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allotypic determinant 33 alternative complement pathway
may also occur after administration of antibodies specific
for the paternal allotype to heterozygous newborn rabbits.
Animals conditioned in this way remain deficient for the
suppressed allotype for months and possibly years thereafter.
The animal switches to a compensatory increase in the
production of the nonsuppressed allotype. In homozygotes,
suppression involves heavy-chain switching from one Ig
class to another.
allotypic determinant
Epitope on serum immunoglobulin (Ig) molecules present
in selected members of a species. Allotypic determinants
are present in addition to other markers characteristic of the
molecule as a whole for the respective species. The allotypic
determinants or allotopes are characteristic of a given class
and subclass of immunoglobulin and have been demonstrated
in several species. The inheritance of genes controlling these
determinants is strictly Mendelian and is not sex linked. Both
H and k L chains contain such determinants; the encoding
genes are not linked and are codominant in an individual.
This means that markers present both in the father and mother
are expressed phenotypically in a heterozygote. However, an
individual immunoglobulin-producing cell expresses only one
of a pair of allelic genes, as a single cell can utilize only one
parental chromosome. In an individual, some cells use the
information encoded on the chromosome derived paternally
and other cells use that derived from the maternal contribution.
Thus, the individual is heterozygous, but a single cell secretes
only the products of one allele because of allelic exclusion. The
allotypic markers of human IgG are designated Gm determinants.
The Km(Inv) markers are characteristic for the C region
of k light chains.
allotypic marker
Refer to allotypic determinant or allotope.
allotypic specificities
Genetically different antibody classes and subclasses
produced within individuals of the same species. They are
detected as changes in the amino acid residues present in
specific positions in various polypeptide chains. The allotypic
specificities are also called genetic markers. Gm and Km(Inv)
markers are examples of allotypes of human immunoglobulin
G (IgG) heavy chains and k light chains, respectively.
Alopecia areata.
allotypy
A term that describes the various allelic types or allotypes
of immunoglobulin molecules.
alopecia areata
A partial or patchy loss of hair from the scalp or other
hair site that is believed to have an autoimmune basis,
even though no autoantigenic molecules in hair follicles
have been identified. The inheritance is polygenic with
a contribution from major histocompatibility complex
(MHC) genes. Other autoimmune diseases associated
with alopecia areata include the thyrogastric group,
pernicious anemia, Addison’s disease, and diabetes, as
well as vitiligo, systemic lupus erythematosus (SLE),
and others. There is supportive serological evidence for
autoimmunity in alopecia areata. Organ-specific autoantibodies
are increased in frequency, especially to thyroid
micosomal antigen and to other tissue antigens as well.
Affected hair follicles are encircled by dense lymphocytic
infiltrates that consist of T cells with CD8 + T cell subset
predominance.
alpha–beta T cells
T lymphocytes that express an αβ TCR. They comprise
Th, Tc, and regulatory T cell populations and mediate very
specific and broadly diverse adaptive immune responses.
ALPS
Abbreviation for autoimmune lymphoproliferative
syndromes.
ALS (antilymphocyte serum) or ALG (anti-lymphocyte
globulin)
Refer to antilymphocyte serum.
altered peptide ligand (APL)
Analog of immunogenic peptide in which the T cell receptor
contact sites have been altered, usually by substitution
with another amino acid. Even though these peptides fail
to stimulate T cell proliferation, they activate some T cell
receptor-mediated functions. Antagonist peptides specifically
downmodulate the agonist-induced response. APLs
can act therapeutically by modulating the cytokine patterns
of T cells or they may induce a form of anergy in T cells.
They stimulate partial responses from T lymphocytes specific
for the agonist peptide.
altered self
The concept that the linkage of non-self peptide to major
histocompatibility complex (MHC) yields a peptide–MHC
structure different from any found in normal cells of the
individual.
Alternaria species
Aeroallergenic fungi that can induce hypersensitivity
pneumonitis (HP). These fungi cause a form of HP known
as woodworker’s lung disease, as well as immunoglobulin E
(IgE)-mediated allergic disease.
alternative C5 convertase
A participant in the alternative pathway of complement
activation, comprised of two C3b molecules linked to Β
(C3b 2Bb) and splits C5 into C5a and C5b.
alternative complement pathway
Activation of complement not by antibody but through
the binding of complement protein C3b to the surface
of a pathogenic microorganism. This innate immune
mechanism amplifies complement activation through the
classic pathway. A non-antibody-dependent pathway for
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