Hypersensitivity Part 2

Question 1

What is Goodpasture’s Syndrome?

Answer 1

• when IgG binds to a self-component causing a type II hypersensitivity reaction
• antibodies bind to basement membrane collagen type IV
• causes glomerulonephritis in the kidney and pulmonary haemorrhage in the lung

Question 2

Describe what can happen to a person with a penicillin allergy

Answer 2

• type II hypersensitivity reaction
• penicillin binds to components of RBC membrane
• can form a complex which is taken up by macrophages
• complex can form neo-antigen which activates T cells that interact with B cells and antigen presenting cells to drive forward antibodies that recognise penicillin RBC complex
• immunoglobulins bind to RBC when penicillin is bound resulting in complement activation causing:
• lysis of RBCs
• binds to Fc receptor on macrophage to cause phagocytosis

Question 3

What is responsible for clearing type III hypersensitivity reactions and what causes pathology?

Answer 3

• cleared by reticuloendothelial system (macrophages, neutrophils in liver spleen and bone marrow that ingest and degrade immune complexes)
• pathology is caused by excess immune complex deposition in tissues

Question 4

Describe the progression of a type III hypersensitivity reaction

Answer 4

• locally injected antigen in immune individual with IgG antibody
• local immune-complex formation
• activation of complement release inflammatory mediators and induces mast cell degranulation
• causes local inflammation, movement of fluid and protein into tissue and blood vessel occlusion

Question 5

What are the sites of type III immune complex depositon?

Answer 5

• glomeruli of kidney
• blood vessel walls: accumulates on veins and arteries causing vasculitis
• synovial membranes: RA can develop (when IgG of immune complexes becomes antigen itselg)
• skin: causes rashes
• systemic sites: if systemic lupus erythematosus it deposits in kidney, joints, skin, vasculature, muscle and other organs

Question 6

What causes the majority of type IV hypersensitivity reactions?

Answer 6

• delayed type hypersensitivity reactions (DTH)
• some can be prolonged and damaging (eg. listerial and TB)
• can lead to walling off infectious sites, granuloma

Question 7

Describe the progression of a type IV hypersensitivity reaction

Answer 7

• antigen introduced into subcutaneous tissue and processed by local antigen-presenting cells
• a TH1 effector cell recognises antigen and releases cytokines which act on vascular endothelium
• results in recruitment of T cells, phagocytes, fluid and proteins to site of antigen injections to cause lesion

Question 8

What are contact sensitivities?

Answer 8

• a special category of DTH reaction in which antigen is not infectious but a chemical that binds to cell surface
• eg. heavy metal sensitivity and poison Ivy

Question 9

Describe examples of autoimmune diseases that can be classified according to type II hypersensitivity reactions

Answer 9

• haemolytic anaemia: caused by blood group antigens resulting in destruction of rbc causing anaemia
• acute rheumatic fever caused by strep cell wall autoantigen (Ab x-react to cardiac muscle) causing arthritis, myocarditis and valve scarring

Question 10

Describe examples of autoimmune diseases that can be classified according to type III hypersensitivity reactions

Answer 10

• SLE caused by DNA/histones/ribosome autoantigens resulting in glomerulonephritis, vasculitis and rash
• RA caused by rheumatoid factor IgG complexes resulting in arthritis

Question 11

Describe examples of autoimmune diseases that can be classified according to type IV hypersensitivity reactions

Answer 11

• insulin dependent diabetes mellitus: caused by pancreatic B-cell antigen causing B-cell destruction
• RA: caused by synovial joint antigen resulting in joint inflammation and destruction