IL-15Rα chaperones IL-15 to stable dendritic cell membrane complexes that activate NK cells via trans presentation

Natural killer (NK) cells are innate immune effectors that mediate rapid responses to viral antigens. Interleukin (IL)-15 and its high affinity IL-15 receptor, IL-15Rα, support NK cell homeostasis in resting animals via a novel trans presentation mechanism. To better understand how IL-15 and IL-15Rα support NK cell activation during immune responses, we have used sensitive assays for detecting native IL-15 and IL-15Rα proteins and developed an assay for detecting complexes of these proteins. We find that IL-15 and IL-15Rα are preassembled in complexes within the endoplasmic reticulum/Golgi of stimulated dendritic cells (DCs) before being released from cells. IL-15Rα is required for IL-15 production by DCs, and IL-15 that emerges onto the cell surface of matured DCs does not bind to neighboring cells expressing IL-15Rα. We also find that soluble IL-15–IL-15Rα complexes are induced during inflammation, but membrane-bound IL-15–IL-15Rα complexes, rather than soluble complexes, support NK cell activation in vitro and in vivo. Finally, we provide in vivo evidence that expression of IL-15Rα specifically on DCs is critical for trans presenting IL-15 and activating NK cells. These studies define an unprecedented cytokine–receptor biosynthetic pathway in which IL-15Rα serves as a chaperone for IL-15, after which membrane-bound IL-15Rα–IL-15 complexes activate NK cells via direct cell–cell contact

Homeostatic MyD88-dependent signals cause lethal inflamMation in the absence of A20

Toll-like receptors (TLRs) on host cells are chronically engaged by microbial ligands during homeostatic conditions. These signals do not cause inflammatory immune responses in unperturbed mice, even though they drive innate and adaptive immune responses when combating microbial infections. A20 is a ubiquitin-modifying enzyme that restricts exogenous TLR-induced signals. We show that MyD88-dependent TLR signals drive the spontaneous T cell and myeloid cell activation, cachexia, and premature lethality seen in A20-deficient mice. We have used broad spectrum antibiotics to demonstrate that these constitutive TLR signals are driven by commensal intestinal flora. A20 restricts TLR signals by restricting ubiquitylation of the E3 ligase tumor necrosis factor receptor–associated factor 6. These results reveal both the severe proinflammatory pathophysiology that can arise from homeostatic TLR signals as well as the critical role of A20 in restricting these signals in vivo. In addition, A20 restricts MyD88-independent TLR signals by inhibiting Toll/interleukin 1 receptor domain–containing adaptor inducing interferon (IFN) β–dependent nuclear factor κB signals but not IFN response factor 3 signaling. These findings provide novel insights into how physiological TLR signals are regulated

Macrophage-and Dendritic-Cell-Derived Interleukin-15 Receptor Alpha Supports Homeostasis of Distinct CD8+ T Cell Subsets

International audienceInterleukin-15 receptor alpha (IL-15Rα) is a pleiotropically expressed molecule that chaperones and trans-presents IL-15 to NK and T cells. To investigate whether IL-15Rα presented by different cells perform distinct physiological functions, we have generated four lines of mice lacking IL-15Rα in various cell types. We find that IL-15Rα expression on macrophages but not dendritic cells (DCs) supports the early transition of antigen specific effector CD8 + T cells to memory cells. After memory CD8 + T cell differentiation, IL-15Rα expression on DCs selectively supports central memory CD8 + T cells, whereas IL-15Rα expression on macrophages supports both central and effector memory CD8 + T cells. By contrast, mice lacking IL-15Rα on macrophages, DCs, or both, exhibit equivalent defects in NK cell homeostasis and activation. These studies define unique roles for macrophage expression of IL-15Rα and show that NK cells rely upon distinct IL-15Rα dependent IL-15 signals than memory CD8 + T cells. Moreover, they demonstrate the diversity, specification , and geographic restriction of cytokine signals

Activation of IFN-γ secretion by NK cells co-cultured with various combinations of poly I:C–stimulated BMDCs and supernatants from these BMDCs

BMDCs from various genotypes (indicated along the x axis of graph) were activated with poly I:C and then supplemented with supernatants exchanged from similarly activated BMDCs. Genotypes of DCs from which supernatants were derived are indicated by individual columns (gray, WT; white, 15KO; black, RαKO; checkered, mixture of 15KO and RαKO). ELISA quantitation of NK cell IFN-γ secretion is indicated on the y axis. Note that WT DCs activate NK cells regardless of the type of supernatant added. Note also that WT DC–derived supernatants containing IL-15–sIL-15Rα complexes fail to support or augment NK cell activation.<p><b>Copyright information:</b></p><p>Taken from "IL-15Rα chaperones IL-15 to stable dendritic cell membrane complexes that activate NK cells via trans presentation"</p><p></p><p>The Journal of Experimental Medicine 2008;205(5):1213-1225.</p><p>Published online 12 May 2008</p><p>PMCID:PMC2373851.</p><p></p

ELISA measurement of IL-15Rα (A) and IL-15 (B) proteins and IL-15–IL-15Rα complex (D) expression in lysates of poly I:C–stimulated BMDCs at the indicated time points

(C) ELISA determination of IL-15 protein levels after dissociation of IL-15–IL-15Rα protein complexes with 0.01% SDS and boiling. Lines represent data from WT (▪), (▴), and (▾) BMDCs. All data are representative of at least three separate experiments.<p><b>Copyright information:</b></p><p>Taken from "IL-15Rα chaperones IL-15 to stable dendritic cell membrane complexes that activate NK cells via trans presentation"</p><p></p><p>The Journal of Experimental Medicine 2008;205(5):1213-1225.</p><p>Published online 12 May 2008</p><p>PMCID:PMC2373851.</p><p></p

ELISA determination of sIL-15Rα, IL-15, and IL-15–sIL-15Rα proteins in sera from intact (A–C, on left) or chimeric (D–F, on right) mice stimulated with 25 μg/g poly I:C or PBS

Sera were collected 24 h after stimulation and IL-15 (B and E), sIL-15Rα (A and D), and IL-15–sIL-15Rα complex (C and F) protein levels were measured by ELISA. Each symbol reflects values obtained from individual mice.<p><b>Copyright information:</b></p><p>Taken from "IL-15Rα chaperones IL-15 to stable dendritic cell membrane complexes that activate NK cells via trans presentation"</p><p></p><p>The Journal of Experimental Medicine 2008;205(5):1213-1225.</p><p>Published online 12 May 2008</p><p>PMCID:PMC2373851.</p><p></p