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X cell
See XYZ cell theory.
X4 viruses
HIV strains that have become incapable of infecting macrophages
and preferentially attack CD4 + T lymphocytes.
Previously called T-tropic viruses.
xenoantibodies
Antibodies formed in one species that are specific for antigens
of a separate species.
xenoantibody
An antibody specific for xenoantigen.
xenoantigen
Tissue antigens of one species that induce an immune
response in members of a different species. Antigen of a
xenograft. Also called heteroantigen.
xenobiotics
Exposure of humans to xenobiotics including chemicals
and drugs may lead to autoimmune responses resembling
responses to infections with microorganisms, but true autoimmune
disease is observed less frequently. Various animal
models of autoimmunity such as drug-induced lupus have
been induced by chemicals. The models do not correspond
exactly to the human disease although renal autoimmune
disease caused by metals shows close similarity in animals
and humans. Isoniazid, hydralazine, and procainamide have
been implicated in drug-induced lupus. Iodine administration
to experimental animals prone to spontaneous autoimmune
thyroiditis favors the development of this disease.
Toxic oil syndrome has been induced in B10.S mice by
the intraperitoneal administration of oleic acid anilide.
HgCl 2 administration to rats, mice, and rabbits led to the
production of autoimmune kidney disease. Streptozotocin
administration induced an experimental model of insulindependent
diabetes mellitus in animal models. The halothane
anesthetic induced liver changes in rabbits and rats
that led to the formation of halothane antigens. Complete
Freund’s adjuvant can induce adjuvant arthritis in rats.
Xenobiotics are nonliving substances derived from drugs,
TCR
CD-28
Ag
B7
CTLA41g
X
metals, or industrial or natural chemicals that may interact
with self proteins to yield neo-antigens.
xenogeneic
Tissues or organs transplanted from one species to a genetically
different species (e.g., a baboon liver transplanted to a
human). It refers to the genetic relationship of an individual
of one species to a member of a different species.
xenograft
A tissue or organ graft from a member of one species
(donor) to a member of a different species (recipient); also
called a heterograft. Antibodies and cytotoxic T cells reject
xenografts several days following transplantation.
Xenopus
Anuran amphibian that serves as an excellent model for
investigating the ontogeny of immunity. Comparative
immunologic research employs isogeneic and inbred
families of this amphibian. Xenopus is especially useful
for studying the role of the thymus in immune ontogeny
because early thymectomy of free-living larvae does not
lead to runting.
xenoreactive
A T cell or antibody response to an antigen of a graft
derived from another species. T lymphocytes may recognize
an intact xenogenic major histocompatibility complex
(MHC) molecule or a peptide from a xenogeneic protein
bound to a self MHC molecule.
xenotransplantation
Organ or tissue transplantation between members of different
species. Xenogeneic transplantation may involve concordant
or discordant donors, according to the phylogenetic
distance between the species involved. Natural preformed
antibodies in a recipient specific for donor endothelial antigens
that lead to hyperacute rejection of most vascularized
organ transplants now occur in discordant species combinations.
The immune response to a xenotransplant resembles
the response to an allotransplant; however, greater antigenic
differences exist between donor and host in xenotransplantation
than in allotransplantation. Previously termed
heterotransplantation. The procedure is under investigation
MHC-Ag
Mouse T cell Mouse or human
antigen presenting cell
Induction of tolerance to xenogenic tissue graft.
T cell
proliferation
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X