Untitled - D Ank Unlimited

consensus sequence 193 contact sensitivity (CS) or allergic contact dermatitis
consensus sequence
The typical nucleic acid or protein sequence where a nucleotide
or amino acid residue present at each position is that
found most often during comparison of numerous similar
sequences in a specific molecular region.
constant domain
The immunoglobulin C H and C L regions encoded by the corresponding
constant exon. There is only minor variability in the
amino acid content of constant domains. A globular compact
structure that consists of two antiparallel twisted β sheets.
There are differences in the number and the irregularity of the
β strands and bilayers in variable (V) and constant (C) subunits
of immunoglobulins. C domains have tertiary structures that
closely resemble those of the domains comprised of a fivestrand
β sheet and a four-strand β sheet packed facing one
another. However, the C domain does not have a hairpin loop
at the edge of one of the sheets. Thus, the C domain has seven
or eight β strands rather than the nine that are found in the V
domains. Refers also to the constituent domains or constant
regions of T cell receptor polypeptides.
constant exon
An exon that encodes the C terminal part of either an
immunoglobulin or a T cell receptor protein. The splicing
of a C exon at the mRNA level to a rearranged variable (V)
exon yields a transcript of a complete immunoglobulin or
T cell receptor gene. C exons of the immunoglobulin heavy
chain gene locus are comprised of sub-exons.
constant region
That part of an immunoglobulin polypeptide chain that has
an invariant amino acid sequence among immunoglobulin
chains belonging to the same isotype and allotype. There is a
minimum of two and often three or four domains in the constant
regions of immunoglobulin heavy polypeptide chains.
The hinge region tail end piece (carboxyl terminal region)
constitutes part of the constant region in selected classes of
immunoglobulin. A few exons encode the constant region
of an immunoglobulin heavy chain, and one exon encodes
the constant region of an immunoglobulin light chain. The
constant region is the location for the majority of isotypic
and allotypic determinants. It is associated with a number of
antibody functions. T cell receptor α, β, γ, and δ chains have
constant regions coded for by three to four exons. Major histocompatibility
complex (MHC) class I and II molecules also
have segments that are constant regions in that they show little
sequence variation from one allele to another. Refers also to
the part of a T cell receptor polypeptide chain that does not
vary in sequence among different clones and is not involved in
antigen binding.
constitutive defense system
See innate or constitutive defense system.
consumption test
An assay in which antigen or antibody disappears from
the reaction mixture as a result of its interaction with the
homologous antibody or antigen. The result is ascertained
by quantifying the amount of unreacted antigen or antibody
remaining in the reaction system and comparing it with the
quantity of that reagent that was originally present. The
antiglobulin consumption test is an example.
contact dermatitis
A type IV, T lymphocyte-mediated hypersensitivity reaction
of the delayed type that develops in response to an
allergen applied to the skin.
contact hypersensitivity reaction
A type IV delayed-type hypersensitivity reaction in the
skin characterized by a delayed-type hypersensitivity
(cell-mediated) immune reaction produced by cytotoxic T
lymphocytes invading the epidermis. It is often induced
by applying a skin-sensitizing simple chemical such as
dinitrochlorobenzene (DNCB) that acts as a hapten uniting
with proteins in the skin, leading to the delayed-type hypersensitivity
response mediated by CD4 + T cells. Although
substances such as DNCB alone are not antigenic, they
may combine with epidermal proteins that serve as carriers
for these simple chemicals acting as haptens. Spongiosis,
vesiculation, and pleuritis are present. Poison ivy hypersensitivity
is a type of contact hypersensitivity attributable to
T cell responses to the chemical antigen pentadecatechol
in poison ivy leaves. Langerhans’ cells are leukocytes in
the epidermis that present antigen to CD4 + T cells. They
possess long dendritic processes that course among the
epidermal cells, forming a network that is usually encountered
by any organism or antigen that penetrates through
the stratum corneum barrier. In addition to the cytoplasmic
organelles (Birbeck granules), they have membrane antigens
that include CD1a major histocompatibility complex
(MHC) class II antigens and costimulatory molecules B7-1
and B7-2. They also express adhesion molecules such as
E-cadherin, ICAM-1, and LFA-1. The latter two are requisite
for their migration to the regional nodes and interaction
with T cells.
contact sensitivity (CS) or allergic contact dermatitis
A form of delayed-type hypersensitivity (DTH) reaction
limited to the skin and consisting of eczematous changes.
It follows sensitization by topical drugs, cosmetics, or other
types of contact chemicals. The causative agents, usually
simple, low-molecular-weight compounds (mostly aromatic
molecules), behave as haptens. The development of
sensitization depends on the penetrability of the agent and
its ability to form covalent bonds with protein. Part of the
sensitizing antigen molecule is thus represented by protein,
usually the fibrous protein of the skin. Local skin conditions
that alter local proteins, such as inflammation, stasis, and
others, facilitate the development of CS, but some chemicals
such as penicillin, picric acid, or sulfonamides are unable
to conjugate to proteins. It is believed that in this case the
degradation products of such chemicals have this property.
CS may also be induced by hapten conjugates given by other
routes in adjuvants. The actual immunogen in CS remains
unidentified. CS may also have a toxic, nonimmunologic
component, and frequently both toxic and sensitizing effects
can be produced by the same compound. With exposure to
industrial compounds, an initial period of increased sensitivity
is followed by a gradual decrease in reactivity. This phenomenon
is called hardening and may represent a process of
spontaneous desensitization. The histologic changes in CS
are characteristic. Vascular endothelial cells in skin lesions
produce cytokine-regulated surface molecules such as IL-2.
IL4 mRNA is strongly expressed in allergic contact dermatitis
lesions. IFN-γ mRNA is the predominant cytokine in
tuberculin reactions. IL10 mRNA overexpression in atopic
dermatitis may facilitate upregulation of humoral responses
and downregulation of T H1 responses. Selected allergic
subjects manifest several types of autoantibodies including
IgE and β-adrenergic receptor autoantibodies.
C