Allergy and the skin

Question 1

Define hypersensitivity

Answer 1

Immune response that causes collateral damage to self, exaggeration of normal immune sensitivity

Question 2

What are the types of hypersensitivity reactions and there mediators?

Answer 2

Type 1: Ig-E
Type 2: IgG Mediated
Type 3: Immune complex mediated
Type 4: cell-mediated hypersensitivity

Question 3

Describe the process of type I hypersensitivity

Answer 3

Ag induces crosslinking of IgE bound to mast cells and basophils with release of vasoactive mediators

Question 4

Describe the process of type II hypersensitivity

Answer 4

Ab directed against cell surface antigens mediates cell destruction via complement activation or ADCC

Question 5

Describe the process of type III hypersensitivity

Answer 5

Ag-Ab complexes deposited in various tissues induce complement activation and an ensuing inflammatory response mediated by massive infiltration of neutrophils

Question 6

Describe the process of type IV hypersensitivity

Answer 6

synthesised Th1 cells release cytokines that activate macrophages or Tc cells which mediate direct cellular damage

Question 7

What are the typical manifestations of type I hypersensitivity?

Answer 7

Typical manifestations include systemic anaphylaxis and localised anaphylaxis such as hay fever, asthma, hives, food allergies and eczema

Question 8

What are the typical manifestations of type II hypersensitivity?

Answer 8

Typical manifestations include blood transfusion reactions, erythroblastosis fetalis, and autoimmune haemolytic anaemia

Question 9

What are the typical manifestations of type III hypersensitivity?

Answer 9

Topical manifestations include localised arthus reaction and generalised reactions such as serum sickness, necrotising vasculitis, glomerulonephritis, rheumatoid arthritis, and systemic lupus erythematosus

Question 10

What are the typical manifestations of type IV hypersensitivity?

Answer 10

Typical manifestations include contact dermatitis, tubercular lesions and graft rejection

Question 11

Define allergy

Answer 11

Hypersensitivity disorder of the immune system

allergic reactions occur when a persons immune system reacts to normally harmless substances in the environment

Question 12

What are the ways of coming into contact with an allergen?

Answer 12

Ingestion
Inhalation
Skin Contact
Injection

Question 13

When does urticaria appear?

Answer 13

Typically within 1 hour and lasts 2-6hrs

Question 14

What is angioedema?

Answer 14

localised swelling of subcutaneous tissue or mucous membranes
non pitting oedema
not itchy (unless associated with urticaria)

Question 15

What is anaphylaxis?

Answer 15

• pharyngeal or laryngeal -oedema
• bronchospasm
• tachypnoea
• circulation hypotension
• tachycardia
• mucosal changes

Question 16

What investigations can be done for allergy?

Answer 16

• History
• Specific IgE (RAST)
• Skin prick or patch test
• Challenge test
• serum mast tryptase level

Question 17

How can allergy be managed?

Answer 17

allergen avoidance
prevent effects of mast cell activation (anti-histamines)

anti-inflammatory agent (corticosteroids)

adrenaline autoinjector (for anaphylaxis)

block mast cell activation (mast cell stabilisers- sodium cromoglycate)

immunotherapy

medic alert bracelet

information and education

Question 18

Name some non allergic reactions

Answer 18

Coeliacs

Eosinophilic gastroenteritis

Direct mast cell degranulation- morphine, aspirin, NSAIDS

toxic (scombroid fish toxins)

Question 19

What type of allergy is allergic contact dermatitis?

Answer 19

Type IV

Question 20

When does type IV allergy appear?

Answer 20

24-48hrs

Question 21

Name some causes of IV allergy?

Answer 21

Direct skin contact
Airborne contact
Injection

Question 22

What are the two phases of allergy pathophysiology?

Answer 22

Sensitization phase

Elicitation phase

Question 23

What are the four steps of the afferent phase?

Answer 23

1. Haptens penetrate the epidermis and are taken up by epidermal cells, including skin.
2. Dendritic cells (DCs) migrate to the draining lymph nodes,
3. where they present haptenated peptides to both CD8+ effector T cells and downregulatory CD4+ T cells.
4. Specific T-cell precursors clonally expand in draining lymph nodes, recirculate via the blood, and migrate to tissues, including the skin.

Question 24

What are the steps of the elicitation phase?

Answer 24

1. When the same hapten is applied to the skin, it is taken up by epidermal cells, including skin DCs and keratinocytes,
2. which present haptenated peptides to specific T cells.
3. Activation of CD8+ cytotoxic T lymphocytes induces apoptosis of keratinocytes and production of cytokines and chemokines by skin resident cells.
4. This leads to the recruitment of leukocytes from the blood to the skin. CD4+ T cells may block activation/expansion of CD8+ effectors in lymph nodes during sensitization and in the skin during the elicitation phase of contact hypersensitivity

Question 25

What is the gold standard of testing in suspected ACD?

Answer 25

Patch testing

Question 26

When are readings taken in patch testing?

Answer 26

48 and 96 hrs

Question 27

What is irritant contact dermatitis?

Answer 27

-not immune mediated
contact with agents which abrade, irritate and traumatise skin directly

• no prior sensitisation requirement
  pattern depend on exposure- like ACD

Question 28

How can ACD be managed?

Answer 28

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