Immunology

About Primary Immunodeficiency Diseases

Primary immunodeficiency diseases (PIDs) are a group of more than 500 distinct genetic disorders in which one or more components of the immune system fail to function correctly. They differ fundamentally from secondary immunodeficiencies (caused by human immunodeficiency virus (HIV), chemotherapy, or malnutrition) in that the defect is inherited — present from birth in the genome, even if symptoms do not appear until later in childhood or adulthood.

Specialists now call these conditions “inborn errors of immunity”. The 2024 classification by the International Union of Immunological Societies (IUIS) expert committee lists defects in 508 different genes plus 17 “phenocopies”, 67 of the gene defects new since the June 2022 update. A phenocopy looks like an inherited defect but is caused by autoantibodies that block the body's own immune signalling proteins (cytokines), or by gene changes acquired later in life (somatic mutations) (Poli 2025).

PIDs span a wide spectrum of severity, from selective immunoglobulin A deficiency (affecting 1 in 500 people, often without symptoms) to severe combined immunodeficiency (SCID), which is incompatible with normal life without stem cell transplantation. What unites them is that the immune system's ability to do one or more of its core jobs — recognizing pathogens, killing bacteria and fungi, clearing viruses, regulating inflammation, or distinguishing self from non-self — is impaired.

The Five Arms of Immunity and Their Defects

Understanding which arm of immunity is affected tells you almost everything about which infections a patient will suffer:

• Antibody deficiency (B-cell disorders): Susceptibility to encapsulated bacteria — Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis — and to enteroviruses. Examples: common variable immunodeficiency (CVID), X-linked agammaglobulinemia (XLA), IgA deficiency.
• T-cell deficiency: Susceptibility to viral infections, fungi, Mycobacteria, Pneumocystis jirovecii, and intracellular pathogens. SCID combines T-cell and B-cell failure.
• Phagocyte defects: Susceptibility to catalase-positive bacteria (Staphylococcus aureus, Burkholderia, Serratia) and fungi (Aspergillus). Example: Chronic Granulomatous Disease.
• Complement deficiency: Susceptibility to encapsulated bacteria (early complement) or Neisseria meningitis (terminal complement). Hereditary Angioedema (C1-inhibitor (C1-INH) deficiency) sits in this group but causes attacks of swelling rather than infections.
• Immune dysregulation: Paradoxically, both too little immunity (infection susceptibility) and too much (autoimmunity, lymphoproliferation). Examples: ataxia-telangiectasia (AT), hyper-IgE syndrome (HIES), Wiskott-Aldrich syndrome (WAS).

The Diagnostic Delay Problem

Diagnosis often comes years after the first symptoms. In a North American cohort of 43 patients with genetically confirmed inborn errors of immunity, seen at one specialist centre from 2014 to 2019, the delay averaged 3.3 years; on average 7.9 different medical specialties were involved in each patient's care, and patients had 4.9 hospital stays before definitive treatment. Genetic testing gave most of them a diagnosis (Branch 2021). This delay causes preventable organ damage — bronchiectasis, neurological deterioration, liver disease — that could be minimized with early diagnosis and treatment. The Jeffrey Modell Foundation's "10 Warning Signs of Primary Immunodeficiency" has been widely distributed to raise awareness among both patients and primary care physicians.

Treatment Principles

Treatment depends on the specific defect. Antibody deficiencies are treated with immunoglobulin replacement therapy (intravenous immunoglobulin (IVIG) or subcutaneous immunoglobulin (SCIG)), which provides passive protection against the infections the patient cannot prevent. SCID and some cases of Wiskott-Aldrich Syndrome are treated with hematopoietic stem cell transplantation (HSCT), which can be curative. DOCK8-deficient autosomal recessive hyper-IgE syndrome (AR-HIES) responds particularly well to HSCT. Newer treatments include gene therapy (approved for adenosine deaminase deficiency SCID (ADA-SCID), and since 2026 for Wiskott-Aldrich syndrome) and targeted small-molecule therapies for specific genetic defects.

