Hypersensitivity and immune responses in the skin

Question 1

Which are the key immunological cells in the skin and where are they found?

Answer 1

Keratinocytes - epidermis
Langerhans - epidermis
Melanocytes - epidermis and dermis
Dermal dendritic cells - dermis
Dermal macrophages - dermis
Mast cells - dermis
Lymphocytes - dermis

Question 2

What is the function of dermal dendritic cells

Answer 2

Migrate to lymph node to cause an immune response

Question 3

How do keratinocytes and commensals reduce immune response to normal bacteria on the skin

Answer 3

Keratinocytes and other commensals produce AMPs (antimicrobial peptides) to control microorganisms on the skin.
Commensals also activate T-reg cells reducing immune responses

Question 4

How does the skin recognise and eliminate non-commensal organisms?

Answer 4

Bacteria induces keratinocytes to produce IL-6 and IL-8 -> attract neutrophils which enter the epidermis to phagocytose and destroy bacteria

Question 5

What is bacterial pyoderma?

Answer 5

Neutrophils accumulated at the mouth of hair follicles making a distinct pustule

Question 6

What is a hypersensitivity reaction?

Answer 6

immune responses to innocuous antigens that lead to symptomatic reactions upon re-exposure

Question 7

Explain Type I (immediate) hypersensitivity

Answer 7

IgE-mediated
Sensitisation to the allergen occurs in the past
On next exposure - allergen specific IgE (on mast cells and basophils) binds allergen -> crosslinking and degranulation releasing many mediators (histamine, cytokines etc)
Response within 30 mins

Question 8

What are the results of a type I hypersensitivity reaction?

Answer 8

Vascular dilation
Increased vascular permeability
Smooth muscle contraction
Airway constriction
Swelling and oedema
Worst case = anaphalaxis
Cellular recruitment
Pruritus

Question 9

Explain Type IIa hypersensitivity

Answer 9

IgG antibody recognises cell surface or matrix antigens (self or non-self) and binds to it leading to ->
Complement lysis of the cell (complement mediated cell cytotoxicity)
Or
Removal by the reticuloendothelial system
Result in 5-10 hrs

Question 10

Explain type IIb hypersensitivity

Answer 10

IgG antibody recognises cell surface or matrix antigens and binds to it (self or non-self) leading to ->
Destruction of the target cell by effector cells (macrophages, NK cells, eosinophils, neutrophils)
Anti-body dependent cellular toxicity (ADCC)
Result in 5-10 hrs

Question 11

Explain type III hypersensitivity

Answer 11

IgG and/or IgM binds to soluble antigens which is then carried to an area where it becomes trapped in a vessel e.g., tail, ears, feet
This leads to complement damage to vessel wall
Macrophages, neutrophils and mast cells may be activated by the complexes and cause more damage
Results in swelling, partial ischaemia and tissue necrosis
Occurs after 4-8hrs

Question 12

Explain type IV hypersensitivity

Answer 12

T-cells orchestrate specific immune responses through production of cytokines or through direct cell contact
Reactions occur after 24-72 hours

Question 13

What is canine atopic dermatitis

Answer 13

a genetically predisposed inflammatory and pruritic allergic skin disease associated with IgE antibodies

Question 14

What type of hypersensitivity reactions are seen in canine atopic dermatits

Answer 14

I and IV