Study of antigenic variation in Malaria for malaria vaccine.

血清(丝氨酸重复抗原，113 kDa)是恶性疟原虫的一种寄生空泡抗原。一种血清蛋白，可与流行区人血浆中的免疫球蛋白发生交叉反应，并在体外与抑制寄生虫生长的单抗交叉反应。为了开发疟疾疫苗，我们通过构建密码子用法改变的合成基因，建立了重组血清蛋白在大肠杆菌中的表达系统。我们构建了含47 kDa N-末端结构域、23 kDa中央结构域和C-末端结构域(Sugiyama et al.，in Press)的合成基因，用编码血清17-382个氨基酸残基(N-末端结构域)的重组产物SE47‘蛋白免疫小鼠和大鼠，诱导产生针对培养寄生虫的生长抑制抗血清。用无佐剂的十二烷基硫酸钠变性的SE47‘蛋白免疫动物，获得的抗血清抑制率最高。这一观察结果表明，SE47‘蛋白的一级结构对应于生长抑制抗体的诱导。由于蛋白质倾向于聚集在水溶液中，分子内或分子间的疏水相互作用可能掩盖了关键区域对宿主免疫系统的有效呈现。我们推测弗氏佐剂可能与SE47‘蛋白具有疏水相互作用(Sugiyama等人，同上)。SERA基因在分离株中被认为是很保守的，但我们发现诱导保护性抗体的N末端区域比基因的其他部分更容易发生氨基酸变化。针对N-末端区域开发的保护性免疫可能会加快该区域的进化速度(Morimatsu，Horii等人，正在准备中)。

SERA (serine repeat antigen, 113 kDa) is a parasitophorous vacuole antigen of Plasmodium falciparum. SERA protein that cross-reacts with IgG in human plasma from an endemic area and with a monoclonal antibody inhibitory against the parasite growth in vitro. For developing malaria vaccine, we have developed the expression system of recombinant SERA proteins in E.coli by constructing the synthetic genes with the altered codon usage. We have constructed synthetic genes covering three parts of SERA including N-terminal domain with 47 kDa, central domain with 23 kDa and C-terminal domain with (Sugiyama et al., in press).When mice or rats were immunized with SE47' protein that is one of the recombinant products encoding 17-382 amino acid residues of SERA (N-terminal domain), the growth inhibitory anti-sera against the cultural parasites were induced. The most inhibitory anti-sera was obtained when the animals were immunized with SDS-denatured SE47' protein without any adjuvants. This observation suggests that the primary structure of SE47' protein corresponds to the induction of growth inhibitory antibodies. Since the protein tends to aggregate in the aqueous solution, the hydrophobic interaction of intra or inter molecules might mask the effective presentation of the critical region to the host immune system. We suppose that the Freund's adjuvant may have a hydrophobic interaction with SE47' protein (Sugiyama et al., ibid).SERA gene is thought to be well conserved among the isolated strains, however, we found that the amino acid changes are more often occurred in the N-terminal region that induce protective antibody than the other parts of gene. The protective immunity developed against the N-terminal region may accelerate the evolution speed in the region (Morimatsu, Horii et al., in preparation).