Hypersensitivity

Question 1

Type III hypersensitivity

Answer 1

• As with Type II, Type III are caused by antibody, usually IgG, but also sometimes IgM.
• Type III antibodies directed to soluble antigens
• Formation of antibody-antigen complexes is a normal part of immune response.
• Usually cleared by reticuloendothelial system (RES): macrophages, neutrophils in liver spleen and bone marrow that ingest and degrade immune complexes
• Excess immune complex deposition in tissues leads to pathology

Question 2

sites of immune complex deposition: Glomeruli

Answer 2

kidney, filtration process makes it very common site in IC deposition, damage driven by complement activation

Question 3

sites of immune complex deposition: Blood vessel walls

Answer 3

IC accumulate on veins and arteries, causes vasculitis, often seen as skin lesions if close to surface

Question 4

sites of immune complex deposition: Synovial membranes

Answer 4

Rheumatoid arthritis, in which the IgG of the immune complexes can become an antigen itself, and IgM Rheumatoid Factor antibodies develop.

Question 5

sites of immune complex deposition: skin

Answer 5

common site for IC deposition, causes rashes.

Question 6

sites of immune complex deposition: systemic sites

Answer 6

in case of Systemic Lupus Erythematosus (SLE) IC deposits in kidney, joints, skin, vasculature, muscle and other organs.

Question 7

Type IV Hypersensitivity

Answer 7

cell mediated
Complement does not play a role in Type IV.
• Most Type IV reactions are caused by CD4+ delayed type hypersensitivity (DTH) reactions. ‘Delayed’ refers to reaction occurring 2 to 4 days after antigen exposure
• Macrophages that cause damage are not specific, harm infected and non-infected tissue