APRIL and BAFF connect autoimmunity and cancer

Past and present discovery of the BAFF/APRIL system - A bibliometric study from 1999 to 2023

Cytokines from the Tumour Necrosis Factor (TNF) family are important regulators of both physiological and pathological processes. The discovery of novel TNF ligands and receptors, BAFF and APRIL, have opened up new possibilities for scientists to explore the effect of these cytokines on the human immune system. The role of BAFF/APRIL system in B lymphocytes is particularly important for survival and maintenance of homeostasis. Aberrant expression of the system is associated with various immunological disorders. Hence, this study provides a comprehensive overview of the past and present BAFF/APRIL system research development in a bibliometric perspective. To our best knowledge, this is the first ever bibliometric analysis conducted focusing on the BAFF/APRIL system. A total of 1055 relevant documents were retrieved from WoSCC. Microsoft Excel, VOSviewer, and Biblioshiny of R studio were bibliometric tools used to analyse the scientific literature. From 1999, the annual publications showed an upward trend, with Journal of Immunology being the most productive journal. USA leads the race for BAFF/APRIL system research developments. Pascal Schneider, a senior researcher affiliated with University of Lausanne, Switzerland was recognised as the most productive author and institution in the BAFF/APRIL system research field. The research focus transitioned from focusing on the role of the system in B cell biology, to immunological disorders and finally to development of BAFF/APRIL targeting drugs. Despite several studies elucidating briefly the pathway mechanism of BAFF/APRIL system in B-cell selection, substantial research on the mechanism of action in disease models and T cell activation and development of immunomodulating drugs from natural origins remains largely unexplored. Therefore, future research focusing on these areas are crucial for the deeper understanding of the system in disease manifestations and progression allowing a better treatment management for various immunological disorders.

APRIL and BAFF play a key role in differentiating vitreoretinal lymphoma from uveitis

BACKGROUND

Early diagnosis of vitreoretinal lymphoma (VRL) is critical for the successful treatment of this rare intraocular malignancy. However, fast and reliable diagnosis of VRL in patients presenting with intermediate or posterior non-infectious uveitis remains a challenge. A proliferation-inducing ligand (APRIL) and B-cell activating factor (BAFF) are vital factors in the pathophysiology, diagnosis, and prognosis of primary central nervous system lymphoma (PCNSL) and systemic autoimmune diseases. However, their utility as biomarkers for the diagnosis of VRL and uveitis remains unclear.

METHODS

In this retrospective study, we analyzed APRIL and BAFF levels in the aqueous humor (AH) of 43 eyes of 40 patients, including 23 eyes of 20 patients with VRL, eight eyes of eight patients with uveitis, and 12 eyes of 12 patients with other ocular diseases (OODs). Additionally, we measured their levels after induction of chemotherapy in five eyes of five patients with VRL.

RESULTS

AH levels of APRIL reliably distinguished VRL from uveitis, with a specificity of 78.3% and sensitivity of 75%. BAFF also showed similar potential. Serial AH analysis of patients with VRL during chemotherapy demonstrated a corresponding decline in AH levels of APRIL and BAFF.

CONCLUSION

This study extends the spectrum of valuable diagnostic biomarkers for VRL and uveitis. In patients with uveitis, the assessment of AH APRIL may help accelerate the diagnosis of VRL. Moreover, our results underline the important role of APRIL and BAFF in therapeutic monitoring of VRL.

A Proliferation-Inducing Ligand and B-Cell Activating Factor Are Upregulated in Patients with Essential Thrombocythemia

A proliferation-inducing ligand (APRIL) and B-cell activating factor (BAFF) are cytokines belonging to the tumor necrosis factor family which play an essential role in B-cell maturation, differentiation, and survival. Recent evidence indicates their importance in hematological disorders; however, their function in essential thrombocytosis (ET) pathogenesis remains elusive. Therefore, we aimed to analyze the role of APRIL and BAFF in megakaryocytopoiesis in ET patients. We observed elevated levels of APRIL and BAFF in the plasma of ET patients compared with healthy controls, while no differences were found among patients with different JAK2(V617F) statuses. In addition, APRIL levels were positively associated with the number of platelets and WBC count. In the bone marrow, APRIL but not BAFF levels were higher in ET patients with the JAK2(V617F) mutation; however, JAK2(V617F)-negative patients showed slightly reduced levels of BAFF. In ET patients, we showed that the differentiation of CD34+ progenitor cells towards megakaryocytes induces the expression of both APRIL and BAFF. More importantly, APRIL neutralization significantly reduced platelet production. In conclusion, our data provide evidence that blocking APRIL signaling, which acts as an autocrine growth factor for terminal megakaryocytopoiesis, inhibits platelet production in ET patients, regardless of the status of JAK2(V617F) mutation.

The TNFSF Members APRIL and BAFF and Their Receptors TACI, BCMA, and BAFFR in Oncology, With a Special Focus in Breast Cancer

Tumor necrosis factor (TNF) superfamily consists of 19 ligands and 29 receptors and is related to multiple cellular events from proliferation and differentiation to apoptosis and tumor reduction. In this review, we overview the whole system, and we focus on A proliferation-inducing ligand (APRIL, TNFSF13) and B cell-activating factor (BAFF, TNFSF13B) and their receptors transmembrane activator and Ca²⁺ modulator (CAML) interactor (TACI, TNFRSF13B), B cell maturation antigen (BCMA, TNFRSF17), and BAFF receptor (BAFFR, TNFRSF13C). We explore their role in cancer and novel biological therapies introduced for multiple myeloma and further focus on breast cancer, in which the modulation of this system seems to be of potential interest, as a novel therapeutic target. Finally, we discuss some precautions which should be taken into consideration, while targeting the APRIL–BAFF system.

Myeloid loss of Beclin 1 promotes PD-L1hi precursor B cell lymphoma development

Beclin 1 (Becn1) is a key molecule in the autophagy pathway and has been implicated in cancer development. Due to the embryonic lethality of homozygous Becn1-deficient mice, the precise mechanisms and cell type-specific roles of Becn1 in regulating inflammation and cancer immunity remain elusive. Here, we report that myeloid-deficient Becn1 (Becn1ΔM) mice developed neutrophilia, were hypersusceptible to LPS-induced septic shock, and had a high risk of developing spontaneous precursor B cell (pre-B cell) lymphoma with elevated expression of immunosuppressive molecules programmed death ligand 1 (PD-L1) and IL-10. Becn1 deficiency resulted in the stabilization of MEKK3 and aberrant p38 activation in neutrophils, and mediated neutrophil-B cell interaction through Cxcl9/Cxcr3 chemotaxis. Neutrophil-B cell interplay further led to the activation of IL-21/STAT3/IRF1 and CD40L/ERK signaling and PD-L1 expression; therefore, it suppressed CD8+ T cell function. Ablation of p38 in Becn1ΔM mice prevented neutrophil inflammation and B cell tumorigenesis. Importantly, the low expression of Becn1 in human neutrophils was significantly correlated with the PD-L1 levels in pre-B acute lymphoblastic lymphoma (ALL) patients. Our findings have identified myeloid Becn1 as a key regulator of cancer immunity and therapeutic target for pre-B cell lymphomas.

