| Research Abstract |
Various species of Gram-positive bacteria produce cholesterol-dependent cytolysins(CDCs). We have constructed several. CDC proteins including amino- acid replacement and truncation, in-order to analyze the molecular mechanism of cytolysis and cytokine induction. CDC family proteins LLO, LSO and PLY produced by L. monocytogenes, L. seeligeri, and S. pneumoniae, respectively showed domain 4-deperident cytolytic activity and cytokine-inducing activity that was not dependent on domain 4 as well. It was found that the different domains of the same protein molecule are responsible for different biological activities. LLO induced IL-12 and IL-18 production from macrophages, and in turn these cytokines induced NK-cell dependent IFN-g. TLR2/TLR4/CD14 appeared to be involved in the cytokine response of macrophages, and domain 1-3 was capable of inducing NF-kB activation. Though most of the recombinant CDC proteins exhibited the cytokine-inducing ability, ILO derived from L. ivanovii was not active in cytokine induction despite of the high homology to LLO and LSO. It appeared that N-terminal sequence of domain 1 was highly essential for the cytokine-inducing activity, we have constructed various amino acid replacement. It was found that the PEST sequence is important in the activity. This study clearly indicated that many CDC family proteins of Gram-positive bacteria are active in cytokine-induction that is different from a well-known cytolytic activity. This novel activity appeared to be involved in the host response in the infection by CDC-producing Gram-positive bacteria.
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