IL-4 down-regulates the surface expression of CD5 on B cells and inhibits spontaneous immunoglobulin and IgM-rheumatoid factor production in patients with rheumatoid arthritis.

There is evidence to suggest that CD5+ B cells may be associated with autoimmunity, e.g. they are increased in patients with rheumatoid arthritis (RA). In this study, we found that the expression of CD5 on RA B cells increased spontaneously, following culture for up to 4 days in vitro in the absence of T cells, supporting the idea that the CD5+ B cell possesses distinctive features. The spontaneous increase of CD5 expression was down-regulated by recombinant IL-4 (rIL-4). Other cytokines studied (rIL-1 alpha, rIL-2, rIL-5, rIL-6) did not alter CD5 expression. Studies of antibody production showed that rIL-4 could reduce spontaneous production of total IgG and IgM in non-stimulated RA T plus B cell cultures. Spontaneous production of IgM rheumatoid factor (IgM-RF), measured by a newly developed avidin-biotin complex ELISA, was also reduced by rIL-4. Furthermore, rIL-4 reduced the increase in IgM-RF production observed on stimulation with Staphylococcus aureus Cowan I (SAC) or pokeweed mitogen (PWM). Thus, IL-4 might act as a regulator of the development of abnormal B cell differentiation in patients with RA.     

Complete sequence of the genes encoding the VH and VL regions of low- and high-affinity monoclonal IgM and IgA1 rheumatoid factors produced by CD5+ B cells from a rheumatoid arthritis patient.

We have characterized the VH and VL genes of three low-affinity polyreactive and two high-affinity monoreactive IgM and IgA1 rheumatoid factor (RF) mAb generated using circulating CD5+ B cells from a single rheumatoid arthritis patient. We found that four and one RF mAb utilized genes of the VHIV and VHIII families, respectively. The VHIV gene usage by these RF mAb differs from the preferential VHIII, VHI, and, to a lesser extent, VHII gene usage by the IgM with RF activity found in patients with mixed cryoglobulinemia, Waldenstrom's macroglobulinemia, and other monoclonal gammopathies. In addition, in contrast to the preponderant kappa L chain usage by the RF in these patients, a lambda L chain was utilized by all RF mAb from our rheumatoid arthritis patient. Two RF mAbs utilized V lambda I, two V lambda IV, and one V lambda III L chains. The VH genes of the two low-affinity polyreactive IgM RF mAb were in germline configuration. When compared with the deduced amino acid sequence of the putatively corresponding genomic segment, the VH gene of the high-affinity monoreactive IgM RF mAb displayed five amino acid differences, all of which are in the complementarity determining regions (CDR), possibly the result of a process of somatic point mutation and clonal selection driven by Ag. The unavailability of the corresponding genomic VH segment sequences made it impossible to infer whether the VH genes utilized by the two IgA1 RF were in a germline or somatically mutated configuration. Sequencing of the genes encoding the H chain CDR3 (D segments) revealed that all three low-affinity polyreactive RF mAb displayed a much longer D segment (36-45 bases) than their high-affinity monoreactive counterparts (15-24 bases), raising the possibility that a long D segment may be one of the factors involved in antibody polyreactivity.     

Expression of CD5 and CD72 on T and B cell subsets in rheumatoid arthritis and Sjögren's syndrome.

A minority of B cells express the CD5 marker, which is found on virtually all T cells, and CD72 has been defined as the CD5 ligand on the B cell membrane. The mean fluorescence intensity (MFI) of the CD5 molecules was shown to be higher on CD4+CD29+ than CD4+CD45RA+ in peripheral blood (PB) and synovial fluid (SF) of rheumatoid arthritis (RA) patients (P < 0.0001 and < 0.001), and PB of Sjögren's syndrome (SS) patients and normal controls (P < 0.02 and < 0.03). This MFI declined once the CD4 expressed HLA-DR in PB of SS patients (P < 0.004) and normal controls (P < 0.02) or CD25 in PB of RA (P < 0.004) and SS patients (P < 0.0004). There was a correlation between the CD5 MFI on CD4+CD45RA+ and CD4+CD29+ in RA (P < 0.001) as well as SS (P < 0.0007) PB. The CD72 MFI was impressively higher on CD5+ than CD5- B cells in PB and SF of RA patients (P < 0.0001 and P < 0.005) and PB of SS patients (P < 0.005) and normal controls (P < 0.005). Our data suggest that, in association with CD4CD29, CD5 is involved in CD5+B/CD5+ B cell interactions in non-organ-specific autoimmune diseases.     

