B细胞记忆多样性

机体可产生多种类型的记忆B细胞,常见的是经由生发中心产生的长寿命浆细胞和记忆B细胞,还有非依赖生发中心产生的记忆B细胞,以及TI-B记忆细胞.不同类型的记忆B细胞无论在产生路径、BCR类型还是在归巢部位方面均存在差异.这些差异可由抗原性质所决定,也可能是因免疫记忆过程中固有机制在发挥作用.通过对记忆B细胞产生路径、类型及归巢位置等方面进行探索,可更好地了解B细胞记忆形成过程的细节,才能为研制出更有效、更安全的疫苗提供先机.     

T和B记忆细胞

Ｔ和Ｂ记忆细胞是初次免疫应答后克隆消除保留下来的高亲和力细胞，它们有独特的表型，具有淋巴因子分泌、分布和迁移性以及活化的特点。短期免疫记忆要求残存抗原持续性存在，长期免疫记忆与ｂｃｌ－２表达有关。     

人外周血初始B细胞和记忆性B细胞亚群的特征和功能

B淋巴细胞是免疫系统的重要免疫成份,主要功能是介导体液免疫应答。在人外周血中,按照B淋巴细胞的发育阶段及功能的不同,可将B淋巴细胞分为初始成熟B细胞、记忆B细胞和浆细胞。记忆B细胞又可分为IgM记忆B细胞和类型转换的记忆B细胞。近年来的研究表明,B淋巴细胞的亚群远比人想象中的复杂,因此对人B细胞各亚群的起源、发育和功能进行更深入的研究,将有助于治疗自身免疫性疾病,在慢性感染性疾病的治疗过程中找到新的策略,并指导研发安全有效的疫苗。     

人外周血初始B细胞和记忆性B细胞亚群的特征和功能

B淋巴细胞是免疫系统的重要免疫成份,主要功能是介导体液免疫应答.在人外周血中,按照B淋巴细胞的发育阶段及功能的不同,可将B淋巴细胞分为初始成熟B细胞、记忆B细胞和浆细胞.记忆B细胞又可分为IgM记忆B细胞和类型转换的记忆B细胞.近年来的研究表明,B淋巴细胞的亚群远比人想象中的复杂,因此对人B细胞各亚群的起源、发育和功能进行更深入的研究,将有助于治疗自身免疫性疾病,在慢性感染性疾病的治疗过程中找到新的策略,并指导研发安全有效的疫苗.     

人外周血初始B细胞和记忆性B细胞亚群的特征和功能

B淋巴细胞是免疫系统的重要免疫成份,主要功能是介导体液免疫应答.在人外周血中,按照B淋巴细胞的发育阶段及功能的不同,可将B淋巴细胞分为初始成熟B细胞、记忆B细胞和浆细胞.记忆B细胞又可分为IgM记忆B细胞和类型转换的记忆B细胞.近年来的研究表明,B淋巴细胞的亚群远比人想象中的复杂,因此对人B细胞各亚群的起源、发育和功能进行更深入的研究,将有助于治疗自身免疫性疾病,在慢性感染性疾病的治疗过程中找到新的策略,并指导研发安全有效的疫苗.     

