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allergic contact dermatitis 30 allogeneic (or allogenic)
allergic contact dermatitis
Delayed-type hypersensitivity mediated by specifically sensitized
T lymphocytes (type IV hypersensitivity) in response
to the covalent linkage of low molecular weight chemicals,
often less than 1000 M r, to proteins in the skin. The inflammation
induced by these agents is manifested as erythema
and swelling approximately 12 hours after contact and is
maximal at 24 to 48 hours. Blisters form that are filled with
serum, neutrophils, and mononuclear cells. There is perivascular
cuffing with lymphocytes, vesiculation, and necrosis of
epidermal cells. Basophils, eosinophils, and fibrin deposition
appear together with edema of the epidermis and dermis.
Langerhans’ cells in the skin serve as antigen-processing cells
where the allergen has penetrated. Sensitization lasts for many
years and becomes generalized in the skin. Chemicals become
conjugated to skin proteins and serve as haptens; therefore, the
hapten alone can elicit the hypersensitivity once sensitization
is established. After blistering, crust formation and weeping of
the lesion occur. The condition is intensely pruritic and painful.
Metal dermatitis, such as that caused by nickel, occurs as
a patch that corresponds to the area of contact with a metal or
jewelry. Dyes in clothing may produce skin lesions at points of
contact with the skin. The patch test is used to detect sensitivity
to contact allergens. Rhus dermatitis represents a reaction
to urushiols in poison oak and ivy that elicit vesicles and bullae
on affected areas. Treatment is with systemic corticosteroids
or the application of topical steroid cream to localized areas.
Dinitrochlorobenzene (DNCB) and dinitrofluorobenzene
(DNFB) have been used to induce allergic contact dermatitis in
both experimental animals and humans.
allergic disease immunotherapy
The principal immunologic, as opposed to environmental or
pharmacologic, treatment of allergic diseases that include
allergic rhinitis, conjunctivitis, and asthma. The allergen to
which a patient exhibits immunoglobulin E (IgE)-dependent
sensitivity is first identified followed by subcutaneous
administration of minute quantities of natural extracts containing
these allergens. The aim is to modify the immune
response responsible for maintaining atopic symptoms.
allergic granulomatosis
A type of pulmonary necrotizing vasculitis with granulomas
in the lung and pulmonary vessel walls. There may be
infiltrates of eosinophils in the tissues and asthma. Also
called Churg–Strauss syndrome.
allergic orchitis
The immunization of guinea pigs with autologous extracts
of the testes incorporated into Freund’s complete adjuvant
leads to lymphocytic infiltrate in the testes and antisperm
cytotoxic antibodies in the serum 2 to 8 weeks after inoculation.
Human males who have been vasectomized may also
develop allergic orchitis.
allergic reaction
A response to antigens or allergens in the environment as
a consequence of either preformed antibodies or effector
T cells. Allergic reactions are mediated by a number of
immune mechanisms, the most common of which is type I
hypersensitivity in which IgE antibody specific for an
allergen is carried on the surfaces of mast cells. Combining
with specific antigen leads to the release of pharmacological
mediators, resulting in clinical symptoms of asthma, hay
fever, and other manifestations of allergic reactions.
allergic response
A response to antigen (allergen) that leads to a state of
increased reactivity or hypersensitivity rather than a protective
immune response.
allergic rhinitis
A condition characterized by a pale and wet nasal mucosa
with swollen nasal turbinates. When hay fever is seasonal or
environmental it is allergic. One must first distinguish between
infectious and noninfectious rhinitis. Both types of patients
may have nasal polyps, and are often anosmic. Noninfectious
rhinitis that is perennial is difficult to establish as allergic.
allergoids
Allergens that have been chemically altered to favor the
induction of immunoglobulin G (IgG) rather than IgE
antibodies to diminish allergic manifestations in hypersensitive
individuals. These formaldehyde-modified allergens
are analogous to toxoids prepared from bacterial exotoxins.
Some of the physical and chemical characteristics of
allergens are similar to those of other antigens; however, the
molecular weights of allergens are lower.
allergy
A term coined by Clemens von Pirquet in 1906 to describe
the altered reactivity of the animal body to antigen. Currently,
the term refers to altered immune reactivity to a spectrum of
environmental antigens including pollen, insect venom, and
food. Allergy is also referred to as hypersensitivity and usually
describes type I immediate hypersensitivity of the atopic/anaphylactic
type. Allergy is a consequence of the interaction of
antigen (or allergen) and antibody or T lymphocytes produced
by previous exposure to the same antigen or allergen.
allergy, infection
Hypersensitivity, especially of the delayed T cell type, that
develops in subjects infected with certain microorganisms
such as Mycobacterium tuberculosis or certain pathogenic
fungi.
alloantibody
An antibody that interacts with an alloantigen, such as the
antibodies generated in the recipient of an organ allotransplant
(such as kidney or heart) that then may react with the
homologous alloantigen of the allograft. Alloantibodies
interact with antigens that result from allelic variation at
polymorphic genes. Examples include those that recognize
blood group antigens and human leukocyte antigen (HLA)
class I and class II molecules.
alloantigen
An antigen present in some members or strains of a species,
but not in others. Alloantigens include blood group
substances on erythrocytes and histocompatibility antigens
present in grafted tissues that stimulate alloimmune
responses in the recipient not possessing them, as well as
various proteins and enzymes. Two animals of a given
species are said to be allogeneic with respect to each other.
Alloantigens are commonly products of polymorphic genes.
alloantiserum
An antiserum generated in one member or strain of a species
not possessing the alloantigen (e.g., histocompatibility
antigen) with which the strain or species has been challenged
and derived from another member or strain of the
same species.
allogeneic (or allogenic)
An adjective that describes genetic variations or differences
among members or strains of the same species. The term