| Research Abstract |
In recent years, many new staphylococcal enterotoxins (SEs) have been reported. It has been known that certain SE genes are associated with mobile genetic elements such as pathogenicity islands, prophages, and plasmids. These facts imply that superantigenic toxin genes are transferred horizontally between staphylococcal strains. There is a possibility that these mobile genetic elements have played an important role in the evolution of S.aureus as a pathogen. To investigate pathobiology and epidemiology of these newly identified SEs, we had undertaken studies shown in below.
1.We have developed a comprehensive detection system for 18 kinds of classical and newly described staphylococcal superantigenic toxin genes using four sets of multiplex PCR. Superantigenic toxin genotyping of Staphylococcus aureus for 69 food poisoning isolates and 97 healthy human nasal swab isolates revealed 32 superantigenic toxin genotypes and showed that many S.aureus isolates harbored multiple toxin genes. Ana
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lysis of the relationship between toxin genotypes and toxin genes encoding profiles of mobile genetic elements suggests its possible role in determining superantigenic toxin genotypes in S.aureus as combinations of toxin gene-encoding mobile genetic elements (FEMS Microbiology Letters,246 : 191-198,2005).
2.We have determined complete nucleotides sequence of sed, selj and selj encoding plasmid, p196, using transposomics strategy. This plasmid is encoding penicillin resistance operon and Cd-resistance operon, in addition to three kinds of SE (SE1) genes.
3.We characterized a novel staphylococcal entertoxin (SE)-like putative toxin SE1R. The SE1R protein showed significant T cell stimulation activity. MHC class II molecules were required for T cell stimulation by SER. SER stimulated T cells bearing receptors Vβ3,11,12,13.2, and 14. These results suggested that SER acts as a superantigen (Infection and Immunity 72 : 3664,2004).
4.We investigated the biological properties of a novel staphylococcal enterotoxin (SE)-like toxin type P (SE1P). SE1P induced a substantial proliferative response and the production of cytokines IL-2, IFN-γ, TNF-α, and IL-4 from human T cells when administered at a concentration of 0.4 pM or more. The expression of MHC class II molecules on accessory cells was required for T cell stimulation by SE1P. SE1P selectively stimulated a vast number of human T cells bearing receptors Vβ 5.1,6,8,16,18, and 21.3. These results indicated that SE1P acts as a superantigen. SE1P proved to be emetic in the house musk shrew emetic assay, although at a relatively high dose (Infection and Immunity, 73 : in press,2005).
5.We constructed and expressed a non-toxic mutant SEC (mSEC) and investigated whether immunization with mSEC, devoid of superantigenic activity, can protect against S.aureus infection. Mice were immunized with mSEC and challenged with viable S.aureus. Bacteria counts in the organs in mSEC-immunized mice were significantly lower and the survival rate was higher than those of the control group. Immunization with mSEC induced strongly the production of T-helper 2 type antibodies, immunoglobulin G1 and immunoglobulin G2b. Immunization with mSEC devoid of superantigenic properties provides protection against S.aureus infection and the protection might be mediated by the IL-10 and IL-4 induction and down-regulation of IFN-γ, as well as SEC neutralizing antibodies (Infection and Immunity, 73 : 174-180,2005). Less
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