ImmunoSero mod 4

HYPERSENSITIVITY

•An exaggerated immune response to a typically harmless antigen that results to injury to the tissue, disease or even death. (Stevens)

•A heightened state of immune responsiveness

Type I: Anaphylactic/ Immediate

Type II: Antibody Mediated/ Cytotoxic

Type III: Immune Complex-Mediated

Type IV: Cell-Mediated/Delayed

HYPERSENSITIVITY

TYPE I HYPERSENSITIVITY

• Cell-bound antibody reacts with antigen

to release physiologically active

substances

• Key immunologic components: basophils,

mast cell, IgE and eosinophils

• IgE: unique in its ability to bind to specific

receptors on mast cells and basophils.

✓occurs in allergic reactions and helminth

infections

✓occurs within 30 to 60 minutes after

antigen exposure

basophils, mast cell, IgE and eosinophils

Key immunologic components in type 1 hypersensitivity

IgE

unique in its ability to bind to specific receptors on mast cells and basophils.

30 to 60

Type I Hypersensitivity occurs within ___ minutes after antigen exposure

Atopy

a term derived from the Greek word “atopos” (meaning “out of place”)

Atopy

✓refers to an inherited tendency to develop classic allergic responses to naturally occurring inhaled or ingested allergens

IgE

Atopic individuals are characterized by an elevated production of ___ in response to low doses of allergens like pollen, dust mites, or certain foods

initial phases

Defects in genes, which code for pattern recognition receptors such as CD14 and the Toll-like receptors (TLRs), can affect cell interactions with antigens in the ___ of immune defense.

IgE

serves as an antigen receptor on basophils and mast cells

Release of secondary mediators

▪more potent than the primary mediators

▪are responsible for a late phase allergic reaction that can be seen in some individuals 6 to 8 hours after exposure to the antigen.

interleukin-5 (IL-5)

▪released from Th2 cells

▪stimulate the bone marrow to increase production of eosinophils

▪producing eosinophilia

eosinophils are stimulated

▪release a variety of toxic molecules and inflammatory mediators from their granules.

Potential long-term effects:

thickening of smooth muscle, connective tissue, blood and lymphatic vessels, mucus glands, and nerves

route of antigen exposure

Dose of allergen

Frequency of Exposure

Type I hypersensitivity symptoms depend on the following:

Inhalation

Ingestion

Injection into the bloodstream

Route of allergen

Inhalation

cause respiratory symptoms such as asthma or rhinitis.

Ingestion

gastrointestinal symptoms

Injection into the bloodstream

can trigger a systemic response.

Allergic rhinitis

Allergic asthma

Food allergie

Skin reactions

Anyphalaxis

TYPE I HYPERSENSITIVITY Clinical Manifestations

Allergic rhinities

• most common form of atopy, or allergy

• pollen, mold spores, animal dander, and particulate matter from

house dust mites

• “hay fever” : Seasonal allergic rhinitis, triggered by tree and grass

pollens in the air during the spring in temperate climates

Allergic asthma

• Greek word for “panting” or “breathlessness,”

• Allergens reaches the lower respiratory tract

• It can be defined clinically as recurrent airflow obstruction that

leads to intermittent sneezing, breathlessness, and occasionally, a

cough with sputum production.

Food allergies

• most common cause of food allergies

✓ milk, eggs, nuts, soy, wheat, fish,

and shellfish

• Symptoms limited to the gastrointestinal tract

include cramping, vomiting, and diarrhea while

spread of antigen through the bloodstream may

cause hives and angioedema on the skin, as

well as asthma or rhinitis.

Skin reactions

• Local inflammation of the skin or dermatitis

• urticarial/hives

✓ caused by local vasodilation, leakage of fluid into the

surrounding area, and a spreading area of redness around the

center of the lesion

• wheal-and-flare reaction

• angioedema

• atopic eczema

Anyphalaxis

• coined by biologists Paul Portier and Charles Richet in 1902,

the term literally means “without protection.”

