| The c-Jun N-terminal kinase (JNK) belongs to the mitogen-activated protein kinase (MAPK) family, and is implicated in the regulation of a variety of cellular functions, including survival, proliferation, differentiation and apoptosis. There are three isoforms in the JNK kinase family, including JNK1, JNK2and JNK3. JNK3is selectively expressed in brain, heart, and testis, but not in hematopoietic cells, whereas JNK1and JNK2are expressed ubiquitously. JNK is activated by its upstream kinases in response to multiple extracellular stress stimuli and cytokines, and sequentially phosphorylates its downstream substrates. Moreover, the kinase activity of JNK is also regulated by the scaffold proteins. JNK signaling cascade is an important mediator which couples the extracellular stimulating signals into intracellular transcription factors. By cross-talking with other signaling pathways, the JNK signaling pathway becomes a complicated regulation network responding specifically and effectively to extracellular stimulating signals, and is involved in regulation of various cellular processes. The role of JNK depends on the cell type, and each isoform (JNK1and JNK2) has different functions.The levels of JNK expression in T and B cells are very low prior to their activation. The expression of these protein kinases is induced during antigen stimulation. Activation of JNK can be triggered by numerous antigen receptors and cytokine receptors on the surface of immune cells recognizing environmental stimuli. Majority studies have been focused on the role of JNK pathway in T helper cell (Th) responses, including proliferation, differentiation, and maintenance of Thl/Th2polarization. However, there is very limited understanding of JNK functions in governing cell-mediated immune response, especially the individual mechanism of JNK1and JNK2in regulating cellular immunity.Cytolytic T lymphocytes (CTLs) are indispensable effectors in antiviral immunity. After infection, naive CD8+T cells recognize antigens (Ag) and become activated. Following activation, the virus-specific CD8+T cells undergo rapid and massive clonal expansion, and differentiated into the effector CTLs acquiring the MHC class I restriction and antigen specificity. The effector mechanism whereby CTLs execute their function to kill virus-infected target cells is through perforin/granzyme-mediated cytotoxity and by means of secreted antiviral cytokines such as IFN-y.Ectromelia virus (ECTV) and variola virus (VARV) are closely related orthopoxviruses. Both of them are members of the poxvirus family, sharing high homology. The infectivity of ECTV is specie-restricted. ECTV infection in mice causes pathogenesis and host immune response which is similar to that of VARV infection in humans. The mousepox model is considered to be one of the best available animal models to study pathogenesis of and the immune response to poxvirus or even general virus infections. Recovery from ECTV infection is closely related with host immune response and requires the combined actions of macrophage, NK, NKT, CTL and B cells, as well as the effector functions of cytokines such as interferons. However, cellular immunity mediated by CTLs plays a pivotal role in purging viral infection.Using a well-defined mousepox model, we investigated the immune responses of JNK1-deficient and JNK2-deficient mice to ECTV. We demonstrated that JNK may have important effects on conducting CD8+T cell-mediated antiviral responses. Deficiency of either JNK1or JNK2impaired the ability of viral clearance, subsequently resulted in an increased susceptibility in ECTV-resistant mice. The impairment of virus-specific CD8responses in JNK-deficient mice was not directly due to the alteration of effector T cell expansion, since both JNK1and JNK2had limited impact to the activation-induced cell death of CD8+T cells, and only JNK2-deficient mice experienced a significant change in CD8+T cell proliferation after acute ECTV infection. However, absence of either JNK1or JNK2resulted in reduced activation of CD8+T cells and the number of virus-specific CTLs. Moreover, the production of granzyme B and IFN-y is impaired in JNK1-deficient and JNK2-deficient mice. Finally, CTL showed delayed and defective cytotoxicity in the absence of either JNK1or JNK2. Results in this dissertation suggest that JNK pathway acts as a critical intermediate in antiviral immunity through regulating the activation and effector function of CD8+T cells rather than altering the expansion of these cells. In summary, these findings provide further understanding to the functional diversity of different isoform of JNK in the regulation of CTL antiviral immunity. It will not only lead to understand the mechanism underlying CTL response against viral infection, but also may shed light on the development of potential strategies for infectious disease and tumor immunotherapy. |
