HYPERSENSITIVITY REACTIONS

Question 1

how many CLASSES OF HYPERSENSITIVITY REACTIONS and name them

Answer 1

4
type 1
type 2
type 3
type 4

Question 2

hypersensitivity reactions

Answer 2

reactions are exaggerated or inappropriate immune responses to harmless substances, leading to tissue damage

Question 3

type 1 hypersensitivity reactions

Answer 3

aka immediate hypersensitivity

caused by IgE antibodies binding to allergens, triggering mast cells and basophils to release histamine.

Examples: Allergies, asthma, anaphylaxis.

note that in some cases people with this type lose it as they get older

Question 4

type 2 hypersensitivity reactions

Answer 4

aka cytotoxic hypersensitivity

caused by IgG or IgM antibodies targeting antigens on cells, thereby activating the complement system, leading to cell destruction.

Examples: Hemolytic anemia, transfusion reactions.

Question 5

type 3 hypersensitivity reactions

Answer 5

aka immune complex hypersensitivity

caused by Antigen-antibody complexes deposit in tissues, causing inflammation.

Examples: Lupus, rheumatoid arthritis

involves IgM, IgG and sometimes IgA antibodies

Question 6

the most common hypersensitivity reactions

Answer 6

type 1 and 4

Question 7

type 4 hypersensitivity reactions

Answer 7

aka delayed-type hypersensitivty

caused by T-cell mediated response, usually 24-72 hours after exposure.

Examples: Contact dermatitis, tuberculosis skin test.

Question 8

allergens that cause type 1 hypersensitivity can be harmless and more harzadous, true or false

Answer 8

true

pollen, dust, drugs, or insect venoms etc could all cause it

Question 9

anaphalyxis vs prophalyxis

Answer 9

A severe, life-threatening allergic reaction that occurs rapidly after exposure to an allergen, causing symptoms like difficulty breathing, swelling, and a drop in blood pressure

while

A preventive treatment or measure taken to prevent disease or a medical condition, such as vaccines or medications to prevent infections or allergic reactions.

Question 10

some of the effects of type 1 hypersensitivity(what could it lead to)

Answer 10

Nasal allergic rhinitis or hay fever

Ocular allergic conjunctivitis, potentially due to seasonal allergens such as pollen or mould spores

Dermatological hives, atopic eczema, or erythema

Soft tissue angioedema

Pulmonary reactions, such as allergic asthma or hypoxia

Systemic reaction, which is a life-threatening medical emergency, and also known as anaphylaxis.

Question 11

some of the risk factors for type 1 hypersensitivity

Answer 11

geographical distribution

environmental risks such as pollution

socioeconomic status

genetic predisposition

“hygiene hypothesis”.

hygiene hypothesis suggests that our modern society practices of good hygiene
and the lack of early exposure to many microbes or antigens may result in failures of
the immune system functionality.

Question 12

the two stages in the response to an antigen exposure

Answer 12

the sensitization stage: host experiences an
asymptomatic contact with the antigen

the effect stage: the pre-sensitized host is re- introduced to the antigen, which then leads to a type I anaphylactic or atopic immune response.

Question 13

describe IgE mediated mast cell activation and degranulation

Answer 13

Sensitization: Upon first exposure to an allergen (e.g., pollen, dust), B cells produce IgE antibodies specific to that allergen. These IgE antibodies bind to FcεR receptors on the surface of mast cells and basophils, which become “sensitized.”

Re-exposure to Allergen: During subsequent exposure to the same allergen, the allergen cross-links the IgE antibodies bound on the mast cell surface.

Mast Cell Activation: The cross-linking of IgE receptors triggers mast cell activation, leading to intracellular signaling.

Degranulation: Activated mast cells release pre-stored granules containing histamine, cytokines, and other inflammatory mediators into the surrounding tissue.

Allergic Reaction: The released mediators cause vasodilation, increased vascular permeability, smooth muscle contraction, and mucus production, leading to symptoms like itching, swelling, and in severe cases, anaphylaxis.

