IWAKURA Yoichiro University of Tokyo, Professor, 医科学研究所, 教授 (10089120)
TAKAHASHI Michio University of Tokyo, Professor, 農学生命科学研究科, 教授 (30011943)
IGARASHI Ikuo The Research Center for Protozoan Molecular Immunology, Associate Professor, 原虫病分子免疫研究センター, 助教授 (80159582)
NAGASAWA Hidiyuki The Research Center for Protozoan Molecular Immunology, Professor, 原虫病分子免疫研究センター, 教授 (60172524)
SAITO Atushi Department of Beterinary Medicine, Professor, 畜産学部, 教授 (10002263)
(l)Studies on gene knock-out mice
Experiments on the host defense mechanisms against protozoan infection were performed using a macrophage scavenger receptor (SR) knock-out mice. As the SR is known to bind an extraordinary wide range of ligands including bacterial pathogens and mediate macrophage adhesion, it would be of interest to know the response of SR knock-out mice against protozoan infection. After intraperitoneal inoculation with Babesia microti, parasitemia was monitored daily by counting parasitized erythrocytes.
It was found that the course of parasitemia was not different between SR-/- and SR+/+ mice but the decrease in packed cell volume at 16-30 days after infection was less obvious in SR-/- than in SR+/+ mice. Increase in spleen weight after B.microti infection was also smaller in SR-/- than in SR+/+ mice. Flow cytometric studies revealed that the percentages of Thy 1.2+ as well as CD4+ T cells in spleen remained relatively higher in SR-/- mice as compared to those in SR+/
+ mice after infection. These results suggest that the SR knock-out mouse may become a useful model for the analysis of protozoan infection, especially with regard to the recovery processes, although it seems not to be directly involved in the defense mechanisms against B.microti infection.
Studies using other types of knock-out mice, such as IFN gamma and iNOS, were also conducted.
(2) Production of transgenic mice carrying protozoan gene
SAG-i (p30), the major surface protein of Toxoplasma gondii, is considered as an important ligand in the process of host cell invasion. If this protein is produced by host cells and interfere with that of parasites, then the host will become resistant to parasite invasion, Or, it may become more susceptible to infection due to the lack of immune response against p30 antigen. To generate transgenic mice carrying p30 gene, a 3.3kb DNA fragments, containing p30 cDNA fused with CAG promoter, that has been shown to direct a ubiquitous expression of a reporter gene in transgenic mice, were microinjected into one of the pronuclei of one-cell embryos of C57BL/6J, BALB/c or F1 (C57BL/6J x C3H/He) mice. The embryos were transferred to the oviducts of pseudopregnant ICR mice, In the first series of experiment using inbred strains, two p30-positive founders (male C57BL/6J and female BALB/c) were obtained among 159 mice that developed from the injected eggs. Furthermore, we have obtained several P30-founder mice expressing the gene product and transmitting the gene to the next generation, by using F1 (C57BL/6J x C3H/He) embryos. As far as we are aware, this is the first transgenic mice bearing a protozoan gene derived from T.gondii. Less