Characterization of newly defined protective antigens of Plasmodium berghei XAT.

疟疾是热带地区，特别是儿童长期健康不良，有时甚至死亡的一个主要原因。尽管付出了巨大的努力和费用，但在不久的将来不太可能普遍获得高效的疟疾疫苗。我们尚未研制出有效疫苗的原因之一是缺乏关于疟疾寄生虫与人类之间宿主-寄生虫关系的基本信息。海洋疟疾模型是收集这类信息的最佳方法。柏氏疟原虫XAT是辐照诱导的致死菌株P. berghei NK65的减毒变种。之前，我们建立了杂交瘤产生保护性单克隆抗体（mAb）对抗伯氏假体XAT感染。在本研究中，我们建立了检测感染小鼠血浆中保护性单克隆抗体靶抗原b1d6 Ag的双位点检测系统。被动转移实验显示，保护性单抗对BALB/c小鼠的抑制作用可达1 ~ 1000^< >水平，而对C57BL/6小鼠的抑制作用可达1 ~ 50^< >水平，提示保护性抗原的作用可能受宿主遗传背景的影响。采用亲和层析法纯化保护抗原，采用LC-MS/MS法分析肽段。重新测序后估计了保护性抗原肽片段的氨基酸序列。有趣的是，在一种假设的恶性疟原虫（3D7菌株）蛋白中发现了高度同源性的序列，但在海洋疟原虫中却没有。对保护性抗原特性的研究正在进行中。了解保护性单克隆抗体识别的抗原参与保护的机制将为开发血期疟疾疫苗提供重要信息。

Malaria is a major cause of chronic ill health, sometimes of death, in the tropics, particularly in childhood. Despite considerable effort and expense, a generally available and highly effective malaria vaccine is unlikely in the near future. One of the reasons that we have not get the effective vaccine yet would be the lack of basic information regarding host-parasite relationships between malaria parasite and human beings. Marine malaria models would be the best for accumulating such information, Plasmodium berghei XAT is an irradiation induced attenuated variant of the lethal strain, P. berghei NK65. Previously, we established hybridomas producing protective monoclonal antibodies (mAb) against P. berghei XAT infection. In the present study, we established the two-sited assay system for the detection of B 1D6 Ag, that is the target antigen of protective monoclonal antibodies, in plasma of infected mice. Passive transfer experiments revealed that administration of the protective mAb suppressed the parasitemia in BALB/c mice up to 1 to 1000^<th> level although in C57BL/6 mice up to one to 50^<th> level, suggesting that the effect of protective antigens could be affected by the genetic background of hosts. The protective antigens were purified by affinity chromatography and the peptides were analyzed by LC-MS/MS. The amino acid sequences of peptides fragment of the protective antigens were estimated after de novo sequencing. Interestingly, sequences with high homology were found in a hypothetical protein of P. falciparum (3D7 strain) but not in marine malaria parasites. The study of characteristics of the protective antigens is now ongoing. To know the mechanisms by which the antigens recognized by protective mAbs are involved in the protection would provide an important information for the development of a blood-stage malarial vaccine.