Untitled - D Ank Unlimited

immunological escape 380 immunologically privileged sites
immunological escape
A mechanism of escape in which tumors that are immunogenic
continue to grow in immunocompetent syngeneic
hosts in the presence of a modest in vivo antitumor immune
response. Escape mechanisms may facilitate evasion of a fatal
tumoricidal response and render tumors incapable of inducing
such a response. Failure of tumor antigen presentation by
major histocompatibility complex (MHC) class I molecules,
lack of costimulation, and downregulation of tumor-destructive
immune responses by tumor antigens, immune complexes, and
molecules such as TGF-β and P15E are all believed to contribute
to the inefficiency of tumor immunity.
immunological ignorance
A type of tolerance to self in which a target antigen and
lymphocytes capable of reacting with it are both present
simultaneously in an individual without an autoimmune
reaction occurring. Peripheral tolerance to self constituents
present in such small quantities that immature dendritic
cells rather take them up and present them to cognate T
cells. The abrogation of immunologic ignorance may lead to
autoimmune disease.
immunological inertia
Specific immunosuppression related to paternal histocompatibility
antigens during pregnancy, such as suppression
of maternal immune reactivity against fetal histocompatibility
antigens.
immunological infertility
Infertility in 12 to 25% of cases in which couples experience
infertility even though they manifest no significant
abnormalities upon physical examination. These cases
of unexplained infertility may be caused by autoimmune
responses to organ-specific antigens of the reproductive
tract of both males and females and isoimmune reactions of
females against semen components. Immune responses may
cause or contribute to infertility in approximately 10% of
these couples.
immunological memory
The effectiveness of protective immunity against an infectious
agent depends on the ability of the immune system
to retain a memory of the original infective agent in order
to provide an enhanced immune response on re-exposure
to the same agent. This mechanism usually prevents overt
infection and a fatal outcome; however, not all consequences
of immune memory are beneficial. A second infection
with the dengue virus may be more severe than the
first. Another detrimental effect of immunity is sensitization
to an allergen that leads to a hypersensitivity reaction.
During a primary immune response to an infectious agent,
each antigen-specific lymphocyte clone activated produces
numerous memory lymphocytes of identical specificity and
greater affinity. A second attack by the same pathogen leads
to a secondary immune response when memory lymphocytes
are activated, which leads to more rapid and efficient
elimination of the invading pathogen. Immunologic
memory is specific for a particular antigen and is long lasting.
Immunological memory is governed by many factors,
with both B and T cells contributing to it. Immunological
memory depends upon interactions between memory T
cells and memory B cells.
immunological reaction
In vivo or in vitro responses of lymphoid cells to an antigen
they have not previously encountered or for which they are
already primed or sensitized. An immunological reaction
may consist of antibody formation, cell-mediated immunity,
or immunological tolerance. The humoral antibody and cellmediated
immune reactions may mediate either protective
immunity or hypersensitivity, depending on various conditions.
immunological rejection
The destruction of an allograft or even a xenograft in a
recipient host whose immune system has been activated to
respond to the foreign tissue antigens.
immunological suicide
The use of an antigen deliberately labeled with high-dose
radioisotope to kill a subpopulation of lymphocytes with
receptors specific for that antigen following antigen binding.
immunological synapse
The nanometer-scale gap between a T cell and an antigenpresenting
cell, which is the site of interaction between a T
cell antigen receptor and major histocompatibility complex
(MHC) molecule–peptide complex that initiates the adaptive
immune response. Refer to SMAC (supramolecular
activation complex).
immunological unresponsiveness
Failure to form antibodies or develop a lymphoid cellmediated
response following exposure to immunogen
(antigen). Immunosuppression that is specific for only
one antigen, with no interference with the responses to
all other antigens, is termed immunological tolerance.
By contrast, the administration of powerful immunosuppressive
agents such as azathioprine, cyclosporine, or
total body irradiation causes generalized immunological
unresponsiveness to essentially all immunogens to which
the host is exposed.
immunologically activated cell
An immunologically competent cell following its interaction
with antigen. This response may be expressed as lymphocyte
transformation, immunological memory, cell-mediated
immunity, immunologic tolerance, or antibody synthesis.
immunologically competent cell
A lymphocyte, such as a B cell or T cell, that can recognize
and respond to a specific antigen.
immunologically privileged sites
Certain anatomical sites within the animal body provide
an immunologically privileged environment that favors
the prolonged survival of alien grafts. The potential for
development of a blood and lymphatic vascular supply
connecting graft and host may be a determining factor
in the qualification of an anatomical site as an area
that provides an environment favorable to the prolonged
survival of a foreign graft. Immunologically privileged
areas include (1) the anterior chamber of the eye, (2) the
substantia propria of the cornea, (3) the meninges of the
brain, (4) the testis, and (5) the cheek pouch of the Syrian
hamster. Foreign grafts implanted in these sites show a
diminished ability to induce transplantation immunity in
the host. Immunologically privileged sites usually fail to
protect alien grafts from the immune rejection mechanism
in hosts previously or simultaneously sensitized
with donor tissues. The capacity of cells expressing
Fas ligand to cause deletion of activated lymphocytes
provides a possible explanation for the phenomenon of
immune privilege. Animals with a deficiency in either
Fas ligand or the Fas receptor fail to manifest significant
immune privilege. Both epithelial cells of the eye and