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immunoglobulin structure 377 immunohistochemistry
demonstration of intracellular IgG or light chains in paraffin
sections. Monoclonal cytoplasmic staining for either κ
or λ light chains aids the diagnosis of B cell lymphomas.
immunoglobulin structure
Refer to immunoglobulin.
immunoglobulin subclass
The subdivision of immunoglobulin classes according
to structural and antigenic differences in the constant
regions of their heavy polypeptide chains. All molecules
in a subclass must express the isotypic antigenic determinants
unique to that class, but they also express other
epitopes that render that subclass different from others.
Immunoglobulin G (IgG) has four subclasses designated
IgG 1, IgG 2, IgG 3, and IgG 4. Whereas there is only 30% identity
among the five immunoglobulin classes, the similarity
among IgG subclasses is three times that. The IgA class
is divisible into two subclasses, but the remaining three
immunoglobulin classes have not been further subdivided
into subclasses. The structural differences in subclasses are
exemplified by the variations and number of inter-heavy
chain disulfide bonds that the four IgG subclasses possess.
The function of immunoglobulin molecules differs from
one subclass to another, as exemplified by the inability of
IgG 4 to fix complement.
Immunoglobulin superfamily adhesion receptors.
immunoglobulin superfamily
Several molecules that participate in the immune response and
show similarities in structure, causing them to be named the
immunoglobulin supergene family. Included are CD2, CD3,
CD4, CD7, CD8, CD28, T cell receptor (TCR), major histocompatibility
complex (MHC) class I and class II molecules,
leukocyte function-associated antigen 3 (LFA-3), the IgG
receptor, and a dozen other proteins. These molecules share
in common an immunoglobulin-like domain with a length of
approximately 100 amino acid residues and a central disulfide
bond that anchors and stabilizes antiparallel β strands into a
folded structure resembling immunoglobulin. Immunoglobulin
Immunogold labeling.
superfamily members may share homology with constant or
variable immunoglobulin domain regions. Various molecules
of the cell surface with polypeptide chains whose folded
structures are involved in cell-to-cell interactions belong in this
category. Single-gene and multigene members are included.
Protein molecules sharing 15% amino acid homology with
immunoglobulin proteins and possessing one or more immunoglobulin
domains belong to this large molecular family.
immunogold labeling
A technique to identify antigens in tissue preparations by
electron microscopy. Incubating sections with primary antibody
is followed by treatment with colloidal gold-labeled
anti-IgG antibody. Electron-dense particles are localized at
sites of antigen–antibody interactions.
immunogold silver staining (IGSS)
An immunohistochemical technique to detect antigens in
tissues and cells by light microscopy. IGSS offers higher
labeling intensity than most other methods when examined
in a bright field or in conjunction with polarized light. The
technique successfully stains tissue sections from paraffin
wax, resin, or cryostat preparations. It is also effective
for cell suspensions or smears, cytospin preparations, cell
cultures, or tissue sections. Both l- and 5-nm gold conjugates
are used for light microscopy. The l-nm particles are
advantageous in studies of cell penetration. In immunogold
silver staining, primary antibody is incubated with tissues
or cells to localize antigens that are identified with goldlabeled
secondary antibodies and silver enhanced.
immunohematology
The study of blood group antigens and antibodies and their
interactions in health and disease. Both the cellular elements
and the serum constituents of the blood have distinct
profiles of antigens. There are multiple systems of blood
cell groups, all of which may stimulate antibodies and interact
with them. These may be associated with erythrocytes,
leukocytes, or platelets.
immunohistochemistry
A method to detect antigens in tissues that employs an
enzyme-linked antibody specific for antigen. The enzyme
degrades a colorless substrate to a colored insoluble substance
that precipitates where the antibody and, therefore,
the antigen are located. Identification of the site of the
colored precipitate and the antigen in the tissue section
is accomplished by light microscopy. Diagnostic pathology
services routinely offer approximately 100 antigens
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