B1B lymphocytes generate T cell-independent memory

描述（由申请人提供）：压倒性菌血症是美国传染病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保护性抗体以抵抗入侵病原体的能力。T细胞非依赖性（Tl）反应具有很强的保护性，其发展速度明显快于T细胞依赖性（TD）反应。然而，长期以来，人们一直认为免疫反应是短暂的，不能提供持久的保护。回归热细菌赫氏疏螺旋体在血液中生长到非常高的浓度，但以一种Tl方式迅速被清除。我们利用了一个小鼠感染B. hermsii模型来证明这种Tl反应实际上产生了长期的保护作用。这种免疫是由B1b淋巴细胞赋予的，B1b淋巴细胞是B细胞的一个新亚群，其功能尚不清楚。这些B1b细胞随着hermsii感染的消退而扩增，持续存在，并分泌保护性IgM。有趣的是，虽然来自恢复期小鼠的B1b细胞在转移给免疫缺陷小鼠时具有完全的保护作用，但未成熟的B1b细胞仅提供部分和短暂的免疫，这表明恢复期的B1b细胞显然获得了免疫记忆。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，将解决以下问题：(1)保护性B1b衍生的IgM识别哪些B. hermsii抗原？IgM单克隆抗体（mab）将从恢复期B1b细胞衍生的杂杂瘤中产生，这些IgM单克隆抗体识别的B. hermsii抗原将被鉴定，单克隆抗体也将被测试在体外杀死该细菌和在体内保护小鼠的能力。(2)初生和恢复期小鼠中，hermsii特异性B1b细胞的频率和保护能力如何？频率将通过流式细胞术、ELISPOT和VH CDR3谱分型确定。(3)恢复期小鼠与幼年小鼠抗原特异性B1b细胞的内在差异是什么？细胞在各种刺激下的增殖动力学和分化成抗体分泌细胞对hermsii的反应将在体外和体内进行评估。了解由B1b细胞赋予的Tl保护反应持续时间的基础，将为产生针对表达Tl抗原的病原体的有效疫苗提供新方法。

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.