Pfefferkorn E R, Schwartzman J D, Kasper L H
Ciba Found Symp. 1983;99:74-91. doi: 10.1002/9780470720806.ch5.
Toxoplasma gondii, an obligate intracellular parasite, is readily grown in nearly all cultured cells. The host-parasite relationship in these cultures can often be explored by using mutant host cells or mutant parasites. Host cells incapable of incorporating uracil or hypoxanthine, which were excellent precursors for T. gondii, allowed the demonstration that the host cell had no access to the purine or pyrimidine nucleotide pools of the parasite. Conversely, a T. gondii mutant that was defective in the principal pyrimidine salvage pathway allowed the demonstration that the parasite had no access to pyrimidine nucleotide or deoxynucleotide pools of the host cell. One metabolite that must pass from the host cytoplasm to T. gondii is a purine. An absolute defect in purine biosynthesis by the parasite was disclosed by growing T. gondii in a mutant host cell that was, itself, incapable of purine synthesis. T. gondii grew normally at 40 degrees C in a mutant host cell that was incapable of protein synthesis at that temperature. Thus, the parasite did not depend on concomitant protein synthesis in the host cell. An antigenic mutant of T. gondii was isolated with the aid of parasiticidal monoclonal antibody. This mutant lacked a major parasite surface protein, of relative molecular mass (Mr) 22 000. The antibody used to select this mutant immunoprecipitated a protein of this Mr from the wild-type parasite.
刚地弓形虫是一种专性细胞内寄生虫，几乎能在所有培养细胞中轻松生长。在这些培养物中，宿主与寄生虫的关系通常可以通过使用突变的宿主细胞或突变的寄生虫来探究。无法掺入尿嘧啶或次黄嘌呤的宿主细胞，而尿嘧啶和次黄嘌呤是刚地弓形虫的优质前体，这表明宿主细胞无法获取寄生虫的嘌呤或嘧啶核苷酸库。相反，在主要嘧啶补救途径中存在缺陷的刚地弓形虫突变体表明，寄生虫无法获取宿主细胞的嘧啶核苷酸或脱氧核苷酸库。一种必须从宿主细胞质传递到刚地弓形虫的代谢物是嘌呤。通过在自身无法进行嘌呤合成的突变宿主细胞中培养刚地弓形虫，揭示了寄生虫在嘌呤生物合成方面的绝对缺陷。刚地弓形虫在40摄氏度下能在无法在该温度下进行蛋白质合成的突变宿主细胞中正常生长。因此，寄生虫不依赖于宿主细胞中的伴随蛋白质合成。借助杀寄生虫单克隆抗体分离出了刚地弓形虫的一个抗原突变体。该突变体缺乏一种相对分子质量（Mr）为22000的主要寄生虫表面蛋白。用于选择该突变体的抗体从野生型寄生虫中免疫沉淀出了这种相对分子质量的蛋白质。