自外周血记忆B细胞体外活化和分化抗原特异性浆细胞的方法研究

目的 建立自人外周血淋巴细胞(PBMCs)中的记忆B细胞活化和分化特异性抗体分泌细胞(如浆细胞)的体外活化方法,为抗体药物研发提供研究基础.方法 采集两名接种过乙型肝炎疫苗3年和25年健康成年志愿者(Z和L)外周血,分离PBMCs,通过白细胞介素(IL)-2、IL-4和Toll样受体诱导剂(CpG、R848)体外诱导活化记忆B细胞.采用酶联免疫吸附试验(ELISA)检测培养上清中总抗体和HBsAg特异性抗体的含量;通过酶联免疫斑点试验(ELISPOT)检测培养细胞中总抗体分泌细胞(ASC)数量的变化和HBsAg特异性抗体细胞数量.结果 活化第6天,对照组和两个活化组[CpG DNA2006联合IL-2(C组)和R848联合IL-2(R组)]细胞培养上清总免疫球蛋白(Ig)G浓度分别为37.06ng/mL、80.87 ng/mL和85.97 ng/mL,两个活化组(C组和R组)均明显高于对照组(t=23.318,60.639,P均＜0.05).ELISPOT检测ASC数量,结果显示,C组和R组数量均多于对照组,并且R组明显多于C组.两种活化方法均能在体外诱导B细胞活化,但R组活化效果更佳,确立R组为最佳活化方法.用该方法活化两名乙型肝炎疫苗接种者PBMCs,ELISA检测活化组特异性抗体浓度,R组显著高于对照组(t=5.031,11.561,P均＜0.05).不同细胞数量诱导的分组,ELISPOT检测HBsAg特异性抗体分泌细胞数量,R组均明显多于对照组.结论 确立诱导剂R848和细胞因子IL-2联合能够有效地诱导外周血记忆B细胞体外活化和分化抗原特异性浆细胞,为今后抗体药物研发提供了研究基础.     

系统性红斑狼疮患者B细胞亚群谱系分析

目的检测系统性红斑狼疮(systemic lupus erythematosus,SLE)患者外周血B细胞各亚群比例、分析B细胞分化及其临床意义,进一步探讨SLE患者B细胞功能分化在疾病中的作用。方法收取ds-DNA阳性、经过正规疗程激素及免疫抑制剂治疗后,临床治疗仍未达标的21例SLE患者简称难治性SLE患者,同时选取16例健康体检者作为正常对照组。采用流式细胞术检测健康对照及SLE患者外周血淋巴细胞中B细胞亚群比例的变化情况,并与患者的临床指标进行相关性分析。结果与健康人相比,高抗体滴度的SLE患者外周血双阴性记忆B细胞(CD19⁺CD27^-IgD^-)比例明显增多,浆母细胞(CD19⁺CD27⁺CD38⁺)比例明显增多,而非类型转换的记忆B细胞(CD19⁺CD27⁺IgD⁺)比例明显下降。类型转换记忆B细胞(CD19⁺CD27⁺IgD^...     

TLR7/8激动剂R848体外诱导记忆B细胞分化抗原特异性浆细胞的方法研究

目的为了从PBMCs获得病原体特异性浆细胞,我们建立了TLR7/8激动剂R848体外诱导记忆B淋巴细胞分化浆细胞的方法。方法使用TLR7/8激动剂R848联合细胞因子组合,诱导接种乙肝疫苗(3年及以上)的健康志愿者来源的PBMCs,进行体外活化和分化浆细胞。分别利用ELISA和ELISPOT检测培养液上清中总IgG、HBsAg特异性IgG以及总抗体分泌细胞(ASCs)和HBsAg抗原特异性ASCs。结果成功建立R848体外诱导PBMCs中记忆B淋巴细胞分化浆细胞的方法。R848(使用质量浓度在1～2.5μg/ml)仅与IL-2联合使用,最早在第5天即可检测到特异性ASCs。结论通过该方法可以从患者恢复期少量(仅需5～10 ml)的外周血中获得抗原特异性抗体分泌细胞用于分析和分选,为中和抗体的制备提供方法。     

树突状细胞与T,B细胞相互关系研究进展

本文介绍了ＤＣ与Ｔ细胞活化,Ｔ细胞对ＤＣ的作用、ＤＣ对Ｂ细胞的作用,Ｂ细胞对ＤＣ的作用及ＤＣ表面某些重要分子表达上调的途径。     

Characterization of rotavirus specific B cells and their relation with serological memory

We quantified circulating total, rotavirus (RV) and Tetanus toxin (TT) memory B cells (mBc) in healthy adults using a limiting dilution assay (LDA) and a flow cytometry assay (FCA) that permit evaluation of both CD27+ and CD27− mBc.RV mBc were enriched in the CD27−, IgG+ and in the CD27+, IgM+ subsets. The numbers of RV mBc were higher by FCA than by LDA and results of the two assays did not correlate. TT IgGmBc and RV IgA mBc determined by FCA and by LDA correlated with TT plasma IgG and RV plasma IgA, respectively. The mean ratio of specific mBc/μg/ml of the corresponding plasma immunoglobulin was lower for TT IgG than for RV IgA mBc.Our studies contribute to understand the relationship between circulating mBc and serological memory, and enhance our capacity to develop better correlates of protection against RV disease.     

