Analysis of molecular escape mechanism of Theileria

在日本，牛已被发现感染瑟氏泰勒氏菌。通过使用单抗，已经证实了瑟氏锥虫种群或野外分离株之间的抗原性多态。Southern杂交结果也显示了瑟氏锥虫分离株的基因组多样性，作为寄生原虫逃避宿主免疫反应的机制之一，它们以不同的抗原形式表达表面分子。这种抗原变异与疟疾和锥虫在基因组水平上的改变、点突变、缺失或基因重排有关。为了了解瑟氏锥虫的逃避机制，我们分析了裂殖子的主要表面蛋白之一(P32)。从文库中分离出3个克隆，并测定了其核苷酸序列。核苷酸序列比较表明，至少有3个不同的寄生虫种群可能共存，在持续感染过程中可能发生优势寄生虫种群的转变。我们进一步分析了来自不同寄生虫血症高峰的寄生虫的p32抗原性差异。在持续感染过程中，不同高峰期的寄生虫之间存在抗原性差异，其基因变异与抗体应答有很好的相关性。体内种群的变化表明寄生虫逃避宿主免疫反应的机制之一，因为遗传上不同的种群可能表达不同的表面分子。

Cattle in Japan have been found to be infected with Theileria sergenti. Antigenic polymorphism has been demonstrated among stocks or field isolates of T.sergenti by using monoclonal antibodies. The results of Southern blot hybridization have also shown the genomic diversity of T.sergenti isolates.As one of the mechanisms that the parasitic protozoa evade host immune responses, they are known to express surface molecules with variant antigenic forms. This antigenic variation is related to change at genomic level, point mutatation, deletion or gene rearrangement in malaria and trypanosomes.To understand the evasion mechanism of T.sergenti, we analyzed one of the major surface proteins of merozoites (p32). We isolated 3 clones from cDNA library and nucleotide sequences were determined. Comparison of nucleotide sequences reveals at least 3 genetically different parasite population may coexist, and that transition of predominant parasite populations might occur during persistent infection. We further analyzed p32 antigenic difference of parasites obtained from different parasitemia peaks. Antigenic differences were observed among parasites from different peaks during persistent infection.There is a good correlation between the genotype changes and antibody responses. Population change in vivo indicates one of the parasite evasion mechanisms from host immune responses, because genetically different population may express antigenically different surface molecules.