Hypersensitivity refers to undesirable
reactions produced by the normal
immune system, including allergies and
These reactions may be damaging,
uncomfortable, or occasionally fatal.
TYPE I – IMMEDIATE, ATOPIC,
TYPE II – ANTIBODY DEPENDANT
TYPE III – IMMUNE COMPLEX
TYPE IV – CELL MEDIATED / DELAYED TYPE
Type I hypersensitivity is also known as
or anaphylactic hypersensitivity.
The reaction may involve skin
(urticariaand eczema), eyes
(conjunctivitis), nasopharynx (rhinorrhea,
rhinitis), bronchopulmonary tissues
(asthma) and gastrointestinal tract
The reaction may cause a range of
symptoms from minor inconvenience to
The reaction usually takes 15 - 30 minutes
from the time of exposure to the antigen,
although sometimes it may have a
delayed onset (10 - 12 hours).
Mediated by IgE antibody to specific
The primary cellular component in this
hypersensitivity is the mast cell or
The reaction is amplified and/or
modified by platelets, neutrophils and
Mast cells stimulated and release
nonparasite antigens that
can stimulate a type I
Atopy is the term for the genetic trait to have
a predisposition for localized anaphylaxis.
Atopic individuals have higher levels of IgE
Initial introduction of antigen produces
an antibody response. More specifically,
the type of antigen and the way in
which it is administered induce the
synthesis of IgE antibody in particular.
Immunoglobulin IgE binds very
specifically to receptors on the surface
of mast cells, which remain circulating.
Reintroduced antigen interacts with IgE
on mast cells causing the cells to
degranulate and release large amounts
of histamine, lipid mediators and
chemotactic factors that cause smooth
muscle contraction, vasodilation,
increased vascular permeability,
broncoconstriction and edema. These
reactions occur very suddenly, causing
Diagnostic tests for immediate
hypersensitivity include skin (prick and
intradermal) tests , measurement of total
IgE and specific IgE antibodies against the
Total IgE and specific IgE antibodies are
measured by a modification of enzyme
Increased IgE levels are indicative of
an atopic condition, although IgE may be
elevated in some non-atopic diseases (e.g.,
myelomas, helminthic infection, etc.).
› Non-steroidal anti-inflammatories
› Antihistamines block histamine receptors.
› Theophylline OR epinephrine -prolongs or increases
cAMP levels in mast cells which inhibits
› Desensitization (hyposensitization)
also known as allergy shots.
› Repeated injections of allergen to reduce the IgE on
Mast cells and produce IgG.
Type II hypersensitivity is also known as
cytotoxic hypersensitivity and may affect a
variety of organs and tissues.
The antigens are normally endogenous,
although exogenous chemicals (haptens)
which can attach to cell membranes can
also lead to type II hypersensitivity.
Drug-induced hemolytic anemia,
granulocytopenia and thrombocytopenia
are such examples. Pencillin allergy also
belong to this class.
The reaction time is minutes to hours.
Type II hypersensitivity is primarily
mediated by antibodies of the IgM or
IgG classes and complement .
Phagocytes may also play a role.
The lesion contains antibody,
complement and neutrophils.
Rh factor incompatibility
IgG abs to Rh an innocuous rbc antigen
› Rh+ baby born to Rh- mother first time fine. 2nd
time can have abs to Rh from 1st pregnancy.
› Ab crosses placenta and baby kills its own rbcs.
› Treat mother with ab to Rh antigen right after
birth and mother never makes its own immune
Diagnostic tests include detection of
circulating antibody against the tissues
involved and the presence of antibody and
complement in the lesion (biopsy) by
The staining pattern is normally smooth and
linear, such as that seen in Goodpasture's
nephritis (renal and lung basement
Treatment involves anti-inflammatory and
Antigen antibody immune complexes.
Large amount of antigen and antibodies form
complexes in blood.
If not eliminated can deposit in capillaries or
joints and trigger inflammation.
The reaction may be general (e.g.,
serum sickness) or may involve individual
organs including skin (e.g., systemic lupus
erythematosus, Arthus reaction), kidneys
(e.g., lupus nephritis), lungs
(e.g., aspergillosis), joints (e.g.,
rheumatoid arthritis) or other organs.
This reaction may be the pathogenic
mechanism of diseases caused by many
The reaction may take 3 - 10 hours after
exposure to the antigen .
It is mediated by soluble immune complexes.
They are mostly of the IgG class, although IgM
may also be involved.
The antigen may be exogenous (chronic
bacterial, viral or parasitic infections), or
endogenous (non-organ specific
autoimmunity: e.g., systemic lupus
The antigen is soluble and not attached to the
PMNs and macrophages bind to immune
complexes via FcR and phagocytize the
If unable to phagocytize the immune
complexes can cause inflammation via C’
activation ---> C3a C4a, C5a and
Diagnosis involves examination of tissue
biopsies for deposits of immunoglobulin
and complement by
The presence of immune complexes in
serum and depletion in the level of
complement are also diagnostic.
Treatment includes anti-inflammatory
Reaction involves sensitized T cells
and release of
its lymphokines as mediators and
Mediated by cells rather than antibodies
Clinical states: Contact dermatitis, ,
Transplant rejection, Granuloma
Th1 cells release cytokines to activate
macrophages causing inflammation and tissue
Continued macrophage activation can cause
chronic inflammation resulting in tissue lesions,
scarring, and granuloma formation.
Response starts after 48 -72 hrs
Delayed hypersensitivity reactions
Type Reaction time
48-72 hr eczema
tuberculin 48-72 hr
granuloma 21-28 days hardening
Diagnostic tests in vivo include delayed
cutaneous reaction (e.g. Montoux test
and patch test (for contact dermatitis).
In vitro tests for delayed hypersensitivity
include mitogenic response, lympho-
cytotoxicity and IL-2 production.
Corticosteroids and other
immunosuppressive agents are used in
Comparison of Different Types of hypersensitivity
antibody IgE IgG, IgM IgG, IgM None
antigen exogenous cell surface soluble
15-30 minutes minutes-hours 3-8 hours 48-72 hours
weal & flare
antibody antibody antibody T-cells
SLE, farmer's lung