Studies on newly synthesized peptides having parasitocidal activity, and their mechanisms on host immune repsponses.

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(1) Studies on newly synthesized peptidesNewly synthesized peptide (Obioactin to Obiopeptides) of the activity units which were isolated from cytokines as an immunoregulator were examined in the effect of Toxoplasma chronically infected animals. Mice chronically infected with Toxoplasma gondii were treated with cyclophosphamide (Cyp), Obiopeptide- 1 (Obio- 1) and/or anti-CD4 monoclonal antibody to determine the effect of these immunosuppressive agents on the cysts in the brain. In the brain of non-treate, and infected Cyp-Obi-1 treated mice, with hematoxyline-eosine staining or anti-Toxoplasma ABC labelling staining, large typically rounded tissue cysts were mostly detected, and in some regions dividing microcysts were also observed in this experimental studies. In contrast, brain tissue from Cyp only or anti-CD4 treated infected mice had multiple degenerated cysts of varied sizes in some brain regions, as well as clusters of microcysts, however, such change was more striking in the an … More ti-CD4 treated mice. Infected mice treated with a combination of Cyp and Obio- I showed a significantly higher survival of 80% compared to 20% survival in mice treated with Cyp only. These results indicate that reactivation of rupture of tissue cysts in mice treated with Cyp, chronically infected with Toxoplasma, might be mainly mediated by CD4 positive cells rather than other CD8 and CD5 positive cells.(2) Production of transgenic mice carrying protozoan geneSAG-1 (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, BA LB/c or Fl (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/61 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 Fl (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