Autoimmunity and Cancer, the Paradox Comorbidities Challenging Therapy in the Context of Preexisting Autoimmunity

Today, improvements in diagnostic and therapeutic options allow patients with autoimmune diseases (ADs) to live longer and have more active lives compared with patients receiving conventional anti-inflammatory therapy just two decades ago. Current therapies for ADs aim to inhibit immune cell activation and effector immune pathways, including those activated by cytokines and cytokine receptors. Understandably, such goals become more complicated in patients with long-term established ADs who develop parallel chronic or comorbid conditions, including life-threatening diseases, such as cancer. Compared with the general population, patients with ADs have an increased risk of developing hematological, lymphoproliferative disorders, and solid tumors. However, the aim of current cancer therapies is to activate the immune system to create autoimmune-like conditions and eliminate tumors. As such, their comorbid presentation creates a paradox on how malignancies must be addressed therapeutically in the context of autoimmunity. Because the physiopathology of malignancies is less understood in the context of autoimmunity than it is in the general population, we undertook this review to highlight the peculiarities and mechanisms governing immune cells in established ADs. Moreover, we examined the role of the autoimmune cytokine milieu in the development of immune-related adverse events during the implementation of conventional or immune-based therapy.

Differential Roles of Tumor Necrosis Factor Ligand Superfamily Members as Biomarkers in Pancreatic Cancer

The tumor necrosis factor⁻related weak inducer of apoptosis (TWEAK) belongs to the tumor necrosis factor ligand superfamily, which was shown to play an important role in inflammatory and malignant gastrointestinal diseases, including colitis or colorectal cancer. However, in contrast to other members of the TNF ligand superfamily, its role as a biomarker in pancreatic cancer is currently unknown. We analyzed serum levels of A proliferation-inducing ligand (APRIL) and TWEAK in 134 patients with pancreatic cancer. Results were compared with 50 healthy controls and correlated with clinical data. Intratumoral expression of APRIL and TWEAK in pancreatic cancer was analysed using the datasets made available by the TCGA-LIHC project. APRIL serum levels were significantly elevated in patients with pancreatic cancer compared to healthy controls, which is in line with previous findings. Notably, the diagnostic accuracy of circulating APRIL levels was similar to CA19-9, an established tumor marker for pancreatic cancer. In contrast, serum concentrations of TWEAK were decreased in pancreatic cancer patients. Interestingly, no differences in TWEAK concentrations became apparent between different clinical subgroups of pancreatic cancer. Moreover, within our cohort of patients, TWEAK levels did not correlate with the patients' prognosis and the diagnostic as well as prognostic potential of TWEAK was lower than CA 19-9, when analyzed in this setting. Finally, using data from the TCGA-LIHC project, we demonstrate that expression levels of TWEAK and APRIL represent prognostic markers for patients' survival according to Kaplan-Meier curve analyses. TWEAK and APRIL serum concentrations are regulated differently in patients with pancreatic cancer, highlighting diverse roles of variant TNF ligands in this type of cancer.

The role of the BAFF/APRIL system in the T cell-independent specific response to blood stage Plasmodium falciparum hemozoin

BACKGROUND

The B cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL) are tumor necrosis factor family members that regulate B cell maturation, proliferation, survival and function. We have previously shown that blood-stage Plasmodium falciparum hemozoin (HZ) can act as a T-independent antigen (TI Ag) that induces the production of specific IgG to soluble crude P. falciparum Ag through the BAFF pathway. However, we have not yet clarified whether HZ need APRIL signaling in the TI response. Here, we aimed to clarify whether both BAFF and APRIL signaling pathways play roles in HZ induction of specific antibody production without T-cell help.

METHODS

Normal monocytes alone or co-cultured with naïve B cells were stimulated by HZ (10 µM) in vitro. Naïve B cell cultures, with HZ alone or with exogenous recombinant BAFF (rBAFF) and recombinant APRIL (rAPRIL) plus recombinant IL-4 (rIL-4) for 6 and 10 days were used as controls to investigate activation of B cells. At various times, the levels of sBAFF, sAPRIL, and HZ-specific IgG in the culture supernatants were assessed by enzyme-linked immunosorbent assay. The BAFF and APRIL expression levels on the HZ-stimulated monocytes and their specific receptors on activated B cells, including the BAFF receptor (BAFF-R), the transmembrane activator and calcium-modulator and cyclophilin ligand interactor (TACI) and the B cell maturation antigen (BCMA), were determined by flow cytometry. mRNA expression levels for the receptors were validated using Real-Time quantitative PCR.

RESULTS

HZ-activated monocytes released sBAFF and sAPRIL during the 72 h stimulation period. Increased mRNA encoding of their cognate receptors, BAFF-R, TACI, and BCMA, and increased HZ-specific IgG levels were also observed in HZ induction within the monocyte and B cell co-culture. The experiments under control conditions revealed that HZ alone could induce B cell culture to produce a small amount of the specific IgG compared with those in medium alone or rBAFF + rAPRIL + rIL-4.

CONCLUSION

Taken together, we suggest that in the TI response HZ stimulates monocyte and B cell co-culture to produce specific IgG through BAFF, APRIL and other independent complimentary signaling pathways.

Synergisic effect of APRIL knockdown and Jiedu Xiaozheng Yin, a Chinese medicinal recipe, on the inhibition of hepatocellular carcinoma cell proliferation

It is well documented that A proliferation-inducing ligand (APRIL), a member of the tumor necrosis factor superfamily, plays a crucial role in the occurrence and development of tumors. In the present study, we evaluated the synergistic effect of APRIL knockdown and Jiedu Xiaozheng Yin (JXY), a Traditional Chinese Medicinal recipe, on the inhibition of hepatocellular carcinoma (HCC) cell proliferation and elucidated the underlying mechanism. The results demonstrated that both APRIL knockdown using small interfering RNA (siRNA) and JXY treatment could trigger cell cycle arrest and cell apoptosis, and suppress HCC cell proliferation through an NF-κB-related pathway. Synergism was further demonstrated between APRIL knockdown and JXY treatment. In conclusion, these results indicate that APRIL is a target gene for HCC and combination of siRNA-APRIL and JXY application holds great promise as a novel approach for the treatment of APRIL-positive HCC.

