10. Overview of Immunological diseases

Question 1

Type I Hypersensitivity Reaction

-Examples

Answer 1

-IgE antibody directed against allergen triggers mast cell degranulation- release of histamines

E.g. Seasonal rhinitis
Cat allergy

Question 2

Type II Hypersensitivity Reaction

-Examples

Answer 2

-A pathogenic antibody directly causes diseases

antibody mediated disease

E.g. Autoimmune haemolysis- lyses of red blood cells

Question 3

Type III Hypersensitivity Reaction

-Examples

Answer 3

Antibody-antigen complex-mediated disease
- enlarged complex that is not removed as they should be

Eg. Serum sickness
Systemic lupus erythematosis

Question 4

Type IV Hypersensitivity Reaction

-Examples

Answer 4

Inflammation directly mediated by T cells

E.g.
Delayed type hypersensitivity

Contact dermatitis (form of eczema)
Tuberculin reaction

-takes time for allergy to appear(hours)

Question 5

Autoimmune Haemolysis

Answer 5

Type 2 hypersensitivity

Autoantibodies develop against rbcs:
igG anti-red cell response produced de novo
can be destroyed by phagocytes (extracellular hamoysis)
or intravascularly in the spleen

clinical presentation- Anaemia , and jaundice due to release of bilirubin

Question 6

Hypersensitivity pneumonitis

Answer 6

Type III reaction

clinically presents with pts exposed to airbourne (like hay) antigen then develops sudden breathlessness

• produce IgG antibodies
• eventual lung scarring and fibrosis

Question 7

Tuberculin skin test (TST)

Answer 7

Type IV hypersensitivity reaction

• Used to determine previous exposure to TB
• Tuberculin injected intradermally
• Local inflammatory response evolves over 24-72 hours if prev exposed

Antigen is injected sc and processed by local APC

• TH1 recognizes antigen and releases cytokines
• Recruitment of phagocytes and plasma to site of antigen -Injection causes visible lesion

Question 8

Universal recipients belong to which blood group

Answer 8

Group AB

Question 9

Universal blood donors belong to which blood group

Answer 9

Blood Group O

Question 10

Haemolytic disease of the newborn

Answer 10

• ‘D’ antigen (Rhesus) is a secondary classification
• Majority of the population are D+
• IgG antibodies produced by the mother move through placenta

Rhesus-negative mothers with rhesus+ partner are given anti-D IgG during pregnancy

Question 11

Local immune complex disease

Answer 11

Type III reaction

deposition of circulating immune complexes

causing painful lesions

also seen in SLE

Question 12

Serum sickness

Answer 12

Type III reaction

injection of certain immunogenic drugs or anti-sera produced in animals

Presentation: Rash
Fever
Arthritis
Glomerulonephritis

Question 13

Contact dermatitis: sensitisation

Answer 13

Type IV reaction

In the skin:
Highly reactive, small molecule breaks the skin and forms protein-hapten complex
-Complex is taken up by Langerhan cells which migrates to lymph nodes
-Antigen is processed and presented via MHC II in Langerhan cells- recognised as foreign by T cells
-T cells migrate to dermis=inflammation (IFN-gamma, cytokines)

Examples

• Nickel
• Perfume/ cosmetic molecules

Question 14

Interferon gamma release assay (IGRA)

Answer 14

Previous Tb exposure:
Th1 cells recognise antigen. Because this is a secondary immune response, they are ‘primed’ and release cytokines within this short timeframe

No previous Tb exposure:
No primed memory T cells specific for MTB. No interferon gamma produced in such a short timeframe

Question 15

Gell and Coombes

Pros and Cons

Answer 15

useful framework

• oversimplifies immunology
• not particularly used