Kato M, Claveria F G, Maki Y, Sanda K, Tanaka T, Omata Y, Nagasawa H, Suzuki N
Obihiro University, Obihiro, Japan.
Pathobiology. 2007;74(1):50-6. doi: 10.1159/000101051.
We compared the reactivity of IgG1 and IgG2a antibodies in mouse sera after infection with virulent RH and low-virulent S273 and Beverley strains of Toxoplasma gondii against RH SAG1 recombinant p30 (rp30) and synthetic SAG1 peptides.
Infected mouse serum samples were collected 9 days after infection, and the level of total IgG, IgG1 and IgG2a against the RH SAG1 rp30 protein and twenty peptides of the RH SAG1 protein were assessed. The glycosylphosphatidylinositol (GPI) modification site, the hydrophilic-hydrophobic structure, the transmembrane region and the secondary structure of the SAG1 sequence of virulent and low-virulent strains were analyzed using software.
The virulent strain-infected mice produced a higher level of IgG1 but a lower IgG2a against the rp30 antigen, while the low-virulent strain-infected mice produced a higher level of IgG2a than the virulent strain. The difference in the secondary structure of SAG1 protein between the virulent and low-virulent strain was largely confined to amino acid positions 291-336, showing mutations and GPI anchor site.
The difference in the reactivity of IgG against the rp30 antigen and synthetic peptides between virulent and low-virulent strains points to the importance of the primary and secondary structure assumed by antigens in the activation of Th cells and, subsequently, in the induction of IgG and its subclasses.
我们比较了小鼠感染强毒株RH以及低毒株S273和贝弗利株刚地弓形虫后血清中IgG1和IgG2a抗体对RH SAG1重组p30（rp30）和合成SAG1肽段的反应性。
感染后9天收集感染小鼠的血清样本，评估针对RH SAG1 rp30蛋白以及RH SAG1蛋白的20个肽段的总IgG、IgG1和IgG2a水平。使用软件分析强毒株和低毒株SAG1序列的糖基磷脂酰肌醇（GPI）修饰位点、亲水-疏水结构、跨膜区域和二级结构。
感染强毒株的小鼠针对rp30抗原产生较高水平的IgG1但较低水平的IgG2a，而感染低毒株的小鼠产生的IgG2a水平高于感染强毒株的小鼠。强毒株和低毒株之间SAG1蛋白二级结构的差异主要局限于氨基酸位置291-336，表现出突变和GPI锚定位点。
强毒株和低毒株之间IgG对rp30抗原和合成肽段反应性的差异表明抗原呈现的一级和二级结构在激活Th细胞以及随后诱导IgG及其亚类方面的重要性。
