605. CHANGES IN PERIPHERAL IMMUNE FUNCTIONS INCLUDING IMMUNE CHECKPOINT SYSTEMS BY DIRECTLY ACTIVATING STRESS-RESPONSIVE NEURONS

Abstract Background Stress-related anxiety and depression are often accompanied by inflammatory diseases. Conversely, it is known that the risk of depression is higher in cases where there is a history of hospitalization due to infectious diseases or autoimmune disorders. Acute stress temporarily enhances host defense and adaptive responses, whereas chronic stress impairs homeostasis and reduces host defense via immunosuppression. Aims & Objectives In this study, we focused on the physiological function of CRHPVN neurons, which are the starting point of the hypothalamic-pituitary-adrenal (HPA) axis, which is a central regulator of the stress response. In this study, we used pharmacogenetic techniques to selectively activate this neural pathway, and investigated how fluctuations in activity limited to CRHPVN neurons affect peripheral immune regulation. Method We microinjected an adeno-associated virus (AAV) into the PVN of CRH-cre mice to drive the selective expression of a genetically modified human M3 muscarinic receptor (hM3Dq) in CRHPVN neurons. Subsequently, clozapine N-oxide (CNO, 3 mg/kg) was administered intraperitoneally to artificially modulate the activity of these neurons. In the acute activation group, a single dose of CNO was administered and spleen tissues were collected 30 min later, whereas in the chronic activation group, CNO was administered three times daily for 18 days and spleen tissues were harvested on the day following the final injection. The proportions of various immune cell populations in the spleen were then evaluated using FACS, and isolated lymphocytes were further analyzed by RT-qPCR to assess the expression of functional molecules. Results Both acute and chronic activation of CRHPVN neurons changed the proportion of CD4+ T cells in the spleen. A significant change in the proportion of natural killer (NK) cells was observed only in the acute activation group. Furthermore, gene expression analysis of immune checkpoint molecules in CD8+ T cells revealed that expression levels of some inhibitory immune check point receptors were increased in the chronic activation group, compared to the control group. In addition, the mRNA level for a specific chemokine that locally recruits diverse immune cells was increased, and this increased expression showed a strong positive correlation with the increased expression of the immune check point receptor. Discussion & Conclusions Our results showed that acute and chronic activation of CRHPVN neurons induced changes in the composition of immune cells in the spleen. Furthermore, we demonstrated for the first time that the expression of a specific chemokine was increased in splenic T cells during the process of exhaustion under stress-like conditions. These results provide novel insights into the interaction between the central nervous system and the immune system under stress, and deepen our understanding of abnormal immune regulation in the progression of mental diseases. In future research, we plan to further elucidate the molecular mechanisms of the central-peripheral immune circuit mediated by CRHPVN neurons, and clarify the relationship between central dysfunction caused by chronic stress and peripheral immune dysregulation.