rhsBLyS及其突变体对小鼠血清免疫球蛋白分泌及B细胞增殖分化的影响

为了进一步研究所构建的人可溶性B淋巴细胞刺激因子 (hsBLyS)及其突变体hsBY A(Cys14 6→Ala14 6 )和hsBY V(Cys14 6→Val14 6 )在体内的生物活性 ,将 3种重组蛋白注射入BALb C小鼠体内 ,进而分析重组蛋白对小鼠血清免疫球蛋白分泌和脾脏B细胞增殖分化的影响 ,并对 3种蛋白的体内生物活性进行了比较 .结果表明 ,3种蛋白均能促进小鼠血清总IgG和IgM的分泌明显增加 ,统计学检验显示突变体rhsBY V诱导这 2种免疫球蛋白分泌的能力最强 ;3种蛋白还诱导小鼠脾脏增大、脾脏成熟B细胞的相对数量增加 .该高活性突变体hsBY V的获得提示 ,Cys14 6并非BLyS发挥正常功能所必需 ,将Cys14 6突变成Val14 6有可能提高BLyS的生物活性 .     

Two observed regions in B lymphocyte stimulator important for its biological activity

B lymphocyte stimulator (BLyS),a member of the tumor necrosis factor superfamily ofligands,is a crucial survival factor for B cells.We successfully constructed seven mutants of the functionalsoluble fragment of human BLyS (named cBLyS,amino acid 134-285),including three deletion mutants andfour site-directed mutants.All the mutant proteins were expressed in Escherichia coli and purified by Ni-NTA affinity chromatography.The biological activities of these mutants were assessed by the ligand-recep-tor binding assay,B cell proliferation assay and immune effect response in vivo.Our results indicated thatfour residues,H~(218),F~(220),T~(228) and L~(229),are indispensable for the biological activity of cBLyS,whereas tworegions,amino acid 134-148 and amino acid 271-285,are related to the biological activity of BLyS.Theprotein of deletion of amino acid 134-148 leads to a complete defection in raising the antigen-specific IgMtiter.The deletion of amino acid 271-285 reduces the effectiveness compared with the native cBLyS.Thisindicates that the region of amino acid 134-148 is indispensable for cBLyS to function normally.     

B淋巴细胞刺激因子（BLyS）研究进展

B淋巴细胞刺激因子（BLyS）是1999年新发现的一种重要的细胞因子,属于肿瘤坏死因子(TNF)超家族成员.在体液免疫调控中起重要作用.它能强烈地刺激B淋巴细胞的增殖和分化并分泌大量免疫球蛋白(主要为IgM);在体外其过量表达能促进多种B系肿瘤细胞的生长.BLyS转基因小鼠出现严重的红斑狼疮样症状.对BLyS的基因和蛋白质结构、免疫调控功能、受体和信号通路及其在自身免疫性疾病和恶性肿瘤中的作用进行了综述.     

Cutting edge: BLyS enables survival of transitional and mature B cells through distinct mediators

These studies characterize BLyS responsiveness and receptor expression among transitional and mature peripheral B cells. The results show a maturation-associated increase in BLyS binding capacity that reflects differential expression patterns of the three BLyS receptors. Accordingly, BLyS administration enlarges only late transitional and mature peripheral B (MB) cell compartments. Furthermore, bromodeoxyuridine labeling and cell cycle analyses show these effects are mediated through enhanced proportional survival of cells traversing the T2, T3, and MB cell stages, rather than by causing proliferation or slowing transit within these subsets. Despite similar effects on survival, BLyS up-regulates the antiapoptotic genes A1 and bcl-x(L) in MB cells but not immature B cells. Together, these findings show that, while BLyS influences B cell survival in several peripheral differentiation subsets, the downstream mediators differ, thus providing the first direct evidence for an established B lineage survival system whose intermediates change as B cells mature.     

