According to Bloomgren. et at. (2012), natalizumab treatment is connected to development of multifocal leukoencephalopathy (PML). PML is a very rare infection that cannot be treated and cannot be prevented and normally can cause death and disabilities. Natizumab is a monoclonal antibody that attaches the protein that called alpha 4 integrin and this protein can be found on the surface of white blood cells (NIH, 2015). In addition, PML is a disease that targets myelin and myelin form a whitish sheath around nerve cells. Myelin sheath normally located around the axon of a neuron and it is an important function of nervous system. Also, myelin sheath protects the nerve cells and has a protein that affects the immune system (EMedicineHealth,