Expression and purification of soluble human APRIL in Escherichia coli using ELP-SUMO tag

APRIL is a member of the tumor necrosis factor (TNF) family of ligands that mediate tumor cells proliferation as well as survival, depending on the cellular context. In this report, we present a novel method to obtain soluble human APRIL in Escherichia coli using the elastin-like polypeptide and SUMO (ELP-SUMO) tags. The fusion protein with ELP-SUMO tag was expressed in a soluble form at 15°C. After purification based on inverse transition cycling (ITC) method, the purified ELP-SUMO-hAPRIL fusion protein was subsequently cleaved by SUMO protease to release mature hAPRIL. Following affinity chromatography, the target protein was re-purified with high purity. Finally, about 4.8mg recombinant hAPRIL was obtained from 1l bacterial culture with no less than 85% purity. The molecular mass (Mr) of the recombinant hAPRIL was confirmed by MALDI-TOF MS as Mr 16,314. The purified hAPRIL exhibits biological activity on Jurkat cells. It is the first report on soluble production of hAPRIL in E. coli using ELP-SUMO tag.

Anticancer Activities and Mechanisms of Blumea balsamifera Extract in Hepatocellular Carcinoma Cells

Blumea balsamifera (also known as sambong), a medicinal plant, is known to improve physiological disorders such as rheumatism and hypertension. However, its anticancer activity has not been well elucidated. In this study, we found that Blumea balsamifera MeOH extract (BME) induced growth inhibitory activity in rat and human hepatocellular carcinoma cells (McA-RH7777, HepG2, respectively) without cytotoxicity as in with rat hepatocytes used as a normal cell model. BME induced cell cycle arrest at G1 phase via decreases in expression of cyclin-E and phosphorylation of retinoblastoma (Rb) protein in both dose- and time-dependent manners. Furthermore, BME reduced the level of a proliferation related ligand (APRIL) which stimulates tumor cell growth. The anti-proliferative effect of BME was improved slightly but significantly by the treatment with recombinant human APRIL. These findings suggest that BME may have a possible therapeutic potential in hepatoma cancer patients and the depletion of cellular APRIL may be one of the important mechanisms on the growth inhibitory effect of BME.

Loss of PKCδ results in characteristics of Sjögren's syndrome including salivary gland dysfunction

OBJECTIVES

Chronic infiltration of lymphocytes into the salivary and lacrimal glands of patients with Sjögren's syndrome (SS) leads to destruction of acinar cells and loss of exocrine function. Protein kinase C-delta (PKCδ) is known to play a critical role in B-cell maintenance. Mice in which the PKCδ gene has been disrupted have a loss of B-cell tolerance, multiple organ lymphocytic infiltration, and altered apoptosis. To determine whether PKCδ contributes to the pathogenesis of SS, we quantified changes in indicators of SS in PKCδ-/- mice as a function of age. Salivary gland histology, function, the presence of autoantibodies, and cytokine expression were examined.

MATERIALS AND METHODS

Submandibular glands were examined for the presence of lymphocytic infiltrates, and the type of infiltrating lymphocyte and cytokine deposition was evaluated by immunohistochemistry. Serum samples were tested by autoantibody screening, which was graded by its staining pattern and intensity. Salivary gland function was determined by saliva collection at various ages.

RESULTS

PKCδ-/- mice have reduced salivary gland function, B220+ B-cell infiltration, anti-nuclear antibody production, and elevated IFN-γ in the salivary glands as compared to PKCδ+/+ littermates.

CONCLUSIONS

PKCδ-/- mice have exocrine gland tissue damage indicative of a SS-like phenotype.

KR33426, [2-(2,5-dichlorophenyl)-5-methyloxazol-4yl]carbonylguanidine, is a novel compound to be effective on mouse systemic lupus erythematosus

B cell-activating factor (BAFF) is a key regulator of B lymphocyte development. Signals from BAFF are transmitted through binding to a specific BAFF receptor (BAFF-R). Here, we established screening method to find a specific inhibitor for the interference of BAFF-BAFF-R interactions. We screened oxazole-4-carbonylguanidine derivatives and selected KR33426, [2-(2,5-dichlorophenyl)-5-methyloxazol-4yl]carbonylguanidine, as a candidate to interfere BAFF-BAFF-R interactions. KR33426 inhibited BAFF-mediated anti-apoptotic effect on splenocytes as judged by hypodiploid cell formation. KR33426 also increased the degradation of procaspase-3 that was inhibited by BAFF protein. In addition, we examined whether KR33426 was effective on the treatment of systemic lupus erythematosus-like symptom in MRL(lpr/lpr) mouse. When 5 or 10mg/kg KR33426 was intraperitoneally administered to MRL(lpr/lpr) mice for 4 weeks, histopathological changes were ameliorated in the narrowed space between renal glomerulus and glomerulus capsule. KR33426 reduced B220(+) B cell population and B cell mitogen, lipopolysaccharide-stimulated lymphocyte proliferation in splenocytes. KR33426 attenuated an increase in CD43(-)IgM(+) immature pro-B and a decrease in CD21(+) IgM(+) T2-B and IgD(+) IgM(-)recirculating-B cells on B cell development. Data show that KR33426 inhibits BAFF-BAFF-R interactions and it is effective on the treatment of systemic lupus erythematosus-like symptom in MRL(lpr/lpr) mice. Thus, it suggests that KR33426 is a novel candidate to develop anti-autoimmune therapeutics by the interference of BAFF-BAFF-R interactions, specifically.

An increase in B cell apoptosis by interfering BAFF-BAFF-R interaction with small synthetic molecules

B cell-activating factor (BAFF) transmitted signals through binding to specific BAFF receptors (BAFF-R) to regulate B cell survival and development. We used MTT assay to examine the cytotoxicity of chemicals, flow cytometry analysis to measure BAFF-BAFF-R interactions, and western blotting to detect BAFF protein. Here, we established screening method to find specific compounds to interfere with BAFF-BAFF-R interactions in WIL2-NS B lymphoblast cells. According to screening (imidazol-4-ylcarbonyl)guanidine or (oxazol-4-ylcarbonyl)guanidine derivatives, we selected KR32592, KR32673, KR33232, KR33341 and KR33426 as candidates to interfere with BAFF-BAFF-R interaction. No cytotoxicity was detected by KR32592, KR33232, and KR33426 at the concentration of 5 μM, and by KR32673, and KR33341 at the concentration of 0.5 μM. Cell population with BAFF-BAFF-R interactions was reduced by the pre-incubation of chemicals with human BAFF-murine CD8 (BAFF-muCD8). Cell population with BAFF-BAFF-R interactions was also decreased by pre-exposure of WIL2-NS cells to chemicals prior to the incubation with BAFF-muCD8. Chemicals also inhibited LPS-stimulated BAFF production from splenocytes. All these effects of chemicals may contribute to the inhibition of BAFF-mediated anti-apoptosis. These data demonstrate that chemicals interfering with BAFF-BAFF-R interaction may be screened with our experimental condition. It suggests that BAFF-BAFF-R interaction could be a chemical target to develop therapeutics for BAFF-mediated autoimmune diseases.

