|Budget Amount *help
¥6,500,000 (Direct Cost : ¥6,500,000)
Fiscal Year 1997 : ¥1,300,000 (Direct Cost : ¥1,300,000)
Fiscal Year 1996 : ¥1,500,000 (Direct Cost : ¥1,500,000)
Fiscal Year 1995 : ¥3,700,000 (Direct Cost : ¥3,700,000)
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
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