• typically triggered by glycoproteins or large polypeptides

• most severe type of allergic response

• Typical agents

✓venom from bees, wasps, and hornets; drugs such as

penicillin and foods such as shellfish, peanuts, and dairy

products.

• Death

✓asphyxiation because of upper-airway edema and

congestion, irreversible shock, or a combination of these

symptoms.

Avoidance of known allergens

The first line of defense

antihistamines and bronchodilators

effective against asthma

antihistamines and decongestants

Localized allergic reactions, such as hay fever, hives, or rhinitis

Corticosteroids

• Severe Cases

• added to block recruitment of inflammatory cells and their ability to cause tissue damage.

Epinephrine

• For systemic anaphylaxis

Omalizumab

• recombinant humanized antibody composed of human

immunoglobulin G (IgG)

• antibody binds to the Cε3 domain of human IgE, which is the site

that IgE normally uses to bind to FcεRI receptors.

✓Blocking this site prevents circulating IgE from binding to mast

cells and basophils and sensitizing them.

Mepolizumab

• humanized antibody is directed against IL-5

✓a cytokine that plays a major role in the development and

activation of eosinophils; thus, treatment results in reduced

eosinophil number and activity

Dupilumab

• targets a subunit of the IL-4 receptor and blocks intracellular

signaling by IL-4 and IL-13

CUTANEOUS (Prick Test)

Procedure:

1) Using a needle or pricking device a small drop of allergen extract

is introduced into the upper layers of the individual’s skin in the

inner forearm or the back.

2) A panel of allergens is routinely used, with each applied to

separate sites 2 to 2.5 cm apart.

3) After 15 to 20 minutes, the clinician examines the testing spots and

records the reaction.

4) POSITIVE Reaction: wheal-and-flare reaction is based on the

presence or absence of erythema and the diameter of the wheal,

with a diameter larger than 3 to 4 mm correlating best with the

presence of allergy.

Intradermal

• performed when cutaneous test is negative.

✓In intradermal testing, a 1-mL tuberculin syringe is used to

administer 0.01 to 0.05 mL of test solution between layers of the

skin.

Type II Hypersensitivity

Aka Cytotoxic or Antibody-mediated

• Mechanism: Free antibody reacts with antigen associated with cell surfaces

• Key Reactants: IgG and IgM

IgG and IgM

Key reactant in Type II Hypersensiticity

1. The cell can be destroyed.

2. The function of the cell can be inhibited

3. The function of the cell can be increased above normal

TYPE II HYPERSENSITIVITY Immunologic Mechanism

Binding of the antibody to a cell can have one of three major effects, depending on the situation

The function of the cell can be inhibited.

This can occur when antibody blocks the binding of a physiological ligand to its receptor, resulting in dysfunction of the cell.

An example Myasthenia gravis

Myasthenia gavis

affects the neuromuscular junctions. Patients with this disease produce autoantibodies to receptors on muscle cells for the neurotransmitter acetylcholine (ACH

The function of the cell can be increased above normal

antibody to a self-antigen can have the opposite effect, stimulating the cell instead of inhibiting its function

example: Graves disease

Transfusion Reactions

Hemolytic disease of the fetus and newborn (HDFN)

Cold Agglutinins

Autoimmune Hemolytic Anemia

Paroxysmal Cold Hemoglobinuria

Type II Reactions Involving Tissue Antigens

TYPE II HYPERSENSITIVITY Clinical Examples

Transfusion reactions

• ABO blood group is of primary importance in considering transfusions.

✓a person who has type A blood has anti-B in the serum and a

person with type B blood has anti-A antibodies

• An individual with type O blood has both anti-A and anti-B in the

serum because O cells have neither of these two antigens.

• Acute/Immediate HTRs – IgM, intravascular hemolysis due to

complement activation

• Delayed HTRs – IgG, extravascular hemolysis due to splenic

sequestration of coated RBCs

Acute/Immediate HTRs

IgM, intravascular hemolysis due to complement activation

Delayed HTRs

IgG, extravascular hemolysis due to splenic sequestration of coated RBCs

Hemolytic disease of the fetus and newborn (HDFN)

• Mothers have been exposed to blood-group antigens on the baby’s

cells that differ from their own.

