Immunology - Chapter 9 - Hypersensitivity Reactions

What are two different types of skin test

"Prick" test Intradermal test

caused by immune complex generated by Ig G that has infiltrated the tissues combing with the antigen injected intradermally

Arthus reaction

Productions of what can stimulate B-cells to selectively produce large amounts of IgE against the allergen

IL-4 and IL-13

Type I reactions are mediated by

IgE

What were two early tests that evaluated levels of components of the immune response to an allergen

Radioimmunosorbent test (RIST) Radioallergosorbent test (RAST)

How does hemolytic disease of the newborn occur?

RhD - negative mother is carrying a RhD - positive fetus During childbirth some of the fetal red blood cells leak back through the placenta into the maternal circulation if enough of these cells enter the maternal circulation the mother is "immunized" is subsequent child is also RhD - positive - "immunized" mother produces IgG against the RhD antigen

how can type IV hypersensitivity be transferred from one experimental animal by transferring

T cells sensitized to that allergen

hemolytic disease of the newborn

This disease occurs in the fetus if the fetus is Rh+ while the mother is Rh- occurs when a pregnant mother makes IgG against the red blood cells of her fetus IgG antibodies can cross the placenta

D antigen

This is what is referred to as Rh positive or Rh negative and is the most important antigen after A and B. most common antigen involved in hemolytic disease of the newborn

True/False FceRI can bind IgE without the immunoglobulin being bound to an antigen

True

Name the 4 types of hypersensitivity reactions

Type 1 - mediated by IgE (immediate hypersensitivity), mast cell degranulation Type 2 - antibody-mediated cell surface (cause cytotoxicity), complement activations Type 3 - mediated by immune complex, complement activation Type 4 - cell mediated, sensitized T cells, activated by macrophages

the immune response in Type III vs Type II reaction is to

Type III - an antigen in solution rather than on a particular cell or tissue (Type II)

Major players in Type II hypersensitivity

antibody, complement, phagocytes

the mechanism involved in type III hypersensitivity can also take place in certain forms of

autoimmunity

How do antigens stimulate an antibody-dependent immune response in Type I reactions

by causing the activation of the Th2 helper T-cell subsets

Intradermal test

carried out if results from the prick test are negative but there is still a suspicion that the individual tested may still be allergic to a particular allergen

After activation what happens to the mast cells and basophils

degranulated

Hemolytic anemias in type II hypersensitivity reactions

deposition of antibodies on the surface of red blood cells igG and IgM class activate complement and destroy the red blood cells to which they are attached certain medications and chemicals can cause reaction

Type IV can target which areas of the body

dermatitis usually initiated by small substances that get in contact with the skin and penetrate it absorbed into the skin, these molecules attach to host proteins acting as haptens forming hapten-protein complexed

How is immune complex formation damage completed in Type III reaction

due to activation of complement and recruitment of inflammatory cells inflammatory responses designed to clear immune complexes cause the tissue damage target tissues ar blood vessels walls, kidneys (glomerular basement membrane), joints and lungs

majority of the more severe clinical manifestations are due to the

early-phase response

the reactions that occur when the substances released by the mass cell have their biologic effect are called

effector phase

In extreme cases of allergic reactions what medication can be used

epinephrine

What are the two basic approaches for hypersensitivity testing

evaluating levels of components of the immune response to an allergen evaluating the actual physiological reactions of an individual to a particular allergen

What is the concept of hyposensitization

extremely small amounts of allergen are administered to an allergic individual this is repeated over a long period of time during which the amount of allergen gradually increases which eventually switches the response of the individual to the allergen from an IgE to an IgG response

serum sickness characterized by what

fever, chills, generalized rash, arthritis and sometimes kidney damage

clinical approaches to prevention of allergic reactions is

focused on decreasing symptoms rather than finding a "cure"

What are two Type II hypersensitivity diseases

goodpasture's syndrome rheumatic fever

Transfusion reactions

hemolytic reactions that can occur when large amounts of blood are transfused between individuals with incompatible blood groups

What type of hypersensitivity is a result of high circulating levels of soluble immune complexes made up of IgG or IgM Abs?

hypersensitivity III reaction

Hypersensitivity reactions

immune reactions that are overtly injurious to the host

What are symptoms of systemic anaphylaxis

increased blood vessel permeability smooth muscle contraction causes respiratory difficulties edema with severe swelling of the upper airway can lead to asphyxia cardiovascular issues

What are the two types of testing done for hemolytic disease of the newborn

indirect antiglobulin test (IAT) - test mom serum direct antiglobulin test (DAT) - test baby cells

intradermal test

injected between the different layers of the skin caution must be exercised as not to stimulate an anaphylactic reaction

