Online

Yang, Rui

Cell and Molecular Biology Program

2016

PhD

IL-6 is an inflammatory cytokine that contributes to the pathogenesis of many immunological diseases including rheumatoid arthritis, multiple sclerosis, systemic lupus erythematosus, allergic asthma, as well as the protection against infections caused by various pathogens. These are linked to its role in regulating CD4 T cell differentiation and effector function. Most of these functions are dependent on the IL-6-mediated signaling through the transcription factor Stat3. In this thesis, we identify a novel molecular mechanism by which IL-6 regulates CD4 T cell effector function. We show that IL-6-dependent signal raises the levels of mitochondrial Ca2+ late during activation of CD4 T cells. This is further used to prolong the expression of effector cytokines IL-4 and IL-21. The modulation of mitochondrial Ca2+ is mediated by the regulation of mitochondrial Stat3 and the formation of respiratory supercomplexes. Thus, in addition to the canonical signaling of IL-6 through Stat3 as a transcription factor, IL-6 also modulates mitochondrial Stat3 to regulate mitochondrial function in CD4 T cells. This could be an alternative pathway by which IL-6 regulates effector function of CD4 T cells and it could contribute to the pathogenesis of inflammatory disease. Little is known about the effects of IL-6 on CD8 T cells. In this thesis, we reveal a paradigm-shifting mechanism by which IL-6 regulates antibody production by converting CD8 T cells into B cell helpers through IL-21. Briefly, IL-6 promotes the differentiation of a subset of naïve CD8 T cells into a unique population of effector CD8 T cells characterized by the production of high levels of IL-21. IL-21-producing CD8 T cells provide help to B cells to induce isotype switching and protective antibody production during infection. In summary, this thesis provides new insights into both mechanistic and functional aspects of IL-6 in regulating T cell function. These findings may shed light on the development of new therapeutic approaches in treating autoimmune disorders and preventing infectious diseases.