IL-10 interrupts memory B cell expansion in the germinal center by inducing differentiation into plasma cells

Germinal center (GC) B cells undergo proliferation, somatic hypermutation and isotype switching in the course of differentiation into plasma cells to produce high-affinity antibodies. To understand the molecular mechanism regulating the expansion of memory B cells and the termination of expansion by differentiation into plasma cells, we investigated the effect of interleukin-2 (IL-2), IL-4, IL-10 and CD40 ligand (CD40L) on the differentiation of GC B cells in the defined culture system containing a follicular dendritic cell (FDC)-like cell line. IL-2, IL-4 and CD40L are required for the optimum proliferation and differentiation of GC B cells. When IL-10 was added to this culture condition, CD20⁺ CD38⁺ GC B cells sequentially differentiated into CD20⁺ CD38⁻ memory B cells and then CD20⁻ CD38⁺ plasma cells. In the absence of IL-10, the resulting CD20⁺ CD38⁻ memory B cells continued to proliferate and retained its phenotype. The proliferation of memory B cells was interrupted by addition of IL-10 which induced the differentiation into plasma cells. The expression of CD80 and CD86 was up-regulated in the memory B cells, compared to naive B cells and plasma cells. The identity of memory B cells generated in vitro from GC B cells was further substantiated since memory B cells generated in vivo displayed the identical pattern of proliferation and differentiation under the same culture condition. These results highlight the potent role of GCT helper cells in the expansion and differentiation of memory B cells by regulating different cytokine production.     

The development of IgE+ memory B cells following primary IgE immune responses

We studied whether long-lived IgE⁺ memory B cells develop following three types of primary IgE immune responses. Immunization of mice with anti-IgD antibody induced a T cell-dependent, interleukin (IL)-4-dependent primary IgE response and the formation of IgE isotype switched (IgE⁺) memory B cells. These IgE⁺ memory B cells could be stimulated in vivo by injection with goat anti-IgE antibodies to produce a profound IL-4-independent memory IgE response. By contrast, both infection of mice with Nippostrongylus brasiliensis or repeated immunization with benzylpenicilloyl-keyhole limpet hemocyanin (BPO-KLH) in alum stimulated good primary IgE responses and profound memory T cell-dependent antigen-specific IgE responses, but failed to induce the development of long lived IgE⁺ memory B cells because they could not be recalled with goat anti-IgE antibodies. Mice receiving double immunizations combining anti-IgD with either N. brasiliensis infection or BPO-KLH immunization mounted significant goat anti-IgE-induced secondary IgE responses, but no N. brasiliensis or BPO-KLH-specific IgE could be detected. This indicates that the N. brasiliensis and BPO-KLH induced immune responses do not suppress the development of IgE⁺ B cells, but rather, do not provide the necessary conditions for their formation. Taken together these data indicate that long-lived IgE⁺ B cells fail to develop during the primary IgE response to N. brasiliensis infection or BPO-KLH immunization. By contrast, significant numbers of IgE⁺ memory B cells form during the primary IgE immune response induced by anti-IgD immunization. Our observations suggest that immunization protocols involving membrane IgD cross-linking and limited duration of cognate T cell help are necessary for the formation of IgE⁺ memory B cells. It will be important to determine the relevance of membrane IgD interaction with allergens, as this would influence the design of new therapies for the treatment of allergy and asthma.     

