Vascular Endothelium - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 541

adenosine concentrations. Adenosine inhibits adhesion molecules and decreases
vascular permeability. Ecto ADP ribosyl cyclases, such as ADP ribosyl cyclase-1 108
and -2 109 as well as ectopeptidases, such as membrane metalloendopeptidase, 110
alanyl membrane aminopeptidase (AnPep), 111 and dipeptidyl peptidase-4
(DPP4) 112 mediate chemotaxis. Amine oxidase, copper-containing enzyme
AOC3, 113 an ecto-oxidase synthesized by endothelial cells, regulates leukocyte
rolling, firm adhesion, and transmigration.

9.7.8 Migration across Pericyte Sheath and Basement

Membrane

Venules are the primary site of leukocyte transmigration. In capillaries and post-
capillary and collecting venules, pericytes that present gaps between adjacent cells
and are embedded in the venular basement membrane surround endothelial cells
and connect them via protrusions [ 980 ]. Leukocyte migration through the pericyte
sheath can occur by both paracellular and transcellular routes. Neutrophils migrate
across the pericyte sheath through gaps between apposed cells.
The venular basement membrane that is generated by both endothelial cells and
pericytes comprises permissive sites. The composition of the basement membrane
is determined by the degree of collagen-4 crosslinks and types of laminin isoforms.
Regions that contain laminin-411 and -511 promote and prevent cell migration,
respectively [ 980 ]. 114 Yet, laminin-511 has a greater ability to promote human
lymphocyte migration than other laminin isoforms such as laminin-411, at least in
vitro. The influence of the composition of the vascular basement membrane on the
regulation of leukocyte migration may depend on leukocyte species as well as types
of inflammatory stimuli.
Cell migration through the basement membrane involves leukocyte-derived
peptidases as well as endothelial cell-associated enzymes such as matrix

metallopeptidases.

108 A.k.a. cyclic ADP ribose (cADPr) hydrolase-1 and CD38.
109 A.k.a. cyclic ADP ribose (cADPr) hydrolase-2, bone marrow stromal antigen BST1, and CD157.
110 A.k.a. neutral endopeptidase, neprilysin, and CD10.
111 A.k.a. aminopeptidase-M [APm] or -N [APn], microsomal aminopeptidase, myeloid plasma
membrane glycoprotein GP150, and CD13.
112 A.k.a. adenosine deaminase-complexing protein AdCP2 and T-cell activation antigen CD26.
113 A.k.a. vascular adhesion protein-1 (VAP1).
114 Specific laminin isoforms can serve as matrix to maintain embryonic stem cells, such as laminin-
511, but neither laminin-111, -332, nor -411 [ 992 ].