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ICOS 350 idiotype network theory
specific antigen. The antigen from iccosomes taken up by
B cells can be presented on MHC class II molecules to a T
helper cell.
ICOS
A CD28-related protein that develops on activated T
lymphocytes and is able to enhance T cell responses.
Licos, the ligand to which it binds, is distinct from B7
molecules.
IDDM
Abbreviation for insulin-dependent diabetes mellitus.
identity, reaction of
Refer to reaction of identity.
identity testing
See paternity testing.
idiopathic thrombocytopenic purpura
An autoimmune disease in which antiplatelet autoantibodies
destroy platelets. Splenic macrophages remove
circulating platelets coated with immunoglobulin G (IgG)
autoantibodies at an accelerated rate. Thrombocytopenia
occurs even though the bone marrow increases platelet
production, which can lead to purpura and bleeding.
The platelet count may fall below 20,000 to 30,000/μL.
Antiplatelet antibodies are detectable in the serum and
on platelets. Platelet survival is decreased. Splenectomy
is recommended in adults. Corticosteroids facilitate a
temporary elevation in the platelet count. This disease is
characterized by decreased blood platelets, hemorrhage,
and extensive thromboic lesions.
idiosyncrasy
A quantitatively abnormal response usually not corresponding
to the pharmacological action of a drug. The response
does not have an immunological mechanism.
idiotope
An epitope or antigenic determinant in the hypervariable
region of the N terminus of an immunoglobulin molecule,
T cell receptor molecule, or on the V region of an antibody
molecule. This type of antigenic determinant is present on
immunoglobulin molecules synthesized by one clone or a
few clones of antibody-producing cells. It can activate the
synthesis of antibodies following administration to a member
of the same species.
idiotype (Id)
A segment of an immunoglobulin or antibody molecule that
determines its specificity for antigen and is based upon the
multiple combinations of variable (V), diversity (D), and
joining (J) exons. The Id is located in the Fab region, and
its expression usually requires participation of the variable
regions of both heavy and light chains, namely the Fv fragments
that contain antigen-combining sites. The antigenbinding
specificity of the combining site may imply that all
antibodies produced by an animal in response to a given
immunogen have the same Id. This is not true, however, as
the antibody response is heterogeneous. A major Id usually
represents 20 to 70% of the specific antibody response; the
remainder carries different Ids that may crossreact with
the major Id. Crossreacting idiotypy represents the extent
of heterogeneity among the antibodies of a given specificity.
The unique antigenic determinants that govern the Id
of an immunoglobulin molecule occur on the products
of either a single or several clones of cells synthesizing
immunoglobulins. This unique idiotypic determinant is
sometimes called a private Id that appears in all V regions
The idiotype (in black) is determined by the variable regions of heavy and
light chains of an immunoglobulin molecule.
ss
ss
Idiotypic determinants (idiotypes).
Idiotypic determinants
(idiotopes)
of immunoglobulin molecules whose amino acid sequences
are the same. Shared Ids are known as public idiotype
determinants. They may appear in a relatively large number
of immunoglobulin molecules produced by inbred strains
of mice or other genetically identical animals in response
to a specific antigen. The localization of Ids in the antigenbinding
site of the V region of the molecule is illustrated by
the ability of haptens to block or inhibit the interaction of
anti-idiotypic antibodies with their homologous antigenic
markers or determinants in the antigen-binding regions of
antibody molecules.
idiotype network
The interaction of idiotypes and anti-idiotypes that leads
to the regulation of antibody synthesis or of lymphoid cells
bearing receptors that express these idiotypic specificities.
Responses of one or a few lymphocyte clones to antigen
leads to idiotype expansion and anti-idiotype responses that
downregulate the antigen-specific response.
idiotype network theory
Refer to network theory.