Roles of glycans and glycopeptides in immune system and immune-related diseases.

Almost all of the key molecules in organisms involved in the innate and adaptive immune response (including immunoglobulins, cytokines and cytokine receptors, complements, CD molecules, adhesions, T-cell receptors and major histocompatibility complex molecules) are glycoproteins. Besides, foreign antigens, such as many viral envelope proteins, are glycoproteins too. Carbohydrates attached to proteins or peptides are classified by the nature of their linkages to the protein, mostly as either N-linked (N-acetylglucosamine to asparagines) or O-linked (N-acetylgalactosamine to serine or threonine) oligosaccharides. The glycans have three major roles: firstly, the sugars confer stability on the proteins to which they are attached, protecting them from proteases and non-specific protein-protein interactions. Secondly, glycans play key roles in signal transduction, control of cell development and differentiation. Thirdly, specific regions of the oligosaccharide chains provide recognition epitopes, which influence innate and adaptive immune responses. Glycopeptides not only provide specific oligosaccharides, but also have specific information of amino acids sequences. The glycans and glycopeptides not only influence the structure and functions of immune molecules, but also influence the immune response. In addition, changes in glycans or glycopeptides may have a significant role in a variety of human immune-related diseases, such as rheumatoid, autoimmune disease, Wiskott-Aldrich syndrome, infection disease, cancer, etc. In this article, the roles of N-, O-glycans and glycopeptides in immune system and immune-related diseases are discussed. The potential therapeutic significance of the information is also mentioned.