Question 14

eicosanoids

Answer 14

lipid-based signaling molecules that regulate a variety of physiological responses, including inflammation, tissue homeostasis, and host defense

examples are prostaglandins, thromboxanes and Leukotrienes

Question 15

atopy

Answer 15

the tendency to produce an exaggerated IgE immune response to otherwise harmless substances in the environment.

Question 16

normal IgE levels precludes(preevents) atopy, true or false

Answer 16

false

even though atopy is characterised by elevated igE levels, it does not normal levels means there is no atopy

Question 17

risk factors for atopy

Answer 17

family history
high IgE levels
genetics

Question 18

activation of mast cells may lead to some diseases, name some

Answer 18

Hayfever
Allergic Rhinitis
Asthma
Conjunctivitis
Eczema
Dermatitis
Vomiting
Diarrhoea

Question 19

the nasal discharge from allergic rhinitis is often rich in which type of WBC

Answer 19

eisinophils

Question 20

eisinophil function

Answer 20

Eosinophils are released during infections, allergic reactions, and asthma. They consume harmful matter, and swarm inflamed sites to fight disease

Question 21

food allergies are characterised by

Answer 21

activation of mucosal mast cells in the GI tract

Transepithelial fluid loss and increased smooth muscle contraction
causes nausea and diarrhoea in food allergies

Question 22

acute urticaria

Answer 22

a skin condition that causes itchy, raised, red, and swollen areas on the skin

it Follows the subcutaneous
administration of allergen
eg. Insect bite

Question 23

does the route of entry of an allergen define it’s clinical effect on the person?

Answer 23

yes it does

Question 24

how/when does systemic anaphalyxis occur

a severe, potentially fatal allergic reaction that affects multiple organ systems

Answer 24

after intravenous or rapid oral absorption or administration of allergen

Question 25

the effects of systemic anaphalyxis

Answer 25

Connective tissue mast cells associated with all blood vessels become activated Results in vascular permeability (loss of blood pressure, oedema) airway constriction swelling of epiglottis suffocation

Question 26

causes of systemic anaphalyxis

Answer 26

Foreign serum Penicillin injection Bee venom Some foods

Question 27

anaphalytic shock

Answer 27

a severe, potentially life-threatening allergic reaction that can affect the entire body ## Footnote it is a response to allergens that** directly ** enter the blood. in this response, mast cells and basophils are enlisted throughout the body

Question 28

treatment for anaphalytic shock

Answer 28

adrenaline ## Footnote its the first line treatment, and causes bronchodilation, which helps with the wheezing..etc associated with A.S, and causes vasoconstriction, to counter the extreme low BPs in A.S

Question 29

name some clinical tests for allergy

Answer 29

Skin prick tests RASTs (Radio Allergo Sorbant Test)

Question 30

how does the Radio Allergo Sorbant Test(RAST) work in testing for allergies

Answer 30

Blood sample collected the potential allergen is attached to a solid phase, which could be a paper disk or a plastic surface the blood sample is then added to the solid phase, if person allergic to the allergen, then IgE antibodies specific to that specific allergen will be produced A secondary antibody tagged with a radioactive isotope is added. This secondary antibody binds to any IgE attached to the allergen these are then counted to quantify the presence of IgE antibodies, indicating the severity of the allergy ## Footnote note that this test is a bit old and has been largely replaced by tests like immunocap

Question 31

name some treatments for allergies

Answer 31

avoiding the allergens hyposensitization corticosteroids antihistamines etc ## Footnote Hyposensitization, also known as desensitization or allergen immunotherapy, is a medical treatment for asthma and environmental allergies. It involves gradually exposing a patient to larger and larger amounts of an allergen to change the immune system's response there's loads, check workshop book, you'd have made notes about them in there

Question 32

hyposensitization

Answer 32

a long term treatment for allergies, which works by gradually exposing the patient to increasing amounts of the allergen over time, which helps the immune system become less sensitive to it. ## Footnote aka allergy immunotherapy

