Type III hypersensitivity

Hypersensitivity

Also known as immune complex–mediated disorders.

 

Examples

• Arthus reaction
• Cryoglobulinaemia 
• Extrinsic allergic alveolitis (hypersensitivity pneumonitis)
• Lupus nephritis
• Membranous nephropathy 
• Polyarteritis nodosa
• Poststreptococcal glomerulonephritis
• Reactive arthritis 
• Rheumatoid arthritis 
• Serum sickness 
• Sclerosis 
• Systemic lupus erythematosus  
• Sjögren syndrome

Mechanism

• The underlying cause is an excess of antigen in the body. 
• Excessive amounts of antibody are produced to bind the antigen.
• Antigen-antibody complexes known as immune complexes form. There are various sizes of complex.
• Macrophages clear large immune complexes. Small immune complexes can become deposited in the blood vessels, joints, and glomeruli. 
• Complement proteins interact with immune complex deposits, causing inflammation.