Hypersensitivity reactions

Question 1

Explain Type 1 hypersensitivity

Answer 1

• Immediate (minutes)
• IgE antibody mediated
• Allergy, anaphylaxis and atopic disease
• Degranulation of mass cells and basophils, releasing histamines

Question 2

Explain type 2 hypersensitivity

Answer 2

• Occurs within hours to days
• IgM or IgG antibody mediated
• Examples : haemolytic disease of newborn, autoimmune haemolytic anaemia and Goodpastures

Question 3

Explain type 3 hypersensitivity

Answer 3

• Occurs over hours, days or weeks
• Antigen-antibody immune complex mediated
• Examples : RA, SLE and post steptococcal glomerulonephritis.

Question 4

Explain type 4 hypersensitivity

Answer 4

• Delayed (24 to 72 hrs after antigen exposure)
• T cell mediated
• E.g contact dermatitis and mantoux (TB) skin test