Shiels B R, d'Oliveira C, McKellar S, Ben-Miled L, Kawazu S, Hide G
Department of Veterinary Parasitology, University of Glasgow, UK.
Mol Biochem Parasitol. 1995 Jun;72(1-2):149-62. doi: 10.1016/0166-6851(95)00074-b.
The immunodominant merozoite/piroplasm surface antigen of Theileria parasites has potential as a diagnostic reagent and as a component of a sub-unit vaccine. This molecule is known to be antigenically diverse, and it is important to determine the nature and extent of this heterogeneity. In the present study nucleotide sequences, representing alleles of the gene (Tams1) encoding this molecule in Theileria annulata were compared to each other and to sequences of homologous genes in Theileria sergenti, Theileria buffeli and Theileria parva. This analysis revealed that a region of the polypeptide which contains putative N-linked glycosylation sites is particularly diverse and, in analogy to retroviral systems, may indicate selection of variable glycosylation sites or amino acid epitopes to evade the bovine immune response. This conclusion was also made from the results of a phylogenetic analysis which compared the variable region of the genes with a second region, which appeared to show no bias for diversity or functional constraint. The results indicated that the variable sequence encoding putative glycosylation sites has diverged, both within and between Theileria species, at a much faster rate than the rest of the molecule. Southern blot analysis of T. annulata populations from within a single geographical region detected six possible variant Tams1 alleles. However, a correlation between restriction-fragment-length polymorphism (RFLP) patterns detected by the Tams1-1 gene probe and geographical location could not be made. In addition, although a high prevalence of one particular RFLP was found, this is unlikely to be the result of a clonal population structure, as we present evidence for significant parasite genotypic variability within a single endemic region.
泰勒虫属寄生虫的免疫显性裂殖子/梨形虫表面抗原具有作为诊断试剂和亚单位疫苗成分的潜力。已知该分子具有抗原多样性，确定这种异质性的性质和程度很重要。在本研究中，将代表环形泰勒虫中编码该分子的基因（Tams1）等位基因的核苷酸序列相互比较，并与瑟氏泰勒虫、水牛泰勒虫和小泰勒虫中同源基因的序列进行比较。该分析表明，多肽中包含推定的N-连接糖基化位点的区域特别多样，类似于逆转录病毒系统，可能表明选择可变糖基化位点或氨基酸表位以逃避牛的免疫反应。这一结论也是从系统发育分析的结果得出的，该分析将基因的可变区域与第二个区域进行了比较，第二个区域似乎没有多样性或功能限制的偏向。结果表明，编码推定糖基化位点的可变序列在泰勒虫物种内部和物种之间的分歧速度比分子的其余部分快得多。对来自单个地理区域的环形泰勒虫群体进行的Southern印迹分析检测到六个可能的变异Tams1等位基因。然而，无法确定由Tams1-1基因探针检测到的限制性片段长度多态性（RFLP）模式与地理位置之间的相关性。此外，尽管发现一种特定RFLP的患病率很高，但这不太可能是克隆群体结构的结果，因为我们提供了单个流行区域内寄生虫基因型存在显著变异性的证据。
