Primary immunodeficiencies (PID), also termed inborn errors of immunity (IEI) arise usually from genetic mutations in immune-related genes, distinct from the more common secondary immunodeficiencies caused by malnutrition, HIV, or iatrogenic. This article provides an overview of PID pathophysiology and clinical presentations, emphasizing the relationship between specific immune defects and characteristic infectious susceptibilities.
The human immune system comprises interconnected innate and adaptive components that maintain tissue homeostasis through epithelial barriers, pattern recognition receptors, and adaptive lymphocyte responses. Disruption of these mechanisms by PID leads to predictable infection patterns. Antibody deficiencies, the most common PID, cause recurrent sinopulmonary infections with encapsulated bacteria due to impaired opsonization. Complement deficiencies create similar susceptibilities, with terminal complement defects uniquely predisposing to Neisseria infections. Whereas some PID have broader infection susceptibility, there are also sentinel infections such as Candida and mycobacterial infections which may also arise the suspicion of a possible underlying immunological defect. In addition to genetically-derived immune deficiencies, recent recognition of anti-cytokine autoantibodies represents a novel immunodeficiency mechanism.
Diagnostic approaches to patients with PID include functional immune assessments and genomic analysis. Treatment encompasses antimicrobial prophylaxis, immunoglobulin replacement, targeted therapies, and definitive correction through haematopoietic stem cell transplantation or gene therapy.
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