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platelet-associated immunoglobulin G (PAIgG) 578 pluripotent stem cell
Nomenclature and Phenotype Frequency of Human Platelet Antigens
and post-transfusion purpura. The Pl A1 antigen may induce
platelet antibody formation in Pl A1 antigen-negative individuals.
Additional platelet antigens associated with purpura
include Pl A2 , Bak a , and HLA-A2.
platelet-associated immunoglobulin G (PAIgG)
PAIgG is present in 10% of normal individuals, in 50% of
those with tumors, and in 76% of septic patients and may
be induced by graft-vs.-host disease. PAIgG is present in
71% of autologous marrow graft recipients and in 50% of
allogeneic marrow graft recipients.
platelet autoantibodies
Platelets possess surface FcRII that combine with IgG
or immune complexes. The platelet surfaces can become
saturated with immune complexes, as in autoimmune
(or idiopathic) thrombocytopenic purpura (ITP) or AITP.
Fab-mediated antibody binding to platelet antigens may
be difficult to distinguish from Fc-mediated binding of
immune complexes to the surface.
platelet-derived growth factor (PDGF)
A low molecular weight protein derived from human
platelets that acts as a powerful connective tissue mitogen,
causing fibroblast and intimal smooth muscle proliferation.
It also induces vasoconstriction and chemotaxis and
activates intracellular enzymes. PDGF plays an important
role in atherosclerosis and fibroproliferative lesions such as
glomerulonephritis, pulmonary fibrosis, myelofibrosis,
and other processes. It is comprised of a two-chain (A or
B) dimer. It can be an AA or BB homodimer or an AB
heterodimer. Human PDGF-AA is a 26.5-kDa A chain
homodimeric protein comprised of 250-amino acid residues,
whereas PDGF-BB is a 25-kDa B chain homodimeric
protein comprised of 218-amino acid residues. In addition
to platelets, PDGF is released by activated mononuclear
cells, endothelial cells, smooth muscle cells, and fibroblasts.
It plays a physiologic role in wound repair and processes
requiring accumulation of connective tissue. The three
known polypeptide dimers of PDGF include AA, AB, and
BB that bind to α or β dimeric tyrosine kinase receptors.
platelet-derived growth factor receptor (PDGF-R)
A glycoprotein in the membrane that has five extracellular
domains that resemble those of immunoglobulins.
It also has a kinase insert in the cytoplasm. The receptor
protein must undergo a conformational change for
Phenotype Frequency
Antigen System Glycoprotein (GP) location Other Names Antigens Other Names Caucasian Japanese
HPA-1 GPIIIa Zw, Pl A HPA-1a Zw a , Pl A1 97.9 99.9
HPA-1b Zw b , Pl A2 26.5 3.7
HPA-2 GPIb Ko, Sib HPA-2a Ko b 99.3 NT
HPA-2b Ko a , Sib a 14.6 25.4
HPA-3 GPIIb Bak, Lek HPA-3a Bak a , Lek a 87.7 78.9
HPA-3b Bak b 64.1 NT
HPA-4 GPIIIa Pen, Yuk HPA-4a Pen a , Yuk b 99.9 99.9
HPA-4b Pen b , Yuk a 0.2 1.7
HPA-5 GPIa Br, Hc, Zav HPA-5a Br b , Zav 99.2 NT
HPA-5b Br a, Zav a , Hc a 20.6 NT
signal transduction. A gene on chromosome 4q11 encodes
PDGF-R.
platelet endothelial cell adhesion molecule-1 (PECAM-1;
CD31)
An antigen that is a single-chain membrane glycoprotein
with a molecular weight of 140kD. It is found on granulocytes,
monocytes, macrophages, B cells, platelets, and
endothelial cells. Although called gpIIa′, it is different
from the CD29 antigen. At present the function of CD31 is
unknown. It may be an adhesion molecule.
platelet factor 4 (PF-4)
A chemokine that comprises a principal constituent
of platelet α granules. Its sequence resembles that of
β-thromboglobulin (β-TG) and neutrophil-activating
peptide 2 (NAP-2). PF-4 activities include heparin binding,
inhibition of angiogenesis, induction of intercellular adhesion
molecule 1 (ICAM-1) on endothelial cells, promotion
of neutrophil adhesion to endothelium, increased fibrin,
fiber formation, inhibition of other chemotactic factor
effects, in vivo recruitment of neutrophils, fibroblast migration
during wound repair, and reversal of con-A-induced
suppression of lymphocyte activity.
platelet transfusion
The administration of platelet concentrates prepared by
centrifuging a unit of whole blood at low speed to provide
40 to 70 mL of plasma that contains 3 to 4 × 10 11 platelets.
This amount can increase an adult’s platelet concentration
by 10,000 per cubic millimeter of blood. It is best to store
platelets at 20 to 24°C, subjecting them to mild agitation.
They must be used within 5 days of collection.
pleiotropic
The production of multiple actions on the same cell type,
such as a cytokine that influences the activity of numerous
different types of cells.
pluripotency
The versatility to differentiate into one of various different
types of cells.
pluripotent stem cell
A continuously dividing, undifferentiated bone marrow
cell that has progeny consisting of additional stem cells
together with cells of multiple separate lineages. Bone marrow
hematopoietic stem cells may develop into cells of the
myeloid, lymphoid, and erythroid lineages.