B lymphocyte stimulator regulates adaptive immune responses by directly promoting dendritic cell maturation

B lymphocyte stimulator (BLyS) is a well-known direct costimulator of adaptive immune cells, particularly B lineage cells. However, we have reported recently that BLyS is also able to activate monocytes. Other innate immune cells, such as dendritic cells (DCs), play a key role in the initiation of adaptive immune responses and the purpose of the current study was to assess whether there is a direct role for BLyS in modulating human DC functions. In this study, we show that BLyS induces DC activation and maturation. Thus, BLyS strongly induced up-regulation of surface costimulatory molecule expression and secretion of specific cytokines and chemokines in DCs. BLyS-stimulated DCs (BLyS-DCs) were also able to augment allogeneic CD4 T cell proliferation to a greater extent than control DCs. BLyS-DCs secreted elevated levels of the major Th1-polarizing cytokine, IL-12p70, and they promoted naive CD4 T cell differentiation into Th1 T cells. Regarding BLyS receptor expression, DCs primarily express cytoplasmic transmembrane activator and CAML interactor; however, low levels of cell surface transmembrane activator and CAML interactor are expressed as well. Collectively, our data suggest that BLyS may modulate adaptive immune cells indirectly by inducing DC maturation.     

计算机辅助设计可溶性BLyS受体, eBCMA-Fc 融合蛋白及其在大肠杆菌中的表达

B 细胞成熟抗原 (BCMA)是 B淋巴细胞刺激因子(BLyS)的受体之一．它的胞外区与人IgG1 Fc的融合蛋白eBCMA-Fc,又称为诱饵受体,具有拮抗BLyS的活性．为了设计新的拮抗肽,基于BCMA和Fc的晶体结构,通过计算机图形学技术、分子模拟方法,建立了eBCMA-Fc融合蛋白的三维理论结构．利用均方根位移（root mean square distance, RMSD）对eBCMA-Fc融合蛋白与单体eBCMA、Fc构象差异进行分析．融合蛋白eBCMA-Fc中的eBCMA段与单体eBCMA的主链碳原子间RMSD值为0.036 nm,Fc段与单体Fc的主链碳原子间RMSD值为0.064 nm．结果表明,对比单体,融合蛋白eBCMA-Fc并未因eBCMA与Fc直接连接而发生构象的变化．分子对接方法显示,融合蛋白eBCMA-Fc中的BCMA与BLyS作用,而Fc扮演着稳定BCMA构象的支架作用．为进一步验证上述理论分析,构建eBCMA-Fc融合基因,并将载有eBCMA-Fc融合基因的原核表达质粒转化BL21 (DE3)菌、在细菌中表达．目的蛋白经蛋白A亲和柱纯化大约为36 kD,与理论预测值34 kD相近．免疫印迹表明抗人IgG抗体能够识别eBCMA-Fc融合蛋白．ELISA证实,eBCMA-Fc融合蛋白能够结合BLyS．随着eBCMA-Fc融合蛋白增加,结合BLyS的融合蛋白也相应增加．而对照人IgG,即使在高浓度条件下,也不结合BLyS．此外,eBCMA-Fc 融合蛋白能够抑制BLyS对B细胞肿瘤Daudi细胞的作用．这些研究为下一步设计和筛选BLyS拮抗肽提供了实验基础．     

Interaction of the TNF homologues BLyS and APRIL with the TNF receptor homologues BCMA and TACI

BLyS (also called TALL-1, THANK, or BAFF) [1] [2] [3] [4] is a member of the tumor necrosis factor (TNF) gene family that stimulates proliferation and immunoglobulin production by B cells. BLyS interacts with the TNF receptor (TNFR) homologue TACI (transmembrane activator and CAML-interactor) [5], and treatment of mice with a TACI-Fc fusion protein abolishes germinal center formation after antigenic challenge [6]. Here we report a novel interaction between BLyS and another TNFR homologue, BCMA (B cell maturation antigen) [7] [8]. Further, the TNF homologue APRIL [9], a close relative of BLyS, also bound to BCMA and TACI. BLyS or APRIL activated nuclear factor-kappaB (NF-kappaB) through TACI and BCMA, and each ligand stimulated immunoglobulin M (IgM) production by peripheral blood B cells. These results define a dual ligand-receptor system that may play an important role in humoral immunity.     

