TYSABRI 300 mg TYSABRI contains Natalizumab, a recombinant humanized IgG4κ monoclonal antibody produced in murine myeloma cells. It binds specifically to the α4-subunit of α4β1 and α4β7 integrins expressed on the surface of all leukocytes except neutrophils. By blocking α4-integrin interactions with vascular cell adhesion molecule-1 (VCAM-1) and mucosal addressin cell adhesion molecule-1 (MAdCAM-1), it inhibits the transmigration of mononuclear leukocytes across the blood-brain barrier into inflamed central nervous system parenchyma. It is indicated as monotherapy for the treatment of relapsing forms of multiple sclerosis (MS) and for inducing and maintaining clinical response and remission in adult patients with moderately to severely active Crohn's disease.