Untitled - D Ank Unlimited

homologous recombination pathway 339 hookworm immunity
homologous recombination pathway
A DNA repair pathway that employs homologous DNA to
repair major gaps in double-stranded DNA in an
“error-free” manner. Associated with the BLM gene (refer
to Bloom syndrome).
homologous restriction factor (HRF)
An erythrocyte surface protein that prevents cell lysis by
homologous complement on its surface. It bears a structural
resemblance to C8 and C9.
homologous vaccine
Autogenous vaccine.
homology region
A 105- to 115-amino-acid residue sequence of heavy or
light chains of immunoglobulins that have primary structures
resembling other corresponding sequences of the
same size. A homology region has a globular shape and an
intrachain disulfide bond. The exons that encode homology
regions are separated by introns. Light polypeptide chain
homology regions are termed V L and C L. Heavy chain
homology regions are designated V H, C H1, C H2, and C H3.
homology unit
A structural feature of an immunoglobulin domain.
homopolymer
A molecule comprised of repeating units of only one
amino acid.
homotransplantation
Homograft (i.e., allograft) transplantation.
homozygote
An organism whose genotype is characterized by two identical
alleles of a gene.
homozygous
Containing two copies of the same allele.
homozygous typing cell (HTC) technique
An assay that employs a stimulator cell that is homozygous
at the HLA-D locus. The HTC incorporates only a
minute amount of tritiated thymidine when combined with
a homozygous cell in the MLR. This implies that the HTC
shares HLA-D determinants with the other cell type. By
contrast, when an HTC is combined with a nonhomozygous
cell, much larger amounts of tritiated thymidine are incorporated.
Many variations between these two extremes are
noted in actual practice. HTCs are frequently obtained from
the progeny of marriages between cousins.
homozygous typing cells (HTCs)
Cells obtained from a subject who is homozygous at the
HLA-D locus. HTCs facilitate MLR typing of the human
D locus.
Hood, Leroy
Pioneer in immunogenetics and molecular biology. His
work with Tonegawa proved that three separate DNA segments
must be combined to complete the heavy chain variable
region sequence of immunoglobulin. They found yet
another diversity (D) group of DNA segments in addition to
the V and J segments. Hood went on to demonstrate mutations
in these gene segments. The elegant body of scientific
evidence elucidated finally solved one of immunology’s
most mystifying conundrums.
hook effect
An artifact that may be seen in the immunoradiometric
assay (IRMA) when a hormone assayed is present in very
high concentration. The excess amount cannot be measured
by the detector system because it will have reached its
Leroy Hood.
theoretical limit. The diminished counts with the labeled
antibody at the elevated hormone concentration yield spuriously
low results. Thus, IRMA is not an appropriate method
for assaying hormones present in relatively high concentrations,
such as gastrin, prolactin, or hCG. The hook effect
requires measurement of two separate concentrations to
establish linearity.
hookworm immunity
Hookworms in humans induce various antibody responses
that may be assayed by ELISA or the radioimmunoassay
technique. There is a prominent immune response to
excretory–secretory (ES) products and surface antigens, as
well as a sharp rise in specific immunoglobulin isotypes
during infection. Marked elevation of total serum immunoglobulin
E (IgE) occurs in human hookworm disease; the
remaining additional immunoglobulin in the circulation
is not specific for parasite antigens. Serum IgA may be
diminished during hookworm disease, because hookworm
proteases are able to digest host IgA. The greater the burden
of worms, the more intense the antibody response to adult
antigens. Subjects who have fewer worms develop higher
titers of antilarval antibodies that increase the resistance to
larval challenge. Hookworms induce T H2-type responses
together with specific IgE antibodies against ES products
and eosinophilia. Evidence is lacking to support the concept
that T H2-dependent immunity plays a major role in hostprotective
immunity against hookworms. Little is known
concerning cellular responses to hookworms. Eosinophilia
is a common finding in hookworm infection. Production
of superoxide is increased, and chemotaxis of eosinophils
from infected donors is enhanced; yet, the eosinophilia has
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