type 1 hypersensitivity

Question 1

define shock

Answer 1

failure to maintain an adequate cardiac output

Question 2

what are the main types of shock?

Answer 2

hypovolaemic
obstructive
cardiogenic
distributive

Question 3

what is the role of IgG?

Answer 3

block pathogen binding, activate complement and opsonise antigen for phagocytes

Question 4

what is the role of IgM?

Answer 4

block pathogen binding and activate the complement (early stages of immunity.

Question 5

what is the role of IgA?

Answer 5

blocks pathogen binding (neutralisation).

Question 6

what is the role of IgE?

Answer 6

activates mast cells

Question 7

what is the role of IgD?

Answer 7

not secreted and function is unknown

Question 8

in what ways can mast cells and basophils be activated?

Answer 8

1. Cross-linking of surface IgE by antigen
2. Via complement proteins C3a and C5a
3. Via nerves: axon reflex of sensory nerves, substance P (released from primary afferent neurons).
4. Direct contact with the pathogen through innate receptors (PAMP), toll like receptors.

Question 9

what is atopy?

Answer 9

inherited predisposition to make IgE to common environmental antigens

Question 10

what mediators do mast cells release?

Answer 10

histamine, cytokines, leukotrienes

Question 11

what does histamine do?

Answer 11

increase in permeability of post-capillary venules, vasodilation of arterioles, itch and contraction of smooth muscle

Question 12

what do leukotrienes do?

Answer 12

increase in permeability of post-capillary venules as well as chemotaxis

Question 13

what are the 2 clinical manifestations of type 1 hypersensitivity?

Answer 13

• Local = asthma, atopic eczema, urticaria (epidermal and dermal oedema), angioedema (subcutaneous and mucosal oedema).
• Systemic = anaphylactic shock - Patient does not have to be atopic.

Question 14

what are the clinical manifestations of anaphylactic shock?

Answer 14

• Drop in blood pressure - Leak of fluid into interstitial space and dilation of great veins
• Urticaria , raised itchy red rash and sore red itchy eyes.
o Sudden onset of nasal soreness, secretions, sneezing.
• Angioedema: face, lips, hands, feet, pharynx, larynx.
• Bronchoconstriction
o Tries to stop more antigen from entering system.
• Nausea and vomiting, abdominal bloating, diarrhoea
• Headache, confusion, loss of consciousness.
• Feeling of impending doom

Question 15

define urticaria

Answer 15

hives

Question 16

what is a raised itchy red rash?

Answer 16

inflammation in dermis

Question 17

define angiodema?

Answer 17

swelling in subcutaneous tissues

Question 18

define bronchoconstriction

Answer 18

wheeze, respiratory obstruction

Question 19

why does bronchoconstriction occur in anaphylactic shock?

Answer 19

tries to stop more antigen from entering the system

Question 20

give examples of antigens that trigger anaphylaxis

Answer 20

• Drugs = beta lactams (penicillin), monobactams, aspirin, NSAIDS, insulins.
• Latex
• Peanuts
• Bee stings

Question 21

what are acute treatments for anaphylaxis?

Answer 21

• Intramuscular adrenaline 500 micrograms
• Oxygen high flow
• Antihistamines
• Glucocorticosteroidd (200mg hydrocortisone)

Question 22

what is anaphylactoid shock? how is it similar and different to anaphylactic shock?

Answer 22

• Anaphylactoid shock (non-allergic) = same symptoms but IgE not involved.
o Mast cells and basophils are activated by another mechanism

Question 23

how does desensitisation work?

Answer 23

arthropod venoms, drugs, peanuts etc… are administered sublingually/subcutaneously under medical supervision. This induces replacement of IgE response with IgA/IgG or stops.