Serial study of CD5+ and CD5- B cell subpopulations in 335 HIV seropositive patients.

B cell subpopulations, as defined by double-labelling techniques with CD5 and CD19 monoclonal antibodies (MoAbs), were serially studied in 335 HIV-1 seropositive patients. At the time of the first consultation, no important modifications in either CD5+ or CD5- subpopulations were observed, whatever the stage of the disease. However, in 18 out of the 335 patients (5.37%), a sharp increase in B cells exceeding 20% and 300/mm3 was observed. This increase in B cells was mainly accounted for CD5-CD19+ B cell subpopulations and was associated with: (i) evolution of the disease, since only four patients presented it at their first consultation (one lymphadenopathy-associated syndrome (LAS) and three AIDS); (ii) advanced stages of disease since, at the time of B cell augmentation, two patients were staged as LAS, four as ARC and 12 as AIDS; (iii) a high incidence of non-Hodgkin's lymphomas (NHL) since three out of the 18 patients presented a histologically confirmed NHL and three others a clinical pattern compatible with this diagnosis. However, in three patients with B hyperlymphocytosis, polymerase chain reaction (PCR) studies of immunoglobulin gene rearrangement revealed the existence of a polyclonal expansion of B cells. These results justify inclusion of a pan-B cell marker in routine phenotypic studies of HIV-infected individuals, as well as the search for NHL among patients presenting this abnormality.     

IgA rheumatoid factor in mucosal fluids and serum of patients with rheumatoid arthritis: immunological aspects and clinical significance.

In order to gain insight into the production and clinical significance of IgA rheumatoid factor (IgA-RF) in mucosal fluids of patients with rheumatoid arthritis (RA), we examined tear fluid, saliva and serum from 80 patients with RA. Significant correlations were found between IgA-RF levels in tear fluid and saliva (P=0.002, r=0.57), saliva and serum (P<0.001, r= 0.79), and serum and tear fluid (P<0.001, r=0.31). No significant correlations were found between total IgA levels in these fluids. Comparison between circulating and mucosal IgA-RF levels after correction for total IgA, revealed that mucosal IgA-RF levels are on average 2.5 times higher than circulating IgA-RF levels. Analysis of IgA-RF specificity showed that lacrimal and salivary IgA-RF reactivity with various IgG subclasses is similar and differs from serum IgA-RF specificity. These results indicate local production of IgA-RF in salivary and lacrimal glands and support the view of a common origin of IgA-RF producing B cells present in mucosal tissues. Mucosal and circulating levels of IgA and IgA-RF were not associated with tests that quantify tear fluid production. This indicates that mucosal and circulating levels of IgA and IgA-RF in patients with RA cannot be regarded as markers for the development of secondary Sjögren's syndrome.     

Identification and characterization of IgA and Vicia villosa-binding T cell subsets in rheumatoid arthritis.

Autoimmunity may be due to augmentation of immune responses by human CD8 cells which bind the lectin Vicia villosa (VV). We have investigated T cells in rheumatoid arthritis (RA) by double immunofluorescence flow cytometry, in order to assess VV-binding CD8 and CD4 cells from the peripheral blood and synovial fluid. A significant increase in CD8+VV adherent (P less than 0.0001) and CD4+VV adherent cells (P less than 0.001) was found in synovial fluid, as compared with peripheral blood from patients with RA. A significant increase in VV-binding CD8+ or CD4+ cells was, however, not found in the blood of patients with RA, as compared with controls. We suggest that the lack of VV-binding T cells separated from blood, in contrast to those from synovial fluid, may be due to an inhibiting agent expressing N-acetyl D-galactosamine. Indeed, IgA1 is rich in N-acetyl D-galactosamine, it inhibits VV binding to T cells and is significantly bound to CD8 cells (P less than 0.001). The IgA1 was then characterized and in about half the patients J chains and secretory component was found, suggesting that the IgA1 is of the polymeric and secretory variety. IgA bound to the T cells engaged the Fc alpha receptors and a significant decrease in the Fc alpha receptors was found in CD8 cells (P less than 0.0001) and CD4 cells (P less than 0.01). Desorption studies were then carried out on CD8 and CD4 cells which showed that a loss of cell-bound IgA1 was associated with an increase in VV binding. Conversely, adsorption of IgA to T cells was associated with a loss in VV binding. The results suggest that the failure of VV binding to CD8+ and CD4+ cells from peripheral blood of patients with RA can be ascribed to cell-bound IgA1. Cytophilic IgA1 may inhibit the function of CD8+VV binding cells, thereby preventing augmentation of the systemic immune response, consistent with the lack of extra-articular disease in these patients with RA.     