Immune opsonins modulate BLyS/BAFF release in a receptor-specific fashion

TNF ligand superfamily member 13B (B lymphocyte stimulator (BLyS), B cell activating factor (BAFF)) promotes primary B cell proliferation and Ig production. While the soluble form of BLyS/BAFF is thought to be the primary biologically active form, little is known about the regulation of its cleavage and processing. We provide evidence that Fcgamma receptor cross-linking triggers a rapid release of soluble, biologically active BLyS/BAFF from myeloid cells. Surprisingly, this function is primarily mediated by FcgammaRI, but not FcgammaRIIa as defined by specific mAb, and can be initiated by both IgG and C reactive protein as ligands. The generation of a B cell proliferation and survival factor by both innate and adaptive immune opsonins through engagement of an Fcgamma receptor, which can also enhance Ag uptake and presentation, provides a unique opportunity to facilitate Ab production. These results provide a mechanism by which Fcgamma receptors can elevate circulating BLyS levels and promote autoantibody production in immune complex-mediated autoimmune diseases.     

Cutting edge: a role for B lymphocyte stimulator in systemic lupus erythematosus

Increased levels of B lymphocyte stimulator (BLyS) are associated with systemic autoimmunity in animal models of spontaneous autoimmune disease, and transgenic animals expressing BLyS develop typical autoimmune disease. Here, we demonstrate significant elevations of BLyS in the patients with systemic lupus erythematosus (SLE). The BLyS isolated from the sera of SLE patients had the same m.w. as the natural soluble form and was able to stimulate B cell activation in vitro. Increased BLyS in SLE patients was partially associated with higher levels of anti-dsDNA Ab of the IgG, IgM, and IgA classes, but not associated with the disease activity. Our results suggest that BLyS may be a useful marker for early activation of an autoimmune diathesis and likely plays a critical role in triggering activation of self-Ag-driven autoimmune B cells in human SLE. BLyS may provide an effective therapeutic target in systemic autoimmunity.     

Human BLyS facilitates engraftment of human PBL derived B cells in immunodeficient mice

The production of fully immunologically competent humanized mice engrafted with peripheral lymphocyte populations provides a model for in vivo testing of new vaccines, the durability of immunological memory and cancer therapies. This approach is limited, however, by the failure to efficiently engraft human B lymphocytes in immunodeficient mice. We hypothesized that this deficiency was due to the failure of the murine microenvironment to support human B cell survival. We report that while the human B lymphocyte survival factor, B lymphocyte stimulator (BLyS/BAFF) enhances the survival of human B cells ex vivo, murine BLyS has no such protective effect. Although human B cells bound both human and murine BLyS, nuclear accumulation of NF-kappaB p52, an indication of the induction of a protective anti-apoptotic response, following stimulation with human BLyS was more robust than that induced with murine BLyS suggesting a fundamental disparity in BLyS receptor signaling. Efficient engraftment of both human B and T lymphocytes in NOD rag1(-/-) Prf1(-/-) immunodeficient mice treated with recombinant human BLyS is observed after adoptive transfer of human PBL relative to PBS treated controls. Human BLyS treated recipients had on average 40-fold higher levels of serum Ig than controls and mounted a de novo antibody response to the thymus-independent antigens in pneumovax vaccine. The data indicate that production of fully immunologically competent humanized mice from PBL can be markedly facilitated by providing human BLyS.     

Production and purification of recombinant human BLyS mutant from inclusion bodies

B lymphocyte stimulator (BLyS), a member of the tumor necrosis factor superfamily, is an important regulator of B cell homeostasis. In BLyS-deficient mice, B cell development is severely perturbed. On the other hand, mice transgenic for BLyS developed autoimmune disorders, such as increased germinal center formation, production of autoantibodies, and Ig deposition in kidneys. The overexpression of BLyS was found in some human autoimmune diseases. These findings suggest that BLyS has a crucial role in the humoral immune response and may be a therapeutic target for some human autoimmune diseases. To construct and express the therapeutic vaccine BLyS, we coupled a foreign immunodominant T-helper epitope to the N terminus of BLyS (named recombinant BLyS mutant, rBLySM) and expressed rBLySM in Escherichia coli. We have developed a purification process of rBLySM from inclusion bodies. A step-down urea concentration strategy was applied to the rBLySM renaturation process. By this strategy, a stable yield of 4.5mg purified rBLySM per gram of cell paste could be obtained.     

