Project Summary Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system (CNS) and existing treatment options are only modestly effective for slowing eventual disease progression. The United States has approximately 500,000 cases of MS in adults and worldwide there are approximately 2.5 million cases of adult MS. This disease initially involves immune-mediated demyelination and transection of axons within the CNS, and later transitions into a neurodegenerative condition associated with insufficient neurotrophic support in the CNS. Cognitive and walking impairments are common in upwards of 60-80% of persons with MS, and are risk factors for unemployment, disability, and compromised quality of life. These issues underscore the importance of developing new therapy regimens to mitigate and reduce the severity of MS. Immunotherapy through immunosuppressive agents has been the standard of care used to alleviate chronic relapse forms of MS. Many of these drugs work by sequestering lymphocytes to the lymph nodes, thereby reducing the number of circulating white blood cells resulting in fewer cells available to attack the nerve fibers. All of the available immunotherapy agents have side effects associated with the suppression of the immune system with the most critical including increased blood pressure, liver problems and death. Based on the idea that a reduction of lymphocytes can alleviate symptoms of MS, we propose a novel therapeutic intervention for targeting lymphocytes residing in the cervical lymph nodes (CLNs) using focused ultrasound in the experimental autoimmune encephalomyelitis (EAE) rat model of MS. Focused ultrasound allows hyperthermia to be targeted to specific tissues, i.e., the CLNs which primarily service the CNS, to degrade or kill lymphocytes residing in the CLNs. By killing or degrading the function of lymphocytes in the CLNs, we hypothesize that the severity of EAE will be alleviated. Our recent pilot study has provided first ever evidence that this approach results in remittance of EAE symptoms statistically significantly more than without therapy. However, our pilot study was on a limited number of animals with a single exposure condition. To further test our hypothesis and demonstrate the efficacy of this novel EAE therapy, a larger study is warranted to explore a range of therapy exposure conditions, larger animal numbers to detect smaller effects and analyses to elucidate mechanisms responsible for the therapy effects and quantify side effects. To address these needs, two specific aims are proposed. The first specific aim is to explore a range of ultrasound therapy exposure conditions and quantify the effects of the exposure conditions on the therapy outcomes. The range of exposure conditions to be explored include: thermal dose, timing between treatments and EAE injection dose/treatment response. The second specific aim is to elucidate the effects of treatment on susceptibility to an upper-respiratory viral infection. We will quantify any reduction in immune response resulting as a side effect from our FUS therapy.