B1B lymphocytes generate T cell-independent memory

描述(申请人提供)：在美国，压倒性菌血症是传染病导致死亡的主要原因之一。防止菌血症演变为危及生命的感染的一个关键因素是宿主迅速产生针对入侵病原体的保护性抗体的能力。T细胞非依赖性(TL)反应具有高度的保护性，其发展速度明显快于T细胞依赖性(TD)反应。然而，TL反应一直被认为完全是短暂的，不能提供长期的保护。复发发热细菌赫氏疏螺旋体在血液中生长到极高的浓度，但以TL方式迅速清除。我们利用赫氏杆菌感染的小鼠模型来表明，这种TL反应实际上产生了长期保护。这种免疫是由B1B淋巴细胞实现的，B1B淋巴细胞是一种新的B细胞亚群，其功能尚不清楚。这些B1B细胞在Hermsii感染消退的同时扩张，持续存在，并分泌保护性的IgM。有趣的是，当来自恢复期小鼠的B1B细胞转移到免疫缺陷小鼠身上时，可以获得完全的保护，而幼稚的B1B细胞只提供部分和短暂的免疫，这表明康复中的B1B细胞显然已经获得了免疫记忆。为了了解这种TL记忆样反应的基础，并确定B1B细胞靶向的特异性抗原(S)，将解决以下问题：(1)保护性B1B来源的免疫球蛋白M识别哪些赫氏杆菌抗原？从恢复期的B1B细胞产生的杂交瘤将产生IgM单抗(MAbb)，将鉴定这些IgM mAbs识别的Hermsii抗原，并将测试mAbs在体外杀死这种细菌和在体内保护小鼠的能力。(2)幼鼠和恢复期小鼠的Hermsii特异性B1B细胞的频率和保护能力是多少？频率将通过流式细胞术以及ELISPOT和VH CDR3分型来确定。(3)恢复期小鼠和幼稚小鼠的抗原特异性B1B细胞有什么内在区别？将在体外和体内评估细胞对各种刺激的增殖动力学和对Hermsii的反应向抗体分泌细胞的分化。了解B1B细胞提供的TL保护性反应的长寿基础将为开发针对表达TL抗原的病原体的有效疫苗提供新的途径。

DESCRIPTION (provided by applicant): Overwhelming bacteremia is one of the leading causes of death by infectious disease in the United States. A critical factor in preventing bacteremia from evolving into a life-threatening infection is the ability of the host to rapidly generate protective antibodies against the invading pathogens. T cell-independent (Tl) responses are highly protective and develop significantly more rapidly than T cell-dependent (TD) responses. However, Tl responses have been long considered exclusively short-lived and incapable of conferring long-lasting protection. The relapsing fever bacterium Borrelia hermsii grows to exceedingly high concentrations in the blood, but is rapidly cleared in a Tl manner. We have utilized a murine model of B. hermsii infection to show that this Tl response in fact generates long-term protection. This immunity is conferred by B1b lymphocytes, a novel subset of B cells whose functions are not yet well understood. These B1b cells expand concurrent with the resolution of B. hermsii infection, persist, and secrete protective IgM. Interestingly, while B1b cells from convalescent mice confer complete protection when transferred to immunodeficient mice, naive B1b cells provide only partial and short-lived immunity, indicating that the convalescent B1b cells have apparently acquired immunological memory. To understand the basis of this Tl memory-like response, and to identify the specific antigen(s) targeted by B1b cells, the following questions will be addressed: (1) What B. hermsii antigens are recognized by protective B1b-derived IgM? IgM monoclonal antibodies (mAbs) will be generated from hybridomas derived from convalescent B1b cells and the B. hermsii antigens recognized by those IgM mAbs will be identified and mAbs will also be tested for the ability to kill this bacterium in vitro and protect mice in vivo. (2) What is the frequency and protective capability of B. hermsii-specific B1b cells of naive and convalescent mice? Frequencies will be determined by flow cytometry and ELISPOT and VH CDR3 spectratyping. (3) What are the intrinsic differences between antigen-specific B1b cells of convalescent and naive mice? Kinetics of cell proliferation to a variety of stimuli and differentiation into antibody-secreting cells in response to B. hermsii will be assessed in vitro and in vivo. Understanding the basis for the longevity of the Tl protective responses conferred by B1b cells will provide novel approaches to generate effective vaccines against pathogens expressing Tl antigens.