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128 Part II Cellular Basis of Hematology

V
NH 2 NH 2 Hyaluronan- Carbohydrate-
recognition
binding
Ib α domain domain
S S
NH
Ligand-binding 2 S S NH 2
region
α IIb β 3 S S
Ca 2+ Ib IX NH 2
Ca 2+ lg-like β
Ca 2+ domains NH NH
Ca 2+ Cysteine 2 2 Site for
Heavy chain NH 2 NH 2 rich O-linked alternative
splicing of
repeats
Light chain glycans S S exons

COOH COOH COOH COOH COOH COOH COOH COOH
Integrin lg-like GPIb/IX/V CD44 P-selectin
(α β ) receptor complex
IIb 3
(VCAM) -1
Fig. 12.1 SCHEMATIC DIAGRAMS OF SEVERAL TYPES OF CELL SURFACE ADHESION RECEP-
TORS. Integrins consist of noncovalently linked α- and β-subunits, both of which contribute to ligand
binding. The platelet αIIbβ3 integrin is illustrated at far left. Ig-like receptors contain a variable number of
Ig homology domains, of which some bind ligands and others extend the ligand-binding domains from the
membrane. Shown second from left is VCAM-1, which contains seven Ig domains; the two domains that bind
to integrins are shaded. The platelet GPIb–IX–V complex, depicted in the middle diagram, consists of several
leucine-rich protein subunits. CD44, illustrated next, contains an amino-terminal (N-terminal) domain that
binds to hyaluronan. Each of the selectins contains an N-terminal carbohydrate recognition domain that binds
sialylated and fucosylated oligosaccharides on specific cell-surface GP ligands. Illustrated at far right is
P-selectin, the largest of the three selectins. GP, Glycoprotein; Ig, immunoglobulin; VCAM-1, vascular cell
adhesion molecule-1.

TABLE Integrins on Blood Cells
12.1
Integrin
Designation Other Name(s) Expressed by Ligand(s) Function(s)
α 1 β 1 VLA-1 Leukocytes, other cells Collagens, LM Adhesion to ECM
α 2 β 1 VLA-2 GPla/lla Leukocytes, platelets, other cells Collagens, LM Adhesion to ECM
VLA-3 Leukocytes, other cells Collagens, LM, FN Adhesion to ECM
α 3 β 1
VLA-4 Monocytes, lymphocytes, eosinophils VCAM-1, FN Adhesion to cells, ECM
α 4 β 1
VLA-5 GPlc/lla Leukocytes, platelets, other cells FN Adhesion to ECM
α 5 β 1
VLA-6 GPlc/lla Leukocytes, platelets, other cells LM Adhesion to ECM
α 6 β 1
Neutrophils VCAM-1 Adhesion to ECs
α 9 β 1
LFA-1 CD11a/CD18 Leukocytes ICAM-1, -2, -3 Leukocyte aggregation and
α L β 2
adhesion
MAC-1 CR3 CD11b/CD18 Neutrophils, monocytes ICAM-1, FIB, CR for iC3b Neutrophil aggregation and
α M β 2
adhesion to ECs
P150,95 CD11c/CD18 Neutrophils, monocytes CR for iC3b Adhesion to ECs
α X β 2
CD11d/CD18 Eosinophils, monocytes, lymphocytes VCAM-1, ICAM-3 Adhesion to leukocytes and to
α D β 2
ECs
GPllb/llla Platelets FIB, FN, vWF, VN, TSP Platelet adhesion and
α IIb β 3
aggregation
VN receptor Platelets, ECs FIB, FN, vWF, VN, TSP, collagens Platelet adhesion, angiogenesis
α V β 3
α 4 β 7 LPAM-1 Lymphocytes VCAM-1, MAdCAM-1, FN Lymphocyte adhesion to ECs
and ECM
CR, Complement receptor; EC, endothelial cell; ECM, extracellular matrix; FIB, fibrinogen; FN, fibronectin; GP, glycoprotein; LFA-1, leukocyte function-associated antigen;
LM, laminin; LPAM-1, lymphocyte Peyer patch adhesion molecule; MAdCAM-1, mucosal addressin cell adhesion molecule-1; TSP, thrombospondin; VCAM-1, vascular
cell adhesion molecule-1; VLA, very late-appearing antigen; VN, vitronectin; vWF, von Willebrand factor.