Furthermore, B7-1 expression is documented on activated microglia and APCs, such as brain-infiltrating macrophages, in response to a number of cues, including exposure to LPS and proinflammatory cytokines (3, 4), infections of the brain (5), and neurodegenerative diseases such as multiple sclerosis (MS) (6–8) (Table 1). This evidence concerns the gene CD80 and neurodegenerative disease.