京都大学 / 0048 / 新制・課程博士 / 博士(人間健康科学) / 甲第20296号 / 人健博第44号 / 新制||人健||4(附属図書館) / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 高桑 徹也, 教授 三谷 章, 教授 浅野 雅秀 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

After initially being infected with a virus, before an adaptive immune response can be mounted, the innate immune system of a cell recognizes and responds to certain patterns present in pathogenic molecules. I studied the role of two genes—PIR1 and CD200R1—on the innate immune responses in two different mouse models of viral infection, infection with the picornavirus EMCV (encephalomyocarditis virus) and infection with HSV-1 (herpes simplex virus) in a mouse model of herpes simplex encephalitis, respectively. PIR1 is a putative RNA phosphatase that has been shown to play an important role in antiviral small RNA processing in C. elegans. It has also been shown to interact with the RIG-I-like receptor LGP2 in preliminary mammalian experiments. I sought to characterize the effect PIR1 has on the innate immune response to the virus EMCV in mice. By developing a PIR1-null mouse, I have found that the role of PIR1 in the progression of EMCV in mice is limited. However, in vitro studies show that PIR1 might play an important role in regulating foreign RNA recognition during the earliest time points post-infection. CD200R1 is an anti-inflammatory signaling molecule that is expressed on myeloidderived cells, and whose ligand is highly expressed within the central nervous system. I investigated the role of this receptor in an intracranial model of herpes simplex encephalitis. CD200R1KO mice show improved survival following direct intracranial infection with HSV. I found this increased survival can be attributed to decreased levels of viral replication in CD200R1KO compared to wild-type mice. Further investigation has shown that CD200R1 affects the signaling and upregulation of the pattern-recognition receptor TLR-2 (toll-like receptor 2), and thus CD200R1 may impact HSV-1 replication by affecting TLR2 signaling.

All organisms exist in some sort of symbiosis with their environment. The food we eat, air we breathe, and things we touch all have their own microbiota and we interact with these microbiota on a daily basis. As such, we employ a method of compartmentalization in order to keep foreign entities outside of the protected internal environments of the body. However, as other organisms seek to replicate themselves, they may invade our sterile compartments in order to do so. To protect ourselves from unfettered replication of pathogens or from cellular damage, we have developed a series of receptors and signaling pathways that detect foreign bodies as well as abnormal signals from our own perturbed cells. The downstream effector molecules that these signaling pathways initiate can be toxic and damaging to both pathogen and host, so special care is given to the regulation of these systems. One method of regulation is the production of endogenous small ribonucleic acids that can regulate the expression of various receptors and adaptors in the immune signaling pathways. In this dissertation, I present work that establishes an important protein in small ribonucleic acid regulation, Dicer, as an essential protein for regulating the innate immune response to immuno-stimulatory nucleic acids as well as regulating the productive infection of encephalomyocarditis virus. Depleting Dicer from murine embryonic fibroblasts renders a disparate type I interferon response where nucleic acid stimulation in the Dicer null cells fails to produce an appreciable interferon response while infection with the paramyxovirus, Sendai, induces a more robust interferon response than the wild-type control. Additionally, I show that Dicer plays a vital role in controlling infection by the picornavirus, encephalomyocarditis virus. Encephalomyocarditis virus fails to grow efficiently in Dicer null cells due to the inability for the virus to bind to the outside of the cell, suggesting that Dicer has a role in modulating viral infection by affecting host cellular protein levels. Together, this work identifies Dicer as a key protein in viral innate immunology by regulating both the growth of virus and also the immune response generated by exposure to pathogen associated molecular patterns. Understanding this regulation will be vital for future development of small molecule therapeutics that can either modulate the innate immune response or directly affect viral growth.