Types of PID

There are five main types of primary immunodeficiencies (PIDs), that affect the immune system in different ways.

Antibody Deficiencies

Antibodies, also known as immunoglobulins, are proteins made by specialised white blood cells, called B cells (B lymphocytes). Antibodies recognise germs so they can be removed by the rest of the immune system.

Common variable immunodeficiency (CVID) is the most common form of antibody deficiency and usually presents with recurrent chest and sinus infections. Symptoms can start at any age, although most cases are diagnosed in adults.

X-linked agammaglobulinaemia is an antibody deficiency that is usually diagnosed in male infants. Common symptoms include frequent pus producing infections of the ears, lungs, sinuses and bones, chronic diarrhoea and poor growth.

Combined Immunodeficiencies

T cells (T lymphocytes) are specialised white blood cells that are essential for the functioning of the immune system. T cells recognise the body’s own cells, identify germs and invaders, including cancer, and coordinate the rest of the immune system. They help B cells make good antibodies. For this reason, most people with T cell problems have combined immunodeficiencies, because both B and T cell functions are affected.

Severe combined immunodeficiency (SCID) is the most serious of these disorders. SCID is usually diagnosed within the first year of life and requires a haematopoietic stem cell transplant (HSCT) to survive.

Phagocytic Cell Deficiencies

Phagocytes are white blood cells (neutrophils and macrophages), that eat and kill antibody coated foreign invaders. Severe infections can occur if phagocytes are unable to kill germs or move to the site of an infection.

Chronic granulomatous disease (CGD) is the most serious form of phagocytic cell deficiency. In CGD neutrophils can’t capture and kill germs. People with CGD have frequent and severe infections of the skin, lungs and bones. They can also develop chronic inflammation, including inflammatory bowel disease (IBD).

Immune Dysregulation

Immune dysregulation includes a broad group of disorders that occur when the body’s immune system is not being controlled normally, and may react against its own cells. People with immune dysregulation can have fever, damage to organs or blood cells, and increased risk of infection.  Examples of immune dysregulation include immunodysregulation polyendocrinopathy enteropathy x-linked syndrome (IPEX), APECED, autoimmune lymphoproliferative syndrome (ALPS) and autoinflammatory disorders.

Complement Deficiencies

The complement system has an important role in the control of inflammation, killing of germs and clearance of damaged cells. Some complement deficiencies can increase the risk of autoimmune disease, whilst others result in severe infections such as meningitis or septicaemia. 

Hereditary angioedema (HAE) is a different sort of a complement disorder, that is due to C1 esterase inhibitor deficiency. In people with HAE, the small blood vessels leak fluid into the tissues, causing non-itchy swellings known as angioedema. People with HAE can have unpredictable and sometimes severe swellings (HAE attacks) throughout life, that may be life threatening.

For more information go to www.immunodeficiencies.org.au 

Content created March 2019

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