allergy and the skin

Question 1

what is the function of the immune system

Answer 1

defence against external (micro-organisms) and internal antigens (cancer)

Question 2

what is the consequence of the immune system

Answer 2

intended destruction of antigen and incidental collateral tissue damage

Question 3

what is hypersensitivity

Answer 3

immune response that causes collateral damage to itself

Question 4

what is type 1 hypersensitivity

Answer 4

• IgE mediated
• Ag induces cross linking of IgE bound to mast cells and basophils with release of vasoactive mediators
• typical manifestations include systemic anaphylaxis and localised anaphylaxis such as hay fever, asthma, hives, food allergies

Question 5

what is type 2 hypersensitivity

Answer 5

• IgG mediated cytotoxic hypersensitivity
• Ab directed against cell surface antigens mediates cell destruction via complement activation of ADCC
• typical manifestations include blood transfusion reactions, erythroblastosis fettles and autoimmune haemolytic anaemia

Question 6

what is type 3 hypersensitivity

Answer 6

• immune complex mediated hypersensitivity
• Ag-Ab complexes deposited in various tissue induce complement activation and ensuing inflammatory response mediated by massive infiltration by neutrophils
• typical manifestations include localised Arthus reaction and generalised reactions such as serum sickness, necrotising vasculitis, glomerulonephritis, rheumatoid arthritis and systemic lupus erythematosis

Question 7

what is type 4 hypersensitivity

Answer 7

• cell mediated hypersensitivity
• sensitised TH1 cells release cytokines that activate macrophages or Tc cells which mediate direct cellular damage
• typical manifestations include contact dermatitis, tubercular lesions and graft rejection

Question 8

what is an allergy

Answer 8

hypersensitivty disorder of the immune system. Allergic reactions occur when a persons immune system react to normally harmless substances in the environment.

Question 9

what is the hygiene hypothesis

Answer 9

the immune system is no longer getting challenged and hence exaggerated reactions yo normal substances

Question 10

what is a type 1 allergy

Answer 10

• IgE mediated
• Immune reaction - occurs within minutes to hours
• Reproducable reaction
• routes of exposure - skin contact, inhalation, ingestion and injection

Question 11

what is the clinical presentation of a type 1 allergy

Answer 11

Urticaria

• very itchy
• lesions appear within one hour
• lasts 2-6 spurs
• ‘hives’, ‘wheals’

Angioedema

• localised swelling of subcutaneous tissue or mucous membranes
• non pitting oedema
• not itchy

Nausea 
Vomitting
Diarrhoea 
Colicky abdominal pain 
Nasal itching 
Sneezing 
Rhinorrhoea 
Wheezing 

Anaphylaxis
- severe or life threatening hypersensitivity reaction

Question 12

what investigations are done for a type 1 allergic reaction

Answer 12

• history
• skin prick
• specific IgE
• challenge test
• serum mast cell tryptase level

Question 13

how do you manage an type 1 allergic reaction

Answer 13

• allergen avoidance
• prevent effects of mast cell activation (anti histamines)
• anti-inflammatory agent (corticosteroids)
• adrenaline auto injector
• block mast cell activation (mast cell stabilisers - sodium cromoglycate)

Question 14

what is an adrenaline auto injector used for and what are its doses

Answer 14

its used for anaphylaxis and is preloaded adernaline syringe

adult = 300ug 
children = 150ug

Question 15

what is a type 4 allergy

Answer 15

• delayed hypersensitivity
• antigen specific
• T cell mediated
• allergic contact dermatitis
• onset of reaction typically after 12-24 hours

Question 16

what is the pathophysiology of type 4 allergy

Answer 16

1. sensitisation - allergens penetrate the epidermis and are taken up by APCs of the skin (langerhans). B cells migrate to draining lymph nodes where they present the allergens to bot CD8 and CD4 T cells. Recirculate through the blood
2. elicitation - some pathogens applied to the skin and is taken up APC and present allergens to specific T cells. The T cells activated and recruits more T cells from the draining lymph nodes and produce cytokines and chemokines which leads to

Question 17

what is irritant contact dermatitis

Answer 17

• non immunological process
• contact with agents that abrade, irritate and traumatise the skin directly
• doesn’t require prior sensitisation
• pattern depends on exposure

Question 18

how do you manage irritant contact dermatitis

Answer 18

• allergen/irritant avoidance
• allergen/irritant minimisation
• emollients
• topical steroids
• UV phototherapy
• immunosuppressants