Immune Deficiencies and Immunophenotyping

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The immune system provides surveillance and offers protection from pathogenic invaders and prevents detrimental responses against the self that could lead to autoimmunity. Alterations in the innate or adaptive arms of the immune system can lead to immune deficiencies. Persistent lack of adequate immune responses can open the way to chronic inflammatory conditions, which can add another layer of complexity to an already overwhelmed immune system.

Immune disorders versus immune deficiencies

Immune disorders are alterations or dysregulations of components of the immune system, be it in the immune cells or their signaling pathways. These alterations can cause either low- (immune deficiency) or hyper-activity (autoimmunity) of the immune system.

Immune system deficiencies occur when immune responses fail to protect the host against infections.

Primary immune deficiencies (PID), such as severe combined immunodeficiency (SCID), occur when some parts of the immune system are absent or deficient. PIDs are usually congenital, deriving from hereditary genetic defects.¹

Secondary immune deficiencies (SID) are induced by extrinsic factors in an immune system that is intrinsically competent. Common causes of secondary immune deficiencies include immunomodulatory drugs (e.g., glucocorticoids), malnutrition (e.g., vitamin D deficiency) and chronic infection. Secondary immune deficiencies are more common than primary immune deficiencies; the most prominent secondary immune infection is acquired immune deficiency syndrome (AIDS), which results from infection with human immunodeficiency virus (HIV).

Biology of immune deficiency diseases

Impaired immune cell development results in most immune deficiency diseases. SCID, a PID, is a result of impaired T-cell development, leading to severe T-cell lymphopenia and lack of adaptive immune responses.²Common variable immunodeficiency (CVID), another PID, is caused by defects in B-cell function and antibody production.³ In AIDS, a SID, HIV specifically infects and reduces the number of CD4+ subset of T lymphocytes.⁴

Example of immunodeficiency caused by HIV-mediated CD4+ T-cell depletion. Adopted from McCune, 2001.⁴

How are immune deficiencies diagnosed?

Immune disorders can be diagnosed either before or after birth depending on the condition:

Prenatal testing

These tests can be conducted using amniotic fluid, blood or cells from the chorion (future placenta).

Blood tests

Collected blood samples can be screened for counts and variety of immune cells and specifically determine the defective cells.

Genetic tests

Targeted sequencing and whole exome sequencing are also used for diagnosis of immune deficiencies, especially for diagnosing newborn SCID.⁵