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. 2007 Jan 9;104(2):588-93.
doi: 10.1073/pnas.0610115104. Epub 2007 Jan 3.

The IL-15/IL-15Ralpha on cell surfaces enables sustained IL-15 activity and contributes to the long survival of CD8 memory T cells

Noriko Sato  1 , Hiral J Patel, Thomas A Waldmann, Yutaka Tagaya
Affiliations

The IL-15/IL-15Ralpha on cell surfaces enables sustained IL-15 activity and contributes to the long survival of CD8 memory T cells

Noriko Sato et al. Proc Natl Acad Sci U S A. .

Abstract

We previously described unique features of the IL-15 receptor (IL-15R)alpha. IL-15Ralpha by itself forms stable complexes with IL-15 on cell surfaces and presents IL-15 in trans to neighboring natural killer/T cells. Moreover, the membrane IL-15/IL-15Ralpha complexes (membIL-15) undergo endosomal internalization but survive lysosomal degradation, allowing the complexes to recycle back to the cell surface. Here, we show that membIL-15+ cells act as a persistent source of IL-15 for the surrounding microenvironment (intercellular reservoir effect). Additionally, membIL-15+ cells give rise to augmented retention of IL-15 in the circulation as well as in tissues. Curiously, IL-15 retention was particularly associated with lungs, rather than with lymph nodes, in normal unstimulated mice, which correlated with the preferential homing of antigen-specific CD8 T cells to lungs during their contraction phase in an IL-15Ralpha-dependent manner. Furthermore, membIL-15, unlike soluble IL-15, caused sustained IL-15 signal transduction in the target cells. Collectively, these characteristics define IL-15 as a unique cytokine with prolonged in vivo survival and sustained biological action on the target cells, which may account for the proposed persistent action of IL-15 that helps the long-term survival of functional CD8 memory T cells in vivo.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
IL-15Rα-positive cells provide a persistent IL-15 reservoir. (A) Progressive release of the soluble IL-15 after recycling of the IL-15/IL-15Rα complexes. Human 293T cells (negative for IL-15 and IL-15Rα expression) were transfected with a plasmid encoding IL-15Rα (10) and incubated with 1 nM rhIL-15 (PeproTech) for 6 h to facilitate the recycling of IL-15/IL-15Rα complexes. Cells were then stripped of IL-15 (10) from the surface IL-15/IL-15Rα complexes and transferred to a cytokine-free culture. Aliquots were removed from the supernatant at the indicated time points, and the amounts of soluble IL-15 were determined by a specific ELISA. (B) Biological activity of the released IL-15. IL-15 concentrations in the aliquots collected above were determined by a specific ELISA. Biological activities of the released IL-15 and rhIL-15 (matched in concentrations) were compared by using a CTLL-2 proliferation assay. (C) The intercellular reservoir effect. The majority of the recycled IL-15 molecules remain associated with the plasma membrane fraction while a small fraction of the recycled IL-15 is released. Forty-eight hours after the initiation of the recycling experiment, 2 ml of the 293T culture was separated into supernatant and cellular pellets. Cells were homogenized and fractionated over a continuous sucrose-gradient by ultracentrifugation. The plasma-membrane fractions were identified by the migration of biotinylated cell-surface proteins, and the endosomal fractions were identified by the distribution of early endosomal protein 1 (10). Shown is the amount of IL-15 released back into the culture supernatant and those of IL-15 recovered in membrane-associated and endosomal fractions. The IL-15 in the plasma-membrane fractions was considered as cell-retained.
Fig. 2.
Fig. 2.
IL-15 retention in the circulation of WT, IL-15Rα−/−, and IL-15Rα Tg mice. (A) Unique prolonged retention of IL-15 in the circulation of WT mice. Mice were injected with 5 μg of rhIL-15, rhIL-2, and rhIL-7 (i.p.). Serum samples were collected at the indicated timings, and their cytokine concentrations were determined by specific ELISAs (R & D Systems). (B) Rapid clearance of administered IL-15 from IL-15Rα−/− mice. Five micrograms of rhIL-15 was injected (i.p.) into WT or IL-15Rα−/− mice. (C) Augmented IL-15 retention in IL-15Rα Tg mice. Five micrograms of rhIL-15 was injected (i.p.) into IL-15Rα Tg mice or WT mice. Because the serum IL-15 concentrations from WT mice were too compressed to visualize at the given scale, an expanded graph with a readable scale is inserted on the right. (D) Concomitant prolonged expansion of CD44hiCD8 T cells in IL-15-injected IL-15Rα Tg mice. Peripheral blood mononuclear cells from IL-15-injected WT or IL-15Rα Tg mice were analyzed by flow cytometry, and percentages of CD44hi population in the entire CD8 subset are shown.
