RESUMO
LFA-1 signaling is required for the generation of central memory CD8(+) T cells in priming phase. However, its role for effector and memory CD8(+) T cell survival in transition and maintenance phases is elusive. We transferred effector and memory CD8(+) T cells into C57BL/6 and CD54(-/-) mice, which were generated by cultivation of ovalbumin (OVA)-pulsed dendritic cells (DC(OVA)) with naïve CD8(+) T cells derived from transgenic OT I mice and purified from effector CD8(+) T cell-transferred C57BL/6 mice, respectively. We then assessed kinetics of T cell survival using PE-H2-K(b)/OVAI tetramer and FITC-CD8 staining by flow cytometry. We found that survival of transferred effector and memory CD8(+) T cells in CD54(-/-) mice significantly decreased (p<0.05) compared to that in C57BL/6 mice due to an increased T cell apoptosis, which is mediated via downregulation of proapoptotic Bid, anti-apoptotic Bcl-2, Bcl-X(L) and pro-Caspase-8, and up-regulation of apoptotic Bax and cleaved Caspase-3 and -7 by RNA array and Western blotting analyses. Decreased expression of CD27 and IL-15R on transferred CD8(+) T cells with less survival was found to be associated with increased T cell apoptosis, which was confirmed by silencing CD27 with siRNA transfection or using CD8(+) (IL-15R(-/-))T cells for adoptive transfer into C57BL/6 mice. These data indicate that LFA-1 signal defect-induced CD8(+) T cell apoptosis is associated with reduced CD27 costimulation and IL-15R survival signal. Therefore, our study provides important evidence on and elucidates the molecular mechanism associated with the role LFA-1 signaling plays in effector and memory CD8(+) T cell survival.
Assuntos
Linfócitos T CD8-Positivos/imunologia , Linfócitos T CD8-Positivos/metabolismo , Caspases/metabolismo , Antígeno-1 Associado à Função Linfocitária/metabolismo , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Receptores de Interleucina-15/metabolismo , Membro 7 da Superfamília de Receptores de Fatores de Necrose Tumoral/metabolismo , Transferência Adotiva , Animais , Apoptose/imunologia , Apoptose/fisiologia , Sequência de Bases , Linfócitos T CD8-Positivos/citologia , Células Dendríticas/imunologia , Regulação para Baixo , Feminino , Memória Imunológica , Molécula 1 de Adesão Intercelular/genética , Molécula 1 de Adesão Intercelular/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Modelos Imunológicos , RNA Interferente Pequeno/genética , Receptores de Interleucina-15/deficiência , Receptores de Interleucina-15/genética , Transdução de Sinais , Membro 7 da Superfamília de Receptores de Fatores de Necrose Tumoral/antagonistas & inibidores , Membro 7 da Superfamília de Receptores de Fatores de Necrose Tumoral/genéticaRESUMO
Interleukin 15 (IL-15) is a pleiotropic cytokine that is hardly detectable in biological fluids. Here, we show that IL-15 forms functional heterocomplexes with soluble high affinity IL-15 receptor alpha (IL-15Ralpha) chain in mouse serum and cell-conditioned medium, which prevents IL-15 detection by ELISA. We also demonstrate that two soluble IL-15Ralpha (sIL-15Ralpha) sushi domain isoforms are generated through a novel alternative splicing mechanism within the IL-15Ralpha gene. These isoforms potentiate IL-15 action by promoting the IL-15-mediated proliferation of the CTLL cell line and interferon gamma production by murine NK cells, which suggests a role in IL-15 transpresentation. Conversely, a full-length sIL-15Ralpha ectodomain released by tumor necrosis factor-alpha-converting enzyme (TACE)-dependent proteolysis inhibits IL-15 activity. Thus, a dual mechanism of sIL-15Ralpha generation exists in mice, giving rise to polypeptides with distinct properties, which regulate IL-15 function.