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acyclic adenosine monophosphate (cAMP) 18 adenosine
A trichrome stain of a small interlobular artery showing predominantly
humoral rejection. There is tremendous swelling of the intima and
endothelium with some fibrin deposition and a few polymorphonuclear
leukocytes.
Immunofluorescence preparation showing humoral rejection with high
intensity fluorescence of arteriolar walls and some glomerular capillary
walls. This pattern is demonstrable in anti-immunoglobulin and anticomplement
stained sections.
complement molecules that are detectable by immunofluorescence
examination. The antibodies on the cardiac muscle
are found at sarcolemmal and subsarcolemmal sites and in
the pericardium. The crossreactivity also involves heart valve
glycoproteins and the myocardial conduction system. A cellmediated
immune attack, as revealed by the accumulation
of CD4 T lymphocytes in valvular tissues may occur. There
appears to be a positive correlation between the development
of rheumatic fever and HRA titers.
acyclic adenosine monophosphate (cAMP)
Adenosine 3′,5′-(hydrogen phosphate). A critical regulator
within cells. It is produced through the action of
adenylate cyclase on adenosine triphosphate; it activates
protein kinase C and serves as a “second messenger” when
hormones activate cells. Elevated cAMP concentrations
in mast cells diminish their responses to degranulation
signals.
acyclic guanosine monophosphate (cGMP)
Guanosine cyclic 3′,5′-(hydrogen phosphate). A cAMP
antagonist produced by the action of guanylate cyclase on
guanosine triphosphate. Elevated cGMP concentrations
in mast cells accentuate their responses to degranulation
signals.
acyclovir 9 (2-hydroxyethoxy-methylguanine)
An antiviral nucleoside analog that blocks herpes simplex
virus type 2 (HSV-2), the causative agent of genital
herpes. HSV thymidine kinase activates acyclovir through
monophosphorylation, followed by triple phosphorylation
with host enzymes to yield a powerful blocking action of
the DNA polymerase of HSV-2. Acyclovir is prescribed for
the treatment of HSV-2 genital infection.
ADA
Abbreviation for adenosine deaminase.
adaptive differentiation
Acquisition of the ability to identify major histocompatibility
complex (MHC) class II antigens by thymocytes undergoing
differentiation and maturation to CD4 + T helper/
inducer cells in the thymus.
adaptive immune response
The response of B and T lymphocytes to a specific antigen
and the development of immunological memory. The response
involves clonal selection of lymphocytes that respond to a
specific antigen. Also called acquired immune response.
adaptive immunity
Protection from an infectious disease agent as a consequence
of clinical or subclinical infection with that agent
or by deliberate immunization against that agent with
products from it. This type of immunity is mediated by B
and T lymphocytes following exposure to a specific antigen.
It is characterized by specificity, immunological memory,
and self/nonself recognition. This type of immunity is in
contrast to natural or innate immunity.
adaptor proteins
Critical linkers between receptors and downstream signaling
pathways that serve as bridges or scaffolds for recruitment
of other signaling molecules. They are functionally heterogeneous,
yet share an SH domain that permits interaction
with phosphotyrosine residues formed by receptor-associated
tyrosine kinases. During lymphocyte activation, they may be
phosphorylated on tyrosine residues, which enables them to
combine with other homology-2 (SH2) domain-containing
proteins. LAT, SLP-76, and Grb-2 are examples of adaptor
molecules that participate in T cell activation.
ADCC
Abbreviation for antibody-dependent cell-mediated cytotoxicity.
Cell lysis induced by the interaction of the Fc region
of a surface-bound antibody with an FcR expressed by
effector cells such as eosinophils and NK cells. Other cells
capable of mediating ADCC include macrophages, neutrophils,
and monocytes.
Addison’s disease
Refer to autoimmune adrenal disease.
addressin
A molecule such as a peptide or protein that serves as a homing
device to direct a molecule to a specific location (an example
is ELAM-1). Lymphocytes from Peyer’s patches home to
mucosal endothelial cells bearing ligands for the lymphocyte
homing receptor. Mucosal addressin cell adhesion molecule-1
(MadCAM) is the Peyer’s patch addressin in the intestinal wall
that links to the integrin α4β7 on T lymphocytes that home
to the intestine. Thus, endothelial cell addressins in separate
anatomical locations bind to lymphocyte homing receptors,
leading to organ-specific lymphocyte homing.
adenoids
Mucosa-associated secondary lymphoid tissues located in
the nasal cavity. Refer also to tonsils.
adenosine
Adenosine is normally present in the plasma in concentrations
of 0.03 μM in humans and 0.04 μM in dogs. In various