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TNF-related activation-induced cytokine 708 tolerogenic dendritic cells
may bind cell-bound and soluble forms of homotrimers of
TNF-α and LTα. CD120b binds more effectively to cellbound
TNF-α. LTβ-R binds only to heterotrimers of LTα
and LTβ. CD120a, CD120b, and LTβ-R represent single
transmembrane type I proteins. Activation of CD120a in
tissue cultured cells by antibody induces numerous TNF
effects. CD120b may be important in immunoregulatory
activities of TNFs.
TNF-related activation-induced cytokine
See TRANCE (RANK ligand).
TNFR1 pathway
Abbreviation for tumor necrosis factor receptor pathway.
An intracellular signaling circuit in which a ligand unites
with TNFR1 and leads to cell death or survival based on the
signals involved. TRADD, FADD, caspase-8, and caspase-3
cascades mediate death signaling. TRADD, TRAF2/RIP,
and the cIAPs causing NF-KB activation and SAPKIJNK
signaling pathways mediate survival signaling.
TNP
Abbreviation for trinitrophenol group.
togavirus immunity
Lifelong immunity is induced by infection with a number
of togaviruses. Attenuated vaccines have been used to
successfully control Venezuelan equine encephalitis virus
in horses. Induction of vaccinal immunity in livestock can
protect humans through vaccination of the intermediate
host. Antibodies against E1 and E2 proteins can neutralize
and passively protect against α virus infection in mice and
monkeys. Nonstructural protein antibodies can recognize
surface components of infected cells. Anti-NS-1 antibodies
are highly efficient in activating complement on cell
surfaces, leading to lysis of infected cells. Maturation of
these viruses from infected cells is by budding through
the cytoplasmic membrane. The recognition of nonstructural
proteins on infected cell surfaces by T lymphocytes
is a significant immunity mechanism. Vaccinia virus live
vaccines expressing nonstructural proteins have been used
experimentally. E1 proteins of α viruses participate in cell
surface adsorption and fusion. E2 proteins contain significant
virulence determinants.
tolerance
Active state of unresponsiveness by lymphoid cells to a
particular antigen (tolerogen) as a result of their interaction
with the antigen. Immune responses to all other
immunogens are unaffected. Tolerance is acquired
nonresponsiveness to a specific antigen. When inoculated
into a fetus or a newborn, an antigenic substance will
be tolerated by the recipient in a manner that prevents
manifestations of immunity when the individual is challenged
with the antigen as an adult. This treatment has
no suppressive effect on responses to other unrelated
antigens. Immunologic tolerance is much more difficult
to induce in adults whose immune systems are fully
developed. However, it can be accomplished by administering
repetitive minute doses of protein antigens or
administering them in large quantities. Mechanisms of
tolerance induction have been the subjects of numerous
investigations. Clonal deletion is one of these mechanisms.
Helper T or B lymphocytes may be inactivated or suppressor
T lymphocytes may be activated in the process of
tolerance induction. Clonal anergy and clonal balance are
other complex mechanisms proposed to account for self
tolerance in which an animal body accepts its own tissue
antigens as self and does not reject them. Nevertheless,
certain autoantibodies form under physiologic conditions
and are not pathogenic; autoimmune phenomena may form
under disease conditions and play a significant role in the
pathogenesis of autoimmune disease. An immunological
adaptation to a specific antigen is distinct from unresponsiveness,
the genetic or pathologic inability to mount a
measurable immune response. Tolerance involves lymphocytes
as individual cells; unresponsiveness is an attribute
of the whole organism. The humoral or cell-mediated
response may be affected individually or in concert with
tolerance. The genetic form of unresponsiveness has been
demonstrated with the immune response to synthetic antigens
and led to characterization of the immune response
(Ir) locus of the major histocompatibility complex (MHC).
The immune response of experimental animals (classified
as high, intermediate, or nonresponder) is not defective
but is not reactive to the particular antigen. In some cases,
suppressor cells prevent the development of an appropriate
response. Unresponsiveness may also be the result
of immunodeficiency states, some with clinical expression,
or may be induced by immunosuppressive therapy
such as that following x-irradiation, chemotherapeutic
agents, or antilymphocyte sera. Tolerance currently has
a broader connotation and is intended to represent all
instances in which an immune response to a given antigen
is not demonstrable. Immunologic tolerance refers to a
lack of response as a result of prior exposure to antigen.
It may be peripheral which, when abrogated, may lead to
autoimmune disease, or central. Refer to immunological
tolerance, self tolerance, central tolerance, and peripheral
tolerance.
tolerization
The process of rendering an animal tolerant to a specific
antigen.
tolerogen
A foreign antigen recognized by a T or B lymphocyte that
can induce immunologic tolerance, i.e., this antigen renders
lymphocytes refractory to activation. The production of
tolerance rather than immunity in response to antigen
depends on such variables as physical state of the antigen
(soluble or particulate), route of administration, level of
maturation of the recipient’s immune system, and immunologic
competence. Soluble antigens administered intravenously
will favor tolerance in many situations as opposed
to particulate antigens injected into the skin that may favor
immunity. Tolerogens may be orally administered antigens
or large doses of protein administered without adjuvants.
Immunologic tolerance with cells is easier to induce in a
fetus or neonate than in an adult animal that would be more
likely to develop immunity rather than tolerance.
tolerogenic
The capacity of a substance such as an antigen to induce
immunological tolerance.
tolerogenic dendritic cells
They cause naïve T cells to become anergic rather than
activated and/or activate T reg cells induced in vitro by