Skin Immunology

Question 1

Terminal differentiation of ? to ? forms the keratin layer

Answer 1

Of keratinocytes to corneocytes

Question 2

What is the keratin layer also known as?

Answer 2

Stratum corneum

Question 3

How do keratinocytes contribute to the immune function of skin?

Answer 3

• Sense pathogens via cell surface receptors and help mediate an immune response.
• Produce antimicrobial peptides (AMPs) that can directly kill pathogens (AMPs have been found at high levels in skin of patients with psoriasis)
• Produce cytokines and chemokines.

Question 4

What characterises Langerhans cells?

Answer 4

Birbeck granules

Question 5

What is the main immune cell of the skin and what do they do?

Answer 5

Langerhans cells - they are dendritic antigen presenting cells which process antigens and present them to effector T cells

Question 6

Which kind of T cells are mainly found in the epidermis?

Answer 6

CD8+ T cells

Question 7

Which kind of T cells are mainly found in the dermis?

Answer 7

CD4 + and CD8+

Question 8

Interaction between which two things is involved in antigen recognition and T cell activation?

Answer 8

T cell receptor (TCR) and the Major Histocompatibility Complex (MHC)

Question 9

Which co-receptors enhance the interaction between TCR and MHC in antigen recognition and T cell activation?

Answer 9

CD4+ helper T cells and CD8+ cytotoxic T cells

Question 10

Which 2 types of dendritic cells are found in the dermis?

Answer 10

Dermal dendritic cells (antigen presenting and secrete city/chemokine) and plasmacytoid dendritic cells (pDC) - produce INFalpha as an alarm

Question 11

Which cells are MHC class I and MHC class II found?

Answer 11

Class I - on almost all cells and Class II- antigen presenting cells (eg. B cells, macrophages)

Question 12

What is the role of MHC?

Answer 12

Control the immune response through recognition of ‘self’ and ‘non-self’.

Question 13

Which cells mediate psoriasis?

Answer 13

T cell mediated

Question 14

What is the hallmark of skin lesions in psoriasis?

Answer 14

Inflammation

Question 15

What is the pathophysiology of psoriasis?

Answer 15

Psoriasis is a hyperproliferative disorder, involving a complex cascade of inflammatory mediators. Keratinocytes are stimulated so mitotic activity of basal and suprabasal cells is significantly increased, with cells migrating from the basal layer to the stratum corneum in just a few days - this forms the scaly layer of corneocytes

Question 16

What is the pathogenesis of atopic eczema?

Answer 16

Impairment of the skin barrier due to decreased AMP in skin and mutation in the fillagrin gene leads to the dry skin, as fillagrin is nature’s own moisturiser. Impairment of the skin’s barrier function leads to an increased sensitisation to cutaneous antigens

Question 17

What are the 2 types of immunodeficiency?

Answer 17

Primary (genetic) and secondary (acquired)

Question 18

What mediates Type I (Immediate) Hypersensitivity responses?

Answer 18

Antibody mediated - IgE

Question 19

What mediates Type II and Type III Hypersensitivity responses?

Answer 19

Antibody mediated - IgG and IgM

Question 20

What is the pathogenesis of Type I hypersensitivity reactions?

Answer 20

Early exposure to allergen causes the production of IgE, which binds to FcεR1 receptor on mast cells. Later exposure causes rapid crosslinking of the receptors, signal transduction and degranulation of the mast cell.

Question 21

Which type of hypersensitivity reaction is an allergic reaction?

Answer 21

Type I

Question 22

What mediates Type IV (delayed) hypersensitivity reactions?

Answer 22

Cell mediated: Th1 cells

Question 23

What kind of reactions are Type II hypersensitivity reactions?

Answer 23

Cytotoxic reactions

Question 24

What kind of reactions are Type III hypersensitivity reactions?

Answer 24

Immune complex-mediated reactions

Question 25

Hypersensitivity

Answer 25

Immune response that causes collateral damage to self (exaggeration of normal immune mechanisms)

Question 26

Allergic reaction

Answer 26

Occur when a person’s immune system reacts to normally harmless substances in the environment

Question 27

What tests can be done for Type I Immediate Hypersensitivity reactions?

Answer 27

Specific IgE (RAST), skin prick, challenge test (only if skin prick is negative)

Question 28

What is the management for Type I reactions?

Answer 28

Allergen avoidance, anti-histamines, corticosteroids (anti-inflammatories), adrenaline for anaphylaxis

Question 29

What is the pathophysiology of Type IV reactions?

Answer 29

Sensitisation phase: allergen is picked up by APC (skin langerhan cells) take this to lymph node, produce a T cell which enters the skin and remains until the next allergen exposure. Specific T cells will recognise this.

Question 30

What type of reaction is contact reactions normally associated with?

Answer 30

Type IV

Question 31

What is the investigations for Type IV reactions?

Answer 31

Patch testing

Question 32

What causes non-allergic dermatitis?

Answer 32

Contact with agents that abrade, irritate and traumatize skin directly (doesn’t require prior sensitisation)

Question 33

Which surfaces does atopic eczema normally affect?

Answer 33

Flexural

Question 34

Which surfaces does psoriasis normally affect?

Answer 34

Extensor