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APC 71 apoptosis
factors have roles in lymphocyte activation. Immediately
following T cell stimulation, c-fos mRNA is increased, and
the c-fos gene product combines with the c-jun gene product
to form AP-1. A similar series of events occurs following
B cell stimulation; however, the genes regulated by B cell
AP-1 are not known.
APC
Abbreviation for antigen-presenting cell.
APC licensing
The postulate that total activation of a cytotoxic T cell
stimulated by antigen is enabled through costimulation by
a dendritic cell whose costimulatory molecules have been
upregulated following previous CD40–CD40L-mediated
interaction with an antigen-activated Th lymphocyte.
APECED (autoimmune polyendocrinopathy–candidiasis–
ectodermal dystrophy)
An autosomal-recessive disorder characterized by hypoparathyroidism,
adrenal cortical failure, gonadal failure, candidiasis,
and malabsorption. Antithymocyte globulin (ATG)
immunoglobulin G (IgG) isolated from the sera of rabbits
or horses hyperimmunized with human thymocytes is used
to treat aplastic anemia patients and combat rejection in
organ transplant recipients. Equine ATG contains 50 mg/ml
of immunoglobulin and has yielded 50% recovery of bone
marrow and treated aplastic anemia patients.
APD
Alternative abbreviation for autoimmune polyendocrinopathy–candidiasis–ectodermal
dystrophy.
apheresis
Technique whereby blood is removed from the body, its
components are separated, and some are retained for therapeutic
or other use; the remaining elements are recombined
and returned to the donor. Also called hemapharesis.
apical
The surface of an epithelial cell that faces the lumen rather
than the tissue.
aplasia
The disappearance of a particular population of cells
because of their failure to develop.
aplastic anemia
Bone marrow stem cell failure that leads to cessation of
formation of cellular blood components. Bone marrow
transplantation is the recommended treatment.
APO-1
Synonym for fas gene. Fas membrane protein ligation has
been shown to initiate apoptosis. This is the reverse action
of bcl-2 protein, which blocks apoptosis.
apolarity
An aqueous environment is of considerable importance to
the antigen–antibody complex and it may contribute greatly
to its stabilization. A net attractive force results from a
decrease in energy arising from the preference of apolar or
hydrophobic regions of the interacting molecules to associate
with themselves rather than with solvent molecules
(H 2O). The reaction is endothermic (ΔH > 0); in order
for it to be spontaneous (ΔH < 0), it must occur through
a concomitant increase in entropy through an entropydriven
reaction. This can be understood from the following
thermodynamic relationship: ΔG = ΔH – TΔS where ΔG is
the free energy change, ΔH is the enthalpy change, T is the
absolute temperature, and ΔS is the entropy change. When
ΔH > 0 (endothermic reaction), a positive ΔS is needed for
the overall energy decrease (ΔG < 0), resulting in the attractive
force. The binding of this attractive force increases
(ΔG becomes more negative) as ΔH decreases and as the
temperature T increases.
apolipoprotein (APO-E)
A plasma protein involved in many functions including
lipid transport, tissue repair, and regulation of cellular
growth and proliferation. There are three major isoforms
of APO-E encoded by the ε 2, 3, or 4 alleles (APO-E2,
APO-E3, APO-E4). APO-E3 is the most common variant.
There is much interest in the APO-E4 variant, as it may be
implicated in Alzheimer’s disease. Other APO-E polymorphisms
have been implicated in lipid metabolism disorders
and heart disease. APO-E is a 33-kDa protein produced by
nonactivated macrophages but not monocytes. It binds lowdensity
lipids and high density cholesterol esters.
Condensed
chromatin
Apoptosis.
Murine thymocytes
Apoptosis
Phagocytosis
Apoptosis.
Fragmented
nuclei
Apoptotic
body
apoptosis
Programmed cell death in which the chromatin becomes
condensed and the DNA is degraded. The immune
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