T cells and antigen-presenting cells (APCs) such as macrophages produce glutamate, a toxic substance, which injures oligodendroglial cells and underlying axons. The activation of T cells can be blocked by various approaches, including statins and altered peptide ligands (APLs). Statins also inhibit the secretion of metalloproteases, and it has been suggested that they might, therefore, also act to block T cells from entering the central nervous system (CNS). Antibodies specific for alpha4-integrin also block the movement of T cells into the brain. OPN, osteopontin.