Regulation of CCR5 expression and MIP-1alpha production in CD4+ T cells from patients with rheumatoid arthritis

Production of CCR5 expression and MIP-1alpha, a ligand of CCR5, by CD4+ T cells from patients with rheumatoid arthritis (RA) were studied. We analysed further the influence of IL-15 stimulation, CD40/CD40 ligand (CD40L) interaction and CCR5 promotor polymorphism. One hundred and fifty-five RA patients and another 155 age- and sex-matched healthy individuals were enrolled. Peripheral CD4+ and double negative (DN) T cells from patients had lower portions of CCR5, whereas synovial CD4+ and DN T cells showed a much higher CCR5 expression. IL-15 significantly up-regulated the expression of CCR5 on purified CD4+ T cells. CD40L expression on synovial CD4+ T cells was increased greatly in CCR5+ portions by IL-15. MIP-1alpha production by synovial CD4+ T cells was also enhanced by IL-15. Co-culture of CD40 expressing synovial fibroblasts with IL-15-activated synovial CD4+ T cells significantly increased MIP-1alpha production. Expression of CCR5 on patients' CD4+ T cells was not influenced by the promotor polymorphism of CCR5 gene. Taken together, these data suggest CCR5+CD4+ T cells infiltrate the inflamed synovium and IL-15 up-regulates CCR5 and CD40L expression further and enhance MIP-1alpha production in synovial CD4+ T cells. Production of MIP-1alpha by synovial fibroblasts is significantly increased by engagement of CD40 with CD40L. Synovial microenvironment plays a potential role in regulation of CCR5+CD4+ T cells in rheumatoid joints.     

CD21−/low B cells associate with joint damage in rheumatoid arthritis patients

Depletion of B cells is beneficial in rheumatoid arthritis (RA) patients with autoantibodies to citrullinated proteins (ACPA) and/or the Fc portion of immunoglobulins (rheumatoid factor [RF]), suggesting a role for B cells in disease pathogenesis. To date, however, the identity of specifically pathogenic B cell subsets has not been discovered. One candidate population is identified by the low expression or absence of complement receptor 2 (CD21^?/low B cells). In this study, we sought to determine whether there was any correlation between CD21^?/low B cells and clinical outcome in patients with established RA, either ACPA⁺/RF⁺ (n = 27) or ACPA^?/RF^? (n = 10). Healthy donors (n = 17) were included as controls. The proportion of the CD21^?/low CD27^?IgD^? memory B cell subset in peripheral blood (PB) was significantly increased in ACPA⁺/RF⁺ RA patients compared with healthy donors, and the frequency of this subset correlated with joint destruction (r = 0.57, P < 0.04). The levels of the chemokines CXCL‐9 and CXCL‐10 were higher in synovial fluid than in plasma, and PB CD21^?/low cells expressed the receptor, CXCR3. In synovial fluid, most of the B cells were CD21^?/low, approximately 40% of that population was CD27^?IgD^?, and a third of those expressed the pro‐osteoclastogenic factor receptor activator of the nuclear factor κB ligand (RANKL). This subset also secreted RANKL, in addition to other factors such as IL‐6, even in the absence of stimulation. We interpret these data as reason to propose the hypothesis that the CD27^?IgD^? subset of CD21^?/low B cells may mediate joint destruction in patients with ACPA⁺/RF⁺ RA.     

CD5+ B cells and naturally occurring autoantibodies in cancer patients.

We have determined the percentage of CD5+ B lymphocytes in the peripheral blood of cancer patients and healthy controls, using antibodies directed at the CD5 and CD19 (pan-B) markers. The frequencies of CD5+ B cells, expressed as a percentage of total B cells, ranged from 14.3 to 57.5% in the controls and from 14.8 to 82.8% in the patient population. One-third of the cancer patients had frequencies greater than 2 s.d. above the mean of the control population. The CD5+ B cell fraction expressed as a percentage of total lymphocytes was also significantly elevated in this group of cancer patients. These results suggest that the CD5+ B cell compartment may be affected by the malignant process or by the therapy modality employed. The plasma levels of several naturally occurring autoantibodies, the products of the CD5+ B cells, were also assessed in cancer patients and controls. No significant differences were observed when reactivity to several autoantigens was measured. These included nuclear components and phospholipids.     