• Mother makes IgG antibodies in response to these antigens.

• These antibodies cross the placenta and destroy the fetal RBCs.

• D antigen

✓A major cause of severe reactions

✓a member of the Rh blood group

• Sensitization of the mother to paternal blood group antigens may

occur during pregnancy but to a larger extent during the birth process,

when fetal cells leak into the mother’s circulation.

Erythroblastosis fetalis

Severe HDFN may be called

Cold Agglutinins

• Autoantibodies that react with antigens on the RBC membrane at

cold temperatures.

✓these cold-reacting antibodies belong to the IgM class

Autoimmune Hemolytic Anemia

• directed against self-antigens, because individuals with this disease

form antibodies to their own RBCs.

✓Warm AIHA – Abs reacting at 37⁰C, IgG

✓Cold AIHA – Abs reacting at <30⁰C, IgM

• drugs can induce the production of antibodies that can cause

hemolytic anemia.

✓penicillin and cephalosporins, act as haptens after binding to

proteins on the RBC membrane.

✓Other drugs: Quinidine, Phenacetin, Methyldopa

TYPE II HYPERSENSITIVITY

Clinical Examples

Paroxysmal Cold Hemoglobinuria

Patients produce a biphasic autoantibody that binds to the RBCs at cold temperatures and activates complement at 37°C to produce an intermittent hemolysis.

Type II Reactions Involving Tissue Antigens

Anti-glomerular basement membrane (anti-GBM) disease

formerly known as Goodpasture’s syndrome

✓antibody produced during the course of this disease reacts

with basement membrane protein.

✓ Hashimoto’s disease,

✓ Myasthenia gravis

✓Insulin-Dependent Diabetes Mellitus.

Good pasture’s syndrome

Anti-glomerular basement membrane (anti-GBM) disease formerly known as

DIRECT ANTIGLOBULIN TEST (DAT)

INDIRECT ANTIGLOBULIN TEST (IAT)

TYPE II HYPERSENSITIVITY Testing Procedures

DIRECT ANTIGLOBULIN TEST (DAT)

detects RBCs that have

been sensitized with

antibody or complement

in vivo.

• In this technique, patient

RBCs are initially

incubated with

polyspecific anti-human

globulin, which is a

mixture of antibodies to

IgG and complement

components such as C3b

and C3d

INDIRECT ANTIGLOBULIN TEST (IAT)

• detects in vitro

sensitization of RBCs

• used in the

crossmatching of blood

to prevent a transfusion

reaction.

• used either to determine

the presence of a

particular antibody in a

patient or to type

patient red blood cells

for specific blood group

antigens

TYPE III HYPERSENSITIVITY

o Aka Immune-complexes mediated

o Mechanism

• Antibody reacts with soluble antigen to form complexes that precipitate in the tissues.

o Key Reactants: IgG and IgM

Arthus reaction

Serum sickness

Autoimmune diseases

TYPE III HYPERSENSITIVITY Clinical Examples

Arthus reaction

• demonstrated by Maurice Arthus in 1903

• intradermal injection of antigen to immunized rabbits' results to a localized inflammatory reaction (erythema and edema)

Serum sickness

• Patients exposed to such animal sera can

produce antibodies against the foreign

animal proteins.

• passive immunization with animal serum

(horse or bovine); immune complexes

deposits in the tissues

• used to treat such infections as diphtheria,

tetanus, and gangrene

Autoimmune diseases

• Systemic Lupus Erythematosus and Rheumatoid Arthritis

✓Patients produce antibodies against nuclear

constituents such as DNA and histones.

✓They may also produce an antibody against IgG

called rheumatoid factor.

Systemic Lupus Erythematosus and Rheumatoid Arthritis

✓Patients produce antibodies against nuclear

constituents such as DNA and histones.

