Clathrin is a protein that plays a major role in the formation of coated vesicles. Clathrin was first isolated and named by Barbara Pearse in 1975. It forms a triskelion shape composed of three clathrin heavy chains and three light chains. When the triskelia interact they form a polyhedral lattice that surrounds the vesicle. Coat-proteins, like clathrin, are used to build small vesicles in order to safely transport molecules within and between cells. The endocytosis and exocytosis of vesicles allows cells to transfer nutrients, to import signaling receptors, to mediate an immune response after sampling the extracellular world, and to clean up the cell debris left by tissue inflammation. On occasion, this mechanism also provides a pathway for raiding pathogens or toxins.