FoxO3a Modulates the Activation of Innate and Adaptive Immune Cells

• Main Author: Haribabu, Naveen
• Other Authors: Sad, Subash
• Language: en
• Published: Université d'Ottawa / University of Ottawa 2014
• Subjects: FoxO3a; CD8+ T cells; Dendritic cells
• Online Access: http://hdl.handle.net/10393/31782; http://dx.doi.org/10.20381/ruor-6666

The innate immune response mediates immediate control of the pathogen and is followed by the acquired immune response which is slower but ensures comprehensive elimination of the pathogen. Dendritic cells are unique innate immune cells that can phagocytose the pathogen and generate pathogen-associated antigenic peptides for presentation to T cells in order to initiate the acquired immune response. Dendritic cells also express cytokines which facilitate pathogen control and development of acquired immune responses, thus acting as a bridge between innate and acquired immune responses. CD8+ T cells are important cells of the adaptive immune system that play a key role in mediating clearance and protection against intracellular pathogens. Upon engagement by antigen-presenting cells, CD8+ T cells undergo massive expansion followed by a swift, extensive contraction to restore homeostasis. The mechanisms behind the expansion and contraction of CD8+ T cells are yet to be completely elucidated. FoxO3a is a transcription factor that is involved in the regulation of various vital cellular processes ranging from cell proliferation and cell metabolism to stress resistance and cell death. I have, therefore, investigated the role of FoxO3a signaling in the activation of dendritic cells and CD8+ T cells. My initial experiments indicated that FoxO3a regulates the homeostasis of various immune cells including CD8+ T cells and dendritic cells. CD8+ T cells lacking FoxO3a displayed enhanced proliferation, as evaluated by cell imaging, CFSE dilution and Ki67 staining, upon polyclonal stimulation in vitro. The modulation of cell proliferation by FoxO3a seemed to be p27kip-independent, as evaluated by western blotting. At later stages of stimulation, FoxO3a-deficient CD8+ T cells underwent reduced cell death, as assessed by cell counting and 7-AAD staining, and this seemed to be independent of Bim, Caspase 8 or Caspase 3 activation. In addition, FoxO3a regulated cytokine expression by CD8+ T cells while displaying similar NFκB activation in comparison to WT CD8+ T cells. Similar results were observed in dendritic cells upon LPS stimulation in vitro, wherein cytokine expression was higher in the FoxO3a-deficient dendritic cells and they also displayed enhanced antigen presentation to CD8+ T cells, as evaluated by CFSE dilution. Taken together, these results indicate that FoxO3a acts as a negative regulator of CD8+ T cell and dendritic cell activation.