类风湿关节炎患者外周血CD4+T细胞亚群的分析

目的 研究类风湿性关节炎(RA)患者不同时期外周血Treg和Th1、Th2、Th17细胞以及中性粒细胞上CD64的表达水平,及它们与RA的活动性指标和自身抗体的相关性.方法 采集78例RA患者和21例健康人外周静脉血,采用流式细胞术检测淋巴细胞亚群(Treg,Th1、Th2、Th17细胞)的变化.结果 RA的CD3+ CD4+T细胞和CD4+ CD25+T细胞增多,活动期RA组Treg比率高于缓解期RA组和健康对照组,缓解期RA组Th2细胞减少,RA中Th1,TH17细胞与健康对照组相比无统计学意义,Treg和Th1、Th2、Th17细胞与RA的活动性指标(ESR,CRP和PLT)均无关联.结论 CD4+T细胞亚群数量异常可能与RA疾病发展有关.     

High levels of the soluble form of CD30 molecule in rheumatoid arthritis (RA) are expression of CD30+ T cell involvement in the inflamed joints.

The CD30 is a surface molecule expressed by Th2-type lymphokine-producing T cells upon activation. CD30-expressing activated T cells release a soluble form of the molecule, which can be detectable both in vitro and in vivo. In the present study, high levels of soluble CD30 were found in peripheral blood and synovial fluid from patients with RA. However, CD30+ CD3+ cells, either CD4+ or CD8+, were significantly present in synovial fluid, but not in peripheral blood, of RA patients. Serum values of soluble CD30 were higher in active than inactive RA patients and directly correlated with rheumatoid factor serum titres. These data strongly support an involvement of CD30+ T cells in the immune processes of rheumatoid synovitis, and may suggest a relationship between Th2-type cytokine-secreting T cells and the pathological response in RA.     

Increased numbers of CD5+ B cells and T cell receptor (TCR) γδ+ T cells are associated with younger age of onset in rheumatoid arthritis (RA)

Patients presenting with RA before the age of 45 years (younger onset) are known to have more aggressive disease compared with patients presenting after the age of 65 years (older onset). Coordinated expansion of circulating CD5⁺ B cell and TCR γδ⁺ T cell levels has been reported in patients with RA. This study assesses the peripheral blood levels of these two cell types in RA patients with younger and older onset of disease. CD5⁺ B cell levels were significantly elevated in the younger onset RA group (26·6 ± 4·5%) compared with the older onset RA group (14·2 ± 1·2%; P <0·01). TCR γδ⁺ T cell levels were also significantly raised in the young patients (4·0 ± 0·9%) compared with elderly patients (1·6 ± 0·2%; P <0·01). T cell levels (CD3⁺) were similar in both groups (young 66·4 ± 3·3%; old 74·3 ± 3·4% (mean ± s.e.m.); NS). Total B cell levels (CD19⁺) were also similar in these groups (7·7 ± 0·7% versus 8·9 ± 1·8%; NS). A significant positive correlation was observed between the CD5⁻ B and TCR γδ⁺ T cell types in the patients (r = 0·72, P <0.05). Compared with age-matched normal controls, the younger onset patients had similar CD5⁺ B cell and TCR γδ⁺ T cell levels to the elderly controls (CD5⁺ B cells 30·2 ± 3·0%; TCR γδ⁺ T cells 3·0 ± 0·8%). Conversely, older onset RA patients had CD5⁺ B cell levels similar to the young controls (12·3 ± 1·9%). Spontaneous in vitro synthesis of immunoglobulins (IgM, IgA and IgG) and rheumatoid factors (IgM and IgA isotypes) were not significantly different in both patient groups. The coordinate expansion of circulating CD5⁺ B cells and γδ⁺ T cells seen in patients with RA presenting before 45 years of age and not after 65 years of age may suggest a potential role for these cells in more aggressive disease states.     

