Use of bovine-RBC-substituted SCID mice for the studies of Babesia parasites

利用牛红细胞替代（Bo-RBC-SCID）小鼠建立了多种巴贝斯虫寄生虫研究实验系统，获得了以下结果：(1)分离出一种新的巴贝斯虫寄生虫：利用Bo-RBC-SCID小鼠，从日本北海道放牧牛中分离出一种新的巴贝斯虫寄生虫（大岛株）。该分离株在形态、抗原结构和基因组DNA上与卵巴贝虫型菌株Miyake株不同，但具有相同的媒介蜱长角血蜱。因此，提出了奥岛巴贝斯虫。感染巴贝斯虫的Bo-RBC-SCID小鼠表现出多种临床症状，包括血红蛋白尿、黄疸和神经症状，因此可以作为研究巴贝斯虫致病机制的有用模型系统。(2)巴贝斯虫的持续感染和抗原变异：用Bo-RBC-SCID小鼠分离巴贝斯虫进行流行病学调查，发现北海道奥库什里岛牛的巴贝斯虫持续感染较多。在同一只感染动物的不同时间点获得的样本中，观察到抗原谱和基因组DNA的显著差异，这意味着可能存在抗原差异。制备了oovata Oshima菌株的单克隆抗体，并选择了在Bo-RBC-SCID小鼠体内产生抑制寄生虫生长的克隆1A2。我们发现1A2抗体可以识别一个56-kDa的裂殖子表面蛋白（P56），该蛋白可能与抗原变异有关。获得编码P56的cDNA克隆，测序并在大肠杆菌中表达。(3)小鼠脑巴贝斯虫病模型：Bo-RBC-SCID小鼠感染牛巴贝斯虫后出现中枢神经症状。光镜下发现SCID小鼠脑微血管中有被寄生的红细胞。电镜观察显示，感染红细胞表面出现“旋钮”状的锥形突起，感染红细胞粘附在SCID小鼠脑毛细血管内皮上。这些发现与牛脑巴贝斯虫病和人类脑疟疾的发现惊人地相似，因此，在Bo-RBC-SCID小鼠中感染牛双球菌可以用作这些疾病的模型。少

Various experimental systems were developed for the studies of Babesia parasites using bovine-red blood cell-substituted (Bo-RBC-SCID mice), and following results were obtained(1) Isolation of a new Babesia parasite : Using Bo-RBC-SCID mice, a new bovine Babesia parasite (Oshima strain) were isolated from grazing cattle in Hokkaido, Japan. The isolate differed from Miyake strain, which is the type strain of Babesia ovata, in terms of morphology, antigenic structure and genomic DNA,but shared the same vector tick, Haemaphysalis longicornis. Thus, Babesia ovata oshimensis n. var. has been proposed. Bo-RBC-SCID mice infected with Babesia parasites showed various clinical symptoms, including hemoglobinuria, jaundice and nerve symptoms, and therefore may serve as a useful model system for studying the mechanisms of disease caused by Babesia parasites.(2) Persistent infection and antigenic variation of Babesia : Epidemiological survey with parasite isolation using Bo-RBC-SCID mice revealed t … More hat Babesia parasites persistently infect cattle in Okushiri island, Hokkaido. Significant variations in antigenic profiles and genomic DNA were observed among the samples obtained at different time points from a single infected animal, implicating possible antigenic variations. Monoclonal antibodies against B.ovata Oshima strain has been made, and a clone, 1A2, which produces antibody inhibitory to the parasite growth in Bo-RBC-SCID mice was selected. The 1A2 antibody was found to recognize a 56-kDa merozoite surface protein (P56) which may potentially be involved in antigenic variation. The cDNA clone encoding P56 was obtained, sequenced, and expressed in E.coli.(3) A mouse model for cerebral babesiosis : Bo-RBC-SCID mice infected with Babesia bovis were found to display central nerve symptoms. Light microscopy revealed sequestration of parasitized RBC in the microvessels in the brain of SCID mice. Electron microscopy showed the presence of "knob" like conical projections on the surface of infected RBCs, with which the parasitized RBCs appeared to adhere to the capillary endothelium in SCID mice brain. Those findings are strikingly similar to those found in bovine cerebral babesiosis and also in human cerebral malaria, and therefore B.bovis-infection in Bo-RBC-SCID mice can be used as a model for those disease. Less