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immunofluorescent “staining” of C4d 366 immunoglobulin
molecules with fluorochromes does not alter their antigenbinding
specificity. Several immunofluorescence techniques
are available. In the direct test, smears of the substance to
be examined are fixed with heat or methanol and followed
by flooding with a fluorochrome–antibody conjugate. This
is followed by incubating in a moist chamber for 30 to 60
minutes at 37°C, after which the smear is washed first in
buffered saline for 5 to 10 minutes and then in tap water for
another 5 to 10 minutes. The washing procedures remove
uncombined conjugated globulin. After adding a small drop
of buffered glycerol and a cover slip, the smear may be
examined with a fluorescence light microscope. In the indirect
test, which is more sensitive, a smear or tissue section is
first flooded with unlabeled antibody specific for the antigen
sought. After washing, fluorescein-labeled antiimmunoglobulin
of the species of the primary antibody is layered
over the section. After appropriate incubation and washing,
the section is cover slipped and examined as in the direct
method. Variations such as complement staining are also
available. The indirect method is more sensitive and considerably
less expensive; one fluorochrome-labeled antiimmunoglobulin
may be used with multiple primary antibodies
specific for a battery of antigens. The technique is widely
used to diagnose and classify renal diseases and bullous
skin diseases and study cells and tissues in connective tissue
disorders such as systemic lupus erythematosus (SLE).
immunofluorescent “staining” of C4d
In peritubular capillaries of renal allograft biopsies, immunofluorescent
“staining” of C4d reveals a humoral component
of allograft rejection.
immunogen
A substance that can induce a humoral antibody and/or
cell-mediated immune response rather than immunological
tolerance. Immunogen and antigen are sometimes used
interchangeably, but the term signifies the ability to stimulate
an immune response and react with its products (e.g.,
antibodies). By contrast, some use antigen to describe a
substance that reacts with antibody. The principal immunogens
are proteins and polysaccharides, whereas lipids may
serve as haptens.
immunogenetics
The branch of immunology concerned with genetic analysis
of molecules with specific relevance for the immune
system. The term previously referred to the use of antibodies
specific for genetically polymorphic molecules used to
analyze genetic traits including blood group antigens and
major histocompatibility complex (MHC) proteins.
immunogenic
The capacity to induce humoral antibody and/or cellmediated
immune responsiveness, but not immunological
tolerance. Immunogenicity depends on characteristics of the
immunogen and on the injected animal’s genetic capacity to
respond to the immunogen. To be immunogenic, a substance
must be foreign to the recipient. Significant molecular size
and complexity of the immunogen along with host factors
such as previous exposure to the immunogen and immunocompetence
are all critical factors in immunogenicity.
immunogenic carbohydrates
Carbohydrates are important in various immunological processes
that include opsinization and phagocytosis of microorganisms,
and cell activation and differentiation. They
exert their effects through interaction with carbohydrate-
binding proteins or lectins that have a widespread distribution
in mammalian tissues including the immune system.
Immunogenic carbohydrates are usually large polymers
of glucose (glucans and lentinans), mannose (mannans),
xylose, (hemicelluloses), fructose (levans), or mixtures of
these sugars. Complex carbohydrates may stimulate the
immune system by activating macrophages with fungal
glycans or stimulating T cells with lentinan. Acemannin
activates microphages and T cells, thereby influencing both
cellular and humoral immunity. Glucans stimulate immunity
against bacterial diseases by activating macrophages
and stimulating their lysosomal and phagocytic activities.
Complex carbohydrates may activate the immune systems
of patients or experimental animals with neoplastic diseases.
Some mannans and glucans are powerful anticancer
agents. Lentinin, derived from edible mushrooms, exerts
antineoplastic effects against several allogeneic and syngeneic
tumors without mediating cytotoxicity of the tumor
cells. Mannans derived from yeast also produce significant
antitumor effects, as do levans that activate macrophages
and B and T cells as well. Pectin is a galactose-containing
carbohydrate concentrated in citrus that causes an antitumor
effect.
immunogenicity
The ability of an antigen serving as an immunogen to
induce an immune response in a particular species of recipient.
Immunogenicity depends on a number of physical and
chemical characteristics of the immunogen (antigen) and on
the genetic capacity of the host.
Schematic representation of idiotypes present on an immunoglobulin
molecule.
Schematic representation of an antigen receptor on the plasma
membrane of a B cell.
immunoglobulin
A mature B cell product synthesized in response to stimulation
by an antigen. Antibody molecules are immunoglobulins
of defined specificity produced by plasma cells.