The distinctive germinal center phase of IgE+ B lymphocytes limits their contribution to the classical memory response

The mechanisms involved in the maintenance of memory IgE responses are poorly understood, and the role played by germinal center (GC) IgE⁺ cells in memory responses is particularly unclear. IgE⁺ B cell differentiation is characterized by a transient GC phase, a bias toward the plasma cell (PC) fate, and dependence on sequential switching for the production of high-affinity IgE. We show here that IgE⁺ GC B cells are unfit to undergo the conventional GC differentiation program due to impaired B cell receptor function and increased apoptosis. IgE⁺ GC cells fail to populate the GC light zone and are unable to contribute to the memory and long-lived PC compartments. Furthermore, we demonstrate that direct and sequential switching are linked to distinct B cell differentiation fates: direct switching generates IgE⁺ GC cells, whereas sequential switching gives rise to IgE⁺ PCs. We propose a comprehensive model for the generation and memory of IgE responses.IgE antibodies are critical mediators of allergic reactions (Gould and Sutton, 2008). Cross-linking of IgE molecules bound to high affinity FcεRI receptors on mast cells and basophils leads to the rapid release of potent proinflammatory molecules (Kinet, 1999; Galli and Tsai, 2012). In spite of its pathological potential, IgE exhibits the lowest serum concentration and the shortest half-life of all the antibody isotypes (Vieira and Rajewsky, 1988; Gould and Sutton, 2008). The low frequency of IgE-producing cells makes their study particularly challenging. Using mouse models of high IgE responses (Katona et al., 1988; Curotto de Lafaille et al., 2001), we discovered that IgE-producing cells develop via a unique differentiation pathway that occurs during the germinal center (GC) phase of T cell–dependent responses and yet favors the production of plasma cells (PCs; Erazo et al., 2007; Yang et al., 2012). In our early studies a GC IgE⁺ population was not clearly detectable, but the IgE antibodies produced were observed to have undergone affinity maturation, indicating a GC history for IgE⁺ PC. We proposed at the time that high affinity IgE originated from the sequential switching of high affinity IgG1 cells, and hence we speculated that classical IgE⁺ memory cells may be absent in mice (Erazo et al., 2007; Curotto de Lafaille and Lafaille, 2010).Sequential switching of IgG cells to IgE was first discovered by the identification of switch(S)γ region footprints in the Sμ-Sε DNA region of IgE genes (Matsuoka et al., 1990; Yoshida et al., 1990; Jabara et al., 1993; Mandler et al., 1993; Zhang et al., 1994; Baskin et al., 1997), but the biological significance of this finding was at that time unknown. Sequential switching in mice entails two recombination events, Sμ→Sγ1 and SμSγ1→Sε, that may be either continuous or temporally separate events. The latter scenario allows for the existence of an intermediate IgG1 cellular phase in which affinity maturation can occur in GCs. Indeed, stimulation of IgG1 cells in the presence of IL-4 either in vivo or in vitro resulted in the production of IgE antibodies (Erazo et al., 2007; Wesemann et al., 2012). Importantly, mice deficient in class switching to IgG1 due to a mutation in the Iγ1 exon (Lorenz et al., 1995) were unable to produce high affinity IgE antibodies (Xiong et al., 2012a,b), indicating that sequential switching is essential for the formation of high affinity IgE.The recent development of fluorescent reporter mice for IgE has facilitated the identification of IgE GC cells (Talay et al., 2012; Yang et al., 2012). However, the in vivo phenotype and role of IgE GC cells in supporting IgE responses and its relationship with the sequential switching process remain unclear (Lafaille et al., 2012; Xiong et al., 2012a).In the current study, we used a new reporter mouse for class switch recombination (CSR) to IgE, improved methods to functionally study IgE B cells ex vivo and in vivo, and in silico modeling to analyze the origin, functional properties, and population dynamics of IgE GC cells and PC. We show that IgE GC cells are unfit to undergo the conventional GC differentiation program and instead undergo apoptosis at a high rate. This “failure to thrive” of IgE GC cells greatly limits their contribution to the memory pool and high affinity PC compartment. Furthermore, we show that the two types of rearrangement to IgE are associated with distinct B cell differentiation fates. Direct Sμ-Sε rearrangements generate IgE GC cells, whereas sequential switching of IgG1 cells gives rise to IgE PC.     

CXCR4在大鼠海马齿状回发育过程中的表达变化

目的 探讨趋化因子受体CXCR4在不同发育阶段大鼠海马齿状回（DG）区发育过程中的表达变化规律.方法 运用免疫印迹、免疫组织化学染色方法分析不同发育时期大鼠海马DG区CXCR4的表达情况.结果 免疫印迹结果显示,海马DG区CXCR4于出生后1周达最高水平（P〈0.05）,随后呈下降趋势,4周后渐降至成年水平.免疫组化结果显示,CXCR4阳性细胞的胞质呈棕黄色着色,并主要表达于齿状回颗粒细胞下层.结论 研究结果提示CXCR4在生后大鼠海马DG区的表达具有时空差异性,这种差异可能与生后海马DG区细胞结构和功能的发育密切相关.     