雷藤舒在类风湿关节炎中免疫调节机制的研究

探讨(5R)-5-羟基雷公藤内酯醇(雷藤舒)体外在类风湿关节炎(RA)中的免疫调节机制。①CCK-8法检测24h、48h、72h等3个时间段不同浓度雷藤舒对小鼠L929成纤维细胞毒性的影响;②通过3 H胸腺嘧啶脱氧核苷(3 H-TdR)掺入实验,研究雷藤舒对RA患者外周血及滑液中单个核细胞增殖的影响;③流式细胞术检测雷藤舒对RA患者外周血和滑液中Th1细胞、Th17细胞增殖的影响;④ELISA法检测雷藤舒对RA患者外周血及滑液中单个核细胞分泌IFN-γ、TNF-α、IL-17的影响;⑤MTT法研究雷藤舒对RA患者滑膜成纤维细胞(FLS)增殖的影响。结果①雷藤舒≤100nmol/L时在3个时间段(24h、48h、72h)对L929无细胞毒性(P>0.05);②雷藤舒抑制RA患者外周血和滑液中单个核细胞增殖(P<0.05);③雷藤舒抑制Th1(P<0.05)细胞增殖,对Th17细胞增殖有抑制趋势但无统计学意义(P>0.05);④雷藤舒抑制RA患者外周血和滑液中单个核细胞分泌TNF-α、IFN-γ、IL-17水平;⑤雷藤舒抑制RA患者FLS增殖(P<0.05)。雷藤舒对L929细胞无毒性,通过抑制RA患者单个核细胞、Th1、Th17增殖,抑制外周血和滑液中PBMC和SFMC分泌TNF-α、IFN-γ、IL-17,抑制FLS增殖,进而调节RA免疫反应。     

Autoantibodies and B Cells: The ABC of rheumatoid arthritis pathophysiology

Rheumatoid arthritis (RA) is an autoimmune disease characterized by joint inflammation. In the last few decades, new insights into RA-specific autoantibodies and B cells have greatly expanded our understanding of the disease. The best-known autoantibodies in RA—rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA)—are present long before disease onset, and both responses show signs of maturation around the time of the first manifestation of arthritis. A very intriguing characteristic of ACPA is their remarkably high abundance of variable domain glycans. Since these glycans may convey an important selection advantage of citrulline-reactive B cells, they may be the key to understanding the evolution of the autoimmune response. Recently discovered autoantibodies targeting other posttranslational modifications, such as anti-carbamylated and anti-acetylated protein antibodies, appear to be closely related to ACPA, which makes it possible to unite them under the term of anti-modified protein antibodies (AMPA). Despite the many insights gained about these autoantibodies, it is unclear whether they are pathogenic or play a causal role in disease development. Autoreactive B cells from which the autoantibodies originate have also received attention as perhaps more likely disease culprits. The development of autoreactive B cells in RA largely depends on the interaction with T cells in which HLA “shared epitope” and HLA DERAA may play an important role. Recent technological advances made it possible to identify and characterize citrulline-reactive B cells and acquire ACPA monoclonal antibodies, which are providing valuable insights and help to understand the nature of the autoimmune response underlying RA. In this review, we summarize what is currently known about the role of autoantibodies and autoreactive B cells in RA and we discuss the most prominent hypotheses aiming to explain the origins and the evolution of autoimmunity in RA.     

Repertoire of CD5+ and CD5- cord blood B cells: specificity and expression of VH I and VH III associated idiotopes.

Epstein-Barr (EBV)-immortalized B cell clones were established from CD5+ and CD5- cord blood B cells separated by flow cytometry. We have previously shown that IgM from many of the clones was polyreactive, exhibiting reactivity with a number of autoantigens. In this study, IgM produced by the clones was analysed by MoAb for the expression of cross-reactive idiotypes (CRI) associated with rheumatoid factor paraproteins and from defined VH and V kappa subgroups of immunoglobulin heavy and light chains. IgM produced by clones established from CD5+ and CD5- B cells expressed the VH I associated idiotope G8. Furthermore, IgM produced by both sets of clones exhibited a similar frequency of VH III heavy chain subgroup expression, as determined by reactivity with staphylococcal protein A (SpA) and VH III-associated CRI expression (B6 and/or D12). In contrast, expression of the V kappa III-associated 17.109 CRI was significantly higher in IgM antibodies produced by clones established from CD5+ compared with the CD5- clones (32 versus 5%: P less than 0.05). Analysis of the VH and VL subgroup expression by IgM produced by the CD5+ and CD5- cord blood clones, and their autoantigen reactivity profile did not reveal restriction or selection within CD5+ and CD5- populations. However, our data suggest that differences may exist in the expression of certain germ-line genes between CD5+ and CD5- cord blood B cells and might indicate an expansion of CD5+ B cells within the fetal environment.     

