Trypanosoma brucei-induced dyshematopoiesis: blocked B lymphopoiesis

描述（由申请方提供）：非洲锥虫是一种抗原性高度可变的鞭毛原生动物，可导致人和家畜的致命疾病。目前约有30万人患有锥虫病，该疾病威胁着撒哈拉以南非洲另外6000万人，并严重限制了美国面积的农业发展。非洲锥虫在血液和间质液中通过二分裂进行复制，并由针对其可变外壳抗原的宿主抗体反应控制。随着疾病的进展，感染的宿主失去了建立有效抗体应答的能力，导致对新出现的锥虫抗原类型的控制不佳，持续的病理学和最终死亡。我们的长期目标是了解T。布氏杆菌影响B细胞（抗体形成细胞）系统，并利用这一知识开发保护免疫功能和疾病控制的战略干预措施。我们在小鼠模型中进行的分析表明，在骨髓和脾脏中早期B细胞祖细胞迅速扩增，但这些器官中新形成的和成熟的B细胞丢失，造血功能障碍的特征通过用杀锥虫药物Berenil治疗从感染小鼠中清除锥虫体而逆转.这些观察使我们假设T.布氏杆菌诱导B淋巴细胞生成的可逆阻断，阻止新的和成熟的B细胞库的补充，这导致B细胞克隆耗竭和B细胞介导的免疫的崩溃。我们将在以下具体目标中阐述这一假设：i）鉴定在布氏锥虫感染的小鼠中B谱系发育被阻滞的阶段ii）确定B细胞发育的阻滞是否由截短的或异常的B细胞分化引起，iii）确定阻滞的B细胞在置于无锥虫的宿主中或在体外生长时是否恢复发育，如果是，T. brucei或T.防止从发展障碍中逃脱。方法将包括：（i）使用特异于B细胞发育阶段的单克隆抗体的细胞表面分化抗原谱，（ii）通过荧光激活细胞分选（FACS）从正常和锥虫感染小鼠的脾和骨髓分离的离散B细胞发育阶段的转录因子和免疫球蛋白基因表达谱，（iii）如目的ii中FACS分离的B细胞祖细胞的发育分析，并在免疫缺陷小鼠（RAG-/-）中以及在存在和不存在锥虫和提取物的情况下体外生长。公共卫生相关性包括阐明锥虫诱导的B细胞耗竭和宿主产生保护性抗体应答能力丧失的细胞基础。 叙述：丧失产生保护性抗体反应的能力，从而控制寄生虫血症是非洲锥虫病在人、家畜和实验室动物中的共同特征。使用小鼠模型，我们已经显示了感染诱导的B淋巴细胞发育的可逆阻断，其阻止了新形成和成熟B细胞池的维持，导致B细胞克隆耗尽，从而导致体液免疫能力的崩溃。我们建议确定受影响的B细胞的发育阶段和性质的发展块作为一个步骤，阐明这种新发现的疾病相关的免疫抑制机制的分子基础。

DESCRIPTION (provided by applicant): African trypanosomes are highly antigenically variable flagellated protozoa that cause fatal disease of people and domestic animals. About 300,000 persons have trypanosomiasis at present and the disease threatens an additional 60 million individuals in sub-Saharan Africa as well as severely limiting agricultural development in an area the size of USA. African trypanosomes replicate by binary fission in the blood and interstitial fluids and are controlled by host antibody responses against their variable coat antigens. Infected hosts lose the ability to mount an effective antibody response as the disease progresses resulting in poor control of newly arising trypanosome antigenic types, sustained pathology and eventually death. Our long term goal is to understand how T. brucei affects the B cell (antibody forming cell) system and to use this knowledge to develop strategic interventions that will preserve immune function and disease control. Our on- going analyses in the mouse model show that there is a rapid expansion of early B cell progenitors in the bone marrow and spleen, but the loss of newly formed and mature B cells from these organs, features of dyshematopoiesis that are reversed by clearance of trypanosomes from infected mice by treatment with the trypanocidal drug Berenil. These observations lead us to hypothesize that T. brucei induces a reversible block in B lymphopoiesis that prevents replenishment of the pools of new and mature B cell, which leads to B- cell clonal exhaustion and the collapse of B cell-mediated immunity. We will address this hypothesis in the following specific aims: i) identify the stage at which B lineage development is arrested in Trypanosoma brucei-infected mice ii) determine whether the block in B cell development results from truncated or aberrant B cell differentiation, iii) determine whether blocked B cells resume development when placed in trypanosome- free hosts, or grown in vitro, and if so, whether T. brucei or components of T. brucei prevent escape from the block in development. Methodologies will include: (i) cell surface differentiation antigen profiling using monoclonal antibodies specific for B cell developmental stages, (ii) transcription factor and immunoglobulin gene expression profiling of discrete B cell developmental stages isolated by fluorescence activate cell sorting (FACS) from the spleen and bone marrow of normal and trypanosome-infected mice, (iii) developmental analyses of B cell progenitors FACS isolated as in aim ii, and grown in immunodeficient mice (RAG-/-) and in vitro in the presence and absence of trypanosomes and extracts. Public heath relevance includes the elucidation of the cellular basis for trypanosome-induced B cell exhaustion and the loss of host ability to make protective antibodies responses. Narrative: Loss of the ability to make protective antibody responses and consequently to control parasitemia is a common feature of African trypanosomiasis in people, domestic and laboratory animals. Using the mouse model we have shown an infection-induced reversible block in B lymphocyte development that prevents the maintenance of pools of newly formed and mature B cell leading to B cell clonal exhaustion and thus, collapse of humoral immune competence. We propose to identify the affected B cell developmental stage and the nature of the developmental block as a step towards elucidating the molecular basis of this newly identified mechanism of disease-associated immuno-depression.