Altered Peptide Ligands is the name of an experimental treatment for multiple sclerosis. A ligand is a form of chemical bond between molecules. T cells (a type of white blood cell) and antibodies stick to foreign proteins with a bond called a peptide ligand. In MS, it is thought that T cells and antibodies form peptide ligands with the proteins in myelin. By introducing synthetic myelin proteins that are altered very slightly - the altered peptide ligands - researchers hope to reduce the autoimmune response.