title: Profound enhancement of the IL-12/IL-18 pathway of IFN-gamma secretion in human CD8+ memory T cell subsets via IL-15.
abstract: Human memory CD8(+) T cell subsets, termed central memory and effector memory T cells, can be identified by expression of CD45RA, CD62 ligand (CD62L), and CCR7. Accordingly, functional differences have been described for each subset, reflecting unique roles in immunological memory. The common gamma-chain cytokines IL-15 and IL-7 have been shown to induce proliferation and differentiation of human CD8(+) T cell subsets, as well as increased effector functions (i.e., cytokines, cytotoxicity). In this study, we observed that addition of IL-15 or IL-7 to cultures of human CD8(+) T cells profoundly enhanced the IL-12-IL-18 pathway of IFN-gamma production. Importantly, IL-15 and IL-7 lowered the threshold concentrations of IL-12 and IL-18 required for induction of IFN-gamma by 100-fold. Comparison of IL-15 and IL-7 demonstrated that IL-15 was superior in its ability to enhance IL-12-IL-18-induced IFN-gamma, without evidence of a synergistic effect between IL-15 and IL-7. We also observed that IL-15- and IL-7-mediated enhancement of IL-12-IL-18-induced IFN-gamma production was a functional property of effector memory CD8(+) T cells. Despite a lack of association between cell division and acquisition of IL-12-IL-18-induced IFN-gamma, down-regulation of CD62L expression correlated well with increased IL-12-IL-18-induced IFN-gamma. Purified central memory T cells stimulated with IL-15 and IL-7 down-regulated CD62L and acquired potent IL-12-IL-18-induced IFN-gamma similar to effector memory T cells. Thus, in addition to its known role in development of T cell memory, IL-15 may amplify memory CD8(+) T cell effector functions by increasing sensitivity to proinflammatory cytokine stimulation.
authors.affiliation: Department of Microbiology and Immunology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, USA. rbsmeltz@vcu.edu
authors.forename: Ronald B
authors.initials: RB
authors.lastname: Smeltz
mesh_terms: D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects* / Q000276:immunology; D002454:Cell Differentiation; D006801:Humans; D007156:Immunologic Memory; D007371:Interferon-gamma / Q000096:biosynthesis*; D018664:Interleukin-12 / Q000494:pharmacology*; D019409:Interleukin-15 / Q000494:pharmacology*; D020382:Interleukin-18 / Q000494:pharmacology*; D015851:Interleukin-7 / Q000494:pharmacology; D019041:L-Selectin / Q000032:analysis; D008213:Lymphocyte Activation / Q000187:drug effects
chemical_list: D019409:Interleukin-15; D020382:Interleukin-18; D015851:Interleukin-7; D019041:L-Selectin; D018664:Interleukin-12; D007371:Interferon-gamma