Published online before print July 23, 2008
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* Department of Immunology and Microbiology, National Defense Medical College,
Division of Traumatology, National Defense Medical College Research Institute, and
Department of Laboratory Medicine, National Defense Medical College Hospital, Tokorozawa, Japan
1 Correspondence: Department of Microbiology, National Defense Medical College, 3-2 Namiki, Tokorozawa 359-8513, Japan. E-mail: btraums{at}ndmc.ac.jp
We previously proposed that mouse CD8+CD122+ T cells and human CD57+ T cells, which increase with age and exhibit potent IFN-
production, represent a double-edged sword as they play critical roles in host defense and the lethal IL-12/LPS-induced generalized Shwartzman reaction (GSR). However, our proposal was based solely on comparisons of young and old mice. In this study, we attempted to increase CD8+CD122+ T cells in young mice with exogenous IL-15 and confirm their countervailing functions in young mice. After young mice (6 weeks) were injected with IL-15, they showed significant increases in CD8+CD122+ T cells in the liver and spleen. Liver CD8+CD122+ T cells from IL-15-pretreated mice had a potent capacity to produce IFN-
after IL-12 injection or Escherichia coli infection. IL-15-pretreated mice showed increased survival to E. coli infections and enhanced anti-tumor activities against liver metastatic EL4 cells, as well as an exacerbation of the GSR. Correspondingly, liver CD8+CD122+ T cells produced more perforin than CD8+CD122– T cells in EL4-inoculated mice. Unexpectedly, comparable IL-15 treatment did not induce further increases in CD8+CD122+ T cells in aged mice and did not enhance their defenses against bacterial infection or tumor growth. Interestingly, however, nontreated, aged mice (50 weeks) showed twofold higher IL-15 levels (but not TNF or IFN-
) in liver homogenates compared with young mice. Our results further support that CD8+CD122+ T cells, which are increased physiologically or therapeutically by IL-15, are involved in antibacterial immunity, anti-tumor immunity, and the GSR.
Key Words: generalized Shwartzman reaction infection cytotoxicity EL4 liver immunity innate immunity
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