratuzumab on downstream signalling in B cells. Finally, we were able to demonstrate that epratuzumab stimulated the phosphorylation of Tyr(292) on the low affinity inhibitory Fc receptor CD32B which would further attenuate BCR-induced signalling. Together, these data demonstrate that engagement of CD22 with epratuzumab leads to the direct phosphorylation of key upstream inhibitory receptors of BCR signalling and may help to explain how this antibody modulates B cell function.

BAFF overexpression is associated with autoantibody production in autoimmune diseases.

The B-cell activity factor (BAFF) acts as a positive regulator of B-cell function. To gain further insight into the understanding of B-cell hyperactivity in autoimmune diseases, the serum level of BAFF was determined in 43 systemic lupus erythematosus (SLE) patients, 58 primary Sjögren's syndrome (pSS) patients, 28 rheumatoid arthritis (RA) patients, and 68 normal control subjects using an in-house sandwich ELISA. A commercial kit was used to detect soluble CD23 (sCD23) reflecting B-cell activation. In-house assays for the detection of autoantibodies also were used. We found an increased level of BAFF in SLE, pSS, and RA sera compared with normal subjects (respectively, 10.6 +/- 8.5, 15.8 +/- 12.9, 9.7 +/- 1.5 ng/mL vs. 4.6 +/- 2.9 ng/mL, P < .001). sCD23 released on B-cell activation also was found to be elevated in SLE, pSS, and RA compared with normal sera. However, no correlation was found between the circulating BAFF and the level of sCD23. By contrast, we observed that high levels of BAFF were associated with the presence of autoantibodies (anti-double-stranded DNA antibodies in SLE, anti-SSA antibodies in pSS, and rheumatoid factors in RA). Our data suggest that BAFF is influential in driving antibody production rather than activation of the B lymphocytes in autoimmune diseases.

Epratuzumab inhibits the production of the proinflammatory cytokines IL-6 and TNF-α, but not the regulatory cytokine IL-10, by B cells from healthy donors and SLE patients.

INTRODUCTION: Cytokines produced by B cells are believed to play important roles in autoimmune diseases. CD22 targeting by epratuzumab has been demonstrated to inhibit phosphorylation of B cell receptor (BCR) downstream signaling in B cells. It has been shown that other sialoadhesin molecules related to CD22 have immunoregulatory functions; therefore, in the present study, we addressed the role of epratuzumab on the production of key cytokines by B cells of patients with systemic lupus erythematosus (SLE) and of healthy donors (HD). METHODS: Peripheral blood B cells were purified and activated by BCR with or without Toll-like receptor 9 (TLR9) stimulation in the presence or absence of epratuzumab. Cytokine production by B cells (interleukin [IL]-6, tumor necrosis factor [TNF]-α and IL-10) in the supernatant and the induction of IL-10(+) B cells from patients with SLE and HD were analyzed. RESULTS: The secretion of the proinflammatory cytokines TNF-α and IL-6 by anti-BCR and BCR- and/or TLR9-activated B cells from HD and patients with SLE was inhibited by epratuzumab. In contrast, the production of IL-10 by B cells was not affected by epratuzumab under either stimulation condition. Consistently, the induction of IL-10-producing B cells in culture was not affected by epratuzumab. CONCLUSIONS: Epratuzumab, by targeting CD22, was able to inhibit the production of the proinflammatory cytokines IL-6 and TNF-α by B cells, in contrast to IL-10, in vitro. These data suggest that targeting CD22 alters the balance between proinflammatory cytokines (TNF-α, IL-6) and the regulatory cytokine IL-10 as another B cell effector mechanism.

Increased frequency of a unique spleen tyrosine kinase bright memory B cell population in systemic lupus erythematosus.

