Immunology & biochemistry

Question 1

What factors contribute to the skins immune role?

Answer 1

Structure (a thick keratin layer which sheds regularly), presence of immune cells, cytokines, chemokines & antimicrobial peptides

Question 2

Skin is a front-line barrier against pathogens. T/F

Answer 2

True

Question 3

Define autoimmunity, hypersensitivity & immunodeficiency

Answer 3

Autoimmunity - immune response to host tissues
Hypersensitivity - overactive immune response
Immunodeficiency - underactive immune response

Question 4

The keratin layer is also known as what?

Answer 4

Stratum corneum

Question 5

What are some important structural proteins in the epidermis?

Answer 5

Filaggrin, keratin and involucrin

Question 6

What is the role of keratinocytes in the immune response?

Answer 6

Cell surface receptors detect pathogens –> produce AMPs (antimicrobial peptides) to directly kill pathogens –> produce cytokines & chemokines which signal other immune cells

Question 7

What can keratinocytes be inappropriately activated by?

Answer 7

UV light and various chemicals (once sensitised)

Question 8

Langerhan’s cells and macrophages are the main skin immune cells. T/F

Answer 8

False - Langerhan’s cells are by far the most common immune cells in the skin

Question 9

What is the function of Langerhan’s cells?

Answer 9

Present antigens (microbial fragments) to effector T cells & so helps in their activation

Question 10

How are T cells distributed throughout the skin?

Answer 10

CD4 T cells are mainly found in the dermis
CD8 T cells are mainly found in the epidermis (but also present in the dermis in smaller numbers)
Natural killer cells are also present throughout the skin

Question 11

Which types of CD4 T cells are involved in psoriasis and atopic dermatitis?

Answer 11

Th1 - psoriasis
Th2 - atopic dermatitis
Th17 - psoriasis & atopic dermatitis

Question 12

Where are T cells produced and sensitised respectively?

Answer 12

Produced in bone marrow and modified in the thymus

Question 13

Which two receptors are required to activate a T cell?

Answer 13

T cell receptor (TCR) and Major histocompatability complex (MHC)

Question 14

What do Th1 & Th2 cells do?

Answer 14

Th1 - activate macrophages (IL2 & IFN gamma)

Th2 - enhance ability of B cells (IL4,5,6)

Question 15

CD8 cells can kill cells directly and are important in protecting against cancer and bacteria. T/F

Answer 15

False - they protect mainly against cancer and viruses

Question 16

Name and explain the function of the types of dendritic cell found in the dermis

Answer 16

Dermal dendritic cell - antigen presenting & releases chemo/cytokines
Plasmacytoid dendritic cell - produces interferon alpha & is ONLY found is diseased skin

Question 17

What immune cells are found in the dermis?

Answer 17

Dendritic cells
T cells 
Neutrophils
Mast cells
Macrophages

Question 18

What are the preformed inflammatory mediators of mast cells?

Answer 18

Histamine, tryptase, chymase, TNF

Question 19

Describe the differences between MHC class I & II

Answer 19

Class I - found on almost all cells & presents endogenous antigen to CD8 cells
Class II - found on antigen presenting cells (B cells & macrophages) & presents exogenous antigen to CD4 cells

Question 20

Why is MHC particularly important?

Answer 20

Involved in transplant rejection & autoimmunity

Question 21

Which drugs are associated with the development of psoriasis?

Answer 21

Beta-blockers

Question 22

Describe the immunopathology of psoriasis

Answer 22

Keratinocytes under stress produce IL & TNF as well as other factors which stimulate Plasmacytoid dendritic cells to produce interferon alpha –> dendritic cells migrate to lymph nodes and activate T cells –> chemokines draw the activated T cells to the dermis where they produce interleukins which stimulate keratinocyte production, AMP release & neutrophil migration. End result mimics a non-healing late stage of injury

(NOTE - CD8 cells & fibroblasts also play a role)

Question 23

Describe the immunopathology of atopic eczema

Answer 23

Skin barrier breaks down –> invaded by microbes –> cytokines secreted by keratinocytes attract immune cells –> constantly broken down barrier allows microbes to colonise and the body to become sensitised to allergens

Question 24

What gene defect contributes to atopic eczema? How does this affect the disease?

Answer 24

A defect in the filaggrin gene. Causes severe and early onset eczema

Question 25

In skin affected by atopic eczema there will be reduced anti microbial peptide. T/F

Answer 25

True

Question 26

Name three autoimmune conditions involving the skin

Answer 26

Psoriasis, vitiligo & systemic lupus erythematosus

Question 27

List some secondary (acquired) immunodeficiencies

Answer 27

AIDS, malignancy, aging, diabetes, alcoholic cirrhosis, malnutrition, etc

Question 28

What is IgE mediated immune reaction also called?

Answer 28

Type 1 hypersensitivity reaction

Question 29

Type 1 hypersensitivity reactions are fast. T/F

Answer 29

True - IgE binds to mast cell receptors and, upon exposure, cross-linking occurs causing the mass degranulation of mast cells

Question 30

What is an Arthus reaction and what type of hypersensitivity is it associated with?

Answer 30

A reaction slower than type 1 and faster than type 4 hypersensitivity. Associated with type 3 hypersensitivity

Question 31

What are type 2 hypersensitivity reactions and why are they relevant?

Answer 31

Antibody mediated reactions which recognise and react to foreign material in the body. They are important for blood transfusions and organ transplantation

Question 32

What are type 3 hypersensitivity reactions?

Answer 32

Immune complexes which accumulate in tissues and create an immune response (granulomas)

Question 33

What cell type are type 4 hypersensitivity reactions mediated by?

Answer 33

T helper 1 cells