Endothelial Progenitor Cells—Potential New Avenues to Improve Neoangiogenesis and Reendothelialization - International Review of Cell and Molecular Biology - page 51

also on mature ECs, further studies used the more immature HSC marker
CD133 and demonstrated that purified CD133 þ cells can differentiate to
ECs in vitro ( Urbich and Dimmeler, 2004 ). CD133, also known as prominin
or AC133, is a highly conserved antigen with unknown biological activity,
which is expressed on HSCs but is absent on mature ECs and monocytic
cells. Thus, CD133 þ VEGFR2 þ cells more likely reflect immature
progenitor cells, whereas CD34 þ VEGFR2 þ may also represent shed cells
of the vessel wall. At present, it is unclear whether CD133 only represents
a surface marker or has a functional activity involved in the regulation
of neovascularization.
Another way to identify the endothelial-like properties of EPCs is the
uptake of acLDL. This has been widely used for in vitro and in vivo studies
( Asahara et al., 1997; Grieb et al., 2012; Groger et al., 2010; Piatkowski
et al., 2009 ).
CD14 is a membrane-bound GPI-anchored glycosylated protein, which
is able to bind bacterial lipopolysaccharides. It can be found on different
kinds of cells,

for example, epithelial cells, fibroblasts, and B-cells

( Ibelgaufts, 2012 ).
Yoon et al. have confirmed that early EPCs are heterogeneously made up
of both CD14 þ derived from monocytes, and CD14 -derived cells. They
have reported that ECFCs are cultured almost exclusively from CD14
cells, not from CD14 þ cells ( Yoon et al., 2005 ).
CD31 , which is known as an endothelial cell adhesion molecule, has also
been used to identify CECs. In combination with CD146, it can be used to
identify these cells ( Brunner et al., 2008 ). CD31 þ T-cells have been found in
EPC-CFU ( Hur et al., 2007 ). The distinct function of these cells remains
unknown. The use of CD31 in combination with CD34 to identify CEPC
has also been performed, but its use remains scarce and is not widely accepted
( Yip et al., 2011 ).
CD45 is an antigen predominantly expressed on the surfaces of all nucle-
ated hematopoietic cells and is termed the leukocyte common antigen
( Ibelgaufts, 2012 ). It can also be found on macrophages. CD45 has been
described as a positive marker in CAC and as a negative marker in ECFC
and TPC ( Aicher et al., 2007; Alessandri et al., 2001; Asahara et al.,
1997; Wang et al., 2011 ).
CD105 is a transmembrane glycoprotein that is expressed on ECs, sub-
sets of BM cells (erythroid cell precursors), and macrophages. In combina-
tion with the use of CD45 and CD14, it can be used for the isolation of
ECFC. ECFCs are reported to be CD105 þ ( Wagner and Myrup, 2005 ).