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oral tolerance 543 Orthoclone OKT®3
significant in periodontal disease. Individuals with immunodeficiencies
often have increased mucosal infections by
opportunistic microorganisms such as by Candida albicans.
Immunopathologic mechanisms that involve types II, III, and
IV hypersensitivity may be involved in the development and
progression of chronic periodontitis. Vaccines may be used in
the future to prevent or control dental caries and periodontal
diseases. Oral or intranasal routes of vaccine administration
may prove useful to protect against oral infections.
oral tolerance
Antigen-induced specific suppression of humoral and cellmediated
immunity to an antigen following oral administration
of that antigen as a consequence of anergy of
antigen-specific T lymphocytes or the formation of immunosuppressive
cytokines such as transforming growth factor
β (TGF-β). Oral tolerance may inhibit immune responses
against food antigens and bacteria in the intestine. Proteins
passing through the gastrointestinal tract induce antigenspecific
hyporesponsiveness. Oral tolerance is believed to
have evolved to permit the gut-associated immune system to
be exposed to external proteins without becoming sensitized.
If proteins such as ovalbumin or myelin basic protein (MBP)
are fed to animals that are then immunized, the immune
response against the fed antigen, but not against the control
antigen, is subsequently diminished. Based on the quantity
of antigen fed, orally administered antigen may induce
regulatory cells that suppress the antigen-specific response
(low doses) or inhibit antigen-specific T cells by induction of
clonal anergy (high doses). Antigens passing through the gastrointestinal
tract preferentially induce T helper (Th2)-type
T cells that secrete interleukin-4 (IL4), IL10, and TGF-β.
oral unresponsiveness
The selective ability of the mucosal immune system to react
immunologically against antigens of food and intestinal
microorganisms even though it responds vigorously to
pathogenic microorganisms.
organ bank
A site where selected tissues for transplantation, such
as acellular bone fragments, corneas, and bone marrow,
may be stored for relatively long periods until needed.
Several hospitals often share such a facility. Organs such
as kidneys, liver, heart, lung, and pancreatic islets must be
transplanted within 48 to 72 hours and are not suitable for
storage in an organ bank.
organ brokerage
The selling of an organ such as a kidney from a living
related donor to the transplant recipient is practiced in
certain parts of the world but is considered unethical and is
Oral tolerance.
illegal in the United states because it violates the National
Organ Transplant Act (Public Law 98-507, 3 USC).
organ-specific antigen
An antigen that is unique to a particular organ even though
it may be found in more than one species.
organ-specific autoimmune diseases
Autoimmune reactivity against specific organs, such as the
thyroid in Hashimoto’s thyroiditis, leads to cell and tissue
damage to specific organs. By contrast, systemic lupus
erythematosus (SLE) affects a wide variety of tissues and
organs of the body.
organ specific autoimmunity
An autoimmune response directed against a specific anatomical
site.
organism-specific antibody index (OSAI)
The ratio of organism-specific immunoglobulin G (IgG) to
total IgG in cerebrospinal fluid (CSF) compared to the ratio
of organism-specific IgG in serum to total serum IgG. This
is illustrated in the following formula: an index >1 signifying
a greater quantity of organism-specific immunoglobulin
in CSF than in the blood serum implies that organismspecific
IgG is being synthesized in the intra-blood–brain
barrier (IBBB) and suggests that the specific organism of
interest is producing an infection of the central nervous
system. Similar indices can be calculated for IgM and IgA
antibody classes.
original antigenic sin
When an individual is exposed to an antigen that is similar
but not identical to an antigen to which he was previously
exposed by infection or immunization, the immune
response to the second exposure is still directed against
the first antigen. This was first noticed in influenza virus
infection. Due to antigenic drift and shift in influenza virus,
reinfection with an antigenically altered strain generates
a secondary immune response specific for the virus strain
that produced an earlier infection. The antibody response
against a second infection with influenza is restricted to
epitopes that the second strain shares with the first strain
that infected the host. Other highly immunogenic epitopes
on second and subsequent viruses are ignored. B cell clones
activated by an original antigen are reactivated in response
to a new cross reactive antigen that possesses novel B cell
epitopes in addition to T cell epitopes present on the original
antigen.
Orthoclone OKT ® 3
A commercial antibody against the T cell surface marker
CD3. It may be used therapeutically to diminish T cell
reactivity in organ allotransplant recipients experiencing
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