B lymphocyte stimulator (BLyS) isoforms in systemic lupus erythematosus: disease activity correlates better with blood leukocyte BLyS mRNA levels than with plasma BLyS protein levels

Considerable evidence points to a role for B lymphocyte stimulator (BLyS) overproduction in murine and human systemic lupus erythematosus (SLE). Nevertheless, the correlation between circulating levels of BLyS protein and disease activity in human SLE is modest at best. This may be due to an inadequacy of the former to reflect endogenous BLyS overproduction faithfully, in that steady-state protein levels are affected not just by production rates but also by rates of peripheral utilization and excretion. Increased levels of BLyS mRNA may better reflect increased in vivo BLyS production, and therefore they may correlate better with biologic and clinical sequelae of BLyS overexpression than do circulating levels of BLyS protein. Accordingly, we assessed peripheral blood leukocyte levels of BLyS mRNA isoforms (full-length BLyS and DeltaBLyS) and plasma BLyS protein levels in patients with SLE, and correlated these levels with laboratory and clinical features. BLyS protein, full-length BLyS mRNA, and DeltaBLyS mRNA levels were greater in SLE patients (n = 60) than in rheumatoid arthritis patients (n = 60) or normal control individuals (n = 30). Although full-length BLyS and DeltaBLyS mRNA levels correlated significantly with BLyS protein levels in the SLE cohort, BLyS mRNA levels were more closely associated with serum immunoglobulin levels and SLE Disease Activity Index scores than were BLyS protein levels. Moreover, changes in SLE Disease Activity Index scores were more closely associated with changes in BLyS mRNA levels than with changes in BLyS protein levels among the 37 SLE patients from whom repeat blood samples were obtained. Thus, full-length BLyS and DeltaBLyS mRNA levels are elevated in SLE and are more closely associated with disease activity than are BLyS protein levels. BLyS mRNA levels may be a helpful biomarker in the clinical monitoring of SLE patients.     

Fusion Toxin BLyS-Gelonin Inhibits Growth of Malignant Human B Cell Lines In Vitro and In Vivo

B lymphocyte stimulator (BLyS) is a member of the TNF superfamily of cytokines. The biological activity of BLyS is mediated by three cell surface receptors: BR3/BAFF-R, TACI and BCMA. The expression of these receptors is highly restricted to B cells, both normal and malignant. A BLyS-gelonin fusion toxin (BLyS-gel) was generated consisting of the recombinant plant-derived toxin gelonin fused to the N-terminus of BLyS and tested against a large and diverse panel of B-NHL cell lines. Interestingly, B-NHL subtypes mantle cell lymphoma (MCL), diffuse large B cell lymphoma (DLBCL) and B cell precursor-acute lymphocytic leukemia (BCP-ALL) were preferentially sensitive to BLyS-gel mediated cytotoxicity, with low picomolar EC₅₀ values. BLyS receptor expression did not guarantee sensitivity to BLyS-gel, even though the construct was internalized by both sensitive and resistant cells. Resistance to BLyS-gel could be overcome by treatment with the endosomotropic drug chloroquine, suggesting BLyS-gel may become trapped within endosomal/lysosomal compartments in resistant cells. BLyS-gel induced cell death was caspase-independent and shown to be at least partially mediated by the “ribotoxic stress response.” This response involves activation of p38 MAPK and JNK/SAPK, and BLyS-gel mediated cytotoxicity was inhibited by the p38/JNK inhibitor SB203580. Finally, BLyS-gel treatment was shown to localize to sites of disease, rapidly reduce tumor burden, and significantly prolong survival in xenograft mouse models of disseminated BCP-ALL, DLBCL, and MCL. Together, these findings suggest BLyS has significant potential as a targeting ligand for the delivery of cytotoxic “payloads” to malignant B cells.     

B-lymphocyte stimulator/a proliferation-inducing ligand heterotrimers are elevated in the sera of patients with autoimmune disease and are neutralized by atacicept and B-cell maturation antigen-immunoglobulin

Introduction

B-lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL) are members of the tumor necrosis factor (TNF) family that regulate B-cell maturation, survival, and function. They are overexpressed in a variety of autoimmune diseases and reportedly exist in vivo not only as homotrimers, but also as BLyS/APRIL heterotrimers.

