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cromolyn 201 cross tolerance
cromolyn (1,3-bis[2-carboxychromon-5-2-hydroxy-propane])
A therapeutic agent that prevents mast cell degranulation.
It has proven effective in the therapy of selected allergies,
including allergic rhinitis and asthma.
cromolyn sodium
A drug that blocks the release of pharmacological mediators
from mast cells and diminishes the symptoms and tissue
reactions of type I hypersensitivity (i.e., anaphylaxis) mediated
by immunoglobulin E (IgE). Although the mechanism
of action of cromolyn sodium remains to be determined, it
apparently inhibits the passage of calcium through the cell
membrane. It inhibits mast cell degranulation but has no
adverse effect on the linkage of IgE to mast cell surfaces or
their interactions with antigen. Cromolyn sodium is inhaled
as a powder or applied topically to mucous membranes. It is
usually used for the treatment of asthma, allergic rhinitis, and
allergic conjunctivitis, and it has low cytotoxicity.
cross absorption
The use of crossreacting antigens or crossreacting antibodies
to absorb antibodies or antigens, respectively.
cross linking
A process resulting from the joining of multiple identical molecules
by the union of multivalent ligands such as antibodies.
It may occur with both soluble and cell-surface structures.
cross match testing
An assay used in blood typing and histocompatibility testing
to ascertain whether donor and recipient have serum
antibodies specific for each other’s cells that might hinder
successful transfusion of blood products or transplantation
of organs or cells. Cross matching reduces the chances of
graft rejection by preformed antibodies against donor cell
surface antigens, which are usually major histocompatibility
complex (MHC) antigens. Donor lymphocytes are
mixed with recipient serum, complement is added, and the
preparation is observed for cell lysis.
cross matching procedures
The conventional cross matching procedure for organ
transplants involves the combination of donor lymphocytes
with recipient serum. Three major variables in the standard
cross match procedure predominantly affect the reactivity
of the cell–serum sensitization: (l) incubation time and
temperature, (2) wash steps after sensitization, and (3)
the use of additional reagents such as antiglobulin in the
test. Variations in these steps can cause wide variations in
results. Lymphocytes can be separated into T and B cell categories
for cross match procedures conducted at cold (4°C),
room (25°C), and warm (37°C) temperatures. These proce-
Donor
lymphocyte
+ + Complement +
Vital dye
(e.g., trypan
blue)
Patient’s
serum
Cross matching procedure.
Dark blue
positive
crossmatch
White refractile
negative
crossmatch
dures permit the identification of warm antiT cell antibodies
that are almost always associated with graft rejection.
cross presentation
Exogenous peptide antigen presentation on dendritic cell or
macrophage MHC class I molecules. There may be fusion
of a phagosome containing exogenous antigen with an
endoplasmic reticulum-derived vesicle bearing constituents
of the endogenous antigen processing apparatus. Peptide
regurgitation or peptide interception may also represent a
mechanism of cross presentation.
cross priming
Activation or priming of a naïve CD4 + cytotoxic T
lymphocyte specific for antigens of a third cell such as a
virus-infected cell or tumor cell by a professional antigenpresenting
cell (APC). Cross priming takes place when a
professional APC ingests an infected cell and the microbial
antigens are processed and presented in association with
Class I MHC molecules. The professional APC also costimulates
the T cells. Also referred to as cross presentation.
crossreacting antibody
An antibody that reacts with epitopes on an antigen molecule
different from the one that stimulated its synthesis.
The effect is attributable to shared epitopes on the two
antigen molecules.
crossreacting antigen
An antigen that interacts with an antibody synthesized
following immunogenic challenge with a different antigen.
Epitopes shared between these two antigens or epitopes
with a similar stereochemical configuration may account
for this type of crossreactivity. The presence of the same
or a related epitope between bacterial cells, red blood cells,
or other types of cells may result in crossreactions of the
antigens with an antibody produced against either of them.
crossreaction
The reaction of an antigenic determinant or epitope with an
antibody formed against another antigen. The presence of
the same epitope on two different antigens and the presence
of two similar epitopes on separate antigens may lead to
crossreactivity. A laboratory technique used for matching
blood for transfusion and organs for transplantation. In blood
transfusion, donor erythrocytes are combined with the recipient’s
serum. Agglutination occurs if antibody in the recipient’s
serum is specific for donor red cells. This procedure
represents the major part of the cross match. In a negative
test, the presence of incomplete antibodies may be detected
by washing the red blood cells and adding rabbit antihuman
globulin. Agglutination signifies the presence of incomplete
antibodies. The minor part of the cross match test consists of
mixing the recipient’s red blood cells with donor serum. This
procedure is of less importance than the major cross match
because of the limited amount of serum in a unit of blood
compared to the red cell volume of the recipient.
crossreactivity
The ability of an antibody or T cell receptor to react with
two or more antigens that share an epitope in common.
cross sensitivity
Induction of hypersensitivity to a substance by exposure to
another substance containing cross reacting antigens.
cross tolerance
The induction of immunologic tolerance to an antigen by
exposure of the host to a separate antigen containing crossreacting
epitopes under conditions that favor tolerance induction.
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