Fig. 3.
Fig. 3.
Increased IL-15 retention in mice challenged by poly I:C. Mice were injected with 5 μg of rhIL-15 (i.p.) after treatment with or without poly I:C (100 μg, i.p. injected 24 h before the IL-15 injection). The IL-15 concentrations in serum samples were determined by a specific ELISA (n = 5).
Fig. 4.
Fig. 4.
Tissue distribution of injected IL-15. Bars are as follows: A, serum; B, liver; C, kidney; D, spleen; E, lung; F, LN; G, thymus. WT mice were injected with 5 μg of rhIL-15 (i.p.). Nine days after the administration, various tissues were collected from these mice and homogenized (except blood samples), and the IL-15 associated with each tissue was determined by a specific ELISA. Serum, liver, and spleen showed no meaningful levels of IL-15 (<10 pg/ml) whereas values from lungs and LNs appeared significantly positive (n = 4). ∗, P < 0.0001; †, P = 0.0001 compared with serum level.
Fig. 5.
Fig. 5.
Detection of nonhematopoietic IL-15Rα positive cells in lung tissue. (A) IL-15Rα expression in lung cell subsets demonstrated by membIL-15 staining. For the detection of IL-15Rα, cells from the homogenized lung tissue were incubated with 1 nM rhIL-15 for 30 min on ice, followed by staining with anti-IL-15 (10) (R & D Systems), antiCD45, and anti-I-Ab antibodies for 30 min on ice. Four major populations were defined and analyzed by separate gates as shown (Left). From each gate, the morphological information (forward light scatter vs. side light scatter) and IL-15 staining are shown (Right). In addition, mean fluorescence intensity of the surface IL-15 staining is shown for each cell population. Cells from R3 (CD45−) showed significant surface IL-15 staining. (B) Increase of IL-15 retention after poly I:C injection into WT mice. Bars are as follows: A, serum; B, liver; C, kidney; D, spleen; E, lung; F, LN; G, thymus. After systemic poly I:C and 5 μg of rhIL-15 injections, tissue samples were collected and homogenized from mice. The amounts of tissue-associated IL-15 were determined by a specific ELISA, and the fold increase after the poly I:C challenge is shown.
Fig. 6.
Fig. 6.
Prolonged IL-15 signaling in CD8 T cells by the membIL-15. Spleen cells from F5 TCR Tg mice were stimulated with the nominal peptide (NP68) in the presence of H-2b Ag-presenting cells for 2 days, followed by an 18-h cytokine-free culture to arrest them in a quiescent status. MACS-purified CD8 T cells were incubated with soluble rhIL-15 (A), rhIL-15 in the presence of IL-15Rα Tg DCs (B), or rhIL-15 with IL-15Rα−/− DCs (C). The cells were then permeabilized/fixed and analyzed for S6 phosphorylation by two-color flow cytometry. (A) Time kinetics of S6 phosphorylation to various doses of transpresented IL-15 (by membIL-15) in F5 CD8 T cells. (B) S6 phosphorylation to various doses of soluble IL-15 (soluble IL-15 with IL-15Rα−/− DCs). (C) S6 phosphorylation to various doses of soluble IL-15 (IL-15 without any DCs). (D) Kinetic comparison of the S6 phosphorylation pattern in CD8 T cells caused by soluble IL-15 and membIL-15.
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References

    1. Grabstein KH, Eisenman J, Shanebeck K, Rauch C, Srinivasan S, Fung V, Beers C, Richardson J, Schoenborn MA, Ahdieh M, et al. Science. 1994;264:965–968. - PubMed
    1. Bamford RN, Grant AJ, Burton JD, Peters C, Kurys G, Goldman CK, Brennan J, Roessler E, Waldmann TA. Proc Natl Acad Sci USA. 1994;91:4940–4944. - PMC - PubMed
    1. Waldmann TA, Tagaya Y. Annu Rev Immunol. 1999;17:19–49. - PubMed
    1. Kundig TM, Schorle H, Bachmann MF, Hengartner H, Zinkernagel RM, Horak I. Science. 1993;262:1059–1061. - PubMed
    1. Willerford DM, Chen J, Ferry JA, Davidson L, Ma A, Alt FW. Immunity. 1995;3:521–530. - PubMed

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