A proliferation-inducing ligand: a new biomarker for non-small cell lung cancer

To identify a proliferation-inducing ligand (APRIL) expression profile in tumor tissue and sputum of lung cancer, and evaluate the possibility of an assistant diagnosis of lung cancer by real-time fluorescence quantitative polymerase chain reaction (RTQ-PCR) in sputum as well, the authors analyzed the expression of APRIL mRNA in 75 tissue samples and 71 corresponding sputum samples of lung cancer by RTQ-PCR and analyzed their correlation. APRIL protein expression was also observed in tumor tissues by Western blot and immunohistochemistry. The expression analysis revealed APRIL expression was elevated in non-small cell lung cancer (NSCLC) and the expression of APRIL protein was located in the membrane and cytoplasm of tumor cells by immunohistochemiscal staining. Compared to benign pulmonary disease and healthy volunteers, the expression of APRIL mRNA in sputum of lung cancer was elevated (both P <. 001). When cut-off values for positivity were set at the mean + 2SD of mRNA expression in healthy volunteers, the positive rate for APRIL mRNA expression was 81.7% (58/71) in sputum samples of lung cancer, 3.2% (2/62) in benign pulmonary disease, and 1.5% (1/65) in healthy volunteers. The correlation was evident between the expression level of APRIL mRNA of tissue samples and that of sputum samples (P <. 001, r =. 702). These results support the possibility that the APRIL gene may play a key role in lung cancer, especially in NSCLC. The elevated expression level of APRIL mRNA in sputum of NSCLC suggested that APRIL mRNA may serve as an effective and convenient diagnostic biomarker for NSCLC.

Combination of Zizyphus jujuba and green tea extracts exerts excellent cytotoxic activity in HepG2 cells via reducing the expression of APRIL

Hepatocellular carcinoma is a type of tumor highly resistant to available chemotherapeutic agents. The treatment of hepatocellular carcinoma remains a challenge that needs new approaches in the future. In a previous study, we demonstrated that the chloroform fraction (CHCl(3)-F) from Z. jujuba has anticancer activity in human liver cancer cells (HepG2), and that combining CHCl(3)-F with green tea extracts (GTE) results in enhanced effects of anticancer activity in the cells. To further understand the mechanism of the anticancer activity of combining CHCl(3)-F and GTE in HepG2 cells, we investigated whether the addition of a mixture of CHCl(3)-F and GTE would affect the expression of APRIL (a proliferation-inducing ligand), which was expressed in HepG2 cells from 4 hours of incubation in vitro. We have shown that CHCl(3)-F and GTE enhanced anti-cancer activity by reducing the expression of APRIL. We speculate that the CHCl(3)-F and GTE mixture might provide a lead to a new drug design to treat hepatocellular carcinoma in the future.

The BLyS family: toward a molecular understanding of B cell homeostasis

The B Lymphocyte Stimulator (BLyS) family of ligands and receptors regulates humoral immunity by controlling B lymphocyte survival and differentiation. Herein, we review the ligands and receptors of this family, their biological functions, and the biochemical processes through which they operate. Pre-immune B lymphocytes rely on BLyS signaling for their survival, whereas antigen experienced B lymphocytes generally interact more avidly with a homologous cytokine, A Proliferation Inducing Ligand (APRIL). The molecular basis for signaling via the three BLyS family receptors reveals complex interplay with other B lymphocyte signaling systems, affording the integration of selective and homeostatic processes. As our understanding of this system advances, molecular targets for manipulating humoral immunity in both health and disease should be revealed.

Mechanism of growth inhibitory effect of Blumea balsamifera extract in hepatocellular carcinoma

Blumea balsamifera is known to improve physiological disorders such as rheumatism and hypertension, but its anticancer activity has not been well elucidated. In this study, we found that Blumea balsamifera MeOH extract (BME) induced growth-inhibitory activity in rat and human hepatocellular carcinoma cells without cytotoxicity in rat hepatocytes which were used as a normal cell model. BME induced cell cycle arrest at the G1 phase via decreases in the expression of cyclin-E and phosphorylation of retinoblastoma protein. Furthermore, BME reduced the level of a proliferation-inducing ligand, that stimulates tumor cell growth. These findings suggest that BME has possible therapeutic potential in hepatoma cancer patients and that depletion of cellular APRIL is an important mechanism in the growth-inhibitory effect of BME.

Expression of TNF-superfamily members BAFF and APRIL in breast cancer: immunohistochemical study in 52 invasive ductal breast carcinomas

BACKGROUND

Recent studies suggest an association between chronic inflammation, modulating the tissue microenvironment, and tumor biology. Tumor environment consists of tumor, stromal and endothelial cells and infiltrating macrophages, T lymphocytes, and dendritic cells, producing an array of cytokines, chemokines and growth factors, accounting for a complex cell interaction and regulation of differentiation, activation, function and survival of tumor and surrounding cells, responsible for tumor progression and spreading or induction of antitumor immune responses and rejection. Tumor Necrosis Factor (TNF) family members (19 ligands and 29 receptors) represent a pleiotropic family of agents, related to a plethora of cellular events from proliferation and differentiation to apoptosis and tumor reduction. Among these members, BAFF and APRIL (CD257 and CD256 respectively) gained an increased interest, in view of their role in cell protection, differentiation and growth, in a number of lymphocyte, epithelial and mesenchymal structures.

METHODS

We have assayed by immunohistochemistry 52 human breast cancer biopsies for the expression of BAFF and APRIL and correlated our findings with clinicopathological data and the evolution of the disease.

RESULTS

BAFF was ubiquitely expressed in breast carcinoma cells, DCIS, normal-appearing glands and ducts and peritumoral adipocytes. In contrast, APRIL immunoreactive expression was higher in non-malignant as compared to malignant breast structures. APRIL but not BAFF immunoreactivity was higher in N+ tumors, and was inversely related with the grade of the tumors. Neither parameter was related to DFS or the OS of patients.

CONCLUSION

Our data show, for the first time, an autocrine secretion of BAFF and APRIL from breast cancer cells, offering new perspectives for their role in neoplastic and normal breast cell biology and offering new perspectives for possible selective intervention in breast cancer.

