Molecular basis meningococcal group A capsular immunity

描述（由申请人提供）：A群脑膜炎球菌在撒哈拉以南非洲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组具有许多不寻常的特性，包括在婴儿中具有高度免疫原性，并引发增强抗体反应。此外，根据人的年龄或抗原刺激（自然暴露于A组或交叉反应生物体，或结合或非结合的PS疫苗接种），PS可引起杀菌或非杀菌的A组抗囊抗体。非杀菌的A族抗囊抗体在预防A族疾病中的作用尚不清楚，抗体功能活性差异的分子基础也知之甚少。我们的假设是，抗体亲和度和/或精细抗原特异性的差异，由抗体旁翼结构决定，是抗体功能活性差异的基础。在本提案中，我们将描述生活在北美或撒哈拉以南非洲的不同年龄的人自然获得和疫苗诱导的A组抗囊抗体，这两个地区暴露于A组脑膜炎球菌的风险差异很大。将在A组菌血症动物模型中测量被动抗体保护活性。为了确定人对A组PS抗体反应所利用的V区基因，并确定高突变的程度，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。该方法将补充克隆纯化的抗囊抗体的VH和VL区域的有限氨基酸测序，以及通过2D凝胶分离的H链和L链的MALDI-TOF质谱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群PS的分子基础，并将确定抗体保护活性中与年龄和疫苗相关差异的机制。这些结果可能导致建立更可靠的保护性免疫替代物，以评估为消除撒哈拉以南非洲流行性脑膜炎球菌病而开发的新型A组结合疫苗的效力。我们提出的研究也将增加我们对细菌PS抗原的人类抗体识别的认识，并解释为什么一些抗囊性抗体对被囊性细菌具有保护作用，而另一些则没有。

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.