| Research Abstract |
Among HSP families, HSP90 has been given much attention. This protein is involved in cellular functions by forming complexes with many cellular proteins such as kinases, phosphatases, nuclear hormone receptors, actin, tubulin, and the proteasome. Fruit flies with homozygous mutations of HSP90 gene cannot survive and those with heterozygous mutation frequently show morphological abnormalities. Over-expression of HSP90 enhances the virulence of the yeast Saccharomyces cerevisiae in mice. We have studied the expression mechanism of parasite. HSP90 and its correlation with virulence of murine malaria parasite. HSP90 was strongly expressed in parasite from B6 mice infected with the L strain of P. yoelii and only slightly expressed in parasite from mice infected with the L strain. Interestingly, HSP90 expression was not detected in parasites from SCID mice treated with anti-CD4 and anti-TcR-αβ or anti-IFN-γmonoclonal antibodies, but not in parasite from those treated with anti-CD8, anti-TcR-
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γδ or anti-IL-4 antibody. By using SCID mice transferred with CD4ィイD1-ィエD1 or CD8ィイD1-ィエD1 splenic cells of BALB/c, we demonstrated again that CD4ィイD1+ィエD1 T cells but not CD8ィイD1+ィエD1 T cells were indispensable for the expression of parasite HSP90. Immunoelectron microscopic analysis confirmed that massive HSP90 signal was expressed in nuclei of schizonts and merozoits but only slightly in cytoplasma of these parasites and in trophozoits and gametocytes. Reactive oxygen species (ROS) and nitric oxide (NO) but not IFN-γ treatment increased HSP90 expression in parasite cultured in vitro. HSP90 expression was decreased significantly at later period of infection with the L strain, possibly because of immune-suppression during the infection. Parasite from immune-component mice was highly infective than that from SCID mice, suggesting that parasites expressing HSP90 have higher infectivity than parasites not expressing HSP90. Finally, the amino acid sequence of P. yoelii HSP90 was deduced from the cDNA sequence. In conclusion, parasite HSP90 is a virulent factor and induced by host immune response.
In brief, our results show that HSPs appear to play crucial roles in host-parasite interaction. Less
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