OBJECTIVE: Systemic lupus erythematosus (SLE) is characterized by B cell hyperactivity and autoantibody production. As spleen tyrosine kinase (Syk) is pivotal in B cell activation, these experiments aimed to examine the extent to which Syk was abnormally expressed in SLE B cells and the nature of the B cell subset that differently expressed Syk. METHODS: B cells from healthy donors and SLE patients were analyzed by flow cytometry to assess basal expression of Syk and phosphorylated Syk. B cell subsets expressing higher levels of Syk were found, and their detailed phenotype, in vitro differentiation into plasmablasts/plasma cells, and Syk induction by cytokines were determined. RESULTS: Syk expression was higher in CD27+ memory B cells than in naive B cells from SLE patients. However, a significantly increased frequency of CD27- B cells with bright expression of Syk (Syk++) was found in SLE patients. CD27-Syk++ B cells showed enhanced basal expression of p-Syk and stronger Syk phosphorylation upon B cell receptor (BCR) engagement as compared to CD27-Syk+ B cells. CD27-Syk++ B cells were CD38- as well as CD19++, CD20++, and mainly CD21-, with decreased ABCB1 transporter activity. In contrast to CD27-Syk+ B cells, CD27-Syk++ B cells exhibited enhanced differentiation into CD27++ IgG-secreting cells and expressed somatically mutated BCR gene rearrangements. Syk++ B cells were inducible in vitro by stimulation with interferon-γ, lipopolysaccharide, or tumor necrosis factor α. CONCLUSION: SLE patients exhibit an increased frequency of hitherto unknown CD27-Syk++ memory-like B cells, indicating that intracellular Syk density could distinguish CD27- memory B cells from truly naive B cell subsets. Furthermore, the CD27-Syk++ subset is a candidate for a source of increased plasma cells in SLE.

Active systemic lupus erythematosus is associated with a reduced cytokine production by B cells in response to TLR9 stimulation.

INTRODUCTION: Systemic lupus erythematosus (SLE) is an autoimmune disease associated with a break in self-tolerance reflected by a production of antinuclear autoantibodies. Since autoantibody production can be activated via nucleic acid Toll-like receptor 9 (TLR9), the respective pathway has been implicated in the development of SLE and pathogenic B cell responses. However, the response of B cells from SLE patients to TLR9 stimulation remains incompletely characterized. METHODS: In the current study, the response of B cells from SLE patients and healthy donors upon TLR9 stimulation was analyzed in terms of proliferation and cytokine production and correlated with the lupus disease activity and anti-dsDNA titers. RESULTS: B cells from SLE patients showed a reduced response to TLR9 agonist compared to B cells from healthy donors in terms of proliferation and activation. B cells from SLE patients with higher disease activity produced less interleukin (IL)-6, IL-10, vascular endothelial growth factor, and IL-1ra than B cells from healthy donors. Further analyses revealed an inverse correlation of cytokines produced by TLR9-stimulated B cells with lupus disease activity and anti-dsDNA titer, respectively. CONCLUSION: The capacity of B cells from lupus patients to produce cytokines upon TLR9 engagement becomes less efficient with increasing disease activity, suggesting that they either enter an exhausted state or become tolerant to TLR stimulation for cytokine production when disease worsens.

The anti-CD74 humanized monoclonal antibody, milatuzumab, which targets the invariant chain of MHC II complexes, alters B-cell proliferation, migration, and adhesion molecule expression.

INTRODUCTION: Targeting CD74 as the invariant chain of major histocompatibility complexes (MHC) became possible by the availability of a specific humanized monoclonal antibody, milatuzumab, which is under investigation in patients with hematological neoplasms. CD74 has been reported to regulate chemo-attractant migration of macrophages and dendritic cells, while the role of CD74 on peripheral naïve and memory B cells also expressing CD74 remains unknown. Therefore, the current study addressed the influence of milatuzumab on B-cell proliferation, chemo-attractant migration, and adhesion molecule expression. METHODS: Surface expression of CD74 on CD27- naïve and CD27+ memory B cells as well as other peripheral blood mononuclear cells (PBMCs) obtained from normals, including the co-expression of CD44, CXCR4, and the adhesion molecules CD62L, ß7-integrin, ß1-integrin and CD9 were studied after binding of milatuzumab using multicolor flow cytometry. The influence of the antibody on B-cell proliferation and migration was analyzed in vitro in detail. RESULTS: In addition to monocytes, milatuzumab also specifically bound to human peripheral B cells, with a higher intensity on CD27+ memory versus CD27- naïve B cells. The antibody reduced B-cell proliferation significantly but moderately, induced enhanced spontaneous and CXCL12-dependent migration together with changes in the expression of adhesion molecules, CD44, ß7-integrin and CD62L, mainly of CD27- naïve B cells. This was independent of macrophage migration-inhibitory factor as a ligand of CD74/CD44 complexes. CONCLUSIONS: Milatuzumab leads to modestly reduced proliferation, alterations in migration, and adhesion molecule expression preferentially of CD27- naïve B cells. It thus may be a candidate antibody for the autoimmune disease therapy by modifying B cell functions.