In 2026 the United States Food and Drug Administration approved a gene therapy for Wiskott-Aldrich syndrome (Ochs 2026), and the European Medicines Agency authorised etuvetidigene autotemcel, described as the first gene therapy for the treatment of Wiskott-Aldrich syndrome. The European application was brought by a non-profit organisation (Drai 2026).

Key Research Papers

1. Poli MC, Aksentijevich I, Bousfiha AA, Cunningham-Rundles C, Hambleton S, Klein C, Morio T, Picard C, Puel A, Rezaei N, Seppänen MRJ, Somech R, Su HC, Sullivan KE, Torgerson TR, Meyts I, Tangye SG. Human inborn errors of immunity: 2024 update on the classification from the International Union of Immunological Societies Expert Committee. J Hum Immun. 2025;1(1):e20250003. — PubMed PMID: 41608114
2. Branch A, Modi B, Bahrani B, Hildebrand KJ, Cameron SB, Junker AK, Turvey SE, Biggs CM. Diverse clinical features and diagnostic delay in monogenic inborn errors of immunity: A call for access to genetic testing. Pediatr Allergy Immunol. 2021;32(8):1796-1803. — PubMed PMID: 34097760
3. Ochs HD. FDA approves gene therapy for Wiskott-Aldrich syndrome. J Allergy Clin Immunol. 2026;157(6):1256-1257. — PubMed PMID: 41997241
4. Drai C, Carella VC, Barry S, Carleton A, Rogers D, Sepodes B, deCourcey J, Concannon C, Kok IR. An EMA perspective on the regulatory approval of Waskyra®, the first gene therapy for the treatment of Wiskott-Aldrich syndrome. Drug Discov Today. 2026:104847. — PubMed PMID: 42950981

Connections

• All Conditions
• How Vaccines Train Your Immune System — interactive animation
• The Lymphatic System: Your Body’s Drainage & Surveillance — interactive animation
• The Complement System: Your Blood’s Silent Army — interactive animation
• Histamine, Mast Cells & Allergy — interactive animation
• Immune Response — interactive animation
• DiGeorge Syndrome
• Mast Cell Activation Syndrome
• Anemia
• Thrombocytopenia
• Bronchiectasis
• Giardiasis
• Lymphoma
• Immunoglobulin Lab Tests
• Élie Metchnikoff — phagocytes and the birth of cellular immunology
• Paul Ehrlich — antibodies, receptors, and the humoral side of immunity's founding Nobel
• Allison & Honjo — the immune brakes that checkpoint drugs release
• Regulatory T Cells — the 2025 Nobel: the immune system's own brakes, and why "balanced" beats "boosted"
• Finding Human Immunodeficiency Virus — the 1983 discovery, U=U, PrEP, and the cost of denialism
• Susumu Tonegawa — Nobel 1987, the genetic principle behind antibody diversity
• Herbs covered on this site that discuss conditions in this specialty: Elephant's Foot (Elephantopus scaber) · Astragalus (Astragalus membranaceus) · Boneset · Boswellia · Cleavers · Noni (Morinda citrifolia)

All Immunology Articles A–Z

Every article in this specialty, listed alphabetically.

• Ataxia-Telangiectasia (AT)
• Chronic Granulomatous Disease (CGD)
• Common Variable Immunodeficiency (CVID)
• Genetic Susceptibility to Vaccine Adverse Reactions
• Hereditary Angioedema (HAE)
• Hyper-IgE Syndrome (HIES)
• Immunoglobulin A Deficiency (Selective Immunoglobulin A Deficiency)
• SCID (Severe Combined Immunodeficiency)
• Severe Combined Immunodeficiency (SCID)
• Wiskott-Aldrich Syndrome (WAS)
• X-Linked Agammaglobulinemia (Bruton's Agammaglobulinemia)

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