EPIDEMIOLOGICAL STUDY FOR DEVELOPING SERA MALARIA VACCINE

恶性疟原虫富含丝氨酸抗原(血清)是一种很有前途的疟疾疫苗候选抗原。血清是一种126 kDa的无性血液期抗原，在滋养体晚期和裂殖体阶段大量产生。我们通过合成适合在大肠杆菌中表达的改变密码子用法的基因，在大肠杆菌中表达了血清蛋白的N-末端结构域(SE47‘)和中心结构域(SE50A)。SE47‘蛋白可诱导大鼠和小鼠产生寄生虫生长抑制抗体，而SE50A蛋白则不能。在这个项目中，我们检测了乌干达北部疟疾传播区Atopi Parish居民针对SE47‘和SE50A的免疫球蛋白亚类特异性滴度，以了解针对这些重组分子的自然免疫反应。研究表明，在阿托比教区的居民中，IgG3是对SE47‘的主要反应，而IgG3抗体水平的升高与10岁以下儿童的临床免疫有关。而对SE50A的应答以IgG1亚类为主，与临床免疫状态无关。我们进一步发现了以下相关性：1)IgG3水平的升高与居民外周血中寄生虫密度的降低有关。2)单个血清对体外培养的寄生虫的生长抑制作用与血清中抗SE47‘的IgG3抗体水平有关。3)加入重组SE47‘蛋白可中和抗疟原虫生长抑制作用。综上所述，抗SE47’IgG3是人类长期未知的主要抗疟疾免疫应答。获得的信息将为利用血清N端区重组蛋白加速疟疾疫苗的研制奠定基础。

P.falciparum serine rich antigen (SERA) is a promising malaria vaccine candidate antigen. SERA is a 126 kDa asexual blood stage antigen produced in large amounts specifically during late trophozoite and schizont stages. We have expressed N-terminal domain (SE47') and central domain (SE50A) of SERA protein in E.coli by synthesizing the genes with a changed codon usage suitable for expressing in E.coli. SE47'protein but not SE50A protein induced the parasite growth inhibitory antibodies in rat and mouse. In this project, we have examined the IgG subclass specific titers against SE47' and SE50A in residents of Atopi Parish, a region of intense malaria transmission in Northern Uganda, to see the natural immune responses against these recombinant molecules. It has been demonstrated that the IgG3 is the predominant response to SE47' in residents of Atopi Parish and that increased levels of IgG3 antibodies correlated with clinical immunity in children under 10 years old. Predominant response to SE50A was, however, IgG1 subclass and had no correlation with the clinical immunity. We have further found the following correlation ; 1) the increased levels of the IgG3 correlated with the lower parasite density in peripheral blood of the residents. 2) The growth inhibition of the cultured parasites by individual serum correlated with the levels of IgG3 antibodies against SE47' in the serum. 3) The observed parasite growth inhibition was neutralized by adding the recombinant SE47' protein.In summary, we have concluded that the anti-SE47' IgG3 is the major anti-malaria immune response in human that has been long time unknown. The obtained information will accelerate the malaria vaccine development with the recombinant protein of the N-terminal domain of SERA.