Question 33

the two MAIN antibodies involved in hyposensitization, and what they do

Answer 33

IgG and IgE IgE production is reduced, while IgG binds to the allergen before it reaches IgE, blocking it from causing a severe allergic response

Question 34

type 2 hypersensitivity reactions

Answer 34

Antibody-mediated immune reaction in which antibodies (IgG or IgM) are directed against cellular or extracellular matrix antigens. Results in cellular destruction, functional loss, or tissue damage

Question 35

name some common type of type 2 hypersensitivity reactions

Answer 35

Blood transfusion reactions Hemolytic disease of the newborn (Rh disease; mother Rh- and infant Rh+) Autoimmune hemolytic anaemias Drug reactions Drug-induced loss of self-tolerance Hyperacute graft rejection Myasthenia gravis (acetylcholine receptor)

Question 36

name some ways/mechanisms in which damage to cells occur in type 2 hypersensitivity reactions

Answer 36

Antibody binding to cell surface receptors and altering its activity Activation of the complement pathway Antibody dependant cellular cytotoxicity

Question 37

ADCC (Antibody Dependent Cellular Cytotoxicity) ## Footnote usually carried out by IgG

Answer 37

an immune response mechanism in which immune cells target and destroy infected or abnormal cells (like cancer cells) that have been marked or coated by specific antibodies. ## Footnote key in getting rid of abnormal cells

Question 38

main antibodies involved in blood group compatibility are

Answer 38

mainly IGM antibodies, but in some cases they could be IgG

Question 39

what happens during incompatible blood transfusions , i.e where the blood of the donor and the receipient are not compatible ## Footnote note this is in vivo

Answer 39

In an incompatible transfusion, IgM antibodies bind to the donor RBCs, activating the complement system, which leads to cell lysis (destruction). Simultaneously, antibody-antigen(ab-ag) complexes are recognized by tissue-fixed macrophages, leading to phagocytosis and further tissue damage.

Question 40

the name of the in vitro test used to detect antibodies on the surface of RBCs before transfusion ## Footnote these antibodies act agaisnt antigens on the surface of the RBCs, eg if a person with blood type A has in incompatible blood type tranfused to them, then specific antibodies are produced against the donor blood

Answer 40

the antoglobulin test or Coomb's test ## Footnote Direct Coomb's Test (DCT): Uses Coomb's reagent to detect antibodies already attached to red blood cells. Helps diagnose autoimmune hemolytic anemia, transfusion reactions, or hemolytic disease of the newborn. Indirect Coomb's Test (ICT): Uses Coomb's reagent to detect free antibodies in the plasma. Used for blood compatibility testing before transfusions or organ transplants.

Question 41

describe the ABO blood group system, and the main antigens involved in this system

Answer 41

The ABO blood group system is based on the presence or absence of certain antigens on the surface of red blood cells (RBCs). These antigens are carbohydrates that are attached to proteins or lipids on the RBC membrane. the main antigens are A and B antigens

Question 42

name the various blood types and their genotypes(i.e their alleles)

Answer 42

Blood group A-> AA or AO Blood group B-> BB or BO Blood group AB-> AB Blood group O-> OO ## Footnote the genotypes indicate the alleles they inherited from each parent

Question 43

the antiodies contained in the serum of each of the blood types and what they indicate

Answer 43

for blood group A, it has anti-B antibodies, indicating that people with blood group A cannot not receive blood from those with B for blood group B, they have anti-A antibodies, same implies for blood group O, they have Anti-A and Anti-B antibodies. ## Footnote AB blood group does not have any antibodies. O is the universal blood group, so can donate to any blood type. AB is the universal receipient Giving a recipient blood with incompatible antigens can result in a hemolytic transfusion reaction, where the antibodies in the recipient's blood attack the donor's red blood cells, leading to cell lysis and serious complications

Question 44

hypersensitivity reactions can be drug induced, for exmaple by drugs like penicillin, celphalosporin..etc which antibodies or Immunoglobulins are produced when this happens? ## Footnote note that

