Inflammation and Glycosciences - The Sugar Code - page 451

Table 27.1 Selectin - ligand interactions during infl ammation and lymphocyte homing.

Selectin
type

CD Selectin

expressed on

Ligand molecules Ligand

carrier

Ligand
expressed on

Biological
function

L - Selectin CD62L B, T cells,

monocytes,
granulocytes,
NK cells

CD15su >> CD15s GlyCAM 1,

CD34,
MAdCAM

Vascular endothe-
lial cells, HEVs,
Peyer ' s patches

Lymphocyte
homing

> CD15

P - Selectin CD62P Platelets,

endothelial
cells,
megakaryocytes

CD15s CD15

tyrosine sulfate

> PSGL - 1

(CD162)

T cells, leukocytes,
monocytes

Infl ammation

E - Selectin CD62E Endothelial

cells

CD15s CD15

tyrosine sulfate

> PSGL - 1

(CD162),
CD44,
ESL - 1

T cells, leukocytes,
monocytes

Infl ammation

ligands, including sialylated and sulfated structures of the Le blood group family,
are depicted in Table 27.2. The carbohydrate specifi city of selectins may vary
depending on their specifi c tasks. For instance, the ligand for L-selectin (CD62L)
of naïve T lymphocytes on human HEVs has been identifi ed as sialyl- 6 - sulfo - Le x
(CD15su). CD15su is strongly expressed on HEVs and the binding of CD62L to
this oligosaccharide can be inhibited by a specifi c monoclonal antibody. CD62L
apparently prefers carbohydrate 6-sulfation in contrast to CD62P and CD62E that,
in addition to CD15s, require tyrosine sulfate for effi cient binding. The accurate
expression of specifi c ligands of the Le family affords the coordinated activity of
various glycosyl- and sulfotransferases (Table 27.3). Sulfated tyrosine residues at
the N-terminus of the respective mucin-type glycoprotein ligands may also be
involved in the binding of selectins.
It has been proposed that there are signifi cant physiological differences of selec-
tin interactions between sulfated and non- sulfated Le x groups (Table 27.1 ). It is
postulated that - as a rule - CD15s and CD15su on leukocytes/lymphocytes serve
as ligands for CD62E and CD62P. Further, CD15s plays a key role in the recruit-
ment and piloting of leukocytes to sites of infl ammation. CD15su is involved in
the homing of naïve CD62L + T lymphocytes to peripheral lymph nodes [3]. Natural
killer (NK) cells of the peripheral blood system appear to use CD15su interactions.
CD15su is not only expressed on HEVs of peripheral lymph nodes, but also on
HEVs of Peyer's patches of the gastrointestinal immune system. In the mucosal
immune system of the gut, mature CD62L + T helper memory lymphocytes bind
to CD15su + HEVs. These T cells are necessary to maintain immunological homeo-
stasis in the intestine.