Untitled - D Ank Unlimited

immunologic facilitation (facilitation immunologique) 379 immunological deficiency state
Schematic view of antigen excess
IgG2
Antibody against
C3Hf/He(H-2K TS (H-2
)
fibrosarcoma
S ) mouse
immunologic facilitation (facilitation immunologique)
Slightly prolonged survival of certain normal tissue
allografts (e.g., skin) in mice conditioned with isoantiserum
specific for the graft.
immunologic paralysis
Immunologic unresponsiveness induced by the injection
of large doses of pneumococcal polysaccharide into mice,
where it is metabolized slowly. Any antibody that is formed
is consumed and is not detectable. The pneumococcal
polysaccharide antigen remains in the tissue of recipients
for months, during which time they produce no immune
response to the antigen. Immunologic paralysis is much
easier to induce with polysaccharide than with protein
antigens. It is highly specific for the antigen used for its
induction. Felton’s first observation of immunologic paralysis
preceded the demonstration of acquired immunologic
tolerance by Medawar et al.
immunologic tolerance
An active but carefully regulated response of lymphocytes to
self antigens. Autoantibodies are formed against a variety of
self antigens. Maintenance of self tolerance is a quantitative
process. When comparing the ease with which T and B cell
tolerance may be induced, it was found that T cell tolerance
is induced more rapidly and lasts longer than B cell tolerance.
For example, T cell tolerance may be induced in a single day,
whereas B cells may require 10 days for induction. In addition,
100 times more tolerogen may be required for B cell
tolerance than for T cell tolerance. The duration of tolerance
C3H f/He(H-2 K )
fibrosarcoma
Progressive growth of
tumor allograft
Immunologic enhancement (tumor enhancement).
Anti-SIII
Antibody
Immunologic (or immune) paralysis.
Pneumococcus
polysaccharide
SIII
Antigen
Lymphocyte
Fc receptor
site
Central
Fibrosarcoma
epitope
Peripheral
is much greater in T cells (e.g., 150 days) compared to that
in B cells, which is only 50 to 60 days. T suppressor cells
are also very important in maintaining natural tolerance to
self antigens; for example, they may suppress T helper cell
activity. Maintenance of tolerance is considered to require
the continued presence of specific antigens. Low antigen
doses may be effective in inducing tolerance in immature B
cells, leading to clonal abortion, but T cell tolerance does not
depend upon the level of maturation. Another mechanism of
B cell tolerance is cloning exhaustion, in which the immunogen
activates all of the B lymphocytes specific for it, leading
to maturation of cells and transient antibody synthesis,
thereby exhausting and diluting the B cell response. Another
mechanism of B cell tolerance is antibody-forming cell
blockade. Antibody-expressing B cells are coated with excess
antigen, rendering them unresponsive to the antigen.
immunological contraception
A method to prevent an undesired pregnancy. Vaccines that
induce antibodies and cell-mediated immune responses
against either a hormone or gamete antigen significant to
reproduction have been developed. Such vaccines control
fertility in experimental animals. They have undergone
exhaustive safety and toxicological investigations which
have shown the safety and reversibility of some of the vaccines
and with approval of regulatory agencies and ethics
commissions, have undergone clinical trials in humans. Six
vaccines, three in women and three in men, have completed
phase I clinical trials showing their safety and reversibility.
One vaccine has successfully completed phase II trials,
proving efficacy in females. The trials determined the titers
of antibodies and other immunological features. A fertilized
egg makes the hormone hCG. Antibodies that inactivate
one or more hormones involved in the production of gametes
and sex steroids may be expected to impair fertility.
Blocking the action of LHRH would also inhibit the synthesis
of sex steroids. This may prove useful in controlling
fertility of domestic animals but would not be acceptable
for contraception in humans. Two vaccines against LHRH
are in clinical trials in prostate carcinoma patients. An FSH
vaccine would act at the level of male fertility since FSH is
required for spermatogenesis in primates.
immunological deficiency state
Immunodeficiency.
I