Hypersensitivity

Question 1

Describe the two phases of hypersensitivity reactions.

Answer 1

1. ) sensitisation phase: first antigen encounter

2. ) effector phase: clinical pathology upon re exposure to same antigen

Question 2

What are the four types of hypersensitivity reaction?

Answer 2

I - allergy (A)
II- circulating antibody (B)
III- complex deposition (C)
IV- cell mediated (D- delayed)

Question 3

What is an autoimmune disease?

Answer 3

Immune response against self antigens that leads to tissue damage or disturbed physiological function.

Question 4

How can autoimmune diseases be treated generally?

Answer 4

Replace function e.g. Hormones, nutrients
Immunosuppression
Monoclonal antibodies
IV immunoglobulins (block receptors)
Splenectomy (reduced removal of opsonised RBCs and platelets)

Question 5

Describe the patho physiology of type 1 hypersensivity reactions.

Answer 5

First Exposure to antigen–> IgE production–> binds mast cells
Second exposure to antigen –> antigen binds 2 IgEs bound to mast cells
Triggers mast cell Degranulation and histamine release
Histamine–> vasodilation, vascular permeability, bronchoconstriction

Question 6

What are the three presentations of type 1?

Answer 6

Anaphylaxis- systemic vasodilation –> shock
Angioedema- mast cells in dermis
Urticaria- mast cells in epidermis

Question 7

How is anaphylaxis managed?

Answer 7

IM adrenaline- at high conc binds alpha 1 adrenoceptors
Stimulates vasoconstriction, reverses bronchoconstriction, positive inotropy, inhibits mast cell activation
Monitor HR, BP, ECG and pulse oximetry

Question 8

What is the mechanism behind type 2 hypersensitivity?

Answer 8

Opsonisation of cells by Ig and complement
Ig dependent cell mediated cytotoxicity–> phagocytosis or lysis
Altered cell signally–> change in function

Question 9

Give three causes of type 2 hypersensitivity that result in change in function.

Answer 9

Grave’s disease (Ig activates TSH receptor)
Myasthenia Gravis
Pernicious anaemia

Question 10

Give three causes of type 2 hypersensitivity that result in tissue damage.

Answer 10

Good pasture’s (Ig attacks type IV collagen in BM of lungs and glomerulus)
Rhesus haemolytic anaemia
Autoimmune haemolytic anaemia
Transfusion reactions

Question 11

What happens in Rhesus haemolytic anaemia?

Answer 11

Rh+ father and Rh- mother produce first Rh+ foetus
Foetal Rh antigens enter maternal blood during delivery
Mother produces anti Rh IgG
Second Rh+ foetus: maternal anti Rh IgG crosses placenta
Opsonisation and attack of foetal RBCs

Question 12

What can cause Autoimmune Haemolytic anaemia?

Answer 12

Idiopathic
Infection e.g. Epstein Barr virus
SLE
Lymphoproliferative disorder

Question 13

What is a key test used in diagnosis of AIHA? What happens?

Answer 13

Direct Coombs Test
Blood sample with Ig bound RBCs
Add anti human Ig
Anti human Ig binds Ig on RBCs–> agglutination

Question 14

What is the mechanism of type III hypersensitivity?

Answer 14

Ig binds soluble antigens
Complex circulates and deposits
Complement activation and opsonisation
Deposition non specific–> multi systemic tissue damage

Question 15

Give two causes of type 3.

Answer 15

RA
SLE
Post streptococcal glomerulonephritis

Question 16

Give three symptoms and signs of SLE

Answer 16

Malar rash (photosensitive)
Arthritis
Repeated miscarriages
Headache
Hair loss
Coagulopathy- stroke

Question 17

How can type IV hypersensitivity be mediated?

Answer 17

Cytotoxic T lymphocytes (CD8+)- activated by Th1
Th1- macrophage activation
Th2- activation of eosinophils and IgE production

Question 18

Give four examples of type IV hypersensitivity.

Answer 18

Asthma
Type 1 diabetes mellitus
Hashimoto's (hypothyroidism)
Coeliac's disease
TB and Mantoux test
Crohn's
Multiple sclerosis
(Some RA)

Question 19

What is the patho physiology of coeliac’s disease?

Answer 19

Gluten sensitive enteropathy affecting jejunum.

Question 20

What is the histological appearance of the jejunum in coeliac’s disease?

Answer 20

Flattened mucosal surface
Villous atrophy
Lymphocyte mucosal infiltrate

Question 21

What is the histological appearance of TB?

Answer 21

Granulomatous inflammation
Langhan’s giant cells
Caseous necrosis
Lymphocyte infiltrate

Question 22

What other conditions produce granulomatous inflammation?

Answer 22

Leprosy
Schistosomiasis
Sarcoidosis
Crohn's
Pneumocystis jiroveci

Question 23

What does hypersensitivity mean?

Answer 23

Antigen specific immune responses that are inappropriate or excessive and result in harm to the host.