Immunodeficiency Disorders: Primary vs. Secondary – Causes, Types & Management

Immunodeficiency = impaired immune defense → increased infection susceptibility, autoimmunity, malignancy risk.

Primary (Inborn) Immunodeficiency (PID/IEI)

Genetic defects in immune development/function. >480 genes identified (IUIS classification).

Major Categories

• Combined (T+B): SCID (IL2RG, ADA, JAK3, etc.) – fatal without HSCT/gene therapy.
• Predominantly Antibody: CVID (heterogeneous, adult-onset), XLA (BTK, no B cells), Hyper-IgM (CD40L, AICDA).
• Phagocyte Defects: CGD (CYBB, NCF1), Leukocyte adhesion deficiency.
• Immune Dysregulation: IPEX (FOXP3), ALPS (FAS), HLH (PRF1, UNC13D).
• Complement Deficiencies: C1–C9, properdin, factor H/I.
• Innate/Inflammasome: NLRP3 (CAPS), IRAK4/MyD88.

Secondary (Acquired) Immunodeficiency (SID)

Acquired impairment of previously normal immunity.

Major Causes

• HIV/AIDS: CD4+ T-cell depletion.
• Malignancy/Hematologic: CLL, myeloma, lymphoma (hypogammaglobulinemia).
• Immunosuppressive Therapy: Chemo, biologics (anti-CD20, TNF-α), steroids, calcineurin inhibitors, JAK inhibitors.
• Metabolic/Nutritional: Protein-energy malnutrition, vitamin A/D/Zn deficiency, diabetes (neutrophil dysfunction).
• Protein Loss: Nephrotic syndrome, protein-losing enteropathy.
• Splenectomy/Asplenia: Encapsulated organism susceptibility.
• Aging (Immunosenescence): Thymic involution, T-cell repertoire narrowing, inflammaging.

Management Principles

• PID: HSCT, gene therapy, IgRT, prophylactic antimicrobials, cytokine therapy (IFN-γ for CGD).
• SID: Treat underlying cause, IgRT if hypogammaglobulinemic + infections, vaccinate (inactivated), antimicrobial prophylaxis per risk.

Early diagnosis (warning signs: SPUR, Jeffrey Modell) saves lives.