Answer 44

IgM and IgG ## Footnote note that drug indced hypersensitivity occurs when the drugs to plasma proteins or red blood cells (RBCs)

Question 45

describe what happens in type 2 hypersensitivity when; 1. IGM is more abundant in drug induced hypersensitivity 2. IgG is more abundant than IgM

Answer 45

1. When IgM antibodies are more abundant, the immune system activates the complement system, which leads to direct lysis (destruction) of RBCs. This is common when large doses of the drug are given over a long period (several weeks). 2. When IgG antibodies are more abundant, they coat the RBCs, marking them for destruction. The phagocytes (immune cells like macrophages) then recognize and remove these antibody-coated RBCs, causing hemolysis (destruction of red blood cells).

Question 46

Antibodies can activate the complement pathway by binding to self-antigens, consequently leading to neutrophil activation. how does the activation of neutrophils occur when this happens?

Answer 46

when antibodies bind to self antigens, it results to the formation of the complement components C3a and C5a these act as chemotatic factors for neutrophils, bringing them in to the site consequently, neutrophils are activated ## Footnote here activated neutrophils release enzymes and reactive oxygen species to damage the tissues. this is A cause of autoimmunity

Question 47

what happens in goodpasture syndrome

Answer 47

autoantibodies are directed against collagen in glomerular and alveolar basement membranes. this leads to strong activation of the complement system, which recruits leukocytes, resulting in inflammation ## Footnote Autoantibodies are proteins produced by the immune system that attack the body's own cells, tissues, and proteins

Question 48

molecular mimicry meaning

Answer 48

a phenomenon where the immune system mistakenly targets the body’s own tissues because the structure of a foreign antigen (e.g., from a pathogen) closely resembles a self-antigen (e.g., a protein in our own body). This similarity leads to cross-reactivity, which is when antibodies or T cells that are originally designed to fight the pathogen also attack the body's own cells that have a similar structure.

Question 49

a classic example of molecular mimicry, and how it occurs

Answer 49

a classic example is in acute rheumatic fever, a condition developped after infection with Group A Streptococcus, a bacteria. some of these bacteria share structural similarities with human proteins, specifically cardiac myosin. So the antibodies generated to fight against them also bind to cardiac myosin in the heart. Complement system activated, which leads to inflammation and damage to the heart tissue, resulting in** rheumatic heart disease**

Question 50

how does Grave's disease happen, as a type 2 hypersensitivity reaction ## Footnote mainly looking for the role that autoantibodies play in this

Answer 50

the autoantibodies bind to the thyrotropin receptor on thyroid follicular cells resulting in the overproduction of thyroid hormones. Normally the production of thyrotropin by the pituitary is regulated by levels of thyroid hormones in the blood, but these antibodies lead to autonomous production of thyroid hormones by the follicular cells, which are not inhibited by high levels of thyroid hormones in the blood resulting in much higher levels than cause symptoms of thyrotoxicosis. ## Footnote Thyrotropin, also known as thyroid-stimulating hormone (TSH), is a hormone that regulates the thyroid gland's function

Question 51

how myasthenia gravis happens, as a type 2 hypersensitivity reaction

Answer 51

Autoantibodies directed against the nicotinic acetylcholine receptor do not allow acetylcholine to bind to its receptor on muscle cells, leading to muscle weakness.

Question 52

some treatments for type 2 hypersensivity reaction ## Footnote or complications arising from type 2 hypersensitivity reactions, as if you treat the complications, then you practically treat the reaction

Answer 52

Removing the causative agent where possible (drug, allergen etc.) Antibiotics for acute rheumatic fever Acute manifestations (reactive arthritis etc.) can be treated with NSAIDs Graves’ disease anti-thyroid drugs like carbimazole, Propylthiouracil...etc for Myesthenia Gravis, acetylcholinesterase inhibitors, general immunosuppressive therapy (e.g corticosteroids) and thymectomy is also sometimes considered ## Footnote methimazole is the active metabolite of carbimazole(a pro drug)