Molecular basis meningococcal group A capsular immunity

描述（由申请人提供）：A 组脑膜炎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 族多糖具有许多不寻常的特性，包括在婴儿中具有高免疫原性，以及引发加强抗体反应。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，或结合与未结合的 PS 疫苗接种），PS 可以引发杀菌或非杀菌的 A 组抗荚膜抗体。非杀菌性 A 组抗荚膜抗体在预防 A 组疾病中的作用尚不清楚，并且对抗体功能活性差异的分子基础知之甚少。我们的假设是，由抗体互补位的结构决定的抗体亲合力和/或精细抗原特异性的差异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人群中自然获得的和疫苗诱导的 A 组抗荚膜抗体的特征，这两个地区接触 A 组脑膜炎球菌的风险截然不同。将在即将开发的 A 组菌血症动物模型中测量被动抗体保护活性。为了定义人类抗体对 A 组 PS 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库分析。该方法将通过对克隆纯化的抗荚膜抗体的 VH 和 VL 区进行有限氨基酸测序以及通过 MALDI-TOF 质谱法对 2D 凝胶分离的 H 链和 L 链进行质量指纹分析来确定 V 区基因进行补充。总之，这些研究将阐明人类抗体识别 A 组 PS 的分子基础，并将确定抗体保护活性中与年龄和疫苗相关的差异的潜在机制。这些结果可能会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 A 组结合疫苗的功效。我们提出的研究还将增加我们对人类抗体识别细菌 PS 抗原的了解，并解释为什么一些抗荚膜抗体能够针对被荚膜细菌提供保护，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.