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topoisomerase I 710 toxin neutralization (by antitoxin)
organs. There are several types, designated as palatine,
flanked by the palatoglossal and palatopharyngeal arches;
pharyngeal, adenoids in the posterior pharynx; and lingual,
at the base of the tongue. Waldeyer’s ring in the nasopharynx
is composed of the five tonsils: nasopharyngeal, two
lingual and two palatine.
topoisomerase I
A 100-kDa nuclear enzyme that induces autoantibodies. It
is concerned with the relaxation of supercoiled DNA, by
nicking and releasing one strand of the DNA duplex.
TORCH panel
A general serologic screen to identify antenatal infection.
Elevated levels of immunoglobulin M (IgM) in a neonate
reflect in utero infection. The panel may be refined by determining
IgM antibodies specific for certain microorganisms.
TORCH is an acronym for toxoplasma, other, rubella, cytomegalic
inclusion virus, herpes (and syphilis). False-positive
and false-negative reactions occur in quantitative screening.
A positive TORCH panel is indicative of in utero infection
that may bring major consequences. Toxoplasmosis
may result in microglial nodules, thrombosis, necrosis, and
blocking of the foramina, leading to hydrocephalus. Rubella
may cause hepatosplenomegaly, congenital heart disease,
petechiae and purpura, decreased birth weight, microcephaly,
cataracts, and central nervous system manifestations
including seizures and bulging fontanelles. Cytomegalovirus
is characterized by hepatosplenomegaly, hyperbilirubinemia,
microcephaly, thrombocytopenia at birth followed later
by deafness, mental retardation, learning disabilities, and
other manifestations. Herpes simplex can lead to premature
birth. Central nervous system manifestations include
seizures, chorioretinitis, flaccid or spastic paralysis, and
coma. Syphilis is an addendum to the TORCH designation.
Congenital syphilis has increased in recent years and is not
associated with specific clinical findings.
tositumomab
An anti-CD20 monoclonal antibody labeled with iodine 131
( 131 I), used to treat patients with CD20-positive follicular
non-Hodgkin lymphoma refractory to standard therapy.
Toxicities include severe cytopenias including thrombocytopenia
and neutropenia.
total body irradiation (TBI)
The administration to hematopoietic cell transplant recipients
of sufficient ionizing radiation over the whole body to
destroy hematopoietic cells in the bone marrow.
total lymphoid irradiation (TLI)
A technique to induce immunosuppression in which lymphoid
organs are irradiated and other organs are protected from
irradiation. This method has been used to treat lymphomas.
totipotent
Having the potential for developing in various specialized
ways in response to external and internal stimuli; of a cell
or part.
toxic complexes
Increased levels of circulating immune complexes may be
harmful and trigger type III hypersensitivity reactions. The
soluble complexes are pathogenic. The classic description
regards such complexes as toxic, and the toxic complexes
term appeared frequently in the literature. Such complexes
are characterized by (1) formation in a zone of moderate
antigen excess, (2) lack of cytotropic affinity for tissues of
the antibody in the complex, and (3) ability of the complex
to activate the complement system. Complex formation is
associated with conformational changes in the antibody
molecule. The activity of the complex depends on the
antibody, not on the antigen. Antibodies produced in some
species such as rabbits, humans, and guinea pigs have these
properties. Antibodies of other species such as bovines,
chickens, and horses are inactive in this respect. Fixation
of the complexes occurs via the Fc portion of the antibody
in the complex. The complexes stick to cells and basement
membranes, causing injury to the endothelia of small
vessels. The injury may occur at the local site of antigen
injection or may be systemic when antigen is injected
intravenously. The chain of events characteristic for inflammation
is set in motion with liberation of vasoactive amines
and involvement of polymorphonuclear leukocytes.
toxic epidermal necrolysis
A hypersensitivity reaction to certain drugs such as
allopurinol, nonsteroidal anti-inflammatory drugs, barbiturates,
sulfonamides such as sulfmethoxazole–trimethoprim,
carbamazepine, and other agents. It may closely resemble erythema
multiforme. Patients develop erythema, subepidermal
bullae, and open epidermal lesions. They become dehydrated,
show electrolyte imbalances, and often develop abscesses
with sepsis and shock. Toxic epidermal necrolysis may also
be observed in a hyperacute type of graft-vs.-host reaction,
especially in babies receiving bone marrow transplants.
toxic shock syndrome
A potentially lethal acute systemic toxic reaction in which
the patient manifests shock, skin exfoliation, conjunctivitis,
and diarrhea resulting from the excessive production
of cytokines by CD4 + T cells activated by the bacterial
superantigen toxic shock syndrome toxin 1 (TSST-1),
secreted by Staphylococcus aureus. Linked to the improper
use of feminine hygiene products.
toxin
A usually immunogenic poison that stimulates production
of antibodies called antitoxins that have the ability to
neutralize the harmful effects of the toxin eliciting their
synthesis. A toxin molecule synthesized by a pathogenic
microorganism may kill a host cell, inhibit its metabolism,
or modify host immune responses against the pathogen.
The general groups of toxins include (1) bacterial toxins
produced by microorganisms such as those causing tetanus,
diphtheria, botulism, and gas gangrene, including toxins of
staphylococci; (2) phytotoxins including plant toxins such
as ricin of the castor bean, crotein, and abrin derived from
the Indian licorice seed Gerukia; and (3) zootoxins such as
snake, spider, scorpion, bee, and wasp venoms.
toxin neutralization (by antitoxin)
Toxicity is titrated by injection of laboratory animals, and
the activity of antitoxins is evaluated by comparison with
standard antitoxins of known protective ability. Antitoxin
combines with toxin in varying proportions, depending on
the ratio in which they are combined, to form complexes that
prove nontoxic when injected into experimental animals.
Mixing of antitoxin and toxin in optimal proportions may
result in flocculation. If toxin is added to antitoxin in several
fractions at intervals instead of all at once, more antitoxin
is required for neutralization than would be necessary if a
single addition of toxin were made. This means that toxins
are polyvalent. This phenomenon is explained by the ability
of toxin to combine with antitoxin in multiple proportions.