✓They may also produce an antibody against IgG

called rheumatoid factor.

Detecting the presence of antibody in specific disease

Fluorescent staining of tissue section

Measuring complement levels

TYPE III HYPERSENSITIVITY Testing Procedures

Detecting the presence of antibody in specific disease

ELISA and indirect immunofluorescence

Fluorescent staining of tissue sections

used to determine deposition of immune complexes in the tissues

Measuring complement levels

Complement level decreases during high disease

activity

Delayed-type/Cell-mediated Hypersensitivity

TYPE IV HYPERSENSITIVITY also known as

CONTACT DERMATITIS

HYPERSENSITIVITY PNEUMONITIS

TYPE IV HYPERSENSITIVITY Clinical Examples

Contact dermatitis

• Reactions are usually due to low-molecular- weight compounds

that touch the skin.

• Nickel, rubber, formaldehyde, hair dyes and fabric finishes,

cosmetics, medications

✓applied to the skin such as topical anesthetics, antiseptics,

and antibiotics, and latex.

✓function as haptens that bind to glycoproteins on skin cells.

Hypersensitivity pneumonitis

• Caused by sensitized T cells responding to inhaled antigen

• T cells respond to inhaled allergens (microorganisms, especially

bacterial and fungal spores) that individuals are exposed to

from working

• Several names: farmer’s lung, bird breeder’s lung disease, and

humidifier or air-conditioner lung disease

Patch test

Mantoux method

Interferon gamma release assays (IGRA)

Quantiferon TB Gold Plus assay (QFT-Plus)

T-SPOT.TB

TYPE IV HYPERSENSITIVITY Testing Procedures

Patch test

• considered the gold standard in testing for contact dermatitis.

• Procedure:

1. A nonabsorbent adhesive patch containing the suspected contact

allergen is applied on the patient’s back the skin is checked for a

reaction during the next 48 hours.

2. Redness with papules or tiny blisters is considered a positive test.

3. Final evaluation is conducted at 96 to 120 hours.

Mantoux method

• based on the principle that soluble antigens from M. tuberculosis induce a reaction in

people who currently have TB or have been exposed to M. tuberculosis in the past.

• The tuberculin skin test uses an M. tuberculosis antigen extract prepared from a purified

filtrate of the organism’s cell wall, called a purified protein derivative (PPD).

• Procedure:

1. PPD is injected intradermally into the inner surface of the forearm using a fine

needle and syringe

2. examined between 48 and 72 hours, check for the presence of a hardened,

raised area called induration.

Skin testing

can also be used to determine whether the cell-mediated arm of the immune system is functioning properly.

Interferon gamma release assays (IGRA)

These tests are based on detecting a cell-mediated immune response by measuring the production of IFN-γ by patients’ T cells that have been stimulated with M. tuberculosis–specific antigens.

Quantiferon TB Gold Plus assay (QFT-Plus)

• Procedure:

1. patient blood is drawn into specialized collection tubes

containing peptides that are highly specific for M.

tuberculosis (ESAT-6 and CFP-10).

(Early secretory antigen target & Culture Filtrate Protein)

2. During the incubation, T cells from patients who have been

infected with M. tuberculosis will respond to the TB antigens

by producing the cytokine, IFN-γ.

3. The tubes are centrifuged to collect patient plasma, and

the amount of IFN-γ in the plasma is measured by an ELISA.

TYPE IV HYPERSENSITIVITY

Testing Procedures

T-SPOT.TB

• based on the enzyme-linked immunospot (Elispot) technique.

• Procedure:

1. During the incubation, T cells from patients exposed to M.

tuberculosis release IFN-γ in their vicinity.

2. After a wash step, an enzyme-labeled antibody to IFN-γ is

added, and after another incubation and wash, substrate is

added to the wells.

3. Dark blue spots are produced where the IFN-γ–secreting cells

were in the wells,

4. and the number of spots is counted under a magnifying glass

or stereomicroscope

FcεRI

The number of FcεRI receptors on eosinophils increases during the allergic response.