Sulfated glycans control lymphocyte homing

Lymphocyte homing to the secondary lymphoid organs is pivotal for proper immune responses. Studies using sulfotransferase-deficient mice showed that 6-sulfo sialyl Lewis X (6-sulfo sLex), a major ligand for L-selectin that is expressed on the high endothelial venules (HEVs), plays critical roles in lymphocyte homing to the peripheral lymph nodes. More recent studies revealed that 6-sulfo sLex is essential for the homing of CD4(+)CD25(-) conventional T cells to the nasal-associated lymphoid tissues (NALT) and is involved in nasal allergy. Further studies revealed that the homing of the CD4(+)CD25(+) regulatory T cells to the NALT is dependent not only on the L-selectin-sulfated glycan interaction but also on P-selectin glycoprotein ligand-1 and CD44. These findings suggest that different carbohydrate-dependent homing mechanisms are utilized for different lymphocyte subsets. Recent studies indicated that the L-selectin-sulfated glycan interaction is also important for lymphocyte homing in chronic inflammation. In this review, the functions of the sulfated glycans in lymphocyte homing in physiological and pathological conditions are discussed.