Encyclopedia of Health and Medicine

Symptoms and Diagnostic Path
Symptoms vary with the type and severity of the
hypersensitivity reaction. Itching and skin rash or
URTICARIA (hives) are common with type I hypersensitivity
reactions. Symptoms may involve the
airways (allergic asthma) or gastrointestinal tract
(food allergies). Contact reactions typically involve
the surface of the skin though may also produce
widespread systemic symptoms. The diagnostic
path may include blood tests to assess the types
and levels of blood cells present in the circulation
as well as to detect the types and quantities of
immunoglobulins. Allergy testing can help isolate
the specific allergens for type I hypersensitivity
reactions. The doctor may conduct further diaghypersensitivity
reaction 269
Hemolytic ANEMIA, BLOOD TRANSFUSION reactions,
Rhesus (Rh) blood reactions (erythroblastosis
fetalis), PEMPHIGUS, GOODPASTURE’S
SYNDROME, and
many DRUG allergies (notably penicillin) are type II
hypersensitivity reactions.
Type III Hypersensitivity Reaction:
Immune Complex (IC) Reaction
IgG and IgM also mediate type III hypersensitivity
reactions, though through different mechanisms
from those that occur in type II hypersensitivity
reactions. Type III hypersensitivity reactions occur
when unattached antigens enter the blood circulation
and activate an immune response that results
in the formation of an immune complex, a conglomeration
of immune proteins (immunoglobulins),
platelets, neutrophils, and immune-related
substances that surround the antigens. Eventually
these clumps fall out of the blood circulation and
settle into tissues. Type III antibodies are autoantibodies—that
is, antibodies that target the body’s
own antigens.
Researchers do not know what precipitates the
immune response in most type III reactions,
though viruses such as HEPATIS A, serum sickness,
and drug reactions are sometimes accountable.
Symptoms develop 3 to 10 hours after the
immune complex forms. ASPERGILLOSIS, SYSTEMIC
LUPUS ERYTHEMATOSUS (SLE), GLOMERULONEPHRITIS,
polyarteritis and other forms of VASCULITIS, and
RHEUMATOID ARTHRITIS are type III hypersensitivity
reactions.
Type IV Hypersensitivity Reaction:
Delayed Reaction
T-cell lymphocytes (primarily helper T-cells) mediate
type IV hypersensitivity reactions, also called
delayed-type hypersensitivity (DTH) or cell-mediated
hypersensitivity reactions. Type IV reactions
take days to weeks to manifest. The rash of poison
ivy, poison oak, and poison sumac represents a
type IV hypersensitivity reaction. GRANULOMA is
also a typical type IV hypersensitivity reaction,
often to BACTERIA or fungi the body is unable to
completely eliminate. Common therapeutic applications
of a type IV hypersensitivity reaction
include the tuberculin skin test to detect the presence
of Mycobacterium tuberculosis and skin patch
ALLERGY TESTING.
HYPERSENSITIVITY REACTION TYPES AND SYMPTOMS
Type of Reaction Symptoms Typical Onset from Exposure
type I (IgE antibodies) URTICARIA (hives), SKIN RASH, wheezing 15 to 30 minutes
itching
type II (cytotoxic) redness and swelling due to cell or tissue death minutes to several hours
type III (immune complex) redness and swelling (erythema and edema) 3 to 10 hours
pain
type IV (cell mediated) redness and hardness (erythema and induration) 48 to 72 hours (nongranuloma)
PAIN
3 to 4 weeks (granuloma)