Consequences of hemolytic disease of the newborn

jaundice, anemia, to fetal death

Play a major role in more chronic and often very serious manifestations of Type I hypersensitivity like chronic asthma

late-phase allergic reactions

Majority of type I reactions are

localized

Diagnostic test used to identify type IV hypersensitivity

mantoux test

Both prick test and intradermal test employ what types of controls

negative saline control positive histamine control

The clinical manifestations of localized reaction is dependent

on the anatomical site of allergen exposure and entry the amount of allergen also how deep allergen goes into the body

What are the medications that can cause hemolytic anemia - type II hypersensitivity reactions

penicillin and sulfonamides

Allergy

refers to four forms of hypersensitivity

How does the mantoux test work

replaced the tine test to test for mycobacterium tuberculosis positive test does not indicate individual has or has has tuberculosis result means individual has been exposed to mycobacterium tuberculosis (exposed to antigen)

The most common portal of entry for various allergen exposure is

respiratory tract

During the first exposure large amounts of IgE are produced these antibodies then bind to mast cells and basophils that large numbers of receptors for the Fc portion of IgE on their surfaces

sensitization phase

What are the advantages to a skin test

simple easy method very sensitive very specific to a particular allergen examines the final reaction of an individual to that allergen in vivo

What is example of the allergen test that evaluates the actual physiological reaction of an individual to a particular allergen

skin testing

"Prick" test

small amount of sample allergen is injected into the skin several different allergens can be tested positive reaction is usually indicated by the appearance in 15-30 minutes

serum sickness

systemic injury initiated by antigen-antibody complexes that circulate in the blood

Effects of both early responses and late responses tend to be localized around

the area of allergen exposure

What do the clinical manifestations observed in hypersensitivity reactions depend on

the host's response, not the nature of the antigen

The clinical manifestations of Type I reactions are a result from what

the release of either preformed or newly synthesized mediator from mast cells or basophils

Clinical appearance of dermatitis

the skin may present with redness blisters, edema, intense itching, peeling of the skin intensity of the reaction is dependent of the concentration of allergen and the degree of sensitization to the antigen duration of the reaction varis and can range from several days to several weeks after the removal of the antigen

Immediate hypersensitivity refers to

the timing between allergen exposure an the clinical manifestations of the reaction relative to the other forms of hypersensitivity reactions that take longer between exposure and clinical manifestations

Severity of transfusion reaction depends on several factors

titer of antibodies in the recipient serum (ABO high titers) the amount of blood transfused whether the recipient has been transfused wit the ABO-incompatible blood for the first time or for a subsequent time

What are clinical examples of type II reactions

transfusion reactions hemolytic anemias hemolytic disease of newborn (erythroblastosis fetus)

differences between type IV hypersensitivity and other types

type IV is mediated b CD4+ TH1 cells and CD8+ cytotoxic cells

Systemic reactions to food can range from

urticaria (hives) to systemic anaphylaxis

What are common allergens that cause anaphylaxis

venom, bee and wasp peanuts or peanut derived components certain shellfish and certain antibiotics such as penicillin

Why are some antigens allergenic

very small protein antigens on dry particles such as pollen grains become wet in the mucosa and elute proteins into it very low concentrations of proteins (often enzymes) tend to stimulate an IgE response localized to sites that are likely entry points of parasites

The most basic and self-evident method of prevention of allergic reactions is

allergen avoidance

Harmless antigens that can stimulate an IgE response are called

allergens

when an allergen comes in contact with the immune system at these sites an

allergy results

In transfusion reactions the antigens of concern in the blood transfusion are

ABO blood antigens - primary concern Rh antigens Kell and DUffy antigens

Two blood groups that have the most clinical relevance

ABO system Rh group

What is the mnemonic for the types of hypersensitivity

ACID Type 1 - *A*naphylaxis Type II - *C*ell or Surface bound Antibody Type III - *I*mmune Complex mediated Type IV - *D*elayed type hypersensitivity

True/False Foods do not cause both systemic and localized allergic reactions

False

the high affinity receptors for IgE are called

FceRI

Who developed the classification system for hypersensitivity

Gel and Coombs

Why are only certain people allergic

Genes (MHC haplotype and Th2 response) higher levels of circulating IgE

How does the approach of using antibodies against human IgE help with allergic reactions

Monoclonal anti-IgE is though to bind to IgE, thus preventing it from attaching to mast cells. In turn prevents the "arming" of the mast cells

prevention of hemolytic disease of the newborn

With RhoGAM during weeks 26-28 of pregnancy and during and after delivery; antibodies enter the maternal circulation and destroy any fetal RBCs before her immune system can respond and produce antibodies RhoGAM given to pregnant Rh- women Binds fetal agglutinogens in her blood so she will not form anti-D antibodies

The binding of antigen and subsequent cross-linking of surface FceRI by antigen binding to bound IgE is called

activation phase