Molecular basis meningococcal group A capsular immunity

描述(申请人提供)：A组脑膜炎双球菌在撒哈拉以南非洲地区引起脑膜炎和败血症的大规模流行。与其他细菌多糖(PS)相比，A组具有许多不同寻常的特性，包括对婴儿具有高度的免疫原性，并可启动增强抗体反应。此外，根据患者的年龄或抗原刺激(自然暴露于A组或交叉反应生物体，或结合与非结合PS疫苗接种)，PS可激发杀菌或非杀菌A组抗囊抗体。非杀菌性A组抗囊抗体在预防A组疾病中的作用尚不清楚，抗体功能活性差异的分子基础也鲜为人知。我们的假设是，抗体亲和力和/或良好的抗原特异性的差异，由抗体副表位的结构决定，是抗体功能活性差异的基础。在这项提案中，我们将描述居住在北美或撒哈拉以南非洲的不同年龄段人群的自然获得和疫苗诱导的A组抗囊抗体，这两个地区接触A组脑膜炎双球菌的风险截然不同。被动抗体保护活性将在A组菌血症动物模型中进行测量，该模型将被开发出来。为了确定人类对A组PS的抗体反应所利用的V区基因，并确定超突变的程度，我们将对A组PS特异性Fab片段进行组合库克隆和表达文库分析。该方法的补充是对克隆纯化的抗囊抗体的VH和VL区进行有限的氨基酸测序，并通过用2D凝胶分离的H链和L链的MALDI-TOF质谱仪进行质量指纹分析来确定V区基因。总之，这些研究将阐明人类抗体识别A组PS的分子基础，并将确定与年龄和疫苗相关的抗体保护活性差异背后的机制。这一结果可能导致建立更可靠的保护性免疫替代物，用于评估正在开发的用于消除撒哈拉以南非洲流行性脑膜炎球菌病的新的A组结合疫苗的效力。我们提出的研究还将增加我们对细菌PS抗原的人类抗体识别的一般知识，并解释为什么一些抗囊膜抗体对被包裹的细菌具有保护作用，而另一些则不能。

DESCRIPTION (provided by applicant): Group A meningococci cause massive epidemics of meningitis and sepsis in sub-Saharan Africa. Compared to other bacterial polysaccharides (PS), group A has a number of unusual properties including being highly immunogenic in infants, and priming for booster antibody responses. Also, depending on the age of the person, or antigenic stimulus (natural exposure to group A or cross-reacting organisms, or conjugated vs. unconjugated PS vaccination), the PS can elicit bactericidal or non-bactericidal group A anticapsular antibodies. The role of non-bactericidal group A anticapsular antibodies in protection against group A disease is unknown, and the molecular basis for differences in antibody functional activity are poorly understood. Our hypothesis is that differences in antibody avidity and/or fine antigenic specificity, dictated by the structure of the antibody paratope, underlie these disparities in antibody functional activity. In this proposal we will characterize naturally acquired and vaccine-induced group A anticapsular antibodies from persons of different ages living in North America or sub-Saharan Africa, two areas of the world with vastly different risks of exposure to group A meningococci. Passive antibody protective activity will be measured in an animal model of group A bacteremia that will be developed. To define the V region genes utilized by the human antibody response to group A PS, and to determine the extent of hypermutation, we will perform combinatorial repertoire cloning and expression library analyses of group A PS-specific Fab fragments. This approach will be complemented by limited amino acid sequencing of VH and VL regions of clonally purified anticapsular antibodies and determination of V region genes by mass fingerprint analysis by MALDI-TOF mass spectroscopy of H and L chains separated by 2D gels. Together, these studies will elucidate the molecular basis by which human antibodies recognize group A PS, and will identify the mechanisms underlying the age- and vaccine-related disparities in antibody protective activity. The results may lead to establishment of more reliable surrogates of protective immunity for assessment of the efficacy of new group A conjugate vaccines being developed for elimination of epidemic meningococcal disease in sub-Saharan Africa. Our proposed studies also will increase our knowledge of human antibody recognition of bacterial PS antigens in general, and explain why some anticapsular antibodies confer protection against encapsulated bacteria, while others do not.