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Blood, 15 May 2006, Vol. 107, No. 10, pp. 3992-3999. Prepublished online as a Blood First Edition Paper on January 31, 2006; DOI 10.1182/blood-2005-09-3851.
IMMUNOBIOLOGY c-Myc acts downstream of IL-15 in the regulation of memory CD8 T-cell homeostasisFrom the Ludwig Institute for Cancer Research, Lausanne Branch, University of Lausanne; Swiss Institute for Experimental Cancer Research, Epalinges; and Genetics and Stem Cell Laboratory, Swiss Institute for Experimental Cancer Research and Swiss Institute of Technology Lausanne, Epalinges, Switzerland.
A subset of CD8 T cells in normal mice, expressing high levels of activation markers such as CD44, shares many properties with antigen-specific memory CD8 T cells. Homeostasis of CD44high CD8 T cells depends upon cytokines such as interleukin-15 (IL-15); however, the downstream signaling pathways regulating IL-15dependent homeostatic proliferation are poorly defined. Surprisingly, we show here that haploinsufficiency of the protooncogene c-myc leads to a highly selective decrease in CD44high CD8 T cells in mice. Although steady-state proliferation and survival of CD44high CD8 T cells appeared not to be dependent on c-Myc, homeostatic proliferation of c-myc+/ CD44high CD8 T cells in lymphopenic hosts was strongly reduced, and the residual homeostatic proliferation of these cells appeared to occur independently of IL-15. Moreover, c-myc+/ CD44high CD8 T cells responded very poorly to purified IL-15 in vitro. Backcrossing of c-myc+/ mice to IL-15/ mice revealed that the number of CD44high CD8 T cells decreased in an additive fashion in mice heterozygous for c-myc and IL-15. Finally homeostatic proliferation of antigen-specific memory CD44high CD8 T cells was also impaired in c-myc+/ mice. Collectively, our data identify c-Myc as a novel downstream component of the IL-15dependent pathway controlling homeostatic proliferation of memory CD44high CD8 T cells.
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