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hybridoma 344 hyperacute graft rejection (HAR)
hybridoma
A hybrid cell produced by the fusion of an antibody-secreting
cell isolated from the spleen of an animal immunized
against that particular antigen with a mutant myeloma cell
of the same species that no longer secretes its own protein
product. Polyethylene glycol is used to effect cell fusion.
Antibody-synthesizing cells provide the ability to produce
a specific monoclonal antibody. The mutant myeloma
cell line confers immortality upon the hybridoma. If the
nucleotide synthesis pathway is inhibited, the myeloma cells
become dependent on hypoxanthine guanine phosphoribosyl
transferase (HGRPT) and the salvage pathway. The
antibody-synthesizing cells provide the HGPRT, and the
mutant myeloma cell enables endless reproduction. Once
isolated through use of a selective medium such as HAT
(hypoxanthine, aminopterin, and thymidine), hybridoma
cell lines can be maintained for relatively long periods.
Hybridomas produce specific monoclonal antibodies that
may be collected in great quantities for use in diagnosis and
selected types of therapy.
hybridoma, T cell
The immortalization of normal T lymphocytes by fusion
with continuously replicating tumor cells. Fusion randomly
immortalizes T lymphocytes regardless of their
antigen specificity and genetic restrictions to form a T cell
hybridoma. This represents one of two methods to isolate
and propagate T cell lines in clones of defined specificity.
The other technique is to span clones of normal immune
T lymphocytes stimulated with appropriate antigens and
antigen-presenting cells. The hybridoma technique holds
the advantage over T cell cloning in the relative ease of
securing relatively large numbers of T cells of interest and
their biologically active products. Lymphokines and other
regulatory molecules together with their nRNA and DNA
represent T cell hybridoma products. This technology has
also facilitated evaluation of T cell receptors and their
antigen recognition mechanisms. The adoptive (passive)
transfer of autoantigen-specific T cell hybridomas in mice
can induce autoimmune diseases.
H
H
O δ– H δ+
H H
H δ+
O δ–
O δ–
H δ+
O δ–
Hydrogen bonding shown in dotted lines.
hydrogen bonds
Formed between hydrogen atoms covalently linked to an
electronegative atom and a second electronegative atom
containing an unshared pair of electrons. The hydrogen
atom becomes electron-deficient through polarization of
its electron cloud toward the electronegative atom covalently
bonded to it, allowing for an electrostatic attraction
to a relatively negative second electronegative atom. The
contribution of hydrogen bonding to the stability of the
complex is minor compared to the other forces involved
and decreases with the sixth power of the distance between
interaction groups.
H
hydrophilic
A water-soluble substance. A cell membrane or protein
that contains hydrophilic groups on its surface that attract
water molecules.
hydrophobic
A substance that is insoluble in water. Protein or membrane
hydrophobic groups are situated inside these structures
away from water.
hydrophobic bond
A bond generated in an aqueous medium when polar water
molecules thrust hydrophobic, nonpolar chemical groups
together in an effort to generate the minimum nonpolar
surface area possible, thereby maximizing the entropy of
the water molecules.
hydrops fetalis
A hydropic condition that occurs in newborns who may
appear puffy and plethoric; it may be induced by immune or
nonimmune mechanisms. In the immune type, the mother
synthesizes immunoglobulin G (IgG) antibodies specific
for antigens of the offspring, such as anti-RhD erythrocyte
antigen. These IgG antibodies pass across the placenta
into the fetal circulation, causing hemolysis. Nonimmune
hydrops results from various etiologies not discussed here.
hydroxychloroquine
Hydroxychloroquine, also known as 2-[(4-[7-chloro-4-quinolyl]amino)ethyl-amino]ethanol
sulfate, is an antimalarial
agent that has immunosuppressive properties. It is believed
to suppress intracellular antigen processing and loading of
peptides onto MHC class II molecules through elevation of
the pH of lysosomal and endosomal compartments. Thus,
T cell activation is decreased. It has been used in the treatment
of selected autoimmune disorders such as rheumatoid
arthritis and systemic lupus erythematosus and in the
prevention of graft-vs.-host disease.
hydroxychloroquine sulfate (oral)
An antirheumatic agent used in the treatment of lupus erythematosus
and rheumatoid arthritis in patients who have
not responded satisfactorily to standard treatments. It is also
used to treat malaria.
17-hydroxycorticosteroids (17-OHCSs)
Adrenal steroid hormones synthesized by the action of
17-hydroxylase, including cortisone, cortisol, 11-deoxycortisol,
and tetrahydro derivatives of 17-hydroxylase. 17-OHCS
presence in the urine indicates the functional status of
adrenal glands and catabolic rates. 17-OHCSs are elevated
in Cushing’s disease, obesity, pregnancy, and pancreatitis
but decreased in hypopituitarism and Addison’s disease.
hygiene hypothesis
The concept that extreme measures to prevent exposure
of infants to disease-producing microorganisms results
in failure of the immature immune system to become
activated. This is claimed to lead to Th2 responses that may
predispose a subject to hypersensitivity and/or autoimmunity.
Thus, increased hygienic conditions, vaccination, and
antibiotic therapy are claimed to prevent children’s immune
systems from becoming accustomed to interacting with
infectious disease agents in the environment.
hyperactivated macrophage
Refer to macrophage.
hyperacute graft rejection (HAR)
Accelerated allograft rejection attributable to preformed
antibodies in the circulation of the recipient that are