Glossary antibodies - proteins made by the immune system that bind to structures (antigens) they recognize as foreign to the body. antigen - a structure foreign to the body, such as a virus. The body usually responds to antigens by producing antibodies. ataxia - a condition in which the muscles fail to function in a coordinated manner. autoimmune disease - a disease in which the body's defense system malfunctions and attacks a part of the body itself rather than foreign matter. blood/brain barrier - a membrane that controls the passage of substances from the blood into the central nervous system. cerebrospinal fluid - the colorless liquid, consisting partially of substances filtered from blood and partially by secretions released by brain cells, that circulates around and through the cavities of the brain and spinal cord. Physicians use a variety of tests-electrophoresis, isoelectric focusing, capillary isotachophoresis, and radioimmunoassay-to study cerebrospinal fluid for abnormalities often associated with MS. cytokines - powerful chemical substances secreted by T cells. Cytokines are an important factor in the production of inflammation and show promise as treatments for MS. demyelination - damage caused to myelin by recurrent attacks of inflammation. Demyelination ultimately results in nervous system scars, called plaques, which interrupt communications between the nerves and the rest of the body. experimental allergic encephalomyelitis (EAE) - a chronic brain and spinal cord disease similar to MS which is induced by injecting myelin basic protein into laboratory animals. fatigue - tiredness that may accompany activity or may persist even without exertion. gadolinium - a chemical compound given during MRI scans that helps distinguish new lesions from old. human leukocyte antigens (HLAs) - antigens, tolerated by the body, that correspond to genes that govern immune responses. Also known as major histocompatibility complex. immunoglobulin G (IgG) - an antibody-containing substance produced by human plasma cells in diseased central nervous system plaques. Levels of IgG are increased in the cerebrospinal fluid of most MS patients. immunosuppression - suppression of immune system functions. Many medications under investigation for the treatment of MS are immunosuppressants. interferons - cytokines belonging to a family of antiviral proteins that occur naturally in the body. Gamma interferon is produced by immune system cells, enhances T-cell recognition of antigens, and causes worsening of MS symptoms. Alpha and beta interferon probably exert a suppressive effect on the immune system and may be beneficial in the treatment of MS. lesion - an abnormal change in the structure of an organ due to disease or injury. magnetic resonance imaging (MRI) - a non-invasive scanning technique that enables investigators to see and track MS lesions as they evolve. myelin - a fatty covering insulating nerve cell fibers in the brain and spinal cord, myelin facilitates the smooth, high-speed transmission of electrochemical messages between these components of the central nervous system and the rest of the body. In MS, myelin is damaged through a process known as demyelination, which results in distorted or blocked signals. myelin basic protein (MBP) - a major component of myelin. When myelin breakdown occurs (as in MS), MBP can often be found in abnormally high levels in the patient's cerebrospinal fluid. When injected into laboratory animals, MBP induces experimental allergic encephalomyelitis, a chronic brain and spinal cord disease similar to MS. oligodendrocytes - cells that make and maintain myelin. optic neuritis - an inflammatory disorder of the optic nerve that usually occurs in only one eye and causes visual loss and sometimes blindness. It is generally temporary. paresthesias - abnormal sensations such as numbness, prickling, or "pins and needles." plaques - patchy areas of inflammation and demyelination typical of MS, plaques disrupt or block nerve signals that would normally pass through the regions affected by the plaques. receptor - a protein on a cell's surface that allows the cell to identify antigens. retrobulbar neuritis - an inflammatory disorder of the optic nerve that is usually temporary. It causes rapid loss of vision and may cause pain upon moving the eye. spasticity - involuntary muscle contractions leading to spasms and stiffness or rigidity. In MS, this condition primarily affects the lower limbs. T cells - immune system cells that develop in the thymus gland. Findings suggest that T cells are implicated in myelin destruction. transverse myelitis - an acute spinal cord disorder causing sudden low back pain and muscle weakness and abnormal sensory sensations in the lower extremities. Transverse myelitis often remits spontaneously; however, severe or long-lasting cases may lead to permanent disability. white matter - nerve fibers that are the site of MS lesions and underlie the gray matter of the brain and spinal cord.