What do we know about memory B cells in primary Sjögren's syndrome?

Abnormalities of memory B cells seem to be closely involved in the pathogenesis of primary Sjögrens Syndrome (pSS) and its malignant complication, B cell lymphoma. Recent studies on B cells in pSS add to our understanding of the distinct memory B cell subsets in pSS. Reduction of peripheral memory CD27(+) B cells, most strikingly of the CD27(+)IgM(+) subset, may indicate a lack of appropriate censoring mechanisms and incomplete differentiation processes within the ectopic lymphoid tissues in pSS. This ectopically formed lymphoid tissue might protect autoreactive memory B cells from deletion by physiological check-points and, thereby, may contribute to the perpetuation of the disease as well as to an enhanced lymphoma risk. Thus, B cells may be potential targets of direct or indirect treatment in pSS.

Autoreactive B cells and epigenetics.

Autoreactive B cells are central in the pathogenesis of autoimmune diseases (AID) not only by producing autoantibodies but also by secreting cytokines and by presenting autoantigens. Changes in DNA methylation, histone modifications, and miRNA expression, the hallmarks of epigenetic failure, characterize B cells isolated from patients with AID, highlighting the contribution of epigenetic processes to autoreactivity. Additional evidence of epigenetic involvement in the development of B cell autoreactivity comes from in vivo and in vitro studies using DNA demethylating agents as accelerating factors or histone deacetylase inhibitors as repressing factors. As a result, a better understanding of the altered epigenetic processes in AID and in particular in B cells opens perspectives for the development of new therapeutics.

Epratuzumab targeting of CD22 affects adhesion molecule expression and migration of B-cells in systemic lupus erythematosus.

INTRODUCTION: Epratuzumab, a humanized anti-CD22 monoclonal antibody, is under investigation as a therapeutic antibody in non-Hodgkin's lymphoma and systemic lupus erythematosus (SLE), but its mechanism of action on B-cells remains elusive. Treatment of SLE patients with epratuzumab leads to a reduction of circulating CD27(negative) B-cells, although epratuzumab is weakly cytotoxic to B-cells in vitro. Therefore, potential effects of epratuzumab on adhesion molecule expression and the migration of B-cells have been evaluated. METHODS: Epratuzumab binding specificity and the surface expression of adhesion molecules (CD62L, ß7 integrin and ß1 integrin) after culture with epratuzumab was studied on B-cell subsets of SLE patients by flow cytometry. In addition, in vitro transwell migration assays were performed to analyze the effects of epratuzumab on migration towards different chemokines such as CXCL12, CXCL13 or to CXCR3 ligands, and to assess the functional consequences of altered adhesion molecule expression. RESULTS: Epratuzumab binding was considerably higher on B-cells relative to other cell types assessed. No binding of epratuzumab was observed on T-cells, while weak non-specific binding of epratuzumab on monocytes was noted. On B-cells, binding of epratuzumab was particularly enhanced on CD27(negative) B-cells compared to CD27(positive) B-cells, primarily related to a higher expression of CD22 on CD27(negative) B-cells. Moreover, epratuzumab binding led to a decrease in the cell surface expression of CD62L and ß7 integrin, while the expression of ß1 integrin was enhanced. The effects on the pattern of adhesion molecule expression observed with epratuzumab were principally confined to a fraction of the CD27(negative) B-cell subpopulation and were associated with enhanced spontaneous migration of B-cells. Furthermore, epratuzumab also enhanced the migration of CD27(negative) B-cells towards the chemokine CXCL12. CONCLUSIONS: The current data suggest that epratuzumab has effects on the expression of the adhesion molecules CD62L, ß7 integrin and ß1 integrin as well as on migration towards CXCL12, primarily of CD27(negative) B-cells. Therefore, induced changes in migration appear to be part of the mechanism of action of epratuzumab and are consistent with the observation that CD27(negative) B-cells were found to be preferentially reduced in the peripheral blood under treatment.