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activated macrophage 9 acute AIDS syndrome
immunoblasts. The cells increase in size from 15 to 30 mm in
diameter, show increased cytoplasmic basophilia, and develop
vacuoles, lysosomes, and ribosomal aggregates. Pinocytotic
vesicles are present on the cell membrane. The nucleus contains
little chromatin, which is limited to a thin marginal layer, and
the nucleolus becomes conspicuous. The array of changes
following stimulation is called transformation. Such cells are
called transformed cells. An activated B lymphocyte may
synthesize antibody molecules, whereas an activated T cell may
mediate a cellular immune reaction.
activated macrophage
A macrophage that has been stimulated in some manner or
by some substance to increase its functional efficiency with
respect to phagocytosis, intracellular bactericidal activity, or
lymphokine (i.e., IL-1) production. A lymphokine-activated
mononuclear phagocyte is double the size of a resting macrophage.
Major histocompatibility complex (MHC) class II
antigen surface expression is elevated, and lysosomes increase.
The latter changes facilitate antimicrobial defense.
activation
Stimulation of lymphocytes or macrophages to increase
their functional activity or initiation of the multicomponent
complement cascade in serum consisting of a series
of enzyme–substrate reactions leading to the generation of
functionally active effector molecules.
activation-induced cell death (AICD)
A phenomenon first observed in T hybridomas that die
within 24 hours of stimulation. It was also observed in vivo
following systemic stimulation by bacterial sAgs or peptide
antigens. AICD represents a heightened sensitivity of
recently stimulated cells to apoptosis induced by T cell
receptor (TCR) crosslinking, linked to the cell cycle. It can
also eliminate T cells immediately at the time of initial
stimulation, especially in virus-infected individuals. In
clonal exhaustion, AICD can lead to the complete elimination
of all antigen-reactive cells and may represent the basis
for high dose tolerance. Frequently mediated by the Fas
pathway or TNFR1 pathway.
activation-induced deaminase (AID)
A purported RNA- or DNA-editing enzyme requisite
for isotype switching as well as somatic hypermutation.
Germinal center B cells express it selectively.
activation phase
A stage in the adaptive immune response following recognition
that is associated with lymphocyte proliferation and
differentiation into effector cells.
activation protein-1 (AP-1)
DNA-binding transcription factors composed of dimers of
two proteins linked to each other through a shared structural
motif termed a leucine zipper. An example of an AP-1
factor is one comprised of Fos and Jun proteins. Among the
many different genes of the immune system in which AP-1
exerts transcriptional regulation of cytokine genes.
activation unit
Interaction of C3b with C4b2a bound to the cell membrane.
active anaphylaxis
The anaphylactic state induced by natural or experimental
sensitization in atopic subjects or experimental animals. See
also anaphylaxis.
active immunity
Protection attained as a consequence of clinical or subclinical
infection or deliberate immunization with an infectious agent or
its products. A type of adaptive immunity in which lymphocytes
are activated in response to a foreign antigen to which
they have been exposed. Compare with passive immunity.
active immunization
The induction of an immune response either through exposure
to an infectious agent or by deliberate immunization
with products of the microorganism inducing the disease
to develop protective immunity. A clinical disease or
subclinical infection or vaccination may be used to induce
the desired protective effect. Booster immunization injections
given at intervals after primary exposure may lead to
long-lasting immunity through activation of immunological
memory cells. Refer also to vaccination.
H
1
Arg Pro Pro Gly Phe Ser Pro Phe Arg OH
Primary structure of serum bradykinin.
active kinins
The active kinin compounds are characterized by a nonapeptide
amino acid sequence whose prototype is bradykinin,
the active kinin generated from plasma kininogen.
Generation of the other forms depends on the enzyme and
substrate used, and they differ in length and the additional
residues. Tissue kallikreins are best activated by
enzymes such as trypsin and hydrolyze, both low molecular
weight kininogen (LMK) and high molecular weight
kininogen (HMK) to yield kallidin, a tissue form of kinin.
Bradykinin is formed by the action of plasma kallikrein
on HMK or by the action of trypsin on both LMK and
HMK. Met-lys-bradykinin, another kinin, results from
hydrolysis by plasma kallikrein activated by acidification.
Other active kinins have also been described. Besides
being the precursors for the generation of kinins, kininogens
also affect the coagulation system, with activation of
the Hageman factor (HF) being the link between the two
systems.
active site
A crevice formed by the VL and VH regions of an immunoglobulin’s
Fv region. It may differ in size or shape from
one antibody molecule to another. Its activity is governed
by the amino acid sequence in this variable region and
differences in the manner in which VL and VH regions
relate to one another. Antibody molecule specificity is
dependent on the complementary relationship between
epitopes on antigen molecules and amino acid residues
in the recess comprising the antibody active site. The VL
and VH regions contain hypervariable areas that permit
great diversity in the antigen-binding capacity of antibody
molecules.
acumentin
A neutrophil and macrophage motility protein that links to
the actin molecule to control actin filament length.
acute AIDS syndrome
Within the first to sixth week following HIV-1 infection,
some subjects develop the flu-like symptoms of sore throat,
anorexia, nausea and vomiting, lymphadenopathy, maculopapular
rash, wasting, and pain in the abdomen, among
other symptoms. The total leukocyte count is slightly
depressed, with possible CD4 to CD8 ratio inversion.
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