IL-15 plays a major role in the persistence of Tax-specific CD8 cells in HAM/TSP patients

NK cell receptors in antiviral immunity

An array of inhibitory and activating receptors initially identified on NK cells are also expressed by conventional CD8+ alphabeta T cells. New evidence strongly implicates these 'NK cell receptors' in modulating NK cell and virus-specific CD8+ T cell responses against a variety of viral infections. Precise regulation of NK cell and T cell responses by these receptors optimizes antiviral immunity while preventing immunological bystander pathology and autoimmunity.

CD25+CD4+ T cells contribute to the control of memory CD8+ T cells

Previously we demonstrated that IL-15 and IL-2 control the number of memory CD8+ T cells in mice. IL-15 induces, and IL-2 suppresses the division of these cells. Here we show that CD25+CD4+ regulatory T cells play an important role in the IL-2-mediated control of memory phenotype CD8+ T cell number. In animals, the numbers of CD25+CD4+ T cells were inversely correlated with the numbers of memory phenotype CD8+ T cells with age. Treatment with anti-IL-2 caused CD25+CD4+ T cells to disappear and, concurrently, increased the numbers of memory phenotype CD8+ T cells. This increase in the numbers of CD8+ memory phenotype T cells was not manifest in animals lacking CD4+ cells. Importantly, adoptive transfer of CD25+CD4+ T cells significantly reduced division of memory phenotype CD8+ T cells. Thus, we conclude that CD25+CD4+ T cells are involved in the IL-2-mediated inhibition of memory CD8+ T cell division and that IL-2 controls memory phenotype CD8+ T cell numbers at least in part through maintenance of the CD25+CD4+ T cell population.

The IL-2/IL-15 receptor systems: targets for immunotherapy

Although interleukin-2 (IL-2) and -15 (IL-15) share two receptor subunits and many functions, at times they provide contrasting contributions to T-cell-mediated immune responses. IL-2, through its pivitol role in activation-induced cell death (AICD), is involved in peripheral tolerance through the elimination of self-reactive T cells. In contrast, in general IL-15 manifests antiapoptotic actions and inhibits IL-2-mediated AICD. IL-15 stimulates persistence of memory phenotype CD8+ T cells, whereas IL-2 inhibits their expression. Humanized monoclonal antibodies that recognize IL-2Ra, the private receptor for IL-2, are being employed to inhibit allograft rejection and to treat T-cell leukemia/lymphoma. Therapies directed toward inhibiting the actions of the inflammatory cytokine, IL-15, are proposed for an array of autoimmune disorders as well as diseases associated with the retrovirus human T-cell lymphotrophic virus 1.