Inflammatory or degenerative diseases of the brain and spinal cord, such as multiple sclerosis, may be related to problems with an individual s immune system. However, more information is needed on the ways in which the cells of the immune system interact with the central nervous system (CNS). This study will compare tests performed on both healthy volunteers and individuals who have signs or symptoms of immune-related damage to their CNS. This study will include two groups of subjects at least 12 years old. Subjects will either have symptoms of immune-related CNS damage, or will be healthy volunteers selected for comparison purposes. Study participants will visit the NIH Clinical Center on an outpatient basis for an initial evaluation visit. During the visit, patients will provide a comprehensive medical history and undergo a neurological examination, and will provide blood samples for research purposes. The healthy volunteers will be asked to schedule a return visit for a magnetic resonance imaging (MRI) procedure, and may be asked to undergo other tests requested by the study researchers on an as-needed basis. The group of patients with symptoms of immune-related CNS damage will be asked to undergo a series of tests, including the following: * MRI procedures, with a minimum of three brain MRIs and one spinal cord MRI taken approximately 4 weeks apart * A diagnostic lumbar puncture, performed on an outpatient basis * Tests of brain and vision activity * Additional blood and tissue samples Patients with symptoms of immune-related CNS damage may be offered the opportunity to participate in additional followup tests with NIH researchers.