Lyme disease patients make antibodies that recognize Borrelia burgdorferi, the bacteria that cause illness. When the disease progresses from early to late stages, these antibodies may change. A protein on the outside of B. burgdorferi is called VlsE, and antibodies that bind to a portion of it called the membrane-proximal domain illustrate this. These specific antibodies were low in patients with early disease, and were increased in patients with symptoms typical of later illness, such as neurological symptoms.