* Special issue dedicated to Dr. Guido Tettamanti. 1 Experimental Immunology, University Hospital, Hebelstrasse, 20 CH-4031 Basel, Switzerland. 2 Address reprint requests to: Tel: 41 61 265 2327; Fax: 41 61 265 2350; E-mail: Gennaro.DeLibero@unibas.ch A New Aspect in Glycolipid Biology: Glycosphingolipids as Antigens Recognized by T Lymphocytes* G. De Libero, 1,2 A. Donda, 1 H.-J. Gober, 1 V. Manolova, 1 Z. Mazorra, 1 A. Shamshiev, 1 and L. Mori 1 (Accepted March 25, 2002) T cells may recognize a large variety of ligands with different chemical structures. Recently, glycosphingolipids have also been shown to stimulate human T lymphocytes. Recognition of glycosphingolipids is restricted by the nonpolymorphic CD1 molecules, expressed by profes- sional antigen-presenting cells and by macrophages infiltrating inflammatory sites. CD1 mole- cules have a structure resembling that of classical MHC class I molecules, with the terminal extracellular domains characterized by two antiparallel  helices placed on two hydrophobic pockets. The glycosphingolipids bound to CD1 insert the lipid tails in the two pockets and po- sition the hydrophilic head on the external part of CD1. The TCR interacts with aminoacids present in the two  helices and with residues provided by the carbohydrate moiety of glyco- sphingolipids and discriminates their structural variations. T cells recognizing self-glycosphin- golipids release proinflammatory cytokines and may have a pathogenetic role in autoimmune diseases such as multiple sclerosis. KEY WORDS: Glycosphingolipids; T cells; CD1; TCR; autoimmunity; multiple sclerosis. Neurochemical Research, Vol. 27, Nos. 7/8, August 2002 (© 2002), pp. 675–685 675 0364-3190/02/0800 –0675/0 © 2002 Plenum Publishing Corporation origin. Loading of peptides on MHC molecules is a highly regulated process involving several chaperones and occurs in different intracellular organelles. MHC class I molecules load peptides in the endoplasmic reticulum, while MHC class II proteins in a specialized late endosomal multivesicular body compartment. T cells expressing the TCR  recognize small phosphorylated nonpeptidic metabolites (2). Recogni- tion of these nonconventional ligands is very different from recognition of protein antigens as it does not re- quire presentation by classic MHC molecules and is independent of antigen processing. Human T cells ex- pressing the TCR  composed of the V9 and V2 chains represent about 5–10% of circulating T cells, cross-react with a variety of phosphorylated ligands, and are readily activated. They are responsible for an efficient sentinel system, which on detection of bacte- rial infection immediately releases proinflammatory cytokines (3). INTRODUCTION T lymphocytes recognize antigens using a surface T cell receptor (TCR), which is composed of two dif- ferent chains. Two types of TCR exist, which are made by the association of the TCR  and  chains or the  and  chains. T cells expressing the TCR  recognize small peptides as antigens presented by MHC class I and II proteins (1). Peptides are generated after fragmenta- tion of proteins internalized in the antigen-presenting cells by phagocytosis or receptor-mediated internal- ization. Antigenic peptides may also derive from endo- genously synthesized proteins such as proteins of viral