Methods

A proprietary N-terminal trimerization domain was used to produce recombinant BLyS/APRIL heterotrimers. Heterotrimer biologic activity was compared with that of BLyS and APRIL in a 4-hour signaling assay by using transmembrane activator and CAML interactor (TACI)-transfected Jurkat cells and in a 4-day primary human B-cell proliferation assay. A bead-based immunoassay was developed to quantify native heterotrimers in human sera from healthy donors (n = 89) and patients with systemic lupus erythematosus (SLE; n = 89) or rheumatoid arthritis (RA; n = 30). Heterotrimer levels were compared with BLyS and APRIL homotrimer levels in a subset of these samples.

Results

The recombinant heterotrimers consisted mostly of one BLyS and two APRIL molecules. Heterotrimer signaling did not show any significant difference compared with APRIL in the TACI-Jurkat assay. Heterotrimers were less-potent inducers of B-cell proliferation than were homotrimeric BLyS or APRIL (EC₅₀, nMol/L: BLyS, 0.02; APRIL, 0.17; heterotrimers, 4.06). The soluble receptor fusion proteins atacicept and B-cell maturation antigen (BCMA)-immunoglobulin (Ig) neutralized the activity of BLyS, APRIL, and heterotrimers in both cellular assays, whereas B-cell activating factor belonging to the TNF family receptor (BAFF-R)-Ig neutralized only the activity of BLyS. In human sera, significantly more patients with SLE had detectable BLyS (67% versus 18%; P < 0.0001), APRIL (38% versus 3%; P < 0.0002), and heterotrimer (27% versus 8%; P = 0.0013) levels compared with healthy donors. Significantly more patients with RA had detectable APRIL, but not BLyS or heterotrimer, levels compared with healthy donors (83% versus 3%; P < 0.0001). Heterotrimer levels weakly correlated with BLyS, but not APRIL, levels.

Conclusions

Recombinant BLyS/APRIL heterotrimers have biologic activity and are inhibited by atacicept and BCMA-Ig, but not by BAFF-R-Ig. A novel immunoassay demonstrated that native BLyS/APRIL heterotrimers, as well as BLyS and APRIL homotrimers, are elevated in patients with autoimmune diseases.     

Cellular competition independent of BAFF/B lymphocyte stimulator results in low frequency of an autoreactive clonotype in mature polyclonal B cell compartments

The peripheral B cell prosurvival cytokine BAFF/B lymphocyte stimulator (BLyS) has been proposed to participate in the regulation of immunological tolerance. Selective elimination or reconstitution of B cells expressing transgene-encoded, autoreactive BCRs upon systemic BLyS depletion or supplementation, respectively, was observed in two separate studies. Such findings led to a model positing a higher dependency of autoreactive B cells on BLyS. We tested this model by exploiting two targeted IgH transgenic mice (H chain knock-in [HKI]) that produce large numbers of follicular (FO) B cells that are either weakly or strongly autoreactive with nuclear autoantigens. Even though HKI B cells do not exhibit classical features of anergy, we found that mature, naive, autoreactive HKI B cells are outcompeted for representation in the periphery by a polyclonal B cell population. However, this is not due to a higher dependency of HKI B cells on BLyS for survival. Additionally, excess BLyS does not rescue HKI B cells from selective elimination. These findings suggest that some autoreactive FO B cells can fully develop while in competition with non-autoreactive cells for BLyS, but remain at a competitive disadvantage for other trophic factors that regulate peripheral stability. As such, our data indicate the existence of peripheral tolerance mechanisms that regulate the frequency of autoreactive FO B cells independent of the BLyS pathway.     

B Lymphocyte Stimulator (BLyS) Is Expressed in Human Adipocytes In Vivo and Is Related to Obesity but Not to Insulin Resistance

