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self antigen 644 senescent cell antigen
have been substantiated by scientific evidence. The selective
theories maintained that cells were genetically programmed
to react to certain antigenic specificities prior to antigen
exposure. These theories are in sharp contrast to the instructive
theories postulating that antigen was necessary to serve
as a template around which polypeptide chains were folded to
yield specific antibodies. The template theory was abandoned
when antibody was demonstrated in the absence of antigen.
self antigen
Autoantigen. All normal body constituents to which the
immune response would respond were it not for immunologic
tolerance to these self epitopes.
self MHC
The major histocompatibility complex (MHC) molecules of
a single individual.
self marker hypothesis (historical)
A concept suggested by Burnet and Fenner in 1949 to
account for the failure of the body to react against its own
antigens. They proposed that cells contained markers that
identified them to the host’s immunologically competent
cells as self. This recognition system was supposed to
prevent the immune cells of the host from rejecting its
own tissue cells. This hypothesis was later abandoned by
the authors and replaced by the clonal selection theory of
acquired immunity that Burnet proposed in 1957.
self MHC restriction
The confinement of antigens that an individual’s T cells can
recognize to complexes of peptides bound to major histocompatibility
complex (MHC) molecules in the thymus during T
lymphocyte maturation (i.e., self MHC molecules). Positive
selection leads to self MHC restriction of the T cell repertoire.
self peptides
Peptides formed from proteins of the body. In the absence
of infection, these peptides occupy the peptide binding sites
of major histocompatibility complex (MHC) molecules on
cell surfaces.
Thymus
T
DELETION
T
SUPPRESSION
T
T
T
B
T
T
TCR against self
TCR against non-self
HELP
T
T
self recognition
The identification of autoantigens by lymphoid cells of the
immune system. This is a consequence of the establishment
of immunological tolerance of self antigens during
fetal development.
self renewal
The capacity of a cell population to restore itself.
self restriction
Refer to MHC restriction.
self tolerance
The body’s acceptance of its own epitopes as self antigens.
The body is tolerant to these autoantigens that are exposed
to lymphoid cells of the host immune system without
eliciting an immune response. Tolerance to self antigens
is developed during fetal life. Thus, a host is immunologically
tolerant to self or autoantigens. Self tolerance is due
mainly to inactivation or killing of self-reactive lymphocytes
induced by exposure to self antigens. Failure of
self tolerance in the normal immune system may lead to
autoimmune diseases. Refer also to tolerance and immunologic
tolerance.
semisyngeneic graft
A graft that is ordinarily accepted from an individual of one
strain into an F 1 hybrid of an individual of that strain mated
with an individual of a different strain.
senescent cell antigen
A neoantigen appearing on old red blood cells that binds
immunoglobulin G (IgG) autoantibodies. Senescent cell
antigen is also found on lymphocytes, platelets, neutrophils,
adult human liver cells (in culture), and human embryonic
renal cells (in culture). Its appearance on aging somatic
cells probably represents a physiologic process to remove
senescent and injured cells that fulfilled their functions.
Macrophages can identify and phagocytize dying and aging
self cells that are no longer functional without disturbing
mature healthy cells.
T
T
CLONAL
ANERGY
Mechanism of self tolerance.
Inactivation
APC
unable to
produce
costimulators