Autoimmunity and tyrosine sulfation

Homeostasis of the immune system is achieved through refined regulation and communication between immunologically relevant receptor and their cognate ligands amongst mononuclear cells during ontogeny and day to day immune responses. An aberrance in not only the kinetics of receptor expression but also the relative diversity of expression alter these events. More importantly, improper modulation of ligand binding affinity can be a triggering event that results in autoimmunity. As one of the most common post-translational modifications, tyrosine sulfation possesses the ability to regulate mononuclear cell function at various stages of the immune response. For example, removal of sulfated tyrosine residues consistently decreases the binding affinity of the ligand to its corresponding receptor as exemplified by studies of several tyrosine sulfated proteins such as PSGL-1, CD44v5, CCR5, and CXCR4, all known to play a role in a variety of autoimmune diseases. This review defines possible roles that tyrosine sulfated proteins may play in the pathogenesis of autoimmune diseases.