Inflammation and metabolism have been shown to be evolutionary linked and increasing evidence exists that pro-inflammatory factors are involved in the pathogenesis of obesity and type 2 diabetes. Until now, most data suggest that within adipose tissue these factors are secreted by cells of the innate immune system, e. g. macrophages. In the present study we demonstrate that B lymphocyte stimulator (BLyS) is increased in human obesity. In contrast to several pro-inflammatory factors, we found the source of BLyS in human adipose tissue to be the adipocytes rather than immune cells. In grade 3 obese human subjects, expression of BLyS in vivo in adipose tissue is significantly increased (p<0.001). Furthermore, BLyS serum levels are elevated in grade 3 human obesity (862.5+222.0 pg/ml vs. 543.7+60.7 pg/ml in lean controls, p<0.001) and are positively correlated to the BMI (r = 0.43, p<0.0002). In the present study, bariatric surgery significantly altered serum BLyS concentrations. In contrast, weight loss due to a very-low-calorie-formula-diet (800 kcal/d) had no such effect. To examine metabolic activity of BLyS, in a translational research approach, insulin sensitivity was measured in human subjects in vivo before and after treatment with the human recombinant anti-BLyS antibody belimumab. Since BLyS is known to promote B-cell proliferation and immunoglobulin secretion, the present data suggest that adipocytes of grade 3 obese human subjects are able to activate the adaptive immune system, suggesting that in metabolic inflammation in humans both, innate and adaptive immunity, are of pathophysiological relevance.     

B lymphocyte stimulator (BLyS) isoforms in systemic lupus erythematosus: disease activity correlates better with blood leukocyte BLyS mRNA levels than with plasma BLyS protein levels

Considerable evidence points to a role for B lymphocyte stimulator (BLyS) overproduction in murine and human systemic lupus erythematosus (SLE). Nevertheless, the correlation between circulating levels of BLyS protein and disease activity in human SLE is modest at best. This may be due to an inadequacy of the former to reflect endogenous BLyS overproduction faithfully, in that steady-state protein levels are affected not just by production rates but also by rates of peripheral utilization and excretion. Increased levels of BLyS mRNA may better reflect increased in vivo BLyS production, and therefore they may correlate better with biologic and clinical sequelae of BLyS overexpression than do circulating levels of BLyS protein. Accordingly, we assessed peripheral blood leukocyte levels of BLyS mRNA isoforms (full-length BLyS and ΔBLyS) and plasma BLyS protein levels in patients with SLE, and correlated these levels with laboratory and clinical features. BLyS protein, full-length BLyS mRNA, and ΔBLyS mRNA levels were greater in SLE patients (n = 60) than in rheumatoid arthritis patients (n = 60) or normal control individuals (n = 30). Although full-length BLyS and ΔBLyS mRNA levels correlated significantly with BLyS protein levels in the SLE cohort, BLyS mRNA levels were more closely associated with serum immunoglobulin levels and SLE Disease Activity Index scores than were BLyS protein levels. Moreover, changes in SLE Disease Activity Index scores were more closely associated with changes in BLyS mRNA levels than with changes in BLyS protein levels among the 37 SLE patients from whom repeat blood samples were obtained. Thus, full-length BLyS and ΔBLyS mRNA levels are elevated in SLE and are more closely associated with disease activity than are BLyS protein levels. BLyS mRNA levels may be a helpful biomarker in the clinical monitoring of SLE patients.     

NF-kappa B1 p50 is required for BLyS attenuation of apoptosis but dispensable for processing of NF-kappa B2 p100 to p52 in quiescent mature B cells

B lymphocyte stimulator (BLyS), a TNF family protein essential for peripheral B cell development, functions primarily through attenuation of B cell apoptosis. In this study, we show that BLyS activates NF-kappaB through both classical and alternative pathways with distinct kinetics in quiescent mature B cells. It rapidly and transiently enhances the p50/p65 DNA binding activity and induces phosphorylation of IkappaBalpha characteristic of the classical NF-kappaB pathway, albeit maintaining IkappaBalpha at a constant level through ongoing protein synthesis and proteasome-mediated destruction. With delayed kinetics, BLyS promotes the processing of p100 to p52 and sustained formation of p52/RelB complexes via the alternative NF-kappaB pathway. p50 is dispensable for p100 processing. However, it is required to mediate the initial BLyS survival signals and concomitant activation of Bcl-x(L) in quiescent mature B cells ex vivo. Although also a target of BLyS activation, at least one of the A1 genes, A1-a, is dispensable for the BLyS survival function. These results suggest that BLyS mediates its survival signals in metabolically restricted quiescent B cells, at least in part, through coordinated activation of both NF-kappaB pathways and selective downstream antiapoptotic genes.     

To target or not to target APRIL in systemic lupus erythematosus: that is the question!

