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isoelectric point (pI) 421 isotypes
A density gradient or a gel is used to stabilize the pH gradient.
Proteins or peptides focus into distinct bands at the
parts of the gradient that are equivalent to their isoelectric
points. Isoelectric focusing permits the separation of protein
substances on the basis of their isoelectric characteristics.
Thus, it can be used to define heterogeneous antibodies and
also to purify homogeneous immunoglobulins from heterogeneous
pools of antibody.
isoelectric point (pI)
The pH at which a molecule has no charge—the number of
positive and negative charges is equal. At isoelectric pH, a
molecule does not migrate in an electric field. The solubility
of most substances is minimal at their isoelectric points.
isoforms
Different versions of a protein encoded by alleles of a gene
or by different but closely related genes.
isogeneic (isogenic)
Implying genetic identity, e.g., identical twins. Although
used as a synonym for syngeneic when referring to a genetic
relationship between members of an inbred strain (of mice),
the inbred animals never show the absolute dentity (identical
genotypes) observed in identical twins.
isograft
A tissue transplant from a donor to an isogeneic recipient.
Grafts exchanged between members of an inbred strain
of laboratory animals such as mice are syngeneic rather
than isogeneic.
isohemagglutinins
Naturally occurring immunoglobulin M (IgM) antibodies
in some members of a species that recognize erythrocyte
isoantigens on the surfaces of red blood cells from other
members of the same species. In the ABO blood group system,
the anti-A antibodies in the sera of group B individuals
and the anti-B antibodies in the sera of group A individuals
are examples of isohemagglutinins. They may be formed as
a result of immunization by bacteria in the gastrointestinal
and respiratory tracts.
IgG showing the isotype, designated in black, is determined by the heavy
chain.
isoimmunization
An immune response induced in the recipient of a blood
transfusion in which the donor red blood cells express
isoantigens not present in the recipient. The term also refers
to maternal immunization by fetal red blood cells bearing
isoantigens the mother does not possess.
isoleukoagglutinins
Antibodies in the sera of multiparous females and patients
receiving multiple blood transfusions that recognize surface
isoantigens of leukocytes and lead to their agglutination.
isologous
Derived from the same species; also called isogeneic or
syngeneic.
isophile antibody
An antibody induced by and specifically reactive with
erythrocytes but not reactive with other species’ red blood
cells. These antibodies are against antigens of red blood
cells unique to the species from which they were derived.
isophile antigen
Antigen that is species-specific; often refers to erythrocyte
antigens.
isoproterenol
Its chemical name is dl-β-[3,4-dihydroxyphenyl]-αisopropylaminoethanol;
a β-adrenergic amine used to
treat patients with asthma. It relaxes the bronchial smooth
muscle constriction that occurs in asthmatics.
isoschizomer
One of several restriction endonucleases derived from different
organisms that identify the same DNA base sequence
for cleavage but do not always cleave DNA at the same location
in the sequence. Target sequence methylation affects
the actions of isoschizomers that are valuable in investigations
of DNA methylation.
isotope
An isotypic determinant or epitope of an isotype.
isotopic (radionuclide) labeling
The introduction of a radioactive isotope into a molecule
via external labeling through tagging molecules with 125 I or
another appropriate isotope or by internal labeling in which
14 C- or 3 H-labeled amino acids are added to tissue culture,
allowing cells to incorporate the isotope. Once labeled,
molecules can be easily traced and their fate monitored by
measuring radioactivity.
isotypes
Antigens that determine the class or subclass of heavy
chains or the type and subtype of light chains of immunoglobulin
molecules, based on the amino sequences of their
constant regions. Mice and humans have five different Ig
heavy chain constant regions, Cμ, Cδ, Cα , Cγ, and Cε,
that define the five antibody isotypes IgM, IgD, IgA, IgG
and IgE, respectively. Every normal member of a species
expresses each isotype. Immunoglobulin subtypes are found
in all normal individuals. Among the immunoglobulin
classes, immunoglobulin G (IgG) and IgA have subclasses
designated by Arabic numerals. They are distinguished
according to domain number and size and also the number
of intrachain and interchain disulfide bonds in the constant
region. The four isotypes of IgG are designated IgG 1,
IgG 2, IgG 3, and IgG 4. The two IgA isotypes are designated
IgA 1 and IgA 2. Each of the μ, δ, and ε heavy chains and
the κ and λ light chains has one isotype. Immunoglobulin
isotypes are responsible for the biological effector functions
of an antibody molecule. IgM, IgG, IgD, IgA, and IgE that
differ in heavy chain constant regions constitute antibody
classes or isotypes. Light chain isotypes are defined by
either a κ light chain constant region (Cκ) or one of several
λ light chain constant regions ( Cλ).
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