CD44和CD62P在IgA肾病中变化的临床意义

目的　观察IgA肾病患者外周血粘附分子CD44 (细胞表面糖蛋白 )和CD6 2P (P选择素 )表达水平的变化 ,并探讨CD44和CD6 2P在IgA肾病发病中的作用及临床意义。方法　采用流式细胞术 ,对 40例IgA肾病患者外周血CD44和CD6 2P表达进行研究 ,以 36例正常人作为对照。结果　IgA肾病患者外周血CD44、CD6 2P的表达分别为 33.89%± 13.2 9%、8.5 8%± 5 .17%明显高于正常对照组 19.73 %± 6 .82 %、3.2 6 %± 1.76 % ,差异有显著性 (P <0 .0 1) ;其中在IgA肾病Ⅳ级和Ⅴ级患者CD44、CD6 2P的表达水平亦明显高于Ⅱ级和Ⅲ级 ;相关性检验结果显示 :IgA肾病患者外周血CD44表达水平与CD6 2P的表达水平呈显著正相关 (r=0 .39,P <0 .0 5 )。结论　CD44和CD6 2P在IgA肾病患者外周血表达增强 ,在IgA肾病的发病机制中起重要作用 ,可能参与了IgA肾病的病理发展过程。     

CD4+CD25high调节性T细胞在类风湿性关节炎病程中的消长及其意义

目的研究类风湿性关节炎(RA)患者病情发展不同阶段外周血及滑液中CD4 CD25high调节性T细胞数量的差别,及其与类风湿性关节炎活动程度的相关性,探讨CD4 CD25highT细胞在RA发生发展中所发挥的免疫抑制和调节作用。方法分别选取未经过缓解病情抗风湿药(DMARDs)治疗的活动性RA患者11例,经DMARDs治疗病情缓解的RA患者12例,和DMARDs治疗后效果不佳的RA患者9例,以及正常对照8例,检测他们的外周血淋巴细胞,以流式细胞术检测CD4 CD25high调节性T细胞的百分率,并研究CD4 CD25highT细胞百分率与抗环瓜氨酸(CCP)抗体,C反应蛋白(CRP),血沉(ESR)及类风湿因子(RF)的相关性。对其中部分患者的血液和关节滑液同时进行分析。结果RA未经治疗组和治疗效果不佳组CD4 CD25highT细胞的百分率(分别是5.24%和6.43%)明显低于正常对照组和治疗后病情缓解组(分别是17.17%和11.79%,P<0.01)。RA患者CD4 CD25highT细胞的百分率与抗CCP抗体(58.0Ru/mL),ESR(38.8mm/h)及CRP(2.73μg/L)呈明显负相关(P<0.05),与类风湿因子(RF=14.4Iu/mL)无明显的相关性(P=0.054)。正常对照组的CD4 CD25highT细胞百分率与抗CCP抗体(均<5.0Ru/mL),ESR(4.67mm/h),CRP(0.15μg/L)及RF(1.37)无明显相关性(P>0.1)。RA患者关节滑液中CD4 CD25highT百分率明显低于强直性脊柱炎(ankilosing spondylitis,AS)关节积液患者(P<0.05)。结论试验结果表明未经缓解病情治疗和治疗后效果不佳者的外周血中,CD4 CD25high调节性T细胞相对减少,且与病情活动程度负相关,这可能是RA发生和发展的一个重要因素。     

Presentation of the candidate rheumatoid arthritis autoantigen aggrecan by antigen-specific B cells induces enhanced CD4(+) T helper type 1 subset differentiation

Effective immune responses require antigen uptake by antigen-presenting cells (APC), followed by controlled endocytic proteolysis resulting in the generation of antigen-derived peptide fragments that associate with intracellular MHC class II molecules. The resultant peptide-MHC class II complexes then move to the APC surface where they activate CD4(+) T cells. Dendritic cells (DC), macrophages and B cells act as efficient APC. In many settings, including the T helper type 1 (Th1) -dependent, proteoglycan-induced arthritis model of rheumatoid arthritis, accumulating evidence demonstrates that antigen presentation by B cells is required for optimal CD4(+) T cell activation. The reasons behind this however, remain unclear. In this study we have compared the activation of CD4(+) T cells specific for the proteoglycan aggrecan following antigen presentation by DC, macrophages and B cells. We show that aggrecan-specific B cells are equally efficient APC as DC and macrophages and use similar intracellular antigen-processing pathways. Importantly, we also show that antigen presentation by aggrecan-specific B cells to TCR transgenic CD4(+) T cells results in enhanced CD4(+) T cell interferon-γ production and Th1 effector sub-set differentiation compared with that seen with DC. We conclude that preferential CD4(+) Th1 differentiation may define the requirement for B cell APC function in both proteoglycan-induced arthritis and rheumatoid arthritis.