Type III hypersensitivity occurs when antigens and antibodies (IgG or IgM

IGM

IGM as an acronym or abbreviation can refer to:* Immunoglobulin M , the primary antibody against A and B antigens on red blood cells* International Grandmaster, a chess ranking* intergalactic medium* Intragroup medium - see: Intracluster medium...

) are present in roughly equal amounts, causing extensive cross-linking.

Presentation

Type III hypersensitivity occurs when there is little antibody and an excess of antigen, leading to small immune complexes being formed that do not fix complement and are not cleared from the circulation. It is characterized by solvent antigens that are not bound to cell surfaces (which is the case in type II hypersensitivity

Type II hypersensitivity

In type II hypersensitivity the antibodies produced by the immune response bind to antigens on the patient's own cell surfaces...

). When these antigens bind antibodies, immune complex

Immune complex

An immune complex is formed from the integral binding of an antibody to a soluble antigen. The bound antigen acting as a specific epitope, bound to an antibody is referred to as a singular immune complex....

es of different sizes form. Large complexes can be cleared by macrophages but they have difficulty binding to small immune complexes for clearance. These immune complexes insert themselves into small blood vessels, joints, and glomeruli

Glomerulus

A glomerulus is a capillary tuft that is involved in the first step of filtering blood to form urine.A glomerulus is surrounded by Bowman's capsule, the beginning component of nephrons in the vertebrate kidney. A glomerulus receives its blood supply from an afferent arteriole of the renal...

, causing symptoms.

They deposit in tissues and induce an inflammatory response, and can cause damage wherever they precipitate.

The reaction can take hours, days, or even weeks to develop.

Examples

Some clinical examples:

Disease	Target antigen	Main effects
Systemic lupus erythematosus Systemic lupus erythematosus Systemic lupus erythematosus , often abbreviated to SLE or lupus, is a systemic autoimmune disease that can affect any part of the body. As occurs in other autoimmune diseases, the immune system attacks the body's cells and tissue, resulting in inflammation and tissue damage...	Nuclear antigens	Nephritis Nephritis Nephritis is inflammation of the nephrons in the kidneys. The word "nephritis" was imported from Latin, which took it from Greek: νεφρίτιδα. The word comes from the Greek νεφρός - nephro- meaning "of the kidney" and -itis meaning "inflammation".... Skin lesions Arthritis
Post-streptococcal glomerulonephritis	Streptococcal cell wall antigens	Nephritis
Polyarteritis nodosa Polyarteritis nodosa Polyarteritis nodosa is a vasculitis of medium & small-sized arteries, which become swollen and damaged from attack by rogue immune cells. Polyarteritis nodosa is also called Kussmaul disease or Kussmaul-Maier disease...	Hepatitis B virus Hepatitis B virus Hepatitis B is an infectious illness caused by hepatitis B virus which infects the liver of hominoidea, including humans, and causes an inflammation called hepatitis. Originally known as "serum hepatitis", the disease has caused epidemics in parts of Asia and Africa, and it is endemic in China...  antigen	Systemic vasculitis Vasculitis Vasculitis refers to a heterogeneous group of disorders that are characterized by inflammatory destruction of blood vessels. Both arteries and veins are affected. Lymphangitis is sometimes considered a type of vasculitis...
Reactive arthritis Reactive arthritis Reactive arthritis , is classified as an autoimmune condition that develops in response to an infection in another part of the body. Coming into contact with bacteria and developing an infection can trigger the disease. Reiter's syndrome has symptoms similar to various other conditions collectively...	Several bacterial antigens	Acute arthritis
Serum sickness Serum sickness Serum sickness in humans is a reaction to proteins in antiserum derived from an non-human animal source. It is a type of hypersensitivity, specifically immune complex hypersensitivity . The term serum sickness–like reaction is occasionally used to refer to similar illnesses that arise from the...	Various	Arthritis Vasculitis Nephritis
Arthus reaction Arthus reaction In immunology, the Arthus reaction is a type of local type III hypersensitivity reaction. Type III hypersensitivity reactions are immune complex-mediated, and involve the deposition of antigen/antibody complexes mainly in the vascular walls, serosa , and glomeruli.-History:The Arthus reaction was...	Various	Cutaneous vasculitis
Unless else specified in boxes, then ref is:

Other examples are:

• Subacute bacterial endocarditis
• Symptoms of malaria
  Malaria
  Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...
  
  
• Farmer's lung
  Farmer's lung
  Farmer's lung is a hypersensitivity pneumonitis induced by the inhalation of biologic dusts coming from hay dust or mould spores or other agricultural products. It results in a type III hypersensitivity inflammatory response and can progress to become a chronic condition which is considered...
  
  (Arthus-type reaction)