ANTIGENIC VARIATON IN GIARDIA LAMBLIA

贾第鞭毛虫主要表面抗原可变表达的发现 为人类遗传变化的研究提供了一个很好的模型 真核生物。我们通过使用一种 针对170kD主要表面抗原的细胞毒性单抗的筛选 WB贾第鞭毛虫滋养体克隆群体的抗原性变异。通过 从基因组中克隆170 DK表面抗原基因的一部分 表达文库，我们获得了该抗原来自于 经历频繁DNA重排的多基因家族。DNA 该基因片段的序列编码一个富含半胱氨酸(12%)的多肽和 贾第鞭毛虫滋养体代谢标记证实半胱氨酸含量高 170kD表面抗原(富含半胱氨酸的蛋白；CRP170)的含量 以及一种抗原变异体。CRP170是一种免疫显性基因 分子是在大的生物学角度下产生的。我们计划 从cDNA文库中克隆ENTER CRP170基因并进行序列比较 与其他已知的序列，特别是那些来自 其他生物，以深入了解CRP的结构和功能 170蛋白质。为了确定170的表达是如何在 抗原性变异体，CRP170的转录将用 用引物延伸法确定转录起始点 分析。这一区域的基因组克隆将与 从平面图绘制包含C反应蛋白的染色体(S)的等效区域 170基因的脉冲场电泳法并寻找差异 在表达CRP170和不表达CRP170之间。这些方法是 可能提供关于变异表面如何表达的信息 抗原已关闭。此外，我们计划克隆富含半胱氨酸的 来自抗原性变体的蛋白基因，并执行相同类型的 分析。这将提供有关 富含半胱氨酸的蛋白质以及一种新的变异抗原基因的线索 已打开。这些研究的发现应该会产生重要的 关于贾第虫如何逃避免疫反应的信息，并可能 与疫苗开发直接相关。

The discovery of variable expression of a major surface antigen of Giardia has provided an excellent model for the study for genetic change in eukaryotic organisms. We demonstrated antigenic variation by using a cytotoxic monoclonal antibody for a major 170 kD surface antigen to select antigenic variants from cloned populations of WB Giardia trophozoites. By cloning a portion of the gene for the 170 dK surface antigen from a genomic expression library, we obtained evidence that the antigen is from a multigene family which undergoes frequent DNA rearrangements. The DNA sequence of the gene fragment encodes a cysteine-rich (12%) polypeptide and metabolic labeling of Giardia trophozoites verified the high cysteine content of the 170 kD surface antigen (cysteine-rich protein; CRP 170) as well as that of an antigenic variant. CRP 170 is an immunodominant molecule which is produced in large biologic perspectives. We plan to clone the enter CRP 170 gene from a cDNA library and compare the sequence with other known sequences, especially those of cysteine-rich protein from other organisms, to gain insight into the structure and function of the CRP 170 protein. In order to determine how expression of 170 is lost in the antigenic variants, transcription of CRP 170 will be analyzed with determination of the transcription initiation site by primer extension analysis. A genomic clone of this region will be compared to the equivalent region from the plan to map the chromosome(s) containing the CRP 170 gene by using pulsed field electrophoresis and to look for difference between lines expressing and not expressing CRP 170. These approaches are likely to provide information about how expression of a variant surface antigen is turned off. In addition, we plan to clone the cysteine-rich protein gene from an antigenic variant and perform the same types of analyses. This will provide information about the relationship of the cysteine-rich proteins as well as clues to how a new variant antigen gene is turned on. The findings of these studied should yield important information about how Giardia evades the immune response and may have direct relevance for vaccine development.