Primary immunodeficiency

Primary immunodeficiencies are inherited disorders caused by defects in immune-system development or function. They can increase susceptibility to infections and disrupt immune regulation.

Innate immune system: The immune system's rapid defenses, including barriers, phagocytes, complement, and natural killer cells. Inherited defects in innate defenses can cause recurrent bacterial or fungal infections.
V(D)J recombination: A DNA rearrangement process that creates diverse antigen receptors in developing B and T cells. Defects in this process can prevent functional lymphocyte receptors from forming.
Newborn screening for severe combined immunodeficiency: A screening approach that detects low T-cell production in newborns, commonly using T-cell receptor excision circles. Early detection can prevent exposure to dangerous infections before symptoms emerge.
Severe combined immunodeficiency: A group of inherited disorders with profound defects in T-cell development and often impaired B-cell or natural-killer-cell function. It illustrates how severe combined defects can make ordinary infections life-threatening early in life.
Secondary immunodeficiency: Impaired immune function caused by external conditions or diseases rather than an inherited immune-system defect. It contrasts inherited primary disorders with immune weakness acquired during life.
Adaptive immune system: The antigen-specific immune system formed by B cells, T cells, and their memory responses. Many primary immunodeficiencies impair adaptive responses or their coordination.
Class-switch recombination: A B-cell DNA rearrangement that changes antibody class while preserving antigen specificity. Its failure can produce hyper-IgM immunodeficiency with impaired class-switched antibodies.
Immunoglobulin replacement therapy: Treatment that supplies pooled antibodies to people who cannot make enough effective immunoglobulin. It reduces infections in many antibody-deficiency disorders.
Common variable immunodeficiency: A heterogeneous antibody deficiency marked by low immunoglobulin levels and impaired specific antibody responses. It shows that primary immunodeficiency can first become apparent in adulthood.
HIV/AIDS: HIV infection progressively damages CD4 T cells and can cause acquired immunodeficiency. It is a major acquired cause of immune deficiency, unlike inherited primary disorders.

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