Hypersensitivity

What is hypersensitivity?

exaggerated immune response to harmless antigens

What does hypersensitivity lead to?

tissue injury and disease

What are the types of hypersensitivity?

Type I, II, III, IV

What are the immediate reactions of hypersensitivity?

develop minutes to hours after antigen exposure

type I, II, III

What are the delayed reactions to hypersensitivity?

develop 24 to 48 hours after antigen exposure

type IV

What is type I hypersensitivity also known as?

anaphylactic hypersensitivity

What is type I hypersensitivity thought as?

allergies

What are the characteristics of type I hypersensitivity?

antibodies involved

usually IgE

complement is not needed

release of serotonin and histamine

What is the sensitization phase?

APCs process allergens and present them to Th cells

Th2 induces production of IgE

IgE binds to FceRI

What is the activation phase?

allergen cross-linkds adjacent cell-bound IgEs

mast cells and basophils degranulate

chemical mediators are released

allergy symptoms produced

What are common allergies?

pollen, mold, animal dander, dust mites, latex

What are the clinical manifestations of type I hypersensitivity?

rhinitis

asthma

food allergies

hives

eczema

systemic anaphylaxis

What are the treatments for type I hypersensitivity?

avoidance

drug therapy

monoclonal anti-IgE antibody

allergy immunotherapy

What is allergy immunotherapy?

administer gradually increasing doses of allergen

What is the testing for type I hypersensitivity?

percutaneous or intradermal

What is percutaneous testing?

allergens are applied to the upper layers of the skin with a needle or pricking device to the inner forearm or the back

What is intradermal testing?

higher doses of allergens are injected between the layers of the skin in the inner forearm or upper arm

What is allergen-specific IgE testing?

RAST test

patient serum is incubated with a solid phase to which an allergen is bound, followed by addition of an enzyme-labeled anti-IgE

fluorescence is produced

What is testing for total IgE?

RIST test

Patient serum is incubated with a solid phase to which an anti-IgE is bound, followed by addition of an enzyme-labeled anti-IgE

What is type II hypersensitivity also known as?

antibody-mediated cytotoxic hypersensitivity

What are the characteristics of type II hypersensitivity?

IgG and IgM

complement

leads to cytolysis and destruction

What are the cell damages in type II hypersensitivity?

activation of classical pathway

opsonization and phagocytosis

antibody dependent cellular cytotoxicity

What are the three phases in the classical pathway of the complement cascade?

Recognition, Activation, MAC

What are the clinical examples of type II hypersensitivity?

transfusion reactions

hemolytic disease of the newborn

autoimmune hemolytic anemia

What is hemolytic disease of the newborn?

caused by development of antibodies by a pregnant woman to red blood cell group antigens, often D ag, on the RBCs of the fetus

What are the tests for type II hypersensitivity?

direct antiglobulin test and indirect antiglobulin test

What is direct antiglobulin test?

detects red blood cells coated with complement components or IgG antibody

What is the indirect antiglobulin test?

Coomb's test

tests patient serum for antibodies to RBC antigens

What is type III hypersensitivity also known as?

complex-mediated hypersensitivity

What are the characteristics of type III hypersensitivity?

IgG and IgM

small antigens

complement

increases vasodilation

tissue damage due lysosomal enzymes

What is Arthus reaction?

skin reaction caused by type III hypersensitivity

localized inflammation with redness and edema

What is serum sickness?

caused by passive immunization

produces antibodies against foreign animal proteins

causes immune complexes to form

What are conditions associated with type III hypersensitivity?

autoimmune diseases

reactions to bee stings

drug reactions

What is the laboratory testing for type III hypersensitivity?

testing for ANAs

testing for rheumatoid factor

testing complement levels

What is type IV hypersensitivity?

no antibodies

sensitized T cells

Th1 cells involved

What happens during type IV hypersensitivity?

APCs present antigen to naive Th cell

Th1 cells release cytokines that attract macrophages

macrophages induce inflammation

Tc cells destroy target cells

What are the clincal examples of type IV hypersensitivity?

infections with intracellular pathogens

contact dermatitis

pneumonitis

What is contact dermatitis?

compounds contact the skin and act as haptens to sensitize Th1 cells

What is the testing for type IV hypersensitivity?

patch test and mantoux method

What is a patch test?

antigen is applied to the skin's surface

What is the mantoux method?

antigen injected intradermally