A role for the VLA-4 integrin in the activation of human memory B cells

It is generally recognized that activation through membrane effector molecules such as CD40 or the B cell receptor (BCR) is mandatory to allow B cells to proliferate and differentiate into antibody (Ab)-secreting cells in response to cytokines. We show here that purified tonsillar B cells can be stimulated directly by a cytokine combination to proliferate and secrete immunoglobulins when cultures are performed at high cell density. The contact-mediated activation of B cells in this experimental system is strongly inhibited both by anti-very late antigen (VLA)-4 monoclonal Ab and by a peptide containing the LDV sequence specifically recognized by the α4 integrin binding site. These reagents also significantly suppressed the B cell responses elicited by engagement of the BCR or CD40. Our data reveal that memory B cells but not virgin or germinal center B cells are sensitive to the direct stimulatory effect of cytokines in high-density cultures. Finally, we found that the dual expression of the α and β chains of VLA-4 is a distinctive feature of the memory B cell population. Collectively, our findings support the notion that VLA-4-dependent homotypic B cell interactions can mediate a co-stimulatory signal to human memory B cells and might participate in the B cell activation triggered through the BCR and CD40.     

Differential compartmentalization of memory B cells versus plasma cells in salmonid fish

The disposition of teleost memory and plasma cells (PCs) has essentially been un‐explored. As the organization of the teleost immune system differs significantly from that of mammals (i.e. no bone marrow or lymph nodes, hematopoietic anterior kidney), this disposition could be essential in understanding how comparable functions are achieved. To address this question, the primary and secondary antibody‐secreting cell, B memory cell, and antibody responses to T‐independent and T‐dependent antigens were analyzed in trout. Although the TI and TD antibody responses did not differ substantively from one another, the secondary responses to both were significantly prolonged compared with the primary responses. Logarithmic increases in titer and affinity were achieved for both antigens during the primary, with only modest increases during the secondary response. Antibody‐secreting cells, both PCs and plasmablasts, quantitatively paralleled antibody production, with antibody‐secreting cells skewing to the hematopoietic anterior kidney for both antigens. However, the enhanced antigen‐inducible response of immune fish (indicative of the memory pool) skewed to the peripheral blood and spleen. This pattern of memory versus PC disposition parallels that observed in mammals even though the organization of the respective immune systems differs considerably.     

The enigma of memory B cells in malaria

Malaria is a major public health problem particularly in the tropics. It is caused by protozoan parasites belonging to the genus Plasmodium and is transmitted by Anopheles mosquitoes. Currently, strategies to control malaria include vector control measures, chemoprophylaxis, and efficient diagnosis and treatment. The availability of a highly efficacious malaria vaccine would greatly facilitate malaria control and possibly eradicate malaria. Efforts to design such malaria vaccines are underway but are greatly hampered by the poor understanding of how immune memory to malaria is generated and maintained. In this issue of the European Journal of Immunology, Wykes and colleagues [Eur. J. Immunol. 2012. 42: 3291–3301] demonstrate that experimental malaria infection lowers the expression of B‐cell‐activating factor in DCs, thereby compromising the ability of these DCs to stimulate memory B cells and sustain the survival of Ab‐secreting cells. These findings provide potential clues in the quest for better understanding of immunity to malaria as discussed in this Commentary.     

Recirculating and germinal center B cells differentiate into cells responsive to polysaccharide antigens

Antibodies against bacterial capsular polysaccharides play a critical protective role. Responses to these antigens can occur without the help or control of T cells and are associated with marginal zone (MZ) B cells. Capsular antigens are diverse and some cross-react with self-carbohydrate epitopes. This diversity may explain the recruitment of non-autoreactive recirculating B cells and memory B cells to the MZ in addition to other B cells, some of which are weakly autoreactive cells, that are recruited to the MZ without entering the recirculating pool. To test whether memory B cells respond to polysaccharide-based antigens, mice with hapten-specific memory B cells were challenged with hapten-polysaccharide. Hapten-specific plasma cells producing high affinity antibody with Ig V-region mutations were induced. To test whether naive recirculating B cells can form MZ cells that respond to polysaccharide, recirculating B cells from lymph nodes were transferred into Rag-1-deficient mice. MZ cells differentiated from the donor cells without proliferation or T cell help and responded to polysaccharide-based antigen. The differentiation of B cells both from germinal centers and the recirculating pool to the MZ phenotype is likely to make an important contribution to the repertoire of B cells that respond to polysaccharide antigens.