Hypersensitivity

Question 1

what is an allergy

Answer 1

reaction produced by the normal immune system against innocuous antigen in a pre-sensitised host

Question 2

what are the 4 types of hypersensitivity

Answer 2

type 1 - anaphylactic
2 - cytotoxic
3 - immune complex
4 - delayed

Question 3

what is the pathogenesis of type 1 hypersensitivity

Answer 3

dendritic cells ingest allergen and present antigen - recognised by TH2, release IL4 to stimulate B cells and release IgE

Question 4

what happens which IgE is released from B cells in type 1 hypersensitivity

Answer 4

crosslinks via allergen which then binds to mast cells and release performed and de novo inflammatory mediators

Question 5

what are some examples of de novo and performed inflammatory mediators related by mast cells

Answer 5

performed - histamine, chemokine, proteases

de novo - prostaglandins, leukotrines

Question 6

describe the secondary / late phase response in type 1 hypersensitivity
how can this be avoided

Answer 6

eosinophils release prostaglandins and leukotrienes (lipid mediators)
give steroids to prevent this

Question 7

what effect does the release of inflammatory mediators have

Answer 7

blood clots, gastric secretion, vasodilation, bronchoconstriction, increase permeability of vessels, adrenaline release, tachycardia

Question 8

what happens in a mild vs severe type 1 hypersensitivity reaction

Answer 8

mild - itchy eyes, sneezing

severe - anaphylaxis - abdominal pain, vomiting SOB, cough, hypotension, dizziness, reparatory arrest, angioedema

Question 9

what are the specific clinical features of a type 1 hypersensitivity reaction

Answer 9

fast onset (15-30 minutes) 
wheal and flare reaction (swelling and redness)

Question 10

what is the dual allergen exposure hypothesis

Answer 10

body is sensitised on first exposure and memory B cells produced (exposure through skin)
allergy is polygenic
tolerance occurs if allergen is consumed orally

Question 11

what is the atopic triad

Answer 11

asthma
rhinitis
eczema

Question 12

what is atopy

Answer 12

genetic tendency to develop allergic diseases s

Question 13

what is rhinitis (allergens and treatment)

Answer 13

perennial or seasonal, blocked runny nose, eye symptoms
allergens - house mite dust, animals, pollen
treatment - nasal steroids and antihistamines

Question 14

define asthma and how can long term damage happen

Answer 14

disease of inflammation and hyperactivity of the small airways due to allergens in the air
damage to airways due to late phase response

Question 15

what is eczema

Answer 15

atopic dermatitis

intense itching, blistering, cracking of skin

Question 16

what is atopic march and give an example

Answer 16

progression of allergies

baby has eczema or food allergy from milk which leads to asthma in later childhood and rhinitis in adulthood

Question 17

what is the pathogenesis of type 2 hypersensitivity

Answer 17

IgG/IgM gains an antigen at the cell surface - complement activation and reaction to the antigen

Question 18

what are the clinical features of type 2 hypersensitivity

Answer 18

onset mi utes to hours, cell damage by lysis and necrosis

Question 19

what one of the most common antigens for a type two hypersensitivity reaction

Answer 19

penecillin - binds to erythrocyte cell surfaces causing immune response against cells

Question 20

what are two diseases that result from type 2 hypersensitivity

Answer 20

good pastures nephritis

blood transfusion reaction - causes activation of complement and cytotoxic effect ie MAC attack complex

Question 21

what is type 3 hypersensitivity and what is the pathogenesis

Answer 21

immune complex

IgG/IgM against soluble antigen - immune complex deposition

Question 22

what are the clinical features of type 3 hypersensitivity

Answer 22

onset 3-8 hours, vasculitis

Question 23

what is a major disease associated with type 3 hypersensitivity

Answer 23

systemic lupus erythematosus (SLE)

- test for C3 and 4 as they are in high amount in SLE

Question 24

what is type 4 hypersensitivity and what is the pathogenesis

Answer 24

delayed

antigen specific T cell mediated cytotoxicity (presentation via langerhans cells in the skin)

Question 25

what are the clinical features of type 4 hypersensitive

Answer 25

delayed onset - 48-72 hours, erythema induration (red itch)

Question 26

what are some common antigens for type 4 hypersensitivity

Answer 26

metals (nickel) tuberculin test poison ivy

Question 27

what is the tuberculin test

Answer 27

type 4 hypersensitive provides a positive result

ie there are T cell sin the blood against TB

Question 28

what diseases form as a result of type 4 hypersensitivity

Answer 28

contact dermatitis

poison ivy reactions - urushiol (antigen) picks up through skin and presents to T cells, TH1 release IL 2 for more T cells to produce IF-g which recruits macrophages and skin inflammation

Question 29

name innocuous antigens for the 4 hypersensitiveness

Answer 29

1 - pollen hay fever
2 - penecillin
3 - mouldy hay-farmers lung
4 - tuberculin test, poison ivy