Untitled - D Ank Unlimited

avidity hypothesis 90 AZT
Percent Antibody Precipitated
100
50
0
be greater than the strength of binding of the individual
antibody–antigen combinations contributing to the overall
avidity of a particular interaction. K A, the association constant
for the Ab + Ag = AbAg interaction, is frequently used
to indicate avidity. Avidity may also describe the strength
of cell-to-cell interactions mediated by numerous binding
interactions between cell surface molecules. Avidity is distinct
from affinity, which describes the strength of binding
between a single molecular site and its ligand.
avidity hypothesis
Previously known as the affinity hypothesis of T cell selection
in the thymus, the avidity hypothesis is based on the
concept that T cells must have a measurable affinity for
self major histocompatibility complex (MHC) molecules to
mature but not an affinity sufficient to cause activation of
the cell when it matures, as this would necessitate deletion
of the cell to maintain self tolerance.
Avionics®
Interferon-β-1a preparation approved for the treatment of
multiple sclerosis.
avr-R system
Plant immune response mechanism in which the disease
resistance (R) plant genes and microbial avirulent (avr)
interact. For a plant to be able to isolate or wall off and
degrade a pathogen, its R product and the avr product of the
invading pathogen must match.
axenic
Free from association with or contamination by other
organisms, e.g., germ-free mice raised in isolation; also
refers to pure cultures of microorganisms. Also referred to
as gnotobiotic and germ-free.
azathioprine
A slow-acting immunosuppressive agent that suppresses
delayed hypersensitivity and cellular cytotoxicity
to a greater degree than antibody responses.
Immunosuppressive and therapeutic effects in animal
models are dose-related. A nitroimidazole derivative
of 6-mercaptopurine, a purine antagonist. Following
administration, it is converted to 6-mercaptopurine in
vivo. Its principal action is to interfere with DNA synthesis.
It interferes with purine nucleic acid metabolism at
stages requisite for lymphoid cell proliferation following
antigenic stimulation. The purine analogs act as cytotoxic
agents that fatally injure stimulated lymphoid cells. These
50
B C
A
100
D
Ab Ag in Precipitate
18
B
C
D
A
Units Dnp – HSA Added
Precipitation curves showing differences in avidity of four antisera for the same antigen. The order of avidity of the sera is A > B > C > D.
28
8
50
N
S
N
O 2 N
100
analogs have less effect on messenger RNA synthesis
needed for sustained antibody formation by plasma cells
than on nucleic acid in proliferating cells. The cytotoxic
agents can depress cellular immunity as well as primary
and secondary serum antibody responses. Of less significance
is the ability to impair RNA synthesis. Azathioprine
has a greater inhibitory effect on T cell than on B cell
responses, even though it suppresses both cell-mediated
and humoral immunity. It diminishes circulating natural
killer (NK) and killer cell numbers. It has been used
successfully to maintain renal allografts and treat various
autoimmune disorders including rheumatoid arthritis,
other connective tissue diseases, autoimmune blood
diseases, and immunologically mediated neurological disorders.
It is active chiefly against reproducing cells. The
drug has little effect on immunoglobulin levels or antibody
titers, but it does diminish neutrophil and monocyte
numbers in the circulation. The major toxic effect is bone
marrow suppression, often manifested as leukopenia.
azidothymidine
Synonym for zidovudine.
azoprotein
The joining of a substance to a protein through a diazo linkage
–N=N–. Karl Landsteiner (in the early 1900s) made extensive
use of diazotization to prepare hapten–protein conjugates to
define immunochemical specificity. See also diazo reaction.
AZT
3′-azido-3′-deoxythymidine. Refer to zidovudine.
N
N
N
N
CH 3
H
CH
(6-[(1-methyl-4-nitro-1H-imidazol-5-yl)thio]-1H-purine)
Structure of azathioprine.