Among the cytokines that regulate B-cell homeostasis are the TNF-like ligands B-lymphocyte stimulator (BLyS; also B-cell activation factor) and a proliferation-inducing ligand (APRIL). BLyS and APRIL share two receptors; that is, B-cell maturation antigen and transmembrane activator and CAML interactor. Therapeutic approaches using biologics are limited for treatment of lupus patients. One previously approved drug is belimumab, which antagonizes the B-cell stimulator BLyS. Atacicept, another biologic inhibiting BLyS and APRIL, was terminated for serious adverse events - raising the question of whether APRIL should be neutralized in autoimmune diseases.Treamtrakanpon and coworkers analyzed B-lymphocyte stimulator (BLyS; also B-cell activation factor) and a proliferation-inducing ligand (APRIL) expression in patients with lupus nephritis and observed a correlation with renal disease activity and APRIL serum levels [1]. In addition, the authors describe that, upon treatment with immunosuppressors, nonresponding patients had higher APRIL serum levels. They thus concluded that APRIL could be a potential biomarker for predicting difficult-to-treat cases of lupus nephritis, and propose the use of APRIL antagonists such as atacicept for treatment of lupus nephritis patients with high APRIL serum levels.These conclusions might be premature, as Treamtrakanpon and coworkers have not found a correlation between the level of APRIL in kidney tissue and renal disease activity. Another hypothesis could be that APRIL has a protective effect in autoimmune diseases. Indeed, the crucial role of BLyS in B-cell maintenance became evident by the analysis of BLyS-deficient mice displaying lower numbers of mature B cells and of BLyS transgenic mice developing severe B-cell hyperplasia. Although APRIL can trigger different B-cell responses in vitro, including proliferation and survival of human and murine B cells, it is less critical than BLyS in B-cell maintenance as APRIL knockout and transgenic mice reveal no gross abnormalities in lymphoid homeostasis [2]. In fact, APRIL was found to modulate specific B-cell responses such as IgA isotype switching, increased IgM secretion and B1 cell activity.Meanwhile, BLyS is an established promoter of B-cell-triggered autoimmmune diseases such as systemic lupus erythematosus and rheumatoid arthritis, whereas the role of APRIL in these pathologies is rather controversial. Neutralizing BLyS with the mAb belimumab displayed a modest, although statistically significant, therapeutic effect in systemic lupus erythematosus [3,4]. But blocking both BLyS and APRIL with atacicept (TACI-Fc) was associated with a pronounced reduction of immunoglobulins, and occurrence of serious infections led to a premature termination of a phase II/III trial in lupus nephritis [5]. The combination of mycofenolate mofetil with atacicept may have contributed to the decrease of immunoglobulins. However, at acicept combined with another drug such as methotrexate in patients with rheumatoid arthritis was also associated with a significant reduction of immunoglobulins (especially IgM). In this autoimmune disease, atacicept failed to demonstrate efficacy on American College of Rheumatology 20 criteria [6]. In contrast, administration of belimumab showed a modest but significant efficacy using the same evaluation criteria in rheumatoid arthritis [7].These findings suggest distinct roles for BLyS and APRIL in lupus and other B-cell-mediated autoimmune diseases. Elevated serum levels are found for both cytokines in lupus patients, and for BLyS there is a consensus in the literature that this reflects its disease-promoting activity. Elevated APRIL serum levels, however, have been - depending on the respective study - either positively or negatively correlated with disease features [8]. One possible explanation for this discrepancy could be differences in the patient cohorts analyzed. A recent study by Jacob and colleagues analyzed a murine lupus model in APRIL-deficient mice and observed elevated numbers of splenocytes, increased autoantibody production and a tendency towards increased IgG production [9]. Notably, ectopic APRIL expression does not result - in contrast to BLyS transgenic mice - in lupus-like symptoms. In fact, we found that APRIL does dampen collagen-induced arthritis, the most common mouse model for human arthritis [10].Experimental mouse models for autoimmune diseases obviously cannot entirely mimic human diseases. Nevertheless, in vivo data are accumulating that do not support a disease-supporting role for APRIL in B-cell-mediated autoimmunity. The study by Treamtrakanpon and colleagues is putting forward the need to better elucidate the role of APRIL in B-cell-driven diseases before concluding a therapeutic approach.