Morrison W I, Taracha E L, McKeever D J
AFRC Institute for Animal Health, Compton, Near Newbury, UK.
Vet Parasitol. 1995 Mar;57(1-3):177-87. doi: 10.1016/0304-4017(94)03119-h.
Studies of the immune responses of cattle to Theileria parva have provided evidence that immunity to the parasite can operate at two levels, namely the sporozoite and the schizont-infected lymphoblast. Antibodies that neutralize the infectivity of sporozoites have been detected in the serum of hyperimmunized cattle, and a recombinant sporozoite surface antigen has been shown to induce neutralizing antibodies and protection against experimental challenge. However, the immunity that develops following primary infection with T. parva is accompanied by only low levels of antibodies to sporozoites; there is overwhelming evidence that under these circumstances protection is mediated by T cell responses against infected lymphoblasts. Potent class I MHC-restricted cytotoxic T lymphocyte (CTL) responses are detected in animals recovering from infection and treatment or challenge infections. Two recent findings have provided direct evidence for the importance of these responses in immunity. First, the strain specificity of CTL in cattle immunized with one stock of the parasite was found to correlate with the subsequent susceptibility of individual animals to challenge with a heterologous cloned parasite population (in these circumstances some animals are protected whereas others are susceptible to the heterologous challenge). Second, the adoptive transfer of lymphocytes highly enriched for CD8+ T cells, from immune to naive identical twin calves, was found to protect against experimental challenge. The CTL response in individual animals appears to be directed towards a limited number of antigenic epitopes. The antigenic specificity is determined in part by class I MHC phenotype although there is evidence that other phenomena such as antigenic competition are also involved. Current efforts are directed towards identification of the parasite antigens recognized by CTL with the eventual aim of exploring their potential for vaccination.
对牛对泰勒虫免疫反应的研究表明，对该寄生虫的免疫可在两个层面发挥作用，即子孢子和裂殖体感染的淋巴母细胞层面。在超免疫牛的血清中已检测到中和子孢子感染性的抗体，并且一种重组子孢子表面抗原已被证明可诱导中和抗体并提供针对实验性攻击的保护。然而，初次感染泰勒虫后产生的免疫仅伴随着低水平的子孢子抗体；有大量证据表明，在这些情况下，保护是由针对感染淋巴母细胞的T细胞反应介导的。在从感染、治疗或攻击感染中恢复的动物中检测到了强大的I类主要组织相容性复合体（MHC）限制性细胞毒性T淋巴细胞（CTL）反应。最近的两项发现为这些反应在免疫中的重要性提供了直接证据。首先，在用一种寄生虫株免疫的牛中，CTL的株特异性与个体动物随后对异源克隆寄生虫群体攻击的易感性相关（在这些情况下，一些动物受到保护，而另一些动物易受异源攻击）。其次，发现从免疫的同卵双生子犊牛向未免疫的同卵双生子犊牛过继转移高度富集CD8 + T细胞的淋巴细胞可提供针对实验性攻击的保护。个体动物中的CTL反应似乎针对有限数量的抗原表位。抗原特异性部分由I类MHC表型决定，尽管有证据表明其他现象如抗原竞争也参与其中。目前的努力旨在鉴定CTL识别的寄生虫抗原，最终目的是探索它们在疫苗接种方面的潜力。