Organizational analysis of maternal mortality reduction programs in Madagascar

Little is known about the organizational factors involved in policy creation and programs implementation aimed at reducing maternal mortality in Madagascar. A qualitative case study was performed to investigate organizational factors influencing the health system's capacity to elaborate and implement maternal mortality reduction programs. Semi-structured interviews were conducted with 53 participants. A conceptual framework based on Gamson's coalition theory and Hinings and Greenwood's archetypes concept was used. Three major conclusions emerge: the Ministry of Health is a poor leader in the development of national strategies, due to its dependency on external financial resources and expertise, and because of poor transmission of key information from the field; at a meso level (regions and districts), the capacity to adapt programs is highly dependent on the collaboration with NGOs; at the micro level, there are few incentives provided to field workers to participate in a collective effort and little attempt to exploit complementarities between scare resources. The Madagascar health system should consider the need for improvement in data analysis capacity, and implementing behavior-changing tools suitable for stimulating providers who work inside and outside the health care system, to participate to a coordinated collective effort.     

The contribution of reproductive factors and family history towards premenopausal breast cancer risk in Kuala Lumpur, Malaysia

Breast cancer is the most common cancer among Malaysian women. This study aimed to determine the reproductive for premenopausal breast cancer risk in Kuala Lumpur, Malaysia. A case-control study was conducted in 216 histopathologically confirmed cases of premenopausal breast cancer and 216 community-based controls that were matched by age within a 5-year period and ethnicity. The results of this study showed that premenopausal breast cancer risks were strongly related to parity, number of live births and family history of breast cancer. Premenopausal women with these known reproductive and family history risk factors should take extra measures to undergo appropriate screening method for early detection of breast cancer.     

A Murine Model of Chronic Lymphocytic Leukemia Based on B Cell-Restricted Expression of Sf3b1 Mutation and Atm Deletion

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Five types of lymphocytes (lg− θ−, lg− θ+ weak,lg− θ+strong,lg+ θ− and lg+ θ+) characterized by double immunofluorescence and electrophoretic mobility Organ distribution in normal and nude mice

The simultaneous detection of Ig and θ on the surface of mouse lymphocytes permits the detection of four cell types (Ig^?θ^?, Ig^?θ⁺, Ig⁺θ^?, and Ig⁺θ⁺) which also have distinct electrophoretic profiles. All types are present in variable proportions in all lymphoid organs studied. Results obtained in congenitally athymic nude mice and in T-deprived mice define a new type of lymphocyte, the Ig^?θ^+weak. This cell is non-recirculating, Ig^?, with a low density of θ and a slow electrophoretic mobility. It is a candidate for a T-committed prethymic cell.     

Common variants in NLRP2 and NLRP3 genes are strong prognostic factors for the outcome of HLA-identical sibling allogeneic stem cell transplantation

The inflammasomes are macromolecular cytosolic complexes involved in the production of interleukin-1beta (IL-1beta) and IL-18 in response to several pathogen-derived stimuli. Such interleukins have been implicated in the origin of severe allogeneic stem cell transplant (allo-SCT) complications. We analyzed the relationship between the interindividual variability in inflammasome protein-encoding genes in donors and patients and clinical outcome after allo-SCT. Fourteen common genetic variants in 5 genes of the inflammasome, namely, NLRP1, NLRP2, NLRP3, CARD8, and CASP5, were genotyped in 133 human leukocyte antigen-identical sibling pairs undergoing allo-SCT. In the multivariate analysis, donor variants in NLRP2 and NLRP3 were the most important prognostic factors for the clinical outcome after allo-SCT. Thus, donor TT genotype at rs10925027 in NLRP3 was associated with disease relapse (odds ratio (OR) = 6.3, P = 1 x 10(-7)), and donor GG genotype at rs1043684 in NLRP2 was associated with nonrelapse mortality (OR = 4.4, P = 6 x 10(-4)) and overall survival (OR = 3.1, P = .001). In addition, patient AA genotype at rs5862 in NLRP1 was associated with nonrelapse mortality (OR = 2.8, P = .005) and overall survival (OR = 2.0, P = .009). These results suggest that inflammasome genetic variants are important prognostic factors for the outcome of allo-SCT. If validated in larger studies, including unrelated allo-SCT, NLRPs genotype would become an important factor in donor selection.     

中药王不留行中黄酮甙类成分的研究

目的 :对王不留行的化学成分进行研究。方法 :溶剂提取 ,硅胶柱色谱分离 ,根据化合物理化性质和光谱数据鉴定其结构。结果 :分离并鉴定了 3个化合物 ,为洋芹素-6-C-阿拉伯糖 葡萄糖甙 (1) ,洋芹素-6-C-双葡萄糖甙 (2) ,王不留行黄酮甙 (3)。结论 :化合物 1,2为首次从该植物中分得。