Guillain-Barré Syndrome is believed to be an autoimmune disease, a condition in which the immune system attacks its own tissues as though they were foreign substances. Nerves are damaged by the immune system, usually in response to a viral or bacterial infection or other illness. As the immune system produces antibodies to fight the infection or illness, it may also produce antibodies that attack the covering (myelin sheath) of the peripheral nerves and sometimes the nerve fibers (axons). The resulting nerve damage leads to tingling and numbing sensations, muscle weakness, and paralysis.