Act1 modulates autoimmunity through its dual functions in CD40L/BAFF and IL-17 signaling

Coordinated regulation of T and B cell-mediated immune responses plays a critical role in the control and modulation of autoimmune diseases. This review is focused on the adapter molecule Act1 and its regulation of autoimmunity through its impact on both T and B cell-mediated immune responses. Whereas Act1 molecule is an important negative regulator for B cell-mediated humoral immune responses through its function in CD40L and BAFF signaling, recent studies have shown that Act1 is also a key positive signaling component for IL-17 signaling pathway, critical for T(H)17-mediated autoimmune and inflammatory responses. The dual functions of Act1 are evident in Act1-deficient mice that displayed B cell-mediated autoimmune phenotypes (including dramatic increase in peripheral B cells, lymphadenopathy and splenomegaly, hypergammaglobulinemia and Sjogren's disease in association with Lupus Nephritis), but showed resistance to T(H)17-dependent EAE and colitis. Such seemingly opposite functions of Act1 in CD40-BAFFR and IL-17R signaling are orchestrated by different domains in Act1. Whereas Act1 interacts with the IL-17R through the C-terminal SEFIR domain, Act1 is recruited to CD40 and BAFFR indirectly, which is mediated by TRAF3 through the TRAF binding site in Act1. Such delicate regulatory mechanisms may provide a common vehicle to promote balance between host defense to pathogens and tolerance to self.

Autoantibodies in patients with monoclonal gammopathies

Although autoantibody activities are rather often associated to monoclonal gammopathies, only monoclonal immunoglobulins of the IgM isotype are really directed against autoantigens that are often polysaccharides or are formed by highly repetitive structures. This strict association is frequently revealed also by clinical manifestations of the autoimmune response generated by the monoclonal macroglobulin. Most monoclonal immunoglobulins of non-IgM isotype are instead totally inactive toward self-antigens, the autoantibody activity being instead associated, if present, to polyclonal immunoglobulins. Although the same BAFF/APRIL system is involved in perpetuation of humoral autoimmunity as well as in stimulation of clonal B-cell expansion, the autoimmune commitment of B cells of a non-IgM isotype is hardly compatible with their possible involvement in an uncontrolled proliferation pathway, whose prerequisite is the homing of these B cells to the bone marrow compartment. The IgM-secreting cells appear instead to possess a much lower tendency, and/or a looser requirement, for their homing in the bone marrow prior to their actual proliferation. This may explain the quite different consequences, in terms of autoimmunity, between IgM and non-IgM paraproteinemias.

Usefulness of mouse models to study the pathogenesis of Sjögren's syndrome

Sjögren's syndrome (SS) is an autoimmune disorder characterized by ocular and oral dryness as well as systemic manifestations. The immunopathogenesis of SS is complex with different intricate factors. Because of the delay in the appearance of symptoms and due to ethical issues it is very difficult to study the wide array of factors intervening in the pathogenesis of SS in human patients. To circumvent this problem, different animal models have been elaborated for studying the different subsets of the aspects of the physiopathology of this disease. In this review, we focus on the mouse models that have been established to deepen our insight into the immunopathogenesis of SS.

BAFF, a new target for intravenous immunoglobulin in autoimmunity and cancer

Intravenous immunoglobulin (IVIg) has been used to treat autoimmune diseases and lymphoid malignancies with some therapeutic effect. In both these pathological conditions, there is an overproduction of BAFF (for "B-cell-activating factor of the TNF family"), and APRIL (for "a proliferation-inducing ligand"). The presence of antibodies (Abs) with BAFF and APRIL specificities in IVIg preparations was investigated by enzyme-linked immunosorbent assay, and Western Blot analysis. Apoptosis was measured by the annexin-V binding method, and confirmed using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling technique. Nonglycosylated recombinant BAFF, glycosylated affinity-purified BAFF, and recombinant APRIL (but not TNFalpha), were recognized by certain IgG in IVIg, and their F(ab')(2) fragments. Steric hindrance prevented the antiapoptotic effects of BAFF on B-lymphocytes. This work documents the presence of anti-BAFF and anti-APRIL Abs in IVIg. These can functionally neutralize the role of BAFF in B-cell survival. These anti-BAFF IgG might amend deleterious effects of BAFF in B-cell-mediated autoimmune diseases.

BLyS receptor signatures resolve homeostatically independent compartments among naïve and antigen-experienced B cells

The BLyS family of receptors includes two cytokines, BLyS and APRIL; and three receptors, BR3, BCMA and TACI. Together, these regulate the size and composition of peripheral B cell pools. The multiplicity of ligand-receptor sets, in conjunction with differential receptor expression, alternative binding partners and disparate downstream signaling characteristics, affords the potential to establish independently regulated homeostatic niches among primary and antigen-experienced B cell subsets. Thus, BLyS signaling via BR3 is the dominant homeostatic regulator of primary B cell pools, whereas APRIL interactions with BCMA likely govern memory B cell populations. Short-lived antibody forming cell populations and their proliferating progenitors express a TACI-predominant signature. Further, within each niche, relative fitness to compete for available cytokine is determined by exogenous inputs via adaptive and innate receptor systems, affording intramural hierarchies that determine clonotype composition.

B cell-activating factor is a novel diagnosis parameter for asthma

BACKGROUND

Asthma is a life-threatening immediate-type allergic disease. B cell-activating factor (BAFF) is a key regulator of B lymphocyte development and is required to generate and maintain the mature B cell pool.

OBJECTIVES

To investigate the level of BAFF in the serum of asthma patients and the role of BAFF on T cells.

METHODS

The BAFF level was measured by enzyme-linked immunosorbent assay. Peripheral blood mononuclear cells (PBMC) from asthma patients were analyzed by flow cytometry. T8.1 cells were used to test the role of BAFF on T cell-antigen-presenting cell (APC) conjugate formation.

RESULTS

The BAFF level in patient serum was elevated relative to normal serum. Immunoglobulin E (IgE) concentration and the percentage of CD3+ T and CD19+ B cells vary according to the serum BAFF level. Patients with high BAFF and high IgE (group II) and those with high BAFF and low IgE (group III) show a high ratio of CD3+ T to CD19+ B cells, and the opposite is seen for patients with low BAFF and high IgE (group I) and those with low BAFF and low IgE (group IV). The addition of BAFF increased PBMC proliferation and T cell-APC conjugate formation. BAFF concentration in serum decreased after treatment with antiasthmatic drugs including glucocorticoids and immunosuppressants.

CONCLUSION

These findings suggest that the serum BAFF level is high in both IgE-mediated asthma and non-IgE-mediated asthma and extend our knowledge about the fact that BAFF may play a stimulatory role on the proliferation of T cells. Thus, BAFF could be a parameter to monitor the severity of asthma symptoms.

Functional expression of a proliferation-related ligand in hepatocellular carcinoma and its implications for neovascularization

AIM: To detect the expression of a proliferation-related ligand on human hepatocellular carcinoma (HCC) cell lines (SK-Hep1, HLE and HepG2) and in culture medium.

METHODS: APRIL expression was analyzed by Western blotting in HCC cell lines. Effects of APRIL to cell count and angiogenesis were analyzed, too.

RESULTS: Recombinant human APRIL (rhAPRIL) increased cell viability of HepG2 cells and, in HUVEC, rhAPRIL provided slight tolerance to cell death from serum starvation. Soluble APRIL (sAPRIL) from HLE cells increased after serum starvation, but did not change in SK-Hep1 or HepG2 cells. These cells showed down-regulation of VEGF after incubation with anti-APRIL antibody. Furthermore, culture medium from the HCC cells treated with anti-APRIL antibody treatment inhibited tube formation of HUVECs.

CONCLUSION: Functional expression of APRIL might contribute to neovascularization via an upregulation of VEGF in HCC.

The BLyS family of ligands and receptors: an archetype for niche-specific homeostatic regulation

Discovery and characterization of the tumor necrosis factor (TNF) family member B-lymphocyte stimulator (BLyS) has opened a novel chapter in the role of TNF family members in the homeostatic control of lymphocyte populations. BLyS and its sister cytokine APRIL (a proliferation-inducing ligand) act primarily as soluble trimers and serve to regulate the steady-state numbers of nearly all B-cell compartments. This homeostatic regulation is accomplished through the regulation of B-cell production rates, selection thresholds, and lifespan. Differential expression of the three BLyS receptors during differentiation and activation provides related yet distinct homeostatic niches for follicular, marginal zone, and memory B-cell subsets.

Potential role of APRIL as autocrine growth factor for megakaryocytopoiesis

A proliferation-inducing ligand (APRIL) is a new tumor necrosis factor family member implicated in tumor cell proliferation. We investigated the role of APRIL in megakaryocytopoiesis, a developmental hematopoietic process responsible for progenitor cell differentiation to megakaryoblasts and megakaryocytes, leading to platelet formation. APRIL is not expressed in CD34+ progenitor cells from healthy donors, but it is massively up-regulated during the proliferative phase of megakaryocytic cell differentiation. Exogenous APRIL expression in primary cells increases megakaryocytic cell growth, suggesting that APRIL acts as a proliferative factor in megakaryocytopoiesis. More importantly, neutralization of endogenous APRIL was able to dramatically reduce megakaryocyte expansion and platelet production. Thus, our data provide evidence that APRIL acts as a growth factor for terminal megakaryocytopoiesis and may promote physiologic platelet production.

Control of spontaneous B lymphocyte autoimmunity with adenovirus-encoded soluble TACI

OBJECTIVE

Serum B lymphocyte stimulator (BLyS) is increased in autoimmune diseases, both in animal models and in humans. This study examined the effect of BLyS blockade in 3 animal models of lupus.

METHODS

Antibodies and lupus-like disease manifestations were examined in mice after administration of a single injection of an adenoviral construct for the transmembrane activator and CAML interactor receptor (AdTACI) that produces high serum levels of TACI-Fc fusion protein.

RESULTS

In C57BL/6 (B6) lpr/lpr mice (B6.lpr/lpr), which were used to model autoimmunity in the absence of severe disease, treatment of younger mice with AdTACI prevented the development of hypergammaglobulinemia. In contrast, use of AdTACI for BLyS blockade had only transient effects on the levels of IgG in normal B6 mice. AdTACI blocked the development of autoantibodies in younger B6.lpr/lpr mice and reversed the production of autoantibodies in older B6.lpr/lpr mice, and also reduced the numbers of splenic plasma cells. In MRL.lpr/lpr mice, which were used to examine disease manifestations, AdTACI reduced the extent of glomerulonephritis and proteinuria and improved survival, but had little effect on T cell infiltration and interstitial nephritis. However, in (NZB x NZW)F(1) mice, AdTACI induced neutralizing anti-TACI antibodies and failed to reduce the numbers of B cells.

CONCLUSION

BLyS blockade has little effect on IgG levels in normal mice, but reverses the production of spontaneously produced IgM and IgG autoantibodies in the setting of established autoimmunity. Blockade of BLyS ameliorates B cell-dependent disease manifestations even in the MRL.lpr/lpr model, but its effectiveness on autonomous T cell aspects of the disease is limited. Moreover, its effectiveness is neutralized by anti-TACI antibodies when present. These results provide a basis for understanding the potential effects of BLyS blockade in human disease.

CD28 delivers a unique signal leading to the selective recruitment of RelA and p52 NF-kappaB subunits on IL-8 and Bcl-xL gene promoters

CD28 is one of the most important costimulatory receptors necessary for full T lymphocyte activation. The CD28 receptor can enhance T cell antigen receptor (TCR) signals, as well as deliver independent signals. Indeed, CD28 engagement by B7 can generate TCR-independent signals leading to IkappaB kinase and NF-kappaB activation. Here we demonstrate that the TCR-independent CD28 signal leads to the selective transcription of survival (Bcl-xL) and inflammatory (IL-8 and B cell activation factor, but not proliferative (IL-2), genes, in a NF-kappaB-dependent manner. CD28-stimulated T cells actively secrete IL-8, and Bcl-xL up-regulation protects T cells from radiation-induced apoptosis. The transcription of CD28-induced genes is mediated by the specific recruitment of RelA and p52 NF-kappaB subunits to target promoters. In contrast, p50 and c-Rel, which preferentially bind NF-kappaB sites on the IL-2 gene promoter after anti-CD3 stimulation, are not involved. Thus, we identify CD28 as a key regulator of genes important for both survival and inflammation.

Cytokine–receptor pairing: accelerating discovery of cytokine function

Over the past decade, advances in both gene discovery and ligand-receptor pairing techniques have led to the recognition that systematic pairing of 'orphan' database-derived cytokines and/or cytokine receptors with their cognate partners can lead to a marked acceleration in the elucidation of biological function. The sometimes-restricted tissue distribution of the receptor, coupled with the highly specific bioactivity of the corresponding ligand, can direct investigators rapidly towards regulatory function and site-of-action studies. The power of cytokine-receptor pairing to accelerate the understanding of function will be illustrated, citing several examples of candidate drug discoveries. Several of these discoveries, resulting from cytokine-receptor pairings, are at present advancing towards human clinical evaluation.

BAFF and APRIL protect myeloma cells from apoptosis induced by interleukin 6 deprivation and dexamethasone

Identification of growth factors in neoplasias may be a target for future therapies by blocking either growth factor receptor interaction or the induced pathway. Using gene expression profiling, we identified overexpression of 2 receptors for a proliferation-inducing ligand (APRIL) and B-cell activating factor (BAFF) in malignant plasma cells compared with normal plasma cells. APRIL and BAFF are involved in a variety of tumor and autoimmune diseases, including B-cell malignancies. We confirmed the expression of BAFF and APRIL receptors (B-cell maturation antigen [BCMA], transmembrane activator and calcium modulator and cyclophilin ligand interactor [TACI], and BAFF-R) in a majority of 13 myeloma cell lines and in the purified primary myeloma cells of 11 patients. APRIL and BAFF were potent survival factors for exogenous cytokine-dependent myeloma cell lines and were autocrine growth factors for the RPMI8226 and L363 autonomously growing cell lines. These factors activated nuclear factor (NF)-kappaB, phosphatidylinositol-3 (PI-3) kinase/AKT, and mitogen-activated protein kinase (MAPK) kinase pathways and induced a strong up-regulation of the Mcl-1 and Bcl-2 antiapoptotic proteins in myeloma cells. BAFF or APRIL was also involved in the survival of primary myeloma cells cultured with their bone-marrow environment, and protected them from dexamethasone (DEX)-induced apoptosis. Finally, the serum levels of BAFF and APRIL were increased about 5-fold in patients with multiple myeloma (MM) as compared with healthy donors. Altogether, these data suggest that APRIL/BAFF inhibitors may be of clinical value in MM.

Actions of BAFF in B cell maturation and its effects on the development of autoimmune disease

BAFF, a member of the family of tumour necrosis factor (TNF) ligands, is essential for the development of peripheral mature, long lived B lymphocytes. It binds to three different receptors, BCMA, TACI, and BAFF-R, which are all members of the family of TNF receptors. Defects in the genes encoding BAFF or BAFF-R abolish the generation of mature B cells. BAFF is made by myeloid cells whereas BAFF-R is expressed preferentially on B cells. BAFF induces polyclonal maturation of resting, short lived immature B cells to resting, long lived mature B cells without proliferation. Lupus erythematodes prone mice have elevated blood levels of BAFF, and treatment of these mice with the BAFF decoy receptor (BCMA-Ig) prevents the onset of this systemic autoimmune disease. Human lupus patients also have elevated blood levels of BAFF. Treatment with BAFF neutralising agents (decoy receptors, monoclonal antibodies) should prevent, delay, or, at least, slow down the disease.

DeltaBAFF, an alternate splice isoform that regulates receptor binding and biopresentation of the B cell survival cytokine, BAFF

The tumor necrosis family member BAFF is limiting for the survival of follicular B lymphocytes, but excessive BAFF signaling can lead to autoimmunity, suggesting that its activity must be tightly regulated. We have identified a conserved alternate splice isoform of BAFF, called deltaBAFF, which lacks 57 nt encoding the A-A1 loop and is co-expressed with BAFF in many mouse and human myeloid cells. Mouse deltaBAFF appears on the plasma membrane, but unlike BAFF it is inefficiently released by proteolysis. DeltaBAFF can associate with BAFF in heteromultimers and diminish BAFF bioactivity and release. Thus, alternative splicing of the BAFF gene suppresses BAFF B cell stimulatory function in several ways, and deltaBAFF may promote other functions as well.

BAFF AND APRIL: a tutorial on B cell survival

BAFF, a member of the TNF family, is a fundamental survival factor for transitional and mature B cells. BAFF overexpression leads to an expanded B cell compartment and autoimmunity in mice, and elevated amounts of BAFF can be found in the serum of autoimmune patients. APRIL is a related factor that shares receptors with BAFF yet appears to play a different biological role. The BAFF system provides not only potential insight into the development of autoreactive B cells but a relatively simple paradigm to begin considering the balancing act between survival, growth, and death that affects all cells.

The TNF family members BAFF and APRIL: the growing complexity

B cell activating factor belonging to the TNF family (BAFF) and apoptosis-inducing ligand (APRIL) are two related members of the TNF ligand superfamily. Although they share two receptors, TACI and BCMA, transgenic and knockout mice in this system reveal that their functions are not redundant. BAFF is a critical survival/maturation factor for peripheral B cells and this activity is mediated through a BAFF-specific receptor, BAFF-R. Overexpression of BAFF has been linked to autoimmune disease and aspects of B cell neoplasia. APRIL appears to play a role in T-independent type II antigen responses and T cell survival, but can also induce proliferation/survival of non-lymphoid cells. Elevated expression of APRIL has been found in some tumor cell lines and in tumor tissue libraries. Therapies designed to inhibit the BAFF and APRIL pathways holds great promise for the future.

Biological functions of tumor necrosis factor cytokines and their receptors

Tumor necrosis factor (TNF; formerly known as TNFalpha) and lymphotoxin (LT)alpha, originally characterized by their ability to induce tumor cell apoptosis and cachexia, are now considered as central mediators of a broad range of biological activities. These activities encompass beneficial effects for the host in inflammation and in protective immune responses against a variety of infectious pathogens. TNF family members on the other hand also exert host-damaging effects in sepsis, in tumor cachexia as well as in autoimmune diseases. In addition, the essential roles of the core members of the TNF superfamily, LTalpha, LTbeta, TNF, and LIGHT as well as their receptors during the organogenesis of secondary lymphoid organs and the maintenance of the architecture of lymphatic tissues now becomes appreciated. The elucidation of the biological functions of these cytokines and their specific cell surface receptors has been crucially advanced by the study of gene-targeted mouse strains. This presentation summarizes the roles of TNFR and TNF-like cytokines in infection, sepsis and autoimmunity as well as the pivotal involvement of these molecules in the development of secondary lymphoid organs.

Ligand-receptor binding revealed by the TNF family member TALL-1

The tumour necrosis factor (TNF) ligand TALL-1 and its cognate receptors, BCMA, TACI and BAFF-R, were recently identified as members of the TNF superfamily, which are essential factors contributing to B-cell maturation. The functional, soluble fragment of TALL-1 (sTALL-1) forms a virus-like assembly for its proper function. Here we determine the crystal structures of sTALL-1 complexed with the extracellular domains of BCMA and BAFF-R at 2.6 and 2.5 A, respectively. The single cysteine-rich domain of BCMA and BAFF-R both have saddle-like architectures, which sit on the horseback-like surface formed by four coil regions on each individual sTALL-1 monomer. Three novel structural modules, D2, X2 and N, were revealed from the current structures. Sequence alignments, structural modelling and mutagenesis revealed that one disulphide bridge in BAFF-R is critical for determining the binding specificity of the extracellular domain eBAFF-R to TALL-1 instead of APRIL, a closely related ligand of TALL-1, which was confirmed by binding experiments in vitro.

Molecular Biology and Immunology for Clinicians 23

The parsimony of nature can be stated as "if its not broke don't fix it, just tweak it and reuse it again and again." Nature recycles: once a motif is demonstrably useful it shows up again, often in unexpected places. Tumor necrosis factor and its receptor(s) are examples of this. At least 20 molecules have now been identified as being 25% homologous or more identical with tumor necrosis factor and being involved in a variety of immune and nonimmune functions. Members of the receptor superfamily have shared structural motifs and trigger shared intracellular signaling pathways. Rather than having been implicated in arcane and rare syndromes, some of these activities are pivotal in immune function and, when perturbed, some predispose to known immunodeficiency and autoimmune disease. Not surprisingly, some of these are becoming targets for immunomodulation. New members of these 2 superfamilies are currently being described and the newcomers and the "original stock" will show up in the clinic before you know it! Part of the confusion has always been that each laboratory describing a new biologic principle names the mediating compound. Thus, multiple labs, multiple names for the same protein (recall Ro/SS-A, La/SS-B). Thus, special attention is paid below to acronyms and their synonyms.

Inhibition of metalloproteinase cleavage enhances the cytotoxicity of Fas ligand

The Fas ligand (FasL)/Fas receptor (CD95) pathway is an important mediator of apoptosis in the immune system and can also mediate cancer cell death. Soluble FasL (sFasL), shed from the membrane-bound form of the molecule by a putative metalloproteinase (MP), may function to locally regulate the activity of membrane-bound FasL. Using a replication-defective recombinant adenovirus-expressing FasL (RAdFasL), we identified a variable ability of different carcinoma cells to respond to FasL-induced cytotoxicity and to shed sFasL. Blockade of FasL cleavage with an MP inhibitor significantly enhanced RAdFasL-induced apoptosis suggesting that sFasL may antagonize the effect of membrane-bound FasL. In support of this concept, a recombinant adenovirus expressing a noncleavable form of FasL (RAdD4) was found to be a potent inducer of apoptosis even at very low virus doses. Our results highlight the therapeutic potential of noncleavable FasL as an antitumor agent and emphasize the important role of MP via the production of sFasL in regulating the response of the Fas pathway. Moreover, these findings have general implications for the therapeutic exploitation of TNF family ligands and for the possible impact of MP-based therapies on the normal physiology of Fas/TNF pathways.

BLyS and APRIL form biologically active heterotrimers that are expressed in patients with systemic immune-based rheumatic diseases

BLyS and APRIL are two members of the TNF superfamily that are secreted by activated myeloid cells and have costimulatory activity on B cells. BLyS and APRIL share two receptors, TACI and BCMA, whereas a third receptor, BAFF-R, specifically binds BLyS. Both BLyS and APRIL have been described as homotrimeric molecules, a feature common to members of the TNF superfamily. In this study, we show that APRIL and BLyS can form active heterotrimeric molecules when coexpressed and that circulating heterotrimers are present in serum samples from patients with systemic immune-based rheumatic diseases. These findings raise the possibility that active BLyS/APRIL heterotrimers may play a role in rheumatic and other autoimmune diseases and that other members of the TNF ligand superfamily may also form active soluble heterotrimers.

Generation of polyclonal plasmablasts from peripheral blood B cells: a normal counterpart of malignant plasmablasts

A new way to identify tumor-specific genes is to compare gene expression profiles between malignant cells and their autologous normal counterparts. In patients with multiple myeloma, a major plasma cell disorder, normal plasma cells are not easily attainable in vivo. We report here that in vitro differentiation of peripheral blood B lymphocytes, purified from healthy donors and from patients with multiple myeloma, makes it possible to obtain a homogeneous population of normal plasmablastic cells. These cells were identified by their morphology, phenotype, production of polyclonal immunoglobulins, and expression of major transcription factors involved in B-cell differentiation. Oligonucleotide microarray analysis shows that these polyclonal plasmablastic cells have a gene expression pattern close to that of normal bone marrow–derived plasma cells. Detailed analysis of genes statistically differentially expressed between normal and tumor plasma cells allows the identification of myeloma-specific genes, including oncogenes and genes coding for tumor antigens. These data should help to disclose the molecular mechanisms of myeloma pathogenesis and to define new therapeutic targets in this still fatal malignancy. In addition, the comparison of gene expression between plasmablastic cells and B cells provides a new and powerful tool to identify genes specifically involved in normal plasma cell differentiation.

BAFFled B cells survive and thrive: roles of BAFF in B-cell development

Interactions of BAFF (B-cell activating factor) with BAFF-R, one of three BAFF-binding receptors that are preferentially expressed on B cells, are essential for B-cell development, because defects in either the ligand or the receptor arrest progression from immature type-1 B cells to type-2 cells and mature cells; B1 B cells are unaffected. Transgenic BAFF overexpression leads to B-cell hyperplasia and autoimmune disease. In vitro, BAFF increases survival of immature and mature B cells; immature B cells also mature polyclonally to mature B cells, without proliferation. Upon BAFF-influenced differentiation, immature B cells change their surface-IgM signal transduction machinery and proliferate rather than undergoing apoptosis.

Association of BAFF/BLyS overexpression and altered B cell differentiation with Sjögren's syndrome

BAFF (BLyS, TALL-1, THANK, zTNF4) is a member of the TNF superfamily that specifically regulates B lymphocyte proliferation and survival. Mice transgenic (Tg) for BAFF develop an autoimmune condition similar to systemic lupus erythematosus. We now demonstrate that BAFF Tg mice, as they age, develop a secondary pathology reminiscent of Sjögren's syndrome (SS), which is manifested by severe sialadenitis, decreased saliva production, and destruction of submaxillary glands. In humans, SS also correlates with elevated levels of circulating BAFF, as well as a dramatic upregulation of BAFF expression in inflamed salivary glands. A likely explanation for disease in BAFF Tg mice is excessive survival signals to autoreactive B cells, possibly as they pass through a critical tolerance checkpoint while maturing in the spleen. The marginal zone (MZ) B cell compartment, one of the enlarged B cell subsets in the spleen of BAFF Tg mice, is a potential reservoir of autoreactive B cells. Interestingly, B cells with an MZ-like phenotype infiltrate the salivary glands of BAFF Tg mice, suggesting that cells of this compartment potentially participate in tissue damage in SS and possibly other autoimmune diseases. We conclude that altered B cell differentiation and tolerance induced by excess BAFF may be central to SS pathogenesis.