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tuberculin hypersensitivity 719 tumor antigens
tuberculin hypersensitivity
A form of bacterial allergy specific for a product in culture
filtrates of Mycobacterium tuberculosis which, when
injected into the skin, elicits a cell-mediated delayedtype
(type IV) hypersensitivity response. Tuberculin-type
hypersensitivity is mediated by CD4 + T lymphocytes. After
intracutaneous inoculation of tuberculin extract or purified
protein derivative (PPD), an area of redness and induration
develops at the site in 24 to 48 hours in individuals subjected
to present or past interaction with M. tuberculosis.
tuberculin reaction
A test of in vivo cell-mediated immunity. Robert Koch
observed localized skin lesions of tuberculous guinea pigs
inoculated intradermally with broth from a culture of tubercle
bacilli. The body’s immune response to infection with
the tubercle bacillus is signaled by the appearance of agglutinins,
precipitins, opsonins, and complement-fixing antibodies
in the serum. This humoral response is, however, not
marked, and such antibodies are present in low titer. The
most striking response is the development of delayed-type
hypersensitivity (DTH) that plays a protective role in preventing
reinfection with the same organism. Subcutaneous
inoculation of tubercle bacilli in a normal animal produces
no immediate response, but in 10 to 14 days a
nodule develops at the site of inoculation. The nodule then
becomes a typical tuberculous ulcer. The regional lymph
nodes become swollen and caseous. In contrast, a similar
inoculation in a tuberculous animal induces an indurated
area at the site of injection within 1 to 2 days. This becomes
a shallow ulcer that heals promptly. No swelling of the
adjacent lymphatics is noted. The tubercle bacillus antigen
responsible for DTH is wax D, a lipopolysaccharide–protein
complex of bacterial cell walls. The active peptide consists
of diaminopimelic acid, glutamic acid, and alanine. Testing
for DTH to the tubercle bacillus is done with tuberculin,
a heat-inactivated culture extract containing a mixture of
bacterial proteins, or with PPD, a purified protein derivative
of culture in nonproteinaceous media. Each compound
alone is capable of sensitizing the recipient. The protective
role of DTH is supported by the observation that in positive
reactors living cells are usually free of tubercle bacilli and
the bacteria are present in necrotic areas, separated by an
avascular barrier. By contrast, in infected individuals producing
negative reactions, the tubercle bacilli are found in
great numbers in living tissues. The reaction is permanently
or transiently negative in individuals whose cell-mediated
immune responses are transiently or permanently impaired.
tuberculin test
The 24- to 48-hour response to intradermal injection of
tuberculin. If positive, it signifies delayed-type (type IV)
hypersensitivity to tuberculin and implies cell-mediated
immunity to Mycobacterium tuberculosis. The intradermal
inoculation of tuberculin or purified protein derivative
(PPD) produces an area of erythema and induration within
24 to 48 hours in positive individuals. A positive reaction
signifies the presence of cell-mediated immunity to M.
tuberculosis as a consequence of past or current exposure to
the microorganism; however, tuberculin is not a test for the
diagnosis of active tuberculosis.
tuberculin-type reaction
A cell-mediated delayed-type hypersensitivity skin response
to an extract such as candidin, brucellin, or histoplasmin.
Individuals who experience positive reactions have delayedtype
hypersensitivity or cell-mediated immunity mediated
by T lymphocytes following contact with the microorganism
in question.
tuberculosis immunization
The induction of protective immunity through injection of
an attenuated vaccine containing bacille Calmette-Guérin
(BCG). This vaccine was more widely used in Europe
than in the United States in attempts to provide protection
against tuberculosis. A local papule develops several weeks
after injection in individuals who were previously tuberculin-negative.
The vaccine is not administered to positive
individuals. The vaccine is claimed to protect against development
of tuberculosis, although not all authorities agree
on its efficacy for this purpose. In recent years, oncologists
have used BCG vaccine to reactivate the cellular immune
systems of patients bearing neoplasms in the hope of facilitating
antitumor immunity.
tubular basement membrane autoantibodies
Autoantibodies specific for tubular basement membranes
(TBMs). They are detectable by immunofluorescence in
some renal allotransplant patients following certain types
of drug therapy and occasionally without a known cause. In
human tubulointerstitial nephritis (TIN), TBM autoantibodies
generated react with a major 58-kDa antigen (TIN antigen)
and minor 160-, 175-, and 300-kDa antigens related
to laminin and entactin/nidogen. Twenty-two percent of
patients with various types of interstitial nephritis manifest
autoantibodies against TIN antigen. Normal urine may
reveal human TBM antigens that are capable of inducing
TIN in rats. TBM autoantibodies are only rarely detected
in human cases of TIN, but they are often prominent as
glomerular basement membrane (GBM) autoantibodies in
patients with Goodpasture’s syndrome. TBM autoantibodies
are of unknown clinical significance.
tuftsin
A leukokinin globulin-derived substance that enhances
phagocytosis. It is a tetrapeptide comprised of Thr–Lys–
Pro–Arg. The leukokinin globulin from which it is derived
represents immunoglobulin Fc receptor residues 289
through 292. Tuftsin is formed in the spleen. Its actions
include neutrophil and macrophage chemotaxis, enhancing
phagocyte motility, and promoting oxidative metabolism. It
also facilitates antigen processing.
tuftsin deficiency
A tetrapeptide that stimulates phagocytes. Tuftsin is split
from an immunoglobulin by the action of one proteolytic
enzyme in the spleen that cleaves the carboxyl terminus
between residues 292 and 293 and another enzyme
(leukokinase) confined to neutrophil membranes that splits
the molecule between positions 288 and 289. Thus, tuftsin
deficiency, which is transmitted as an autosomal-recessive
trait, results from a lack of this splenic enzyme. Although γ
globulin has been used, there is no known treatment.
tumor
A neoplasm developing as a consequence of uncontrolled
cell proliferation. Benign tumors are self-limiting, whereas
malignant tumors may be invasive.
tumor antigens
Cell surface proteins on tumor cells that can induce a cellmediated
and/or humoral immune response. Refer also to
tumor-associated antigens and tumor-specific antigens.
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