ANTIGENIC VARIATON IN GIARDIA LAMBLIA

贾第虫主要表面抗原可变表达的发现 为研究植物的遗传变化提供了一个很好的模型， 真核生物 我们通过使用一种 针对主要170 kD表面抗原的细胞毒性单克隆抗体， 来自WB贾第虫滋养体克隆群体的抗原变体。 通过 从基因组克隆170 dK表面抗原的基因的一部分， 表达文库中，我们获得的证据表明，抗原是从一个 多基因家族，经历频繁的DNA重排。 的DNA 所述基因片段的序列编码富含半胱氨酸（12%）的多肽， 贾第虫滋养体的代谢标记证实了高半胱氨酸 170 kD表面抗原（富含半胱氨酸的蛋白质; CRP 170）的含量， 以及抗原变体的抗原变体。 CRP 170是免疫显性的 从生物学的角度来看，这是一种分子。 我们计划 从cDNA文库中克隆CRP 170基因， 与其他已知序列，特别是来自 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的表达如何在细胞中丢失， 抗原变体，CRP 170的转录将用 通过引物延伸确定转录起始位点 分析. 该区域的基因组克隆将与 计划中的等效区域，以映射含有CRP的染色体 170基因进行脉冲场电泳分析， 在表达和不表达CRP 170的线之间。 这些方法 可能提供关于变异表面表达如何 抗原被关闭。 此外，我们计划克隆富含半胱氨酸的 蛋白质基因的抗原变体，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新的变异抗原基因如何 这些研究的结果应该会产生重要